Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

John,

Very interesting. We'll have to keep this in mind.

We do have a dual pole contactor in the furnace circuit but the furnace also 
has a SSR for phase control. The contactor only opens and closes when the SSR 
is open (no current). The harmonic emissions from the phase control is why we 
have the large RF Line Filter.

Thanks for the information.
The Other Brian

-Original Message-
From: John Barnes [mailto:jrbar...@iglou.com]
Sent: Tuesday, September 22, 2015 11:53 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Brian,
How is the furnace shut off?  If you are using a contactor between the main 
line filter and the furnace, a phase line might open when it is carrying high 
current.  The inductance of the line filter will try to keep this current 
flowing, generating a very-high kickback spike at the
*output* of the line filter.

Or, since the contacts in the contactor are unlikely to open/close at exactly 
the same time, a common-mode choke in the line filter can act as a transformer 
putting noise on the open phase(s) if only 1 or 2 phases are connected to the 
load.  Some years ago, Bill Kimmel and Daryl Gerke wrote about a case where a 
3-phase product had a contactor between a line filter and the load, which 
generated horrendous Conducted Emissions noise every time the contactor opened 
or closed, because of this transformer action.  The solution was to replace the 
common-mode choke with 3 separate chokes, one for each phase line.

John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, Master EMC
  Design Eng, SM IEEE (retired)
Lexington, KY
http://www.dbicorporation.com/

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Ed Price]

Just a thought about contactors.
Any mechanical contactor will allow some arcing as the contacts open.
Further, in a 3-phase contactor, not all phases will actuate at the exact
same time. At a given instant, you might have one phase open, another arcing
and the third still a solid conductive path. Modeling sounds daunting.
An electronic contactor should have fewer problems, but I wonder, in the
example of a 3-phase electronic contactor, do all three phases get switched
at once or is there some delay scheme to allow each phase to switch at its
own zero-crossing time?

Ed Price
WB6WSN
Chula Vista, CA USA

-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Wednesday, September 23, 2015 5:33 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

John,

Very interesting. We'll have to keep this in mind.

We do have a dual pole contactor in the furnace circuit but the furnace also
has a SSR for phase control. The contactor only opens and closes when the
SSR is open (no current). The harmonic emissions from the phase control is
why we have the large RF Line Filter.

Thanks for the information.
The Other Brian

-Original Message-
From: John Barnes [mailto:jrbar...@iglou.com]
Sent: Tuesday, September 22, 2015 11:53 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Brian,
How is the furnace shut off?  If you are using a contactor between the main
line filter and the furnace, a phase line might open when it is carrying
high current.  The inductance of the line filter will try to keep this
current flowing, generating a very-high kickback spike at the
*output* of the line filter.

Or, since the contacts in the contactor are unlikely to open/close at
exactly the same time, a common-mode choke in the line filter can act as a
transformer putting noise on the open phase(s) if only 1 or 2 phases are
connected to the load.  Some years ago, Bill Kimmel and Daryl Gerke wrote
about a case where a 3-phase product had a contactor between a line filter
and the load, which generated horrendous Conducted Emissions noise every
time the contactor opened or closed, because of this transformer action.
The solution was to replace the common-mode choke with 3 separate chokes,
one for each phase line.

John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, Master EMC
  Design Eng, SM IEEE (retired)
Lexington, KY
http://www.dbicorporation.com/

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Brian O'Connell]

" provoked into spontaneous energetic disassembly." -> Will use that phrase on 
next TRF/report.

The component with least margin tends to the main switch transitor(s). Mostly 
because of peak voltages at end of each cycle. Resonant-mode converters have 
less Vpk but more periodic RMS stressors. But as energy is easily controlled 
for each individual cycle, response to an external disturbance typically 
results in rapid shutdown of the gate drive.

The circuit node that tends to have the most circulating energy is junction of 
PFC choke/diode/switch; and once the choke saturates, bad things start to 
happen. Typical PFC controllers run in transition mode or continuous-current 
mode, but the more recent fixed off-time controllers allows hi-current control, 
and can handle boost-choke saturation.

Power transistors have greatly improved last ten years. Idss leakage spread has 
decreased an order of magnitude and breakdown V has decreased 50%. So if the 
power supply is not using recent stuff, you have no significant margin.

Legacy stuff - cheap but has some evil failure modes buried in most power 
supply designs. New stuff - more cost but less boom.

Brian

-Original Message-
From: John Woodgate [mailto:j...@jmwa.demon.co.uk] 
Sent: Tuesday, September 22, 2015 11:10 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02717445@Mailbox-Tech.lecotech.local>, 
dated Tue, 22 Sep 2015, "Kunde, Brian" <brian_ku...@lecotc.com> writes:

>I'm guessing that under some conditions, there could be some kind of 
>interaction between the rf filter and the power supply which maybe 
>causing our high fallout. Can you propose a test setup where we might 
>be able to simulate such conditions?

I'm guessing the same, just from your report of the damage, but as I 
said about 50 k posts ago, I failed to understand the stability issues 
with PFC circuits. I just know that they can be provoked into 
spontaneous energetic disassembly.
-- 
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Brian Gregory]

 -- Original Message --
From: "Kunde, Brian" 
Date: Mon, 21 Sep 2015 20:13:33 +


Hello Brian,
 
> test to IEC 61000-4-11

 
I think the problem is line surges external to your units, and you are on the 
right track when you suspect that all the test equipment is very 
current-limited, yet the collection systems in your customers' applications are 
not.  Even surge testers have limits, unless the stack is as tall as you are. 
 
> power supplies are failing while the instruments are in Stand-by mode 
> (running but not during an analysis), meaning, 
> the high current filter is not running at the time of the failures. 
 
I've only had so much time to follow this very interesting topic.  To be sure 
it's external circumstances, I'd tie a signal of some sort from the 
high-current furnace into your line analyzer (or feed both that and an external 
trigger from the analyzer into a storage scope).  If a failure or line surge 
corresponds to the furnace coming on, then you look inside your unit.  
Otherwise, Occam's razor is cutting towards line surges from the facility.

 
> failure in our Apps Lab a few nights ago in one of the same units that failed 
> a few weeks ago. We installed a Surge Suppressor in
> an adjacent instrument which did not fail. Our AC Line Analyzer showed a 
> transient  pulse which was clipped off (probably by the
> surge suppressor) at 600 volts with a duration of 14us.  
 
Did you get waveshape capture?  If so, and the peak is quite flat, then it's 
for sure the TVS in the adjacent device clamped the surge.  14 uSec. is longer 
than any of the waveforms provided by standard testers.
 
> power supply blew its fuses (one on each side of the line) plus  opened an 
> upstream 15 amp circuit breaker. ... it did not blow 
> its guts out like previous failures. This one just opened the fuses. We 
> replaced the fuses and the power supply was functional.  
 
I'd say you need some TVS devices...  how widely spread, geographically, have 
been the failures?   Transients (often from power line capacitor switching) 
akin to what was measured in your Lab are more widespread than reported.

 
> Surge Immunity tests on this same instrument with the same surge suppressor 
> according to IEC 61000-4-5 up to 6KV without
> damage.  So something is different from this test setup verses the real 
> world. 
 
Check the surge generator;  I'll bet its current limit is tightly tied to 8/20 
usec waveforms.  Grids are not.   Still, I'm a bit troubled by the sudden 
uptick in failures, including in units (correct assumption?) that have been 
installed and running for a year or more
 
Colorado Brian  

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

John,

Yes, the large rf filter is still in the circuit but only supplying less than 
few amps of current to the 24Vdc power supply. The High Current Furnace branch 
would be an open circuit.

The worst case would be in a 50 amp (rated) instrument where we have a 65 amp 
RF Line filter driving a 500 watt 24Vdc power supply (about 1 amp at 50% load), 
when the furnace is not running. The furnace only runs about 30-60 seconds at a 
time per analysis. So it is off most of the time.

I'm guessing that under some conditions, there could be some kind of 
interaction between the rf filter and the power supply which maybe causing our 
high fallout. Can you propose a test setup where we might be able to simulate 
such conditions?

Thanks for the input.

The Other Brian

-Original Message-
From: John Woodgate [mailto:j...@jmwa.demon.co.uk]
Sent: Monday, September 21, 2015 4:40 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

In message
<64D32EE8B9CBDD44963ACB076A5F6ABB02717398@Mailbox-Tech.lecotech.local>,
dated Mon, 21 Sep 2015, "Kunde, Brian" <brian_ku...@lecotc.com> writes:

>The word we get from the field is that these power supplies are failing
>while the instruments are in Stand-by mode (running but not during an
>analysis), meaning, the high current filter is not running at the time
>of the failures.

When you say 'it's not running', I understand that the furnace current isn't 
flowing, but is the filter connected to the mains supply?  If so, that is 
possibly a more hazardous condition, because a filter with open-circuit output 
can produce high voltages.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn 
my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and 
Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Brian O'Connell]

A failure in PFC section most onerous when a surge finds its way to the 
choke/diode/switch node. Any significant voltage 'reflected' into the gate of 
the PFC transistor will typically cause power supply to puke it guts.

Looks like data that would indicate a root-cause failure remains elusive - 
seems to be a need something non-intrusive that is self-powered and can get 
kicked yet stand back up for more abuse (please sir, may I have another...).

During 2013, tried several commercial loggers over a six-month period and most 
did not survive the end-use environment . The two that lived through their 
ordeals had insufficient bandwidth, or had insufficient dynamic range, or had 
immunity problems, or used too much power, etc. So ignored the 'Not Invented 
Here' accusations and rolled own design.

Second fielded version worked ok and management wanted to turn it into a 
standard product - but were able to convince otherwise by explaining the level 
of customer support required for various windoze computers that would be used 
to suck in the log files; and that marketing said could sell  no more than 3 
units per month of a specialty product (mostly used to monitor power 
converters, transformers, and reactors used on PV arrays).

My latest incarnation of The One True Monitor Box looks at seven thermocouple 
channels, four Vdc (200-1500V) channels, three RMS (230-480V), two light sensor 
channels, and seven current channels; an array of four peak V (envelope 
detector) channels that can be paralleled with the voltage channels(mostly to 
detect when to go to hi-speed sample rate and use different data structure); 
and four comparator channels (hi-rate event triggers).  The support from the 
good engineers at LT, ADI, Micrel, and TI was instrumental (pun intended) in 
this design. 

Have recently started using these loggers to monitor long-term Type Tests where 
there is a risk that the test conditions might kill my standard lab setup 
(Agilent34970/computer combo - $100 vs $3000 USD of equipment).

The (im)moral of the story is that compliance engineering thrives where 
reliable *end-use* empirical product data is available.

Brian

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Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02717445@Mailbox-Tech.lecotech.local>, 
dated Tue, 22 Sep 2015, "Kunde, Brian"  writes:


I'm guessing that under some conditions, there could be some kind of 
interaction between the rf filter and the power supply which maybe 
causing our high fallout. Can you propose a test setup where we might 
be able to simulate such conditions?


I'm guessing the same, just from your report of the damage, but as I 
said about 50 k posts ago, I failed to understand the stability issues 
with PFC circuits. I just know that they can be provoked into 
spontaneous energetic disassembly.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[John Barnes]

Brian,
How is the furnace shut off?  If you are using a contactor between the
main line filter and the furnace, a phase line might open when it is
carrying high current.  The inductance of the line filter will try to
keep this current flowing, generating a very-high kickback spike at the
*output* of the line filter.  

Or, since the contacts in the contactor are unlikely to open/close at
exactly the same time, a common-mode choke in the line filter can act as
a transformer putting noise on the open phase(s) if only 1 or 2 phases
are connected to the load.  Some years ago, Bill Kimmel and Daryl Gerke
wrote about a case where a 3-phase product had a contactor between a
line filter and the load, which generated horrendous Conducted Emissions
noise every time the contactor opened or closed, because of this
transformer action.  The solution was to replace the common-mode choke
with 3 separate chokes, one for each phase line.

John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, Master EMC  
  Design Eng, SM IEEE (retired)
Lexington, KY
http://www.dbicorporation.com/

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Richard Nute]

I would look at the various overvoltage protection
circuits.

When OVP operates, it may protect the immediate
circuits from damage.  But, when an OVP operates,
the energy stored in the supply circuit
inductances and capacitances has to be dissipated
somewhere else.  The energy can go anywhere on the
supply network.

"An SPD puts a momentary very low impedance to
earth on the distribution system.  Such a tactic
assumes transient overvoltages can be eliminated
by connecting them to earth.  The sudden change in
current causes a change in the field of an
inductor which causes a transient voltage across
the inductor."*

*“Diverting Surges to Ground: Expectations versus
Reality,” François D. Martzloff, Proceedings, Open
Forum on Surge Protection Application,
NISTIR-4654, August 1991, National Institute of
Standards and Technology, Gaithersburg, MD

Joe Randolph presented a paper at the 2013
Symposium, and re-published this year in In
Compliance magazine.  His hypothesis is that OVP
operation created the failures that he could not
otherwise explain.  He had data which supported
his hypothesis.


Best regards,
Rich

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

Yes, we test our products to IEC 61000-4-11, however, our test equipment can 
only handle 16 amps single phase so we cannot perform this test when the high 
current furnace is running.

The word we get from the field is that these power supplies are failing while 
the instruments are in Stand-by mode (running but not during an analysis), 
meaning, the high current filter is not running at the time of the failures.

UPDATE: We had another power supply failure in our Apps Lab a few nights ago in 
one of the same units that failed a few weeks ago. We installed a Surge 
Suppressor in an adjacent instrument which did not fail. Our AC Line Analyzer 
showed a transient  pulse which was clipped off (probably by the surge 
suppressor) at 600 volts with a duration of 14us.  The power supply blew its 
fuses (one on each side of the line) plus  opened an upstream 15 amp circuit 
breaker. An analysis of the power supply showed that it did not blow its guts 
out like previous failures. This one just opened the fuses. We replaced the 
fuses and the power supply was functional.

So the power supply still drew enough power to blow the fuses but did not 
permanently damage any components this time.

We performed Surge Immunity tests on this same instrument with the same surge 
suppressor according to IEC 61000-4-5 up to 6KV without damage.  So something 
is different from this test setup verses the real world.

The investigation continues.

Thanks to all for the input.

The Other Brian


From: McDiarmid, Ralph [mailto:ralph.mcdiar...@schneider-electric.com]
Sent: Monday, September 21, 2015 2:52 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

>This lab area has surge protection, so again, we believe the problem is some 
>kind of low voltage transient, voltage dropout, or >waveform distortion that 
>we have been unable to detect and simulate.

Was it tested against IEC 61000-4-11 (voltage dips, short interruptions, 
variations ) ?
___

Ralph McDiarmid  |   Schneider Electric   |  Solar Business  |   CANADA  |   
Regulatory Compliance Engineering


From:

"Kunde, Brian" <brian_ku...@lecotc.com<mailto:brian_ku...@lecotc.com>>

To:

EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>,

Date:

09/17/2015 06:40 AM

Subject:

Re: [PSES] Unexplained High Fallout of Power Supplies






Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current protector (5, 10 or 15 amp) driving 
the lower current non-furnace electronics such as the dc power supply, cooling 
fans and blowers, etc..

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.

We use no additional inrush limiting other that what is built into the power 
supplies themselves. Other than a thermistor of some kind, how can the inrush 
be limited?

We have also seen on several occasions in the field where a power supply will 
blow up in one instrument which causes the power supply in a nearby instrument 
to also fail.

Two weeks ago we had an "event" occur right here at our own campus in our 
Application Lab where 40-50 instruments of different models and ages are being 
used daily to develop test methods. An instrument was power on but was not 
running an analysis (high current furnace wasn't running in what we call 
Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two R engineers 
who have been working on our fallout problem in the field to investigate. They 
found the power supply had failed in the same way as those in the field. No 
other failed component in the instrument was found. The power supply was 
replaced and the instrument was once again functional. AS THE Engineers turned 
to walk back to their office, BAM!! The power supply blew up in the instrument 
installed NEXT to 

Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02717398@Mailbox-Tech.lecotech.local>, 
dated Mon, 21 Sep 2015, "Kunde, Brian"  writes:


The word we get from the field is that these power supplies are failing 
while the instruments are in Stand-by mode (running but not during an 
analysis), meaning, the high current filter is not running at the time 
of the failures.


When you say 'it's not running', I understand that the furnace current 
isn't flowing, but is the filter connected to the mains supply?  If so, 
that is possibly a more hazardous condition, because a filter with 
open-circuit output can produce high voltages.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[McDiarmid, Ralph]

>This lab area has surge protection, so again, we believe the problem is 
some kind of low voltage transient, voltage dropout, or >waveform 
distortion that we have been unable to detect and simulate.

Was it tested against IEC 61000-4-11 (voltage dips, short interruptions, 
variations ) ? 
___ 


Ralph McDiarmid  |   Schneider Electric   |  Solar Business  |   CANADA  | 
  Regulatory Compliance Engineering 
 



From:
"Kunde, Brian" <brian_ku...@lecotc.com>
To:
EMC-PSTC@LISTSERV.IEEE.ORG, 
Date:
09/17/2015 06:40 AM
Subject:
Re: [PSES] Unexplained High Fallout of Power Supplies



Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz 
which powers two separate internal circuits; one being a relatively low 
current electronics powered by a purchased over-the-shelf 24Vdc power 
supply, and second, a high current furnace of some type; inductive, 
electrode, resistive heating elements, etc.. Because of the high overall 
current of the instruments, typically between 30A and 50A, the instrument 
is plugged into a high current branch circuit with a huge high current 
line filter. Internally, we usually have a smaller supplementary 
over-current protector (5, 10 or 15 amp) driving the lower current 
non-furnace electronics such as the dc power supply, cooling fans and 
blowers, etc..

The issues we are having are with these purchased power supplies blowing 
up. And because we pre-test power supplies and our finished products so 
extensively and we are not able to cause a power supply failure with the 
same damage pattern as we are seeing in the field, we believe that in the 
real world our products are seeing some kind of condition that we are not 
able to simulate in our EMC Lab. Identifying and understanding such 
conditions is our goal at this time.

We use no additional inrush limiting other that what is built into the 
power supplies themselves. Other than a thermistor of some kind, how can 
the inrush be limited?

We have also seen on several occasions in the field where a power supply 
will blow up in one instrument which causes the power supply in a nearby 
instrument to also fail.

Two weeks ago we had an "event" occur right here at our own campus in our 
Application Lab where 40-50 instruments of different models and ages are 
being used daily to develop test methods. An instrument was power on but 
was not running an analysis (high current furnace wasn't running in what 
we call Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two 
R engineers who have been working on our fallout problem in the field to 
investigate. They found the power supply had failed in the same way as 
those in the field. No other failed component in the instrument was found. 
The power supply was replaced and the instrument was once again 
functional. AS THE Engineers turned to walk back to their office, BAM!! 
The power supply blew up in the instrument installed NEXT to the one they 
just repaired. This second instrument is a different model with a 
different manufacturer of power supply. An AC Power Line monitor/analyzer 
was installed on the AC Mains circuit and has been c!
 hecked every morning since. No unusual transients or power dropouts have 
been detected.

This lab area has surge protection, so again, we believe the problem is 
some kind of low voltage transient, voltage dropout, or waveform 
distortion that we have been unable to detect and simulate.

Thanks to all.

The Other Brian

-Original Message-
From: Bob LaFrance [mailto:b...@creare.com]
Sent: Thursday, September 17, 2015 8:46 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

I am curious to what you are using for inrush limiting.  Sorry if you 
already told us but I missed that.

Regards,
Bob LaFrance
N9NEO
Design Engineer
Creare Inc.
16 Great Hollow Road
Hanover, NH
603-640-2539





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Re: [PSES] Unexplained High Fallout of Power Supplies

[McDiarmid, Ralph]

I recall that PFC circuits are generally based on a boost converter and 
that circuit arrangement if often challenging to tune for stable 
closed-loop response.  I think PFC applications try to regulate both input 
current and output voltage; one is tightly regulated, the other is not.
___ 


Ralph McDiarmid  |   Schneider Electric   |  Solar Business  |   CANADA  | 
  Regulatory Compliance Engineering 




From:
John Woodgate <j...@jmwa.demon.co.uk>
To:
EMC-PSTC@LISTSERV.IEEE.ORG, 
Date:
09/17/2015 08:53 AM
Subject:
Re: [PSES] Unexplained High Fallout of Power Supplies



In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02716FE8@Mailbox-Tech.lecotech.local>, 
dated Thu, 17 Sep 2015, "Kunde, Brian" <brian_ku...@lecotc.com> writes:

>
>These power supplies are power-factor corrected. I will check with 
>engineering if such components are damaged.

As you describe the damage, the PFC circuit would be in that area, so it 
is involved.
>
>The large line filters are internal to our instruments so yes, they are 
>always in the circuit ahead of all AC within the instrument.

I suspect that something is causing the stored energy in the filter to 
be dumped into the PFC circuit. This may be due to the PFC circuit 
itself. I was marginally involved in a discussion of stability issues in 
PFC circuits, but it was highly mathematical so I didn't learn much.
-- 
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02716FA6@Mailbox-Tech.lecotech.local>, 
dated Thu, 17 Sep 2015, "Kunde, Brian"  writes:


This lab area has surge protection, so again, we believe the problem is 
some kind of low voltage transient, voltage dropout, or waveform 
distortion that we have been unable to detect and simulate.


There really isn't enough energy in any of those, if they are so far 
undetected, to cause the destruction you describe. Something is dumping 
probably hundreds of joules into the parts between the mains inlet and 
the rectifier, including the latter. I think you said that the diodes 
are short-circuit, but at least they were not vaporized, like the other 
parts. So the energy seems to enter from the mains, which still points 
me towards that high-current filter.


I know you can't create the fault, but can you take the mains feed for 
the power supply from upstream of the high-current filter, so it is much 
less likely to cause anything?

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Bob LaFrance]

I am curious to what you are using for inrush limiting.  Sorry if you already 
told us but I missed that.  

Regards,
Bob LaFrance
N9NEO
Design Engineer
Creare Inc.
16 Great Hollow Road
Hanover, NH 
603-640-2539


-Original Message-
From: CR [mailto:k...@earthlink.net] 
Sent: Wednesday, September 16, 2015 2:56 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

On 9/15/2015 4:53 PM, Kunde, Brian wrote:
> we have not been able to find the reason for the fallout. The power 
> supplies have all shown arc damage to the AC front end, signs of 
> arcing and traces burned or vaporized, blown fuses, and shorted FETs 
> and/or Rectifiers. These failures have occurred on several different 
> locations, on different power supply models, different manufactures 
> and on different instruments. Some instruments have been in service 
> for years; some for only a few weeks before they fail. Some 
> instruments even have surge suppression modules installed and though 
> the power supplies fail the surge modules tested out fine. The 
> failures did not occur during any known lightning storm or any other 
> known transient.
Brian,

The circumstances you describe -- arcing with no external transient seen
-- point to an on-board occurrence, not an external one.  I'd suspect (in no 
particular order and on little information -- heh) ) PWB material with 
insufficient dielectric withstand, and/or oscillation in a power FET due to its 
characteristics (or another device's) having changed enough to make the control 
loop unstable.  You might have an oscillator the controller can't even detect.

I'm on LinkedIn if you need help, eh?

Cortland Richmond

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Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02717001@Mailbox-Tech.lecotech.local>, 
dated Thu, 17 Sep 2015, "Kunde, Brian"  writes:


hey would power our instrument with an AC Power Line Conditioner that 
turned out was Under-rated for the current our instrument needed. Under 
full load, this line condition would do something strange which blew up 
the power supply.


That has some similarities with my conjecture. Do you really need active 
PFC in your small DC power supply? If not, you might consider using a 
product that doesn't have it.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

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Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02716FE8@Mailbox-Tech.lecotech.local>, 
dated Thu, 17 Sep 2015, "Kunde, Brian"  writes:




These power supplies are power-factor corrected. I will check with 
engineering if such components are damaged.


As you describe the damage, the PFC circuit would be in that area, so it 
is involved.


The large line filters are internal to our instruments so yes, they are 
always in the circuit ahead of all AC within the instrument.


I suspect that something is causing the stored energy in the filter to 
be dumped into the PFC circuit. This may be due to the PFC circuit 
itself. I was marginally involved in a discussion of stability issues in 
PFC circuits, but it was highly mathematical so I didn't learn much.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Gary McInturff]

Brian

Have you tracked the time to failures and put it on a Weibull analysis to see 
if these are truly random failures. I'm wondering if the power supply 
components are not properly derated and are overstressed. Maybe they are 
failing not from a transient event but components are being overdrive. I 
presume a similar set of components are failing - could be a few rather than a 
single one - in these units. I know you could reproduce the failures in-house. 
I would, if you haven't, get a hold of the manufacturers reliability folks and 
talk about their anticipated failure modes.

-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Thursday, September 17, 2015 8:16 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

James,

No. We are seeing a high fallout of purchased power supplies across most (but 
not all) product lines regardless of the furnace type.


John,

The power supplies have an internal fuse. We add a supplementary over-current 
protector upstream of the power supply but it is sized to protect the wiring, 
connectors, and traces on the distritrabution board; not the power supply 
itself. So, yes, the OCP can be 2x or 3x the size of the fuse in the power 
supply.

When these power supplies fail (BAM!), the black soot is a 2" diameter area 
between the AC input connector and the bridge rectifier. The input traces are 
often vaporized off the PC card and the rectifier has failed shorted and of 
course the fuse(s) on the power supply are open. It is hard to tell if the 
damage was caused by high voltage arcing or by high current turning the traces 
into a flash bulb.

These power supplies are power-factor corrected. I will check with engineering 
if such components are damaged.

The large line filters are internal to our instruments so yes, they are always 
in the circuit ahead of all AC within the instrument.

Thanks,
The Other Brian

-Original Message-
From: Pawson, James [mailto:james.paw...@echostar.com]
Sent: Thursday, September 17, 2015 10:10 AM
To: Kunde, Brian; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Unexplained High Fallout of Power Supplies

Hi Brian,

Is the furnace type common to all the failed pieces of equipment? If not 
common, similar?

Reading on with interest
James



-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: 17 September 2015 14:37
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current protector (5, 10 or 15 amp) driving 
the lower current non-furnace electronics such as the dc power supply, cooling 
fans and blowers, etc..

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.

We use no additional inrush limiting other that what is built into the power 
supplies themselves. Other than a thermistor of some kind, how can the inrush 
be limited?

We have also seen on several occasions in the field where a power supply will 
blow up in one instrument which causes the power supply in a nearby instrument 
to also fail.

Two weeks ago we had an "event" occur right here at our own campus in our 
Application Lab where 40-50 instruments of different models and ages are being 
used daily to develop test methods. An instrument was power on but was not 
running an analysis (high current furnace wasn't running in what we call 
Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two R engineers 
who have been working on our fallout problem in the field to investigate. They 
found the power supply had failed in the same way as those in the field. No 
other failed component in the instrument was found. The power supply was 
replaced and the instrument was once again functional. AS THE Engineers turned 
to walk back to their office, BAM!! The power supply blew up in the instru

Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

Cortland,

It is quite possible that we are fighting a similar ghost. I imagine that there 
are an infinite number of strange conditions that can occur on the AC Mains 
which could cause such a failure. Who knows? For instance, the problem might be 
a third party product that is becoming popular in labs that commonly purchase 
our  instruments that is creating some kind of strange signal or transient that 
is causing our power supplies to self-destruct.

Another example:

Several years ago we had an instrument as a customer site (in India) that was 
blowing up the power supply every time they turned the furnace up to its 
highest power level. We spent two months trying to simulate the condition here 
in our EMC lab without any luck. Our company even shipped them a replacement 
instrument which ended up having the same problem. At the point we knew the 
problem was external. When we pressed our customer for more information we 
found out that when our service personnel was not on site, they would power our 
instrument with an AC Power Line Conditioner that turned out was Under-rated 
for the current our instrument needed. Under full load, this line condition 
would do something strange which blew up the power supply. Unfortunately we 
were never able to determine what this condition was.

With the many good advice we have received so far and our determination to 
resolve this I know it is just a matter of time before we figure it out.

Thanks again for everyone's help.
The Other Brian


-Original Message-
From: CR [mailto:k...@earthlink.net]
Sent: Thursday, September 17, 2015 11:10 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

On 9/17/2015 9:37 AM, Kunde, Brian wrote:
> The issues we are having are with these purchased power supplies blowing up. 
> And because we pre-test power supplies and our finished products so 
> extensively and we are not able to cause a power supply failure with the same 
> damage pattern as we are seeing in the field, we believe that in the real 
> world our products are seeing some kind of condition that we are not able to 
> simulate in our EMC Lab. Identifying and understanding such conditions is our 
> goal at this time.

Let me back up a bit... suppose it Is an external event; you will need to know 
how bad it is and what it looks like in order to track it down and protect 
against it.

Some years ago I was able to resolve a mystery problem because (on a
hunch) I'd taken along a 10 Hz-5 MHz loop and was watching a 'scope connected 
to it. None of the normal GR-1039 tests would have caught it, as the 
failuresoccurred inside an operating[test] telco Central Office.
I was seeing a large magneticfieldtransientcaused by ring-tone current 
switching affecting customer-premisesmodems temporally placed inside the 
CO.That problem went away once they were moved down the hall.

A problem quite similarto yours occurred later, on remote digital loop 
equipment cabinets connected to outside plant wiring; protector blocks were 
failing destructively, evenin the absence of lightning or any known stresses. I 
was laid off in a downsizing and that employer no longer exists, so I don't 
know if it was solved, or even if it was pursued after I left, but Isuspect 
that (again) the observed failures were caused by events we could have foreseen 
had we thought past the tests required by the standardto which we conformed. *I 
now suspect **charges inducedi**n a **the extensive outside plant overheard 
wiring **as **highly charged clouds drifted past.*

You have an even larger outside plant. I suspectyour problemis of a like sort, 
onenot just outside the box; outside the BOOK. Plausible, possible and 
detectable, if you know what to look for.

Cortland Richmond

-

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mistake, plea

Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02716FA6@Mailbox-Tech.lecotech.local>, 
dated Thu, 17 Sep 2015, "Kunde, Brian"  writes:


This lab area has surge protection, so again, we believe the problem is 
some kind of low voltage transient, voltage dropout, or waveform 
distortion that we have been unable to detect and simulate.


You are clearly experiencing some very unusual effect. Obviously, it's 
even more difficult to diagnose by email. However, I suspect an 
interaction inside the products is responsible, and a few things come to 
mind:


- I suppose you do have fuse (or equivalent) protection for this DC 
power supply appropriate for its full-load current, not 10 times as 
much. I still see 30 W supplies 'protected' by 1 amp fuses.


- Exactly what goes 'BAM'? and is it the same parts in different 
designs?


- Do the power supplies have active power-factor correction? If so, are 
those parts particularly damaged?


- Were the high-current line filters in circuit when the two lab 
failures occurred?


- Are these filters inside the products or external boxes?
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

This message is from the IEEE Product Safety Engineering Society emc-pstc discussion 
list. To post a message to the list, send your e-mail to 

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher:  
David Heald: 

Re: [PSES] Unexplained High Fallout of Power Supplies

[CR]

On 9/17/2015 9:37 AM, Kunde, Brian wrote:

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.


Let me back up a bit... suppose it Is an external event; you will need 
to know how bad it is and what it looks like in order to track it down 
and protect against it.


Some years ago I was able to resolve a mystery problem because (on a 
hunch) I'd taken along a 10 Hz-5 MHz loop and was watching a 'scope 
connected to it. None of the normal GR-1039 tests would have caught it, 
as the failuresoccurred inside an operating[test] telco Central Office. 
I was seeing a large magneticfieldtransientcaused by ring-tone current 
switching affecting customer-premisesmodems temporally placed inside the 
CO.That problem went away once they were moved down the hall.


A problem quite similarto yours occurred later, on remote digital loop 
equipment cabinets connected to outside plant wiring; protector blocks 
were failing destructively, evenin the absence of lightning or any known 
stresses. I was laid off in a downsizing and that employer no longer 
exists, so I don’t know if it was solved, or even if it was pursued 
after I left, but Isuspect that (again) the observed failures were 
caused by events we could have foreseen had we thought past the tests 
required by the standardto which we conformed. *I now suspect **charges 
inducedi**n a **the extensive outside plant overheard wiring **as 
**highly charged clouds drifted past.*


You have an even larger outside plant. I suspectyour problemis of a like 
sort, onenot just outside the box; outside the BOOK. Plausible, possible 
and detectable, if you know what to look for.


Cortland Richmond

-

This message is from the IEEE Product Safety Engineering Society emc-pstc discussion 
list. To post a message to the list, send your e-mail to 

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher:  
David Heald: 

Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current protector (5, 10 or 15 amp) driving 
the lower current non-furnace electronics such as the dc power supply, cooling 
fans and blowers, etc..

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.

We use no additional inrush limiting other that what is built into the power 
supplies themselves. Other than a thermistor of some kind, how can the inrush 
be limited?

We have also seen on several occasions in the field where a power supply will 
blow up in one instrument which causes the power supply in a nearby instrument 
to also fail.

Two weeks ago we had an "event" occur right here at our own campus in our 
Application Lab where 40-50 instruments of different models and ages are being 
used daily to develop test methods. An instrument was power on but was not 
running an analysis (high current furnace wasn't running in what we call 
Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two R engineers 
who have been working on our fallout problem in the field to investigate. They 
found the power supply had failed in the same way as those in the field. No 
other failed component in the instrument was found. The power supply was 
replaced and the instrument was once again functional. AS THE Engineers turned 
to walk back to their office, BAM!! The power supply blew up in the instrument 
installed NEXT to the one they just repaired. This second instrument is a 
different model with a different manufacturer of power supply. An AC Power Line 
monitor/analyzer was installed on the AC Mains circuit and has been c!
 hecked every morning since. No unusual transients or power dropouts have been 
detected.

This lab area has surge protection, so again, we believe the problem is some 
kind of low voltage transient, voltage dropout, or waveform distortion that we 
have been unable to detect and simulate.

Thanks to all.

The Other Brian

-Original Message-
From: Bob LaFrance [mailto:b...@creare.com]
Sent: Thursday, September 17, 2015 8:46 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

I am curious to what you are using for inrush limiting.  Sorry if you already 
told us but I missed that.

Regards,
Bob LaFrance
N9NEO
Design Engineer
Creare Inc.
16 Great Hollow Road
Hanover, NH
603-640-2539


-Original Message-
From: CR [mailto:k...@earthlink.net]
Sent: Wednesday, September 16, 2015 2:56 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

On 9/15/2015 4:53 PM, Kunde, Brian wrote:
> we have not been able to find the reason for the fallout. The power
> supplies have all shown arc damage to the AC front end, signs of
> arcing and traces burned or vaporized, blown fuses, and shorted FETs
> and/or Rectifiers. These failures have occurred on several different
> locations, on different power supply models, different manufactures
> and on different instruments. Some instruments have been in service
> for years; some for only a few weeks before they fail. Some
> instruments even have surge suppression modules installed and though
> the power supplies fail the surge modules tested out fine. The
> failures did not occur during any known lightning storm or any other
> known transient.
Brian,

The circumstances you describe -- arcing with no external transient seen
-- point to an on-board occurrence, not an external one.  I'd suspect (in no 
particular order and on little information -- heh) ) PWB material with 
insufficient dielectric withstand, and/or oscillation in a power FET due to its 
characteristics (or another device's) having changed enough to make the control 
loop unstable.  You might have an oscillator the controller can't even detect.

I'm on LinkedIn if you need help, eh?

Cortland Richmond

-
--

Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

James,

No. We are seeing a high fallout of purchased power supplies across most (but 
not all) product lines regardless of the furnace type.


John,

The power supplies have an internal fuse. We add a supplementary over-current 
protector upstream of the power supply but it is sized to protect the wiring, 
connectors, and traces on the distritrabution board; not the power supply 
itself. So, yes, the OCP can be 2x or 3x the size of the fuse in the power 
supply.

When these power supplies fail (BAM!), the black soot is a 2" diameter area 
between the AC input connector and the bridge rectifier. The input traces are 
often vaporized off the PC card and the rectifier has failed shorted and of 
course the fuse(s) on the power supply are open. It is hard to tell if the 
damage was caused by high voltage arcing or by high current turning the traces 
into a flash bulb.

These power supplies are power-factor corrected. I will check with engineering 
if such components are damaged.

The large line filters are internal to our instruments so yes, they are always 
in the circuit ahead of all AC within the instrument.

Thanks,
The Other Brian

-Original Message-
From: Pawson, James [mailto:james.paw...@echostar.com]
Sent: Thursday, September 17, 2015 10:10 AM
To: Kunde, Brian; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Unexplained High Fallout of Power Supplies

Hi Brian,

Is the furnace type common to all the failed pieces of equipment? If not 
common, similar?

Reading on with interest
James



-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: 17 September 2015 14:37
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current protector (5, 10 or 15 amp) driving 
the lower current non-furnace electronics such as the dc power supply, cooling 
fans and blowers, etc..

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.

We use no additional inrush limiting other that what is built into the power 
supplies themselves. Other than a thermistor of some kind, how can the inrush 
be limited?

We have also seen on several occasions in the field where a power supply will 
blow up in one instrument which causes the power supply in a nearby instrument 
to also fail.

Two weeks ago we had an "event" occur right here at our own campus in our 
Application Lab where 40-50 instruments of different models and ages are being 
used daily to develop test methods. An instrument was power on but was not 
running an analysis (high current furnace wasn't running in what we call 
Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two R engineers 
who have been working on our fallout problem in the field to investigate. They 
found the power supply had failed in the same way as those in the field. No 
other failed component in the instrument was found. The power supply was 
replaced and the instrument was once again functional. AS THE Engineers turned 
to walk back to their office, BAM!! The power supply blew up in the instrument 
installed NEXT to the one they just repaired. This second instrument is a 
different model with a different manufacturer of power supply. An AC Power Line 
monitor/analyzer was installed on the AC Mains circuit and has been c!
 hecked every morning since. No unusual transients or power dropouts have been 
detected.

This lab area has surge protection, so again, we believe the problem is some 
kind of low voltage transient, voltage dropout, or waveform distortion that we 
have been unable to detect and simulate.

Thanks to all.

The Other Brian

-Original Message-
From: Bob LaFrance [mailto:b...@creare.com]
Sent: Thursday, September 17, 2015 8:46 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

I am curious to what you are using for 

Re: [PSES] Unexplained High Fallout of Power Supplies

[Pawson, James]

Hi Brian,

Is the furnace type common to all the failed pieces of equipment? If not 
common, similar?

Reading on with interest
James

 

-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: 17 September 2015 14:37
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current protector (5, 10 or 15 amp) driving 
the lower current non-furnace electronics such as the dc power supply, cooling 
fans and blowers, etc..

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.

We use no additional inrush limiting other that what is built into the power 
supplies themselves. Other than a thermistor of some kind, how can the inrush 
be limited?

We have also seen on several occasions in the field where a power supply will 
blow up in one instrument which causes the power supply in a nearby instrument 
to also fail.

Two weeks ago we had an "event" occur right here at our own campus in our 
Application Lab where 40-50 instruments of different models and ages are being 
used daily to develop test methods. An instrument was power on but was not 
running an analysis (high current furnace wasn't running in what we call 
Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two R engineers 
who have been working on our fallout problem in the field to investigate. They 
found the power supply had failed in the same way as those in the field. No 
other failed component in the instrument was found. The power supply was 
replaced and the instrument was once again functional. AS THE Engineers turned 
to walk back to their office, BAM!! The power supply blew up in the instrument 
installed NEXT to the one they just repaired. This second instrument is a 
different model with a different manufacturer of power supply. An AC Power Line 
monitor/analyzer was installed on the AC Mains circuit and has been c!
 hecked every morning since. No unusual transients or power dropouts have been 
detected.

This lab area has surge protection, so again, we believe the problem is some 
kind of low voltage transient, voltage dropout, or waveform distortion that we 
have been unable to detect and simulate.

Thanks to all.

The Other Brian

-Original Message-
From: Bob LaFrance [mailto:b...@creare.com]
Sent: Thursday, September 17, 2015 8:46 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

I am curious to what you are using for inrush limiting.  Sorry if you already 
told us but I missed that.

Regards,
Bob LaFrance
N9NEO
Design Engineer
Creare Inc.
16 Great Hollow Road
Hanover, NH
603-640-2539


-Original Message-
From: CR [mailto:k...@earthlink.net]
Sent: Wednesday, September 16, 2015 2:56 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

On 9/15/2015 4:53 PM, Kunde, Brian wrote:
> we have not been able to find the reason for the fallout. The power 
> supplies have all shown arc damage to the AC front end, signs of 
> arcing and traces burned or vaporized, blown fuses, and shorted FETs 
> and/or Rectifiers. These failures have occurred on several different 
> locations, on different power supply models, different manufactures 
> and on different instruments. Some instruments have been in service 
> for years; some for only a few weeks before they fail. Some 
> instruments even have surge suppression modules installed and though 
> the power supplies fail the surge modules tested out fine. The 
> failures did not occur during any known lightning storm or any other 
> known transient.
Brian,

The circumstances you describe -- arcing with no external transient seen
-- point to an on-board occurrence, not an external one.  I'd suspect (in no 
particular order and on little information -- heh) ) PWB mater

Re: [PSES] Unexplained High Fallout of Power Supplies

[Brian O'Connell]

>From one Brian to another, we gotta get a root cause for your problem.

Methinks Gary's statistical/analytical approach is relevant. After desperation, 
despair, and panic have set in, you may want to consider building a small 
microcontroller module with an SD card to constantly log stuff. Have resorted 
to this several times with customers' field failures that made no sense. And in 
one case, we identified a very hazardous condition that could have trashed the 
customer's site.

Easy to do with some of those amazing chips from Atmel, TI, Freescale, etc (do 
not recommend Microchip stuff). Favorite chip is the Cortex M4 (MK20 series) 
from Freescale. Very versatile, powerful, and much I/O.

Wishing much luck to the other Brian

Brian

-Original Message-
From: Gary McInturff [mailto:gary.mcintu...@esterline.com] 
Sent: Thursday, September 17, 2015 8:45 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Brian

Have you tracked the time to failures and put it on a Weibull analysis to see 
if these are truly random failures. I'm wondering if the power supply 
components are not properly derated and are overstressed. Maybe they are 
failing not from a transient event but components are being overdrive. I 
presume a similar set of components are failing - could be a few rather than a 
single one - in these units. I know you could reproduce the failures in-house. 
I would, if you haven't, get a hold of the manufacturers reliability folks and 
talk about their anticipated failure modes.

-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Thursday, September 17, 2015 8:16 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

James,

No. We are seeing a high fallout of purchased power supplies across most (but 
not all) product lines regardless of the furnace type.


John,

The power supplies have an internal fuse. We add a supplementary over-current 
protector upstream of the power supply but it is sized to protect the wiring, 
connectors, and traces on the distritrabution board; not the power supply 
itself. So, yes, the OCP can be 2x or 3x the size of the fuse in the power 
supply.

When these power supplies fail (BAM!), the black soot is a 2" diameter area 
between the AC input connector and the bridge rectifier. The input traces are 
often vaporized off the PC card and the rectifier has failed shorted and of 
course the fuse(s) on the power supply are open. It is hard to tell if the 
damage was caused by high voltage arcing or by high current turning the traces 
into a flash bulb.

These power supplies are power-factor corrected. I will check with engineering 
if such components are damaged.

The large line filters are internal to our instruments so yes, they are always 
in the circuit ahead of all AC within the instrument.

Thanks,
The Other Brian

-Original Message-
From: Pawson, James [mailto:james.paw...@echostar.com]
Sent: Thursday, September 17, 2015 10:10 AM
To: Kunde, Brian; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Unexplained High Fallout of Power Supplies

Hi Brian,

Is the furnace type common to all the failed pieces of equipment? If not 
common, similar?

Reading on with interest
James



-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: 17 September 2015 14:37
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current protector (5, 10 or 15 amp) driving 
the lower current non-furnace electronics such as the dc power supply, cooling 
fans and blowers, etc..

The issues we are having are with these purchased power supplies blowing up. 
And because we pre-test power supplies and our finished products so extensively 
and we are not able to cause a power supply failure with the same damage 
pattern as we are seeing in the field, we believe that in the real world our 
products are seeing some kind of condition that we are not able to simulate in 
our EMC Lab. Identifying and understanding such conditions is our goal at this 
time.

We use no additional inrush limiting other that what is built into the power 
supplies themselves. Other than a thermistor of some kind, how can th

Re: [PSES] Unexplained High Fallout of Power Supplies

[Nyffenegger, Dave]

>Methinks Gary's statistical/analytical approach is relevant. After 
>desperation, despair, and panic have set in, you may want to consider building 
>a small microcontroller module with an SD >card to constantly log stuff. Have 
>resorted to this several times with customers' field failures that made no 
>sense. And in one case, we identified a very hazardous condition that could 
>have >trashed the customer's site.

Or just buy a microcontroller data logger, I think there are lots of them out 
there.

-Dave

-Original Message-
From: Brian O'Connell [mailto:oconne...@tamuracorp.com] 
Sent: Thursday, September 17, 2015 1:34 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

>From one Brian to another, we gotta get a root cause for your problem.

Methinks Gary's statistical/analytical approach is relevant. After desperation, 
despair, and panic have set in, you may want to consider building a small 
microcontroller module with an SD card to constantly log stuff. Have resorted 
to this several times with customers' field failures that made no sense. And in 
one case, we identified a very hazardous condition that could have trashed the 
customer's site.

Easy to do with some of those amazing chips from Atmel, TI, Freescale, etc (do 
not recommend Microchip stuff). Favorite chip is the Cortex M4 (MK20 series) 
from Freescale. Very versatile, powerful, and much I/O.

Wishing much luck to the other Brian

Brian

-Original Message-
From: Gary McInturff [mailto:gary.mcintu...@esterline.com]
Sent: Thursday, September 17, 2015 8:45 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Brian

Have you tracked the time to failures and put it on a Weibull analysis to see 
if these are truly random failures. I'm wondering if the power supply 
components are not properly derated and are overstressed. Maybe they are 
failing not from a transient event but components are being overdrive. I 
presume a similar set of components are failing - could be a few rather than a 
single one - in these units. I know you could reproduce the failures in-house. 
I would, if you haven't, get a hold of the manufacturers reliability folks and 
talk about their anticipated failure modes.

-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: Thursday, September 17, 2015 8:16 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

James,

No. We are seeing a high fallout of purchased power supplies across most (but 
not all) product lines regardless of the furnace type.


John,

The power supplies have an internal fuse. We add a supplementary over-current 
protector upstream of the power supply but it is sized to protect the wiring, 
connectors, and traces on the distritrabution board; not the power supply 
itself. So, yes, the OCP can be 2x or 3x the size of the fuse in the power 
supply.

When these power supplies fail (BAM!), the black soot is a 2" diameter area 
between the AC input connector and the bridge rectifier. The input traces are 
often vaporized off the PC card and the rectifier has failed shorted and of 
course the fuse(s) on the power supply are open. It is hard to tell if the 
damage was caused by high voltage arcing or by high current turning the traces 
into a flash bulb.

These power supplies are power-factor corrected. I will check with engineering 
if such components are damaged.

The large line filters are internal to our instruments so yes, they are always 
in the circuit ahead of all AC within the instrument.

Thanks,
The Other Brian

-Original Message-
From: Pawson, James [mailto:james.paw...@echostar.com]
Sent: Thursday, September 17, 2015 10:10 AM
To: Kunde, Brian; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Unexplained High Fallout of Power Supplies

Hi Brian,

Is the furnace type common to all the failed pieces of equipment? If not 
common, similar?

Reading on with interest
James



-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: 17 September 2015 14:37
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductive, electrode, resistive 
heating elements, etc.. Because of the high overall current of the instruments, 
typically between 30A and 50A, the instrument is plugged into a high current 
branch circuit with a huge high current line filter. Internally, we usually 
have a smaller supplementary over-current pro

Re: [PSES] Unexplained High Fallout of Power Supplies

[Gary McInturff]

I've had unexplained high fallout with those controllers - bwaaahha

-Original Message-
From: Nyffenegger, Dave [mailto:dave.nyffeneg...@bhemail.com] 
Sent: Thursday, September 17, 2015 11:47 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

>Methinks Gary's statistical/analytical approach is relevant. After 
>desperation, despair, and panic have set in, you may want to consider building 
>a small microcontroller module with an SD >card to constantly log stuff. Have 
>resorted to this several times with customers' field failures that made no 
>sense. And in one case, we identified a very hazardous condition that could 
>have >trashed the customer's site.

Or just buy a microcontroller data logger, I think there are lots of them out 
there.

-Dave

-Original Message-
From: Brian O'Connell [mailto:oconne...@tamuracorp.com]
Sent: Thursday, September 17, 2015 1:34 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

>From one Brian to another, we gotta get a root cause for your problem.

Methinks Gary's statistical/analytical approach is relevant. After desperation, 
despair, and panic have set in, you may want to consider building a small 
microcontroller module with an SD card to constantly log stuff. Have resorted 
to this several times with customers' field failures that made no sense. And in 
one case, we identified a very hazardous condition that could have trashed the 
customer's site.

Easy to do with some of those amazing chips from Atmel, TI, Freescale, etc (do 
not recommend Microchip stuff). Favorite chip is the Cortex M4 (MK20 series) 
from Freescale. Very versatile, powerful, and much I/O.

Wishing much luck to the other Brian

Brian

-Original Message-
From: Gary McInturff [mailto:gary.mcintu...@esterline.com]
Sent: Thursday, September 17, 2015 8:45 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Brian

Have you tracked the time to failures and put it on a Weibull analysis to see 
if these are truly random failures. I'm wondering if the power supply 
components are not properly derated and are overstressed. Maybe they are 
failing not from a transient event but components are being overdrive. I 
presume a similar set of components are failing - could be a few rather than a 
single one - in these units. I know you could reproduce the failures in-house. 
I would, if you haven't, get a hold of the manufacturers reliability folks and 
talk about their anticipated failure modes.

-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: Thursday, September 17, 2015 8:16 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

James,

No. We are seeing a high fallout of purchased power supplies across most (but 
not all) product lines regardless of the furnace type.


John,

The power supplies have an internal fuse. We add a supplementary over-current 
protector upstream of the power supply but it is sized to protect the wiring, 
connectors, and traces on the distritrabution board; not the power supply 
itself. So, yes, the OCP can be 2x or 3x the size of the fuse in the power 
supply.

When these power supplies fail (BAM!), the black soot is a 2" diameter area 
between the AC input connector and the bridge rectifier. The input traces are 
often vaporized off the PC card and the rectifier has failed shorted and of 
course the fuse(s) on the power supply are open. It is hard to tell if the 
damage was caused by high voltage arcing or by high current turning the traces 
into a flash bulb.

These power supplies are power-factor corrected. I will check with engineering 
if such components are damaged.

The large line filters are internal to our instruments so yes, they are always 
in the circuit ahead of all AC within the instrument.

Thanks,
The Other Brian

-Original Message-
From: Pawson, James [mailto:james.paw...@echostar.com]
Sent: Thursday, September 17, 2015 10:10 AM
To: Kunde, Brian; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Unexplained High Fallout of Power Supplies

Hi Brian,

Is the furnace type common to all the failed pieces of equipment? If not 
common, similar?

Reading on with interest
James



-Original Message-
From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: 17 September 2015 14:37
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Bob and all.

Good question. Before I answer your questions, let me describe the typical 
architecture of the products that we make.

Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which 
powers two separate internal circuits; one being a relatively low current 
electronics powered by a purchased over-the-shelf 24Vdc power supply, and 
second, a high current furnace of some type; inductiv

Re: [PSES] Unexplained High Fallout of Power Supplies

[ce-test, qualified testing bv - Gert Gremmen]

Hi Brian,

Apart from ESD problems :

My 2 cents...
High inrush currents, due to (renewed) electrical installations ?
Inrush current may happen also after a sudden interruption...

Residential mains systems have limited capacity of prospective short circuit 
current.
Industrial mains may have 10's or 100'x more ...

Impossible to test in the lab without a really high power supply.


Gert Gremmen

-Original Message-
From: Brian O'Connell [mailto:oconne...@tamuracorp.com] 
Sent: Tuesday 15 September 2015 23:36
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

If you have nothing between the p/s and mains, and you cannot detect any 
surges, and there are no similar operating conditions for the failed units, 
then:

1. have QC look at all of the component PCNs.
2. audit factory ESD from component receiving to final test and packing.
3. audit all internal ECNs for changes to control circuit and layout.

Recommend three immediate p/s comparative tests to see is something changed 
from old to new stuff 1. efficiency.
2. waveforms on the main switch(s) (g/s and g/d) during turn-on and load-steps.
3. conducted emissions.

Brian

From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: Tuesday, September 15, 2015 1:53 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Unexplained High Fallout of Power Supplies

Our company's Service Department provides monthly field repair reports to our 
R department who looks for patterns and high fallout of components. Over the 
last 6 to 12 months, we have noticed a high fallout of Power Supplies in the 
United States. However, we have not been able to find the reason for the 
fallout. The power supplies have all shown arc damage to the AC front end, 
signs of arcing and traces burned or vaporized, blown fuses, and shorted FETs 
and/or Rectifiers. These failures have occurred on several different locations, 
on different power supply models, different manufactures and on different 
instruments. Some instruments have been in service for years; some for only a 
few weeks before they fail. Some instruments even have surge suppression 
modules installed and though the power supplies fail the surge modules tested 
out fine. The failures did not occur during any known lightning storm or any 
other known transient. Very strange.

Of those of you who read these emails, have you experienced an unusual increase 
in such field failures in the last year? 

Anyone have an idea of what might be causing this increase?

We test our products and power supplies to the IEC 61000-4-4 and 4-5 fast 
transient and surge immunity tests. We actually test beyond what is required 
for CE in Europe (often to the limit of our test equipment which is 5kV) and we 
audit every family of products about once a year. We have performed additional 
testing of production power supplies of known models that have failed in the 
field yet no unusual problems have been found.  We also perform radiated and 
conducted RF immunity tests, ESD, voltage dips and dropouts, frequency 
variation testing, and harmonic and inter-harmonic immunity tests with no 
discernable problems found.

We have AC Line Analyzers running for months at several customer locations and 
have not detected any unusual transients or reason for the high fallout of 
power supplies.

Two weeks ago we had a power supply blow in one of our own labs on an 
instrument that had been running for several years. Two R engineers were sent 
over to investigate. They changed out the power supply and verified the 
instrument was running properly. As they turned to walk out of the room, POW!!, 
the power supply in the instrument next to the one they just fixed blew up. A 
power line analyzer has been running ever since but not unusual transients have 
been detected, yet. 

Are we missing something? Is there additional transient tests that we are not 
performing that we should be?  Is there something we should be looking for and 
are not? Has this last year been unusually bad for power grid problems, sun 
spots, alien transmissions, ??

We are stumped. Thanks for any advice and comments. 

The Other Brian




LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you. 
-

This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send your e-mail to 
<emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the 
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Instru

Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
, 
dated Wed, 16 Sep 2015, Pat Lawler  writes:



Have there been changes to the design of your system,


including 'improvements'. (;-)
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Ken Wyatt]

Hi Brian,

Pat offers some great advice with respect to filter stability and resulting 
ringing. This is not something normally tested using a transient generator, so 
should be examined.

I’d also like to add an observation. During the time I worked for HP/Agilent in 
their scopes division, we also started noticing in the late-1990s that power 
supplies had become the #1 field failure. We pretty much determined (maybe more 
of a guess at that point) that due to the variety of failures across different 
products and vendors, that it was most likely a reliability issue, rather than 
due strictly to over stress. In fact, in the mid-1970s, the NAVY had come to 
the same conclusion and had instituted similar reliability research on power 
supplies. 

Our environmental test engineer, Brian Dahl (the “other other Brian”), who was 
also an expert (a black belt) in reliability, instituted two major changes in 
our power supply vendor selection process:

1. HALT testing of all power supplies (as well as whole products)

2. Life Testing of all power supplies

For those unfamiliar, HALT (highly accelerated life testing) is a combination 
of very fast changing temperature extremes (high to low and visa versa in 1-2 
minutes) in combination with three-axis vibration. He would run HALT on samples 
of power supplies prior to our selecting a final vendor.

Those supplies that passed the HALT were then subjected to long term life 
testing in a large walk-in temperature chamber. He’d take a sample of 10 to 20 
power supplies from each potential vendor, place them under full resistive 
loads and cycle the temperature every 5 to 10 minutes for 1 to 2 months.

After starting this program, field failures of power supplies dropped almost 
off the list.

Here are some references that might be helpful:

http://www.cui.com/catalog/resource/reliability-considerations 


http://www.astrodynetdi.com/pdf/MTBF_and_Power_Supply_Reliability.pdf 


http://www.sre.org/pubs/Mil-Hdbk-338B.pdf 


http://snebulos.mit.edu/projects/reference/MIL-STD/MIL-HDBK-217F-Notice2.pdf 


I might add that Brian was a nominee for EDN's “Test Engineer of the Year” back 
then. If anyone would like to pick his brain, he may be reached at 
brian_d...@keysight.com . I’m copying him on 
this email.

Cheers, Ken

___

I'm here to help you succeed! Feel free to call or email with any questions 
related to EMC or EMI troubleshooting - at no obligation. I'm always happy to 
help!

Kenneth Wyatt
Wyatt Technical Services LLC
56 Aspen Dr.
Woodland Park, CO 80863

Phone: (719) 310-5418

Email Me!  | Web Site 
 | Blog 
The EMC Blog (EDN) 
Subscribe to Newsletter 
Connect with me on LinkedIn 
> On Sep 16, 2015, at 6:50 AM, Pat Lawler  wrote:
> 
> Hi Brian,
> 
> - Have there been changes to the design of your system, specifically
> the AC EMI filter?  Increased inductor values, either by design or
> vendor change (filter manufacturer, or type of core used in the
> filter) could cause excessive ringing at the input of the power supply
> at turn-on.
> - Try putting high-voltage scope probes at the input of the power
> supply to see the common and differential mode voltage at turn-on, or
> during line surge testing at 200V levels.  I had one case where the
> filter caused ringing to 2x the applied voltage!
> - Is your equipment installed differently now, either by installation
> or removal of isolation transformers or grounding changes?
> 
> I once had a customer claim that our power supplies no longer met the
> IEC 61000-4-5 line surge requirement, and the equipment was resetting.
> After many heated conference calls, they admitted the equipment was
> actually a redesign, with the addition of a Wi-Fi module.  Not knowing
> what else to try, I asked if they disconnected the Wi-Fi module,
> returning the system to it's previous design configuration.
> It turns out the noise from the line surge test was being picked up by
> the Wi-Fi module and getting conducted into the rest of the system.
> 
> Pat
> 
> On Tue, Sep 15, 2015 at 1:53 PM, Kunde, Brian  wrote:
>> Our company’s Service Department provides monthly field repair reports to
>> our R department who looks for patterns and high fallout of components.
>> Over the last 6 to 12 months, we have noticed a high fallout of Power
>> Supplies in the United States. However, we have not been able to find the
>> reason for the fallout. The power supplies have all shown arc 

Re: [PSES] Unexplained High Fallout of Power Supplies

[Pat Lawler]

Hi Brian,

- Have there been changes to the design of your system, specifically
the AC EMI filter?  Increased inductor values, either by design or
vendor change (filter manufacturer, or type of core used in the
filter) could cause excessive ringing at the input of the power supply
at turn-on.
- Try putting high-voltage scope probes at the input of the power
supply to see the common and differential mode voltage at turn-on, or
during line surge testing at 200V levels.  I had one case where the
filter caused ringing to 2x the applied voltage!
- Is your equipment installed differently now, either by installation
or removal of isolation transformers or grounding changes?

I once had a customer claim that our power supplies no longer met the
IEC 61000-4-5 line surge requirement, and the equipment was resetting.
After many heated conference calls, they admitted the equipment was
actually a redesign, with the addition of a Wi-Fi module.  Not knowing
what else to try, I asked if they disconnected the Wi-Fi module,
returning the system to it's previous design configuration.
It turns out the noise from the line surge test was being picked up by
the Wi-Fi module and getting conducted into the rest of the system.

Pat

On Tue, Sep 15, 2015 at 1:53 PM, Kunde, Brian  wrote:
> Our company’s Service Department provides monthly field repair reports to
> our R department who looks for patterns and high fallout of components.
> Over the last 6 to 12 months, we have noticed a high fallout of Power
> Supplies in the United States. However, we have not been able to find the
> reason for the fallout. The power supplies have all shown arc damage to the
> AC front end, signs of arcing and traces burned or vaporized, blown fuses,
> and shorted FETs and/or Rectifiers. These failures have occurred on several
> different locations, on different power supply models, different
> manufactures and on different instruments. Some instruments have been in
> service for years; some for only a few weeks before they fail. Some
> instruments even have surge suppression modules installed and though the
> power supplies fail the surge modules tested out fine. The failures did not
> occur during any known lightning storm or any other known transient. Very
> strange.
>
>
>
> Of those of you who read these emails, have you experienced an unusual
> increase in such field failures in the last year?
>
>
>
> Anyone have an idea of what might be causing this increase?
>
>
>
> We test our products and power supplies to the IEC 61000-4-4 and 4-5 fast
> transient and surge immunity tests. We actually test beyond what is required
> for CE in Europe (often to the limit of our test equipment which is 5kV) and
> we audit every family of products about once a year. We have performed
> additional testing of production power supplies of known models that have
> failed in the field yet no unusual problems have been found.  We also
> perform radiated and conducted RF immunity tests, ESD, voltage dips and
> dropouts, frequency variation testing, and harmonic and inter-harmonic
> immunity tests with no discernable problems found.
>
>
>
> We have AC Line Analyzers running for months at several customer locations
> and have not detected any unusual transients or reason for the high fallout
> of power supplies.
>
>
>
> Two weeks ago we had a power supply blow in one of our own labs on an
> instrument that had been running for several years. Two R engineers were
> sent over to investigate. They changed out the power supply and verified the
> instrument was running properly. As they turned to walk out of the room,
> POW!!, the power supply in the instrument next to the one they just fixed
> blew up. A power line analyzer has been running ever since but not unusual
> transients have been detected, yet.
>
>
>
> Are we missing something? Is there additional transient tests that we are
> not performing that we should be?  Is there something we should be looking
> for and are not? Has this last year been unusually bad for power grid
> problems, sun spots, alien transmissions, ??
>
>
>
> We are stumped. Thanks for any advice and comments.
>
>
>
> The Other Brian
>
>
>
>
>
>
>
> 
>
> LECO Corporation Notice: This communication may contain confidential
> information intended for the named recipient(s) only. If you received this
> by mistake, please destroy it and notify us of the error. Thank you.
>
> -
> 
>
> This message is from the IEEE Product Safety Engineering Society emc-pstc
> discussion list. To post a message to the list, send your e-mail to
> emc-p...@ieee.org
>
> All emc-pstc postings are archived and searchable on the web at:
> http://www.ieee-pses.org/emc-pstc.html
>
> Attachments are not permitted but the IEEE PSES Online Communities site at
> http://product-compliance.oc.ieee.org/ can be used for graphics (in
> well-used formats), large files, 

Re: [PSES] Unexplained High Fallout of Power Supplies

[CR]

On 9/15/2015 4:53 PM, Kunde, Brian wrote:
we have not been able to find the reason for the fallout. The power 
supplies have all shown arc damage to the AC front end, signs of 
arcing and traces burned or vaporized, blown fuses, and shorted FETs 
and/or Rectifiers. These failures have occurred on several different 
locations, on different power supply models, different manufactures 
and on different instruments. Some instruments have been in service 
for years; some for only a few weeks before they fail. Some 
instruments even have surge suppression modules installed and though 
the power supplies fail the surge modules tested out fine. The 
failures did not occur during any known lightning storm or any other 
known transient.

Brian,

The circumstances you describe -- arcing with no external transient seen 
-- point to an on-board occurrence, not an external one.  I'd suspect 
(in no particular order and on little information -- heh) ) PWB material 
with insufficient dielectric withstand, and/or oscillation in a power 
FET due to its characteristics (or another device's) having changed 
enough to make the control loop unstable.  You might have an oscillator 
the controller can't even detect.


I'm on LinkedIn if you need help, eh?

Cortland Richmond

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

Thanks to all for your input and suggestions. You all have given us several 
areas to look at.

The power supply failures have been on six different models or power supplies 
and two different manufacturers. We have also seen a couple line filters fails 
which are unusual. The failures have occurred in both new products and in 
products that have been operating in the field for several years.

Because of the architecture of our products, many have large high current AC 
Line Filters upstream from these small AC/DC power supplies (generally 150-300 
watt 24Vdc output).  We are aware of the phenomena where the Surge pulse gets 
amplified due to the large cores in the line filters. This is why we 
pre-qualify all power supplies with the line filter intended to be used. We 
will also test surges up to 5kV (test to failure) so we can see how the Power 
Supply fails under those conditions. Some models pass, but when power supplies 
do fail during this test they generally just such down and won’t restart. No 
BANG, no smoke, no flash. However, the power supplies failing in the field are 
blowing their guts out (described earlier).

We will be looking again at the Inrush currents observed during a momentary 
voltage dropout. We perform the voltage dropout test with a programmable power 
supply and large transformer to be able to generate a limited amount of Inrush 
Current. However, our 300 watt power supplies are used in a product that is 
plugged into a 30A – 50A single phase branch circuit. I assume that such a 
circuit in a commercial or industrial environment can produce much larger 
inrush currents than is possible with our test equipment in the EMC Lab. Maybe 
high inrush currents are over-taxing the bridge rectifier causing its 
self-destruction. We have something to play around with.

If you have any other ideas, please let me know.

Thanks for your help as always.

The Other Brian


From: Ken Wyatt [mailto:k...@emc-seminars.com]
Sent: Wednesday, September 16, 2015 9:33 AM
To: Pat Lawler; Kunde, Brian
Cc: EMC-PSTC@LISTSERV.IEEE.ORG; Brian Dahl
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

Hi Brian,

Pat offers some great advice with respect to filter stability and resulting 
ringing. This is not something normally tested using a transient generator, so 
should be examined.

I’d also like to add an observation. During the time I worked for HP/Agilent in 
their scopes division, we also started noticing in the late-1990s that power 
supplies had become the #1 field failure. We pretty much determined (maybe more 
of a guess at that point) that due to the variety of failures across different 
products and vendors, that it was most likely a reliability issue, rather than 
due strictly to over stress. In fact, in the mid-1970s, the NAVY had come to 
the same conclusion and had instituted similar reliability research on power 
supplies.

Our environmental test engineer, Brian Dahl (the “other other Brian”), who was 
also an expert (a black belt) in reliability, instituted two major changes in 
our power supply vendor selection process:

1. HALT testing of all power supplies (as well as whole products)

2. Life Testing of all power supplies

For those unfamiliar, HALT (highly accelerated life testing) is a combination 
of very fast changing temperature extremes (high to low and visa versa in 1-2 
minutes) in combination with three-axis vibration. He would run HALT on samples 
of power supplies prior to our selecting a final vendor.

Those supplies that passed the HALT were then subjected to long term life 
testing in a large walk-in temperature chamber. He’d take a sample of 10 to 20 
power supplies from each potential vendor, place them under full resistive 
loads and cycle the temperature every 5 to 10 minutes for 1 to 2 months.

After starting this program, field failures of power supplies dropped almost 
off the list.

Here are some references that might be helpful:

http://www.cui.com/catalog/resource/reliability-considerations

http://www.astrodynetdi.com/pdf/MTBF_and_Power_Supply_Reliability.pdf

http://www.sre.org/pubs/Mil-Hdbk-338B.pdf

http://snebulos.mit.edu/projects/reference/MIL-STD/MIL-HDBK-217F-Notice2.pdf

I might add that Brian was a nominee for EDN's “Test Engineer of the Year” back 
then. If anyone would like to pick his brain, he may be reached at 
brian_d...@keysight.com<mailto:brian_d...@keysight.com>. I’m copying him on 
this email.

Cheers, Ken

___

I'm here to help you succeed! Feel free to call or email with any questions 
related to EMC or EMI troubleshooting - at no obligation. I'm always happy to 
help!

Kenneth Wyatt
Wyatt Technical Services LLC
56 Aspen Dr.
Woodland Park, CO 80863

Phone: (719) 310-5418

Email Me!<mailto:k...@emc-seminars.com> | Web Site<http://www.emc-seminars.com> 
| Blog<http://design-4-emc.com/>
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Subscribe to Newsletter<http:

Re: [PSES] Unexplained High Fallout of Power Supplies

[Joe Randolph]

Hi Brian:

 

When evaluating field failures due to surges, I find it very helpful to 
carefully inspect each unit returned from the field to try and identify the 
path that the surge took through the equipment.  Then, the components in that 
path are carefully examined for clues about what happened.  Usually, much can 
be learned by carefully studying units that suffered unexpected damage in the 
field.

 

I agree with Courtland Richmond that in your particular case, it is not 100% 
clear that the damage is surge related.  Even so, careful inspection of failed 
units should provide some useful clues.

 

I know of one case where the manufacturer, after suffering the type of 
frustration you are having, instituted a policy that every-single-unit that 
failed in the field was sent to one engineer for analysis.  Failed units were 
analyzed and photographed before being discarded.  Certain patterns became 
apparent, and it turned out that there was more than one failure mechanism 
taking place.  Over time, each mechanism was systematically identified and 
steps were taken to upgrade the design accordingly.

 

One thing I don’t think you have mentioned is whether the failures appear to be 
limited to the line side of the isolation barrier, or involve an actual failure 
of the isolation barrier.  These would point to different mechanisms.

 

One last comment.  You mention testing up to 5 kV, but it’s not clear how the 
surge is applied (such as common mode or differential), and the waveforms and 
short-circuit currents are not identified.  Without more information I can’t 
say for sure how much your tests are stressing the power supply.  In general, 
though, I consider 5 kV to be a rather low number in terms of the open-circuit 
voltage of a surge test for an AC mains interface.  

 

This topic can be debated endlessly, but a brief review of IEEE C.62.41 will 
provide some perspective on the problem of identifying appropriate 
surge-tolerance requirements for equipment that connects to the AC mains.  In 
general, I do not think that simply complying with the applicable regulatory 
standards will guarantee reliable performance in the field.

 

 

Joe Randolph

Telecom Design Consultant

Randolph Telecom, Inc.

781-721-2848 (USA)

 <mailto:j...@randolph-telecom.com> j...@randolph-telecom.com

 <http://www.randolph-telecom.com> http://www.randolph-telecom.com

 

From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Wednesday, September 16, 2015 2:54 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

 

Thanks to all for your input and suggestions. You all have given us several 
areas to look at.

 

The power supply failures have been on six different models or power supplies 
and two different manufacturers. We have also seen a couple line filters fails 
which are unusual. The failures have occurred in both new products and in 
products that have been operating in the field for several years. 

 

Because of the architecture of our products, many have large high current AC 
Line Filters upstream from these small AC/DC power supplies (generally 150-300 
watt 24Vdc output).  We are aware of the phenomena where the Surge pulse gets 
amplified due to the large cores in the line filters. This is why we 
pre-qualify all power supplies with the line filter intended to be used. We 
will also test surges up to 5kV (test to failure) so we can see how the Power 
Supply fails under those conditions. Some models pass, but when power supplies 
do fail during this test they generally just such down and won’t restart. No 
BANG, no smoke, no flash. However, the power supplies failing in the field are 
blowing their guts out (described earlier). 

 

We will be looking again at the Inrush currents observed during a momentary 
voltage dropout. We perform the voltage dropout test with a programmable power 
supply and large transformer to be able to generate a limited amount of Inrush 
Current. However, our 300 watt power supplies are used in a product that is 
plugged into a 30A – 50A single phase branch circuit. I assume that such a 
circuit in a commercial or industrial environment can produce much larger 
inrush currents than is possible with our test equipment in the EMC Lab. Maybe 
high inrush currents are over-taxing the bridge rectifier causing its 
self-destruction. We have something to play around with.

 

If you have any other ideas, please let me know. 

 

Thanks for your help as always.

 

The Other Brian

 

 

From: Ken Wyatt [ <mailto:k...@emc-seminars.com> mailto:k...@emc-seminars.com] 
Sent: Wednesday, September 16, 2015 9:33 AM
To: Pat Lawler; Kunde, Brian
Cc:  <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG; Brian Dahl
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

 

Hi Brian,

 

Pat offers some great advice with respect to filter stability and resulting 
ringing. This is not something normally 

Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB02716E48@Mailbox-Tech.lecotech.local>, 
dated Wed, 16 Sep 2015, "Kunde, Brian"  writes:


However, our 300 watt power supplies are used in a product that is 
plugged into a 30A – 50A single phase branch circuit. I assume that 
such a circuit in a commercial or industrial environment can produce 
much larger inrush currents than is possible with our test equipment in 
the EMC Lab.


To drop a worst-case 10% of 230 V at 50 A, the source resistance is 
0.046 ohms, and the prospective short-circuit current is 500 A. You can 
expect real supplies not to be anywhere near worst-case for 
voltage-drop, so think 2500 A or so.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[John Woodgate]

In message , dated Wed, 16 Sep 2015, 
John Woodgate  writes:


To drop a worst-case 10% of 230 V at 50 A, the source resistance is 
0.046 ohms


No, 0.46 ohms, but the rest is OK.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
When I turn my back on the sun, it's to look for a rainbow
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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list. To post a message to the list, send your e-mail to 

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Bob LaFrance]

Or process changes?  New board vendor?  New cleaning process?

Regards,
Bob LaFrance
N9NEO
Design Engineer
Creare Inc.
16 Great Hollow Road
Hanover, NH 
603-640-2539


-Original Message-
From: John Woodgate [mailto:j...@jmwa.demon.co.uk] 
Sent: Wednesday, September 16, 2015 9:20 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Unexplained High Fallout of Power Supplies

In message
<camsb7hssjfdzex4bf0j9_aocs-s6h8c5k2xwk26if5sfx6e...@mail.gmail.com>,
dated Wed, 16 Sep 2015, Pat Lawler <plawl...@gmail.com> writes:

>Have there been changes to the design of your system,

including 'improvements'. (;-)
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn 
my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and 
Associates, Rayleigh, Essex UK

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Re: [PSES] Unexplained High Fallout of Power Supplies

[Brian O'Connell]

If you have nothing between the p/s and mains, and you cannot detect any 
surges, and there are no similar operating conditions for the failed units, 
then:

1. have QC look at all of the component PCNs.
2. audit factory ESD from component receiving to final test and packing.
3. audit all internal ECNs for changes to control circuit and layout.

Recommend three immediate p/s comparative tests to see is something changed 
from old to new stuff
1. efficiency.
2. waveforms on the main switch(s) (g/s and g/d) during turn-on and load-steps.
3. conducted emissions.

Brian

From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Tuesday, September 15, 2015 1:53 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Unexplained High Fallout of Power Supplies

Our company's Service Department provides monthly field repair reports to our 
R department who looks for patterns and high fallout of components. Over the 
last 6 to 12 months, we have noticed a high fallout of Power Supplies in the 
United States. However, we have not been able to find the reason for the 
fallout. The power supplies have all shown arc damage to the AC front end, 
signs of arcing and traces burned or vaporized, blown fuses, and shorted FETs 
and/or Rectifiers. These failures have occurred on several different locations, 
on different power supply models, different manufactures and on different 
instruments. Some instruments have been in service for years; some for only a 
few weeks before they fail. Some instruments even have surge suppression 
modules installed and though the power supplies fail the surge modules tested 
out fine. The failures did not occur during any known lightning storm or any 
other known transient. Very strange.

Of those of you who read these emails, have you experienced an unusual increase 
in such field failures in the last year? 

Anyone have an idea of what might be causing this increase?

We test our products and power supplies to the IEC 61000-4-4 and 4-5 fast 
transient and surge immunity tests. We actually test beyond what is required 
for CE in Europe (often to the limit of our test equipment which is 5kV) and we 
audit every family of products about once a year. We have performed additional 
testing of production power supplies of known models that have failed in the 
field yet no unusual problems have been found.  We also perform radiated and 
conducted RF immunity tests, ESD, voltage dips and dropouts, frequency 
variation testing, and harmonic and inter-harmonic immunity tests with no 
discernable problems found.

We have AC Line Analyzers running for months at several customer locations and 
have not detected any unusual transients or reason for the high fallout of 
power supplies.

Two weeks ago we had a power supply blow in one of our own labs on an 
instrument that had been running for several years. Two R engineers were sent 
over to investigate. They changed out the power supply and verified the 
instrument was running properly. As they turned to walk out of the room, POW!!, 
the power supply in the instrument next to the one they just fixed blew up. A 
power line analyzer has been running ever since but not unusual transients have 
been detected, yet. 

Are we missing something? Is there additional transient tests that we are not 
performing that we should be?  Is there something we should be looking for and 
are not? Has this last year been unusually bad for power grid problems, sun 
spots, alien transmissions, ??

We are stumped. Thanks for any advice and comments. 

The Other Brian




LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you. 
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[PSES] Unexplained High Fallout of Power Supplies

[Kunde, Brian]

Our company's Service Department provides monthly field repair reports to our 
R department who looks for patterns and high fallout of components. Over the 
last 6 to 12 months, we have noticed a high fallout of Power Supplies in the 
United States. However, we have not been able to find the reason for the 
fallout. The power supplies have all shown arc damage to the AC front end, 
signs of arcing and traces burned or vaporized, blown fuses, and shorted FETs 
and/or Rectifiers. These failures have occurred on several different locations, 
on different power supply models, different manufactures and on different 
instruments. Some instruments have been in service for years; some for only a 
few weeks before they fail. Some instruments even have surge suppression 
modules installed and though the power supplies fail the surge modules tested 
out fine. The failures did not occur during any known lightning storm or any 
other known transient. Very strange.

Of those of you who read these emails, have you experienced an unusual increase 
in such field failures in the last year?

Anyone have an idea of what might be causing this increase?

We test our products and power supplies to the IEC 61000-4-4 and 4-5 fast 
transient and surge immunity tests. We actually test beyond what is required 
for CE in Europe (often to the limit of our test equipment which is 5kV) and we 
audit every family of products about once a year. We have performed additional 
testing of production power supplies of known models that have failed in the 
field yet no unusual problems have been found.  We also perform radiated and 
conducted RF immunity tests, ESD, voltage dips and dropouts, frequency 
variation testing, and harmonic and inter-harmonic immunity tests with no 
discernable problems found.

We have AC Line Analyzers running for months at several customer locations and 
have not detected any unusual transients or reason for the high fallout of 
power supplies.

Two weeks ago we had a power supply blow in one of our own labs on an 
instrument that had been running for several years. Two R engineers were sent 
over to investigate. They changed out the power supply and verified the 
instrument was running properly. As they turned to walk out of the room, POW!!, 
the power supply in the instrument next to the one they just fixed blew up. A 
power line analyzer has been running ever since but not unusual transients have 
been detected, yet.

Are we missing something? Is there additional transient tests that we are not 
performing that we should be?  Is there something we should be looking for and 
are not? Has this last year been unusually bad for power grid problems, sun 
spots, alien transmissions, ??

We are stumped. Thanks for any advice and comments.

The Other Brian




LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you.

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discussion list. To post a message to the list, send your e-mail to 


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Website:  http://www.ieee-pses.org/
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