Re: [time-nuts] SMPS or conventional?

[ed breya]

Yes, the physical/thermal stress wear and tear depends on the device 
response relative to the ripple frequency. TECs aren't the only things 
with these issues - even modern high power LEDs used for illumination 
are known to last longest when run from "pure" DC, for a given average 
power level.


For our sorts of applications, the ripple issues should be moot. As has 
been mentioned, we don't want TEC drive ripple signals near precision, 
sensitive circuits either, so properly filtering and cleaning the 
applied power both reduces electrical interference, and prolongs the TEC 
life. Except for the increased complexity, who wouldn't want that?


Ed

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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

Depends very much on what sort of environment it’s in ….

Bob

> On Dec 21, 2020, at 9:03 PM, Dana Whitlow  wrote:
> 
> A properly-tuned PID system does not cycle!
> 
> Dana
> 
> 
> On Mon, Dec 21, 2020 at 6:49 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Finding a data sheet on a TEC that goes past *very* basic stuff is
>> essentially
>> impossible. The bottom line is that the people who make them very much
>> want to sell them to you. Finding information in those data sheets that
>> suggest
>> problems … not so much.
>> 
>> The problem is (mainly) physical. The expansion / contraction of the
>> device is
>> a big deal. KHz level PWM is (likely) not a problem. Aggressive cycling
>> from
>> something like a PID is indeed an issue.
>> 
>> Bob
>> 
>>> On Dec 21, 2020, at 6:43 PM, Hal Murray  wrote:
>>> 
>>> [Old mail, context is TECs]
>>> 
>>> bruce.griffi...@xtra.co.nz said:
 If the drive current ripple is too high fatigue failure from cyclic
 thermomechanical stress can be significant.
>>> 
>>> Do good data sheets say anything about that?
>>> 
>>> Is there a frequency term in there?  Can I use PWM, which is as much
>> ripple as
>>> you can get, as long as the frequency is high enough?  If yes, ballpark
>> of how
>>> high?
>>> 
>>> Physically, where is the heat/cold generated?  Is it mostly at the
>> junction?
>>> 
>>> --
>>> These are my opinions.  I hate spam.
>>> 
>>> 
>>> 
>>> 
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Re: [time-nuts] SMPS or conventional?

[Lux, Jim]

On 12/21/20 5:59 PM, Gerhard Hoffmann wrote:


Both agree that ripple > 1 KHz is harmless. But then the current 
delivered
to the TEC is quite large usually -  and It's a different question if 
you want such
large and dirty currents on your table or in your device. 



Yes.. we were testing a sensitive receiver for 5-30 MHz, and were 
thinking the TEC would be the best way to step it through the 
temperature sequence for calibration.  Even with the receiver in a box, 
and coax for the test signal, the noise from the PWM completely 
obliterated the signals of interest.



On the other hand, we used that same TEC unit to run simulated lunar 
regolith up and down in temperature, hooked up to a gas analyzer.  That 
was fine.


https://tetech.com/product-category/temperature-controllers/



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Re: [time-nuts] SMPS or conventional?

[Dana Whitlow]

A properly-tuned PID system does not cycle!

Dana


On Mon, Dec 21, 2020 at 6:49 PM Bob kb8tq  wrote:

> Hi
>
> Finding a data sheet on a TEC that goes past *very* basic stuff is
> essentially
> impossible. The bottom line is that the people who make them very much
> want to sell them to you. Finding information in those data sheets that
> suggest
> problems … not so much.
>
> The problem is (mainly) physical. The expansion / contraction of the
> device is
> a big deal. KHz level PWM is (likely) not a problem. Aggressive cycling
> from
> something like a PID is indeed an issue.
>
> Bob
>
> > On Dec 21, 2020, at 6:43 PM, Hal Murray  wrote:
> >
> > [Old mail, context is TECs]
> >
> > bruce.griffi...@xtra.co.nz said:
> >> If the drive current ripple is too high fatigue failure from cyclic
> >> thermomechanical stress can be significant.
> >
> > Do good data sheets say anything about that?
> >
> > Is there a frequency term in there?  Can I use PWM, which is as much
> ripple as
> > you can get, as long as the frequency is high enough?  If yes, ballpark
> of how
> > high?
> >
> > Physically, where is the heat/cold generated?  Is it mostly at the
> junction?
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
> >
> > ___
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Re: [time-nuts] SMPS or conventional?

[Gerhard Hoffmann]

Am 22.12.20 um 00:43 schrieb Hal Murray:

[Old mail, context is TECs] bruce.griffi...@xtra.co.nz said:
If the drive current ripple is too high fatigue failure from cyclic 
thermomechanical stress can be significant. 
Do good data sheets say anything about that? Is there a frequency term 
in there? Can I use PWM, which is as much ripple as you can get, as 
long as the frequency is high enough? If yes, ballpark of how high? 
Physically, where is the heat/cold generated? Is it mostly at the 
junction? 


The g**gl search for "TE coolers ripple current" delivers the first 2 
hits of 3.65e6:



< 
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiQ4YK0tuDtAhWKCewKHckIALoQFjAAegQIBRAC&url=https%3A%2F%2Fwww.ii-vi.com%2Fwp-content%2Fuploads%2F2020%2F07%2FMRLW_Working_with_Thermoelectric_Materials.pdf&usg=AOvVaw3pbUbFp4SsfdKsBzRNf-Wi 
   >


(that looks dangerous  :-)  and


< https://www.ferrotec-nord.com/technology-of-thermoelectric-module/    >


Both agree that ripple > 1 KHz is harmless. But then the current delivered
to the TEC is quite large usually -  and It's a different question if 
you want such

large and dirty currents on your table or in your device.

The thermal resistance between the hot and cold side is not very large
and that explains part of the suboptimum efficiency.

You do not want such a thing to regulate the temperature of a crystal etc
because if you externally heat or cool one side, that will soon propagate
to the other side; delta T stays constant until your regulator takes note
and corrects it.


Oh, and the google search shows that everybody and their dogs make
TE controller chips.


Gerhard






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Re: [time-nuts] SMPS or conventional?

[Bruce Griffiths]

Original source about TEC lifetime reduction when the TEC ripple cureent is 
high:
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1991-02.pdf
Page 74
I suspect that someone there may have been bitten by the short TEC life 
experienced without the LC filter. 
Although they used relatively small TECs the size of the individual Peltier 
element is the determining factor for the ripple current frequency dependence 
of TEC life. HP used a 40kHz PWM frequency.

There should be a relatively uniform temperature gradient along the length of 
each Peltier element.

TEC module datasheets are generally silent on the effect of ripple current on 
TEC lifetime.

CUI merely indicate that keeping the TEC ripple current below 5% ensures that 
TEC performance is maximised.

Peltier element solder junctions to the ceramic endplates usually fail after 
3000 cycles or therabouts.
CUI use a compliant thermally conductive adhesive to achieve a longer cycle 
life.
Bruce
> On 22 December 2020 at 12:43 Hal Murray  wrote:
> 
> 
> [Old mail, context is TECs]
> 
> bruce.griffi...@xtra.co.nz said:
> > If the drive current ripple is too high fatigue failure from cyclic
> > thermomechanical stress can be significant. 
> 
> Do good data sheets say anything about that?
> 
> Is there a frequency term in there?  Can I use PWM, which is as much ripple 
> as 
> you can get, as long as the frequency is high enough?  If yes, ballpark of 
> how 
> high?
> 
> Physically, where is the heat/cold generated?  Is it mostly at the junction?
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

Finding a data sheet on a TEC that goes past *very* basic stuff is essentially 
impossible. The bottom line is that the people who make them very much 
want to sell them to you. Finding information in those data sheets that suggest
problems … not so much. 

The problem is (mainly) physical. The expansion / contraction of the device is 
a big deal. KHz level PWM is (likely) not a problem. Aggressive cycling from
something like a PID is indeed an issue. 

Bob

> On Dec 21, 2020, at 6:43 PM, Hal Murray  wrote:
> 
> [Old mail, context is TECs]
> 
> bruce.griffi...@xtra.co.nz said:
>> If the drive current ripple is too high fatigue failure from cyclic
>> thermomechanical stress can be significant. 
> 
> Do good data sheets say anything about that?
> 
> Is there a frequency term in there?  Can I use PWM, which is as much ripple 
> as 
> you can get, as long as the frequency is high enough?  If yes, ballpark of 
> how 
> high?
> 
> Physically, where is the heat/cold generated?  Is it mostly at the junction?
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] SMPS or conventional?

[Hal Murray]

[Old mail, context is TECs]

bruce.griffi...@xtra.co.nz said:
> If the drive current ripple is too high fatigue failure from cyclic
> thermomechanical stress can be significant. 

Do good data sheets say anything about that?

Is there a frequency term in there?  Can I use PWM, which is as much ripple as 
you can get, as long as the frequency is high enough?  If yes, ballpark of how 
high?

Physically, where is the heat/cold generated?  Is it mostly at the junction?

-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] SMPS or conventional?

[Andrew Rodland]

On Monday, November 23, 2020 7:33:49 AM EST 李 wrote:
> When the Rb clock is working, it needs a high temperature, isn't heat
> dissipation breaking the heat balance?Increased power consumption？

It needs a *stable* temperature. It has a heater to provide regulation. The 
thing about a heater for stabilizing temperature is... it can only heat, it 
can't cool. A modest amount of cooling ensures that the system can respond to 
ambient temperature variations in both directions. A super-insulated device 
that gets too hot is helpless.

Andrew



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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

The physics package is not really that different than an OCXO. It needs to hit 
this or that temperature. You 
derate the parts that go into the “hot zone” in order to hit a “reasonable" 
MTBF. Indeed, some manufacturers 
seem to do a better job in this regard than others. 

The parts on the rest of the device seem to be pretty standard stuff in the 
Rb’s I’ve torn open ( = lots of them ). 
The assumption seems to be that there will be cooling to keep those parts at a 
reasonable temperature. Since
the impact is to MTBF, it’s very much a “only time will tell” if they got it 
right. 

Bob

> On Nov 24, 2020, at 8:29 AM, 李  wrote:
> 
> I see, I've always wondered if the internal electronics are specially made 
> because the modules are really too hot.
> Assuming a temperature increase of 10 degrees and the operating life is 
> reduced by half, the module life should not be long.
> 
> 
>   
> 李
> 邮箱bd...@126.com
>  
> 签名由
>  网易邮箱大师  定制
> 
> On 11/23/2020 22:15, Bob kb8tq  wrote:
> Hi
> 
> There are two “zones” in the typical Rb physics package. They both need to be 
> heated. Unfortunately they need
> to be heated to *different* temperatures. This makes for an interesting 
> design. Insulate things to well and the one
> that is supposed to be at a slightly lower temperature is heated up by energy 
> from the hotter zone. In addition, the 
> board with all the electronics on it ( or boards) are full of very normal 
> electronic components. Their failure rate goes 
> up the hotter they get. 
> 
> Heat sinks do indeed help keep all of this in balance. The heaters are 
> designed to get the physics package to the
> appropriate temperature from some very low point ( 0 or maybe -30C). They 
> have *plenty* of reserve power 
> capability. In addition, they run at relatively low power (relative to their 
> ratings) in normal operation. Optimizing 
> to reduce their failure rate while increasing the failure rate of a few 
> hundred other parts does not improve the life
> of the Rb …
> 
> Bob
> 
> 
>> On Nov 23, 2020, at 7:33 AM, 李 mailto:bd...@126.com>> wrote:
>> 
>> When the Rb clock is working, it needs a high temperature, isn't heat 
>> dissipation breaking the heat balance?Increased power consumption？
>> 
>> 
>> 
>> 
>> 
>>  
>> 李
>> 邮箱bd...@126.com
>>  
>> 签名由
>>  网易邮箱大师  定
>> 
> 

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Re: [time-nuts] SMPS or conventional?

[李]

I see, I've always wondered if the internal electronics are specially made 
because the modules are really too hot.
Assuming a temperature increase of 10 degrees and the operating life is reduced 
by half, the module life should not be long.


| |
李
|
|
邮箱bd...@126.com
|

签名由 网易邮箱大师 定制

On 11/23/2020 22:15, Bob kb8tq wrote:
Hi


There are two “zones” in the typical Rb physics package. They both need to be 
heated. Unfortunately they need
to be heated to *different* temperatures. This makes for an interesting design. 
Insulate things to well and the one
that is supposed to be at a slightly lower temperature is heated up by energy 
from the hotter zone. In addition, the 
board with all the electronics on it ( or boards) are full of very normal 
electronic components. Their failure rate goes 
up the hotter they get. 


Heat sinks do indeed help keep all of this in balance. The heaters are designed 
to get the physics package to the
appropriate temperature from some very low point ( 0 or maybe -30C). They have 
*plenty* of reserve power 
capability. In addition, they run at relatively low power (relative to their 
ratings) in normal operation. Optimizing 
to reduce their failure rate while increasing the failure rate of a few hundred 
other parts does not improve the life
of the Rb …


Bob




On Nov 23, 2020, at 7:33 AM, 李  wrote:


When the Rb clock is working, it needs a high temperature, isn't heat 
dissipation breaking the heat balance?Increased power consumption？





| |
李
|
|
邮箱bd...@126.com
|

签名由 网易邮箱大师 定


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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

There are two “zones” in the typical Rb physics package. They both need to be 
heated. Unfortunately they need
to be heated to *different* temperatures. This makes for an interesting design. 
Insulate things to well and the one
that is supposed to be at a slightly lower temperature is heated up by energy 
from the hotter zone. In addition, the 
board with all the electronics on it ( or boards) are full of very normal 
electronic components. Their failure rate goes 
up the hotter they get. 

Heat sinks do indeed help keep all of this in balance. The heaters are designed 
to get the physics package to the
appropriate temperature from some very low point ( 0 or maybe -30C). They have 
*plenty* of reserve power 
capability. In addition, they run at relatively low power (relative to their 
ratings) in normal operation. Optimizing 
to reduce their failure rate while increasing the failure rate of a few hundred 
other parts does not improve the life
of the Rb …

Bob


> On Nov 23, 2020, at 7:33 AM, 李  wrote:
> 
> When the Rb clock is working, it needs a high temperature, isn't heat 
> dissipation breaking the heat balance?Increased power consumption？
> 
> 
> 
> 
> 
>   
> 李
> 邮箱bd...@126.com
>  
> 签名由
>  网易邮箱大师  定
> 

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Re: [time-nuts] SMPS or conventional?

[李]

When the Rb clock is working, it needs a high temperature, isn't heat 
dissipation breaking the heat balance?Increased power consumption？





| |
李
|
|
邮箱bd...@126.com
|

签名由 网易邮箱大师 定制

On 10/23/2020 20:56, Bob kb8tq wrote:
Hi

I must admit, the longevity of the compressor based setup in the typical kitchen
fridge continues to amaze me. :).

===

TEC’s have a fairly limited “pumping range”. It is not uncommon to discover you
need to stack them to get this or that job done. We wound up with a stack of
5 to get one project working.

In some designs the TEC / stack never does anything other than run at X current.
If the goal is “take care of an Rb out in the (-10 to +45C) garage”, it’s going 
to see
a lot of cycles …

Fun !!

Bob

> On Oct 23, 2020, at 6:29 AM, Poul-Henning Kamp  wrote:
>
> 
>
>> TEC’s are indeed prone to wear out. That said, so is a compressor …..
>
> The mechanism is almost entirely mechanical and running a TEC at a
> stable current almost 100% mitigates it.
>
> The surefire way to force the wearout is to reverse the current
> direction a lot.
>
> Whatever you use to control the TEC, needs to understand that there
> is a 1:3 efficiency difference between the two directions, just
> slapping a PI(D) on a TEC is guaranteed to kill it.
>
> --
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.


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Re: [time-nuts] SMPS or conventional?

[John Moran, Scawby Design]

From: ed breya <mailto:e...@telight.com>
To: mailto:time-nuts@lists.febo.com
Subject: Re: [time-nuts] SMPS or conventional?

"Regarding TEC life, ..."

A really good reference to TECs, especially factors affecting lifetime is here -

https://tetech.com/faqs/

John 


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Re: [time-nuts] SMPS or conventional?

[Poul-Henning Kamp]

Bob kb8tq writes:

> I must admit, the longevity of the compressor based setup in the typical 
> kitchen 
> fridge continues to amaze me. :). 

Thank Mads Clausen for that:


https://www.secop.com/fileadmin/user_upload/files/danfoss_compressor_business_book_english.pdf


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

I must admit, the longevity of the compressor based setup in the typical 
kitchen 
fridge continues to amaze me. :). 

===

TEC’s have a fairly limited “pumping range”. It is not uncommon to discover you
need to stack them to get this or that job done. We wound up with a stack of
5 to get one project working. 

In some designs the TEC / stack never does anything other than run at X 
current. 
If the goal is “take care of an Rb out in the (-10 to +45C) garage”, it’s going 
to see 
a lot of cycles …

Fun !!

Bob

> On Oct 23, 2020, at 6:29 AM, Poul-Henning Kamp  wrote:
> 
> 
> 
>> TEC’s are indeed prone to wear out. That said, so is a compressor …..
> 
> The mechanism is almost entirely mechanical and running a TEC at a
> stable current almost 100% mitigates it.
> 
> The surefire way to force the wearout is to reverse the current
> direction a lot.
> 
> Whatever you use to control the TEC, needs to understand that there
> is a 1:3 efficiency difference between the two directions, just
> slapping a PI(D) on a TEC is guaranteed to kill it.
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.


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Re: [time-nuts] SMPS or conventional?

[Poul-Henning Kamp]

> TEC’s are indeed prone to wear out. That said, so is a compressor …..

The mechanism is almost entirely mechanical and running a TEC at a
stable current almost 100% mitigates it.

The surefire way to force the wearout is to reverse the current
direction a lot.

Whatever you use to control the TEC, needs to understand that there
is a 1:3 efficiency difference between the two directions, just
slapping a PI(D) on a TEC is guaranteed to kill it.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] SMPS or conventional?

[Angus via time-nuts]

   I suspect that one of the main issues these days is the quality of
the module - there is a lot of unbranded stuff out there of unknown
quality.
   Cooling a rubidium is probably a relatively easy life for a peltier
since there are limited temperature changes, but I would still make
sure that I had a spare to drop in if I did have an issue.
   Since you tend to rate cooling for worst case, and it's usually a
lot less efficient there, the peltier will usually spend most of its
time at a fraction of full power.
   I don't think that they like unfiltered PWM, but there are plenty
of other reasons to avoid that in this case anyway.

Angus

On Wed, 21 Oct 2020 21:36:41 -0700, you wrote:

>> like with TEC heat/cool capability
>
>What's the typical MTBF of TEC coolers?  How much does it depend on how much 
>power you put through them?

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Re: [time-nuts] SMPS or conventional?

[Bruce Griffiths]

If the drive current ripple is too high fatigue failure from cyclic 
thermomechanical stress can be significant.

Bruce
> On 23 October 2020 at 10:37 ed breya  wrote:
> 
> 
> Regarding TEC life, in my experience, what wrecks them the most is 
> cooling applications where the cold side is below the dew point, and 
> water condenses out onto and into the TEC Peltier array. This eventually 
> rots the elements from corrosion and electrolysis, until something craps 
> out. If the TEC will be exposed to ambient air, and run below or even 
> near the expected dew point, the sides should be sealed up with silicone 
> goop for longer life. Even then, it's not foolproof, since it will never 
> be a perfect seal.
> 
> If the TEC is in a closed, benign environment or vacuum, then it should 
> last indefinitely, unless abused power-dissipation-wise, or mechanically 
> by thermal stress. When the temperature cycles, the whole part must be 
> allowed to change dimensions slightly, so the mounting needs to have 
> some compliance.
> 
> Ed
> 
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Re: [time-nuts] SMPS or conventional?

[ed breya]

Regarding TEC life, in my experience, what wrecks them the most is 
cooling applications where the cold side is below the dew point, and 
water condenses out onto and into the TEC Peltier array. This eventually 
rots the elements from corrosion and electrolysis, until something craps 
out. If the TEC will be exposed to ambient air, and run below or even 
near the expected dew point, the sides should be sealed up with silicone 
goop for longer life. Even then, it's not foolproof, since it will never 
be a perfect seal.


If the TEC is in a closed, benign environment or vacuum, then it should 
last indefinitely, unless abused power-dissipation-wise, or mechanically 
by thermal stress. When the temperature cycles, the whole part must be 
allowed to change dimensions slightly, so the mounting needs to have 
some compliance.


Ed

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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

The magnetic field sensitivity is dependent on a lot of things. 
Strangely enough, the higher the C field, the more sensitive 
the physics package is ( yes, that’s weird …). All Rb’s incorporate
shielding to reduce the external field impact. Since the shielding
is rarely perfect, there are asymmetries in the response. 

All that turns this into a “field from here at level X” matters on this
Rb and not on that one sort of thing. 

===

The “easy” way to get a feel for what’s what is to rotate the device 
in the horizontal plane. The earth’s mag field (unless you are close
to the magnetic poles) will change in a predictable manner. If you see
a measurable frequency change … you have an answer.

The more complicated approach uses Helmholtz coils. It’s more complicated
mainly because they take time to fab …..

Both approaches are only approximate unless you go a bit crazy on 
a bunch of minor details. 

Bob

> On Oct 22, 2020, at 6:17 AM, Angus via time-nuts  
> wrote:
> 
> Hi,
> 
>   The magnetic field issue has bothered me a little too, but I don't
> know whether it has a practical effect. Maybe putting a fan in a
> plastic or aluminium box close to the Rb might show something - unless
> someone already knows the effects.
> 
>   I have a compass on the bench beside the LPRO, and it does drift a
> bit. What surprised me most was how much the field around the mains
> transformers changed each time they are switched on or off.
> 
> Angus.
> 
> On Wed, 21 Oct 2020 10:04:11 -0400, you wrote:
> 
>> Hi
>> 
>> The only issue with the “controlled fan” approach is that you
>> have a variable magnetic field as a result. That and the vibration
>> both can impact the stability of the Rb. Some means of isolating
>> the fan from the immediate vicinity of the Rb sounds like a good idea. 
>> 
>> Bob
>> 
>>> On Oct 21, 2020, at 9:31 AM, Luiz Alberto Saba  wrote:
>>> 
>>> I am thinking in an black aluminium finned heatsink, the size of the base 
>>> plate, and a fan, controlled by an electronic thermostat (sensor direct 
>>> coupled to the heatsink). Is that ok?
>>> 
>>> Em 21/10/2020 09:40, Wannes Sels escreveu:
 There are conflicting requirements regarding temperature in Rb's:
 
 - For best performance, the rubidium and quartz oscillators must be kept at
 a high and stable temperature.
 - For reliability, the supporting electronics must be kept at a lower
 temperature.
 
 The heater takes care of the high temperature. The stability of the
 temperature can be improved by increasing the thermal mass, i.e. adding a
 block of aluminium or copper.
 The electronics can be kept cooler with a heatsink, and forced ventilation
 if needed.
 
 When you stick both the electronics and physics in a small package, this
 becomes more difficult. For the PRS-10 some form of heatsink is pretty much
 required to keep the electronics cool enough. Although I seem to remember
 reading somewhere that the "benchtop" heatsink they offer now is lighter
 than older units.
 
 If the room temperature is not stable enough, you might want to increase
 the size of the heatsink and add a fan. This reduces the temperature swing
 inside the unit, while still cooling the electronics, at the cost of
 increased power draw for the heater.
 
 
 
 
 On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:
 
>> I spent a lot of years buying Rb’s and putting them on small heatsinks.
> I
>> always was disappointed in their reliability. That continued to be the
> case
>> up to the point that the baseplate temp’s got into the 40C region.  In my
>> case, that took a fan 
> .
> How well did it work if the heat sink wasn't small?  What is your version
> of
> small?
> 
> Do you have any data (or vague memories) of how much it helps to orient
> the
> heat sink so the fins are vertical so they encourage warm air to flow up
> past
> the fins?
> 
> --
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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>>> 
>>> 
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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

TEC’s are indeed prone to wear out. That said, so is a compressor …..

Bob

> On Oct 22, 2020, at 12:36 AM, Hal Murray  wrote:
> 
>> like with TEC heat/cool capability
> 
> What's the typical MTBF of TEC coolers?  How much does it depend on how much 
> power you put through them?
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] SMPS or conventional?

[Angus via time-nuts]

Hi,

   The magnetic field issue has bothered me a little too, but I don't
know whether it has a practical effect. Maybe putting a fan in a
plastic or aluminium box close to the Rb might show something - unless
someone already knows the effects.

   I have a compass on the bench beside the LPRO, and it does drift a
bit. What surprised me most was how much the field around the mains
transformers changed each time they are switched on or off.

Angus.

On Wed, 21 Oct 2020 10:04:11 -0400, you wrote:

>Hi
>
>The only issue with the “controlled fan” approach is that you
>have a variable magnetic field as a result. That and the vibration
>both can impact the stability of the Rb. Some means of isolating
>the fan from the immediate vicinity of the Rb sounds like a good idea. 
>
>Bob
>
>> On Oct 21, 2020, at 9:31 AM, Luiz Alberto Saba  wrote:
>> 
>> I am thinking in an black aluminium finned heatsink, the size of the base 
>> plate, and a fan, controlled by an electronic thermostat (sensor direct 
>> coupled to the heatsink). Is that ok?
>> 
>> Em 21/10/2020 09:40, Wannes Sels escreveu:
>>> There are conflicting requirements regarding temperature in Rb's:
>>> 
>>> - For best performance, the rubidium and quartz oscillators must be kept at
>>> a high and stable temperature.
>>> - For reliability, the supporting electronics must be kept at a lower
>>> temperature.
>>> 
>>> The heater takes care of the high temperature. The stability of the
>>> temperature can be improved by increasing the thermal mass, i.e. adding a
>>> block of aluminium or copper.
>>> The electronics can be kept cooler with a heatsink, and forced ventilation
>>> if needed.
>>> 
>>> When you stick both the electronics and physics in a small package, this
>>> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
>>> required to keep the electronics cool enough. Although I seem to remember
>>> reading somewhere that the "benchtop" heatsink they offer now is lighter
>>> than older units.
>>> 
>>> If the room temperature is not stable enough, you might want to increase
>>> the size of the heatsink and add a fan. This reduces the temperature swing
>>> inside the unit, while still cooling the electronics, at the cost of
>>> increased power draw for the heater.
>>> 
>>> 
>>> 
>>> 
>>> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:
>>> 
> I spent a lot of years buying Rb’s and putting them on small heatsinks.
 I
> always was disappointed in their reliability. That continued to be the
 case
> up to the point that the baseplate temp’s got into the 40C region.  In my
> case, that took a fan ….
 How well did it work if the heat sink wasn't small?  What is your version
 of
 small?
 
 Do you have any data (or vague memories) of how much it helps to orient
 the
 heat sink so the fins are vertical so they encourage warm air to flow up
 past
 the fins?
 
 --
 These are my opinions.  I hate spam.
 
 
 
 
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 time-nuts mailing list -- time-nuts@lists.febo.com
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>>> ___
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>> 
>> 
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>
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Re: [time-nuts] SMPS or conventional?

[Hal Murray]

> like with TEC heat/cool capability

What's the typical MTBF of TEC coolers?  How much does it depend on how much 
power you put through them?

-- 
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Re: [time-nuts] SMPS or conventional?

[ed breya]

Regarding linear versus SMPS, I always prefer linear where possible. As 
others have said, for assessing a SMPS, try it and see. If it does the 
job sufficiently without too much noise, then go with it.


Regarding Rb cooling, I don't know about the newer, smaller ones - I 
only have three big old Efratom M-100s - but if they have provision for 
heatsink or chassis cooling, then use it. The MTBF info Neville put up 
shows the benefit. As far as I know, the "ambient" temperature sometimes 
seen in Rb specs is actually the base plate temperature, assuming use of 
a heatsink large enough that they are roughly the same.


Each of my M-100s came with a very nice black-anodized, extruded Al 
heatsink, perfectly fitted, hardware-wise. In my portable reference 
project, I put the Rb on the inside of the Al back panel, and the 
heatsink opposite on the outside, for convection cooling, and of course, 
a generous film of conductive goop between each interface surface. The 
screws go through the heatsink and back panel, into the base plate, so 
in reality, the back panel is just pinched in between.


The other two units are planned to be together in a dual system, with 
both mounted on a single, heavy Al plate, which is mounted on rubber 
isolation hardware. The thermal plan is to surround everything except 
the plate with foam sheet insulation, and let them self-heat to 
something a bit above the highest expected ambient temperature - maybe 
40-42 deg C. When this range is reached, a variable speed blower will 
feed cooling air to the plate through ducting, to provide some degree of 
temperature regulation, depending on how well I design the arrangement 
and its control system, and squeeze everything into the limited space. 
In anticipation of too cold an ambient temperature, there are also 
heater resistors on the plate for just in case, and of course a thermal 
cutout switch to shut it all down if things go very wrong. Fans and 
blowers are the weakest link in this sort of stuff.


This is all experimental, and only partially built, into an old rack 
style HP instrument carcass. Some day I may finish it. The best approach 
though, would be true regulation at some lower temperature for better 
MTBF, like with TEC heat/cool capability, but this gets to be much 
bigger and more complicated.


Ed

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Re: [time-nuts] SMPS or conventional?

[Skip Withrow]

Hello Time-Nuts,
Though this thread started out asking about power supplies, it seems
to have morphed into a Rb cooling discussion as well.

I undertook a similar PRS-10 project a while back.  Since the PRS-10
uses an SC cut crystal and has decent phase noise for a small rubidium
I went the linear regulator route to try and preserve the 'goodness'.

For cooling, I hate fans.  They are noisy, they fail, and they
generate magnetic fields.  So, I sandwiched a couple of TEC coolers
between the PRS-10 and a heat pipe unit from an old server.  I have an
AD590 sensor and simple control circuit that keeps the baseplate at a
controlled temperature and the heat is transported out to the back of
the box and dissipated by convection. I love it.

My only complaint is the resolution of the PRS-10.  Everything goes
through the uP, including the EFC voltage, and the minimum DDS
resolution is about 2x10E-12.  So you will never get anything better
than a good GPSDO anyway.  Might as well stick with the GPSDO with a
good oscillator, unless you actually need some long-term holdover
performance.

Regards,
Skip Withrow

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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

The only issue with the “controlled fan” approach is that you
have a variable magnetic field as a result. That and the vibration
both can impact the stability of the Rb. Some means of isolating
the fan from the immediate vicinity of the Rb sounds like a good idea. 

Bob

> On Oct 21, 2020, at 9:31 AM, Luiz Alberto Saba  wrote:
> 
> I am thinking in an black aluminium finned heatsink, the size of the base 
> plate, and a fan, controlled by an electronic thermostat (sensor direct 
> coupled to the heatsink). Is that ok?
> 
> Em 21/10/2020 09:40, Wannes Sels escreveu:
>> There are conflicting requirements regarding temperature in Rb's:
>> 
>> - For best performance, the rubidium and quartz oscillators must be kept at
>> a high and stable temperature.
>> - For reliability, the supporting electronics must be kept at a lower
>> temperature.
>> 
>> The heater takes care of the high temperature. The stability of the
>> temperature can be improved by increasing the thermal mass, i.e. adding a
>> block of aluminium or copper.
>> The electronics can be kept cooler with a heatsink, and forced ventilation
>> if needed.
>> 
>> When you stick both the electronics and physics in a small package, this
>> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
>> required to keep the electronics cool enough. Although I seem to remember
>> reading somewhere that the "benchtop" heatsink they offer now is lighter
>> than older units.
>> 
>> If the room temperature is not stable enough, you might want to increase
>> the size of the heatsink and add a fan. This reduces the temperature swing
>> inside the unit, while still cooling the electronics, at the cost of
>> increased power draw for the heater.
>> 
>> 
>> 
>> 
>> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:
>> 
 I spent a lot of years buying Rb’s and putting them on small heatsinks.
>>> I
 always was disappointed in their reliability. That continued to be the
>>> case
 up to the point that the baseplate temp’s got into the 40C region.  In my
 case, that took a fan ….
>>> How well did it work if the heat sink wasn't small?  What is your version
>>> of
>>> small?
>>> 
>>> Do you have any data (or vague memories) of how much it helps to orient
>>> the
>>> heat sink so the fins are vertical so they encourage warm air to flow up
>>> past
>>> the fins?
>>> 
>>> --
>>> These are my opinions.  I hate spam.
>>> 
>>> 
>>> 
>>> 
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>>> 
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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

> On Oct 21, 2020, at 8:40 AM, Wannes Sels  wrote:
> 
> There are conflicting requirements regarding temperature in Rb's:
> 
> - For best performance, the rubidium and quartz oscillators must be kept at
> a high and stable temperature.
> - For reliability, the supporting electronics must be kept at a lower
> temperature.
> 
> The heater takes care of the high temperature. The stability of the
> temperature can be improved by increasing the thermal mass, i.e. adding a
> block of aluminium or copper.

If you are designing the internals of the OCXO or Rb from scratch, this may
help things. If you have a part of eBay … likely not so much. 

> The electronics can be kept cooler with a heatsink, and forced ventilation
> if needed.
> 
> When you stick both the electronics and physics in a small package, this
> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
> required to keep the electronics cool enough. Although I seem to remember
> reading somewhere that the "benchtop" heatsink they offer now is lighter
> than older units.

The PRS-10 is hardly unique in this regard. All of the small Rb’s ( = anything 
other than a 5065 sized unit) that I’ve seen really do need a heatsink in order
to live a long and happy life. 

Bob


> 
> If the room temperature is not stable enough, you might want to increase
> the size of the heatsink and add a fan. This reduces the temperature swing
> inside the unit, while still cooling the electronics, at the cost of
> increased power draw for the heater.
> 
> 
> 
> 
> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:
> 
>> 
>>> I spent a lot of years buying Rb’s and putting them on small heatsinks.
>> I
>>> always was disappointed in their reliability. That continued to be the
>> case
>>> up to the point that the baseplate temp’s got into the 40C region.  In my
>>> case, that took a fan ….
>> 
>> How well did it work if the heat sink wasn't small?  What is your version
>> of
>> small?
>> 
>> Do you have any data (or vague memories) of how much it helps to orient
>> the
>> heat sink so the fins are vertical so they encourage warm air to flow up
>> past
>> the fins?
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
>> 
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>> 
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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

The devices all *worked* just fine, even without any heatsink 
at all. There was no performance impact to the (lack of) heatsink
in a normal lab environment. 

Small in this case is mounting the device to a heatsink that is the
size of the “hot” side and maybe a half inch of fins. Fins always get
oriented to be vertical. 

Again, the only issue is reliability.

Bob

> On Oct 20, 2020, at 11:08 PM, Hal Murray  wrote:
> 
> 
>> I spent a lot of years buying Rb’s and putting them on small heatsinks.  I
>> always was disappointed in their reliability. That continued to be the case
>> up to the point that the baseplate temp’s got into the 40C region.  In my
>> case, that took a fan …. 
> 
> How well did it work if the heat sink wasn't small?  What is your version of 
> small?
> 
> Do you have any data (or vague memories) of how much it helps to orient the 
> heat sink so the fins are vertical so they encourage warm air to flow up past 
> the fins?
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] SMPS or conventional?

[Luiz Alberto Saba]

I am thinking in an black aluminium finned heatsink, the size of the 
base plate, and a fan, controlled by an electronic thermostat (sensor 
direct coupled to the heatsink). Is that ok?


Em 21/10/2020 09:40, Wannes Sels escreveu:

There are conflicting requirements regarding temperature in Rb's:

- For best performance, the rubidium and quartz oscillators must be kept at
a high and stable temperature.
- For reliability, the supporting electronics must be kept at a lower
temperature.

The heater takes care of the high temperature. The stability of the
temperature can be improved by increasing the thermal mass, i.e. adding a
block of aluminium or copper.
The electronics can be kept cooler with a heatsink, and forced ventilation
if needed.

When you stick both the electronics and physics in a small package, this
becomes more difficult. For the PRS-10 some form of heatsink is pretty much
required to keep the electronics cool enough. Although I seem to remember
reading somewhere that the "benchtop" heatsink they offer now is lighter
than older units.

If the room temperature is not stable enough, you might want to increase
the size of the heatsink and add a fan. This reduces the temperature swing
inside the unit, while still cooling the electronics, at the cost of
increased power draw for the heater.




On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:


I spent a lot of years buying Rb’s and putting them on small heatsinks.

I

always was disappointed in their reliability. That continued to be the

case

up to the point that the baseplate temp’s got into the 40C region.  In my
case, that took a fan ….

How well did it work if the heat sink wasn't small?  What is your version
of
small?

Do you have any data (or vague memories) of how much it helps to orient
the
heat sink so the fins are vertical so they encourage warm air to flow up
past
the fins?

--
These are my opinions.  I hate spam.




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Re: [time-nuts] SMPS or conventional?

[Dana Whitlow]

I prefer the use of non-switching power supplies, in part because I am
forced to use
indoor receiving antennas not very far from my equipment setup.  However,
one of my
Rb standards, an used L-Pro which I bought from another ham, came with a
SMPS
and I've never noted any particular problem.  So, my advice is: if you
have  SMPS
that you trust not to fail and blow up your Rb, first give it a try to see
what happens.

Regarding cooling of Rb standards:
Truly, the addition of a fixed-speed fan will reduce the thermal resistance
between
"ambient" temperature and the device being cooled.  However, said reduction
of
the thermal resistance shortens the thermal time constant, increasing the
responsivity
to ambient temperature variations.

I see two likely approaches to improving the situation:

a)  As has been mentioned several times, substantially increase the thermal
mass of
 the device being cooled, combined with fan cooling of the heatsink.  A
downside
 of this is that system warmup time may be increased enough to be
bothersome.

b)  Use a variable-speed fan controlled by a loop which strives to maintain
a constant
 temperature of the heatsink to which the device is attached once a
reasonable
 temperature (moderately above ambient yet still comfortable for the
device) is
 reached.

I believe that (b) is probably the more effective way to go.  If done well,
it could
provide superior frequency stability as well as the shortest warmup time.
However,
choice (b) adds to the system complexity hence risk of an expensive failure.

Dana




On Wed, Oct 21, 2020 at 7:46 AM Wannes Sels  wrote:

> There are conflicting requirements regarding temperature in Rb's:
>
> - For best performance, the rubidium and quartz oscillators must be kept at
> a high and stable temperature.
> - For reliability, the supporting electronics must be kept at a lower
> temperature.
>
> The heater takes care of the high temperature. The stability of the
> temperature can be improved by increasing the thermal mass, i.e. adding a
> block of aluminium or copper.
> The electronics can be kept cooler with a heatsink, and forced ventilation
> if needed.
>
> When you stick both the electronics and physics in a small package, this
> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
> required to keep the electronics cool enough. Although I seem to remember
> reading somewhere that the "benchtop" heatsink they offer now is lighter
> than older units.
>
> If the room temperature is not stable enough, you might want to increase
> the size of the heatsink and add a fan. This reduces the temperature swing
> inside the unit, while still cooling the electronics, at the cost of
> increased power draw for the heater.
>
>
>
>
> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray 
> wrote:
>
> >
> > > I spent a lot of years buying Rb’s and putting them on small heatsinks.
> > I
> > > always was disappointed in their reliability. That continued to be the
> > case
> > > up to the point that the baseplate temp’s got into the 40C region.  In
> my
> > > case, that took a fan ….
> >
> > How well did it work if the heat sink wasn't small?  What is your version
> > of
> > small?
> >
> > Do you have any data (or vague memories) of how much it helps to orient
> > the
> > heat sink so the fins are vertical so they encourage warm air to flow up
> > past
> > the fins?
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
> >
> > ___
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> > To unsubscribe, go to
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> >
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Re: [time-nuts] SMPS or conventional?

[Tom Van Baak]

> Planning to build my "reference box" with a rubidium & a gpsdo.

I went through this power supply decision making process with my first 
OCXO and Rb standards. In the end my conclusions are "if you can't 
measure it then don't worry about it". You can see how that leads to a 
side hobby of noise measurement!


There are any number of subtle decisions with operating a precision 
standard at home. This creates widely varying conditions from one 
person's shack to another person's lab. So for me a universal rule is 
difficult. In addition often the better the standard the more it is 
designed to attenuate external effects like variations in temperature, 
wander in supply voltage, or noise on any of the inputs.


I used to use high quality linear power supplies only. Now I usually use 
switchers. Part of it is that switching technology has progressed well 
over the decades. Part of it is that I can now make incredibly precise 
measurements and if the power supply gives me any PN spurs or any ADEV 
effects, I avoid it. Surprisingly some of the cleanest power supplies 
I've used are $15 switcher desktop or wall wart types. So that's what I 
often use now. If you have a DMM or 'scope or SA put it to use on the 
power supply itself or on the frequency standard output and see what you 
can find.


The other lesson I learned is to keep batteries and AC power supplies 
out of the box if possible. Use the box to hold the OCXO / Rb: for 
mechanical stability, for protection, for RF shielding, and for passive 
thermal management. Give it DC, and make the decision on where to get 
that DC independent of the box you're making. This also makes it much 
easier to implement clean or redundant power to the box. My worst 
experiences are battery chargers inside the box itself. That's too 
chemical, erratic, and noisy an operation to be in close proximity of a 
precision standard. Plus it's a maintenance hassle every few years when 
you have to replace the battery. I also avoid fans if I can. YMMV. These 
are just some of the things I've run into.


/tvb


On 10/19/2020 7:24 AM, Luiz Alberto Saba wrote:

Hi guys

Planning to build my "reference box" with a rubidium & a gpsdo.
SMPS will do a good job or the transformer+bridge+capacitor+regulator 
is best suited for this application?
In the "test phase" I've used a switched ps for the rubidium and a 
conventional for the gpsdo.


Thanks

Luiz Alberto Saba

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Re: [time-nuts] SMPS or conventional?

[Neville Michie]

IN the Datum User’s Guide for the LPRO there is a set of data for MTBF.
Ambient TemperatureMTBF Hours
20  381000
25  351000
30  32
40  253000
50  189000
60  134000
This shows the clear advantage of keeping to unit cool.
The data also shows the improved stability if the temperature is constant.

cheers, Neville Michie




> On 21 Oct 2020, at 23:40, Wannes Sels  wrote:
> 
> There are conflicting requirements regarding temperature in Rb's:
> 
> - For best performance, the rubidium and quartz oscillators must be kept at
> a high and stable temperature.
> - For reliability, the supporting electronics must be kept at a lower
> temperature.
> 
> The heater takes care of the high temperature. The stability of the
> temperature can be improved by increasing the thermal mass, i.e. adding a
> block of aluminium or copper.
> The electronics can be kept cooler with a heatsink, and forced ventilation
> if needed.
> 
> When you stick both the electronics and physics in a small package, this
> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
> required to keep the electronics cool enough. Although I seem to remember
> reading somewhere that the "benchtop" heatsink they offer now is lighter
> than older units.
> 
> If the room temperature is not stable enough, you might want to increase
> the size of the heatsink and add a fan. This reduces the temperature swing
> inside the unit, while still cooling the electronics, at the cost of
> increased power draw for the heater.
> 
> 
> 
> 
> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:
> 
>> 
>>> I spent a lot of years buying Rb’s and putting them on small heatsinks.
>> I
>>> always was disappointed in their reliability. That continued to be the
>> case
>>> up to the point that the baseplate temp’s got into the 40C region.  In my
>>> case, that took a fan ….
>> 
>> How well did it work if the heat sink wasn't small?  What is your version
>> of
>> small?
>> 
>> Do you have any data (or vague memories) of how much it helps to orient
>> the
>> heat sink so the fins are vertical so they encourage warm air to flow up
>> past
>> the fins?
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
>> 
>> ___
>> time-nuts mailing list -- time-nuts@lists.febo.com
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>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>> 
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Re: [time-nuts] SMPS or conventional?

[Wannes Sels]

There are conflicting requirements regarding temperature in Rb's:

- For best performance, the rubidium and quartz oscillators must be kept at
a high and stable temperature.
- For reliability, the supporting electronics must be kept at a lower
temperature.

The heater takes care of the high temperature. The stability of the
temperature can be improved by increasing the thermal mass, i.e. adding a
block of aluminium or copper.
The electronics can be kept cooler with a heatsink, and forced ventilation
if needed.

When you stick both the electronics and physics in a small package, this
becomes more difficult. For the PRS-10 some form of heatsink is pretty much
required to keep the electronics cool enough. Although I seem to remember
reading somewhere that the "benchtop" heatsink they offer now is lighter
than older units.

If the room temperature is not stable enough, you might want to increase
the size of the heatsink and add a fan. This reduces the temperature swing
inside the unit, while still cooling the electronics, at the cost of
increased power draw for the heater.




On Wed, Oct 21, 2020 at 5:38 AM Hal Murray  wrote:

>
> > I spent a lot of years buying Rb’s and putting them on small heatsinks.
> I
> > always was disappointed in their reliability. That continued to be the
> case
> > up to the point that the baseplate temp’s got into the 40C region.  In my
> > case, that took a fan ….
>
> How well did it work if the heat sink wasn't small?  What is your version
> of
> small?
>
> Do you have any data (or vague memories) of how much it helps to orient
> the
> heat sink so the fins are vertical so they encourage warm air to flow up
> past
> the fins?
>
> --
> These are my opinions.  I hate spam.
>
>
>
>
> ___
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> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
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>
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Re: [time-nuts] SMPS or conventional?

[Hal Murray]

> I spent a lot of years buying Rb’s and putting them on small heatsinks.  I
> always was disappointed in their reliability. That continued to be the case
> up to the point that the baseplate temp’s got into the 40C region.  In my
> case, that took a fan …. 

How well did it work if the heat sink wasn't small?  What is your version of 
small?

Do you have any data (or vague memories) of how much it helps to orient the 
heat sink so the fins are vertical so they encourage warm air to flow up past 
the fins?

-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

I spent a lot of years buying Rb’s and putting them on small heatsinks. 
I always was disappointed in their reliability. That continued to be the
case up to the point that the baseplate temp’s got into the 40C region. 
In my case, that took a fan ….

Bob

> On Oct 20, 2020, at 7:32 PM, Bill Notfaded  wrote:
> 
> Here's a couple pictures of my PRS10 running disciplined by LEA-6T.  You
> can see the big heatsink I have it attached to it.  A good heatsink
> attached definitely helps!
> 
> Bill
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Re: [time-nuts] SMPS or conventional?

[Luiz Alberto Saba]

Hi Bob

In a previous tread, someone said that cooling PRS-10 will only make the 
unit consume more energy, since it has to maintain the lamp hot.

Is this wrong?
Before I read the previous tread, I was thinking of electronic 
thermostat/fan but...


Em 20/10/2020 10:34, Bob kb8tq escreveu:

Hi

Not very well organized message here …. I’m still working on my first cup of
coffee …:)

First up: What do I do?

My “lab” is in the basement of our house. There is HVAC running pretty much
year round. The temperature “wanders” between about 20 and 25 C over a
year. It cycles about 2 or 3 C at roughly a 1 to 2 hour rate. I have three 5065
Rb’s running full time on a rack. I have a couple of GPSDO’s running on another
rack. Various OCXO’s get tested on a bench. All of it is “out in the open”.

I have looked into various approaches to temperature control ( thermo electric
heaters ….). I have a big pile of water pumps, TEC’s, piping, and radiators
siting in a dark corner of the room. The more I looked into the power required
to do that, the less I liked the idea ….

I do have a few cardboard boxes and a small pile of “beach towels” that I use.
If the measurement is particularly sensitive, I put a towel over the test set. 
If
the device is large, I put a box over it. That generally works quite well to 
reduce
fast changing temperature from drafts in the room.

==

Are you trying to lock the PRS-10 to the UCCM? If so, don’t bother, the net
result is a PRS-10 that is not very stable. Just use the UCCM’s output.

Practically speaking, the PRS-10 is a 0-50C device. It’s no different than other
Rb’s in that respect. It also is no different than the rest in making those 
limits
really hard to pull out of the data sheet. They talk about 65C baseplate, but
that’s not ambient.

The UCCM has an OCXO in it that is (probably) rated too 70C. It depends a
bit on what version / vendor you happen to have. In still air the OCXO is ok
to 50, in moving air, it should be all right at 70. No idea how the rest of the 
parts
on the board will do above 50C / moving air. ( = I’d bet there will be problems
above 50C).

The PRS-10 needs a heatsink on it or it will quickly die. It will live a longer 
life
with a better / bigger heatsink. With a small one, figure 2 years. With a fan or
something large, figure > 5 years of life. That’s all in a indoor situation 
with a
HVAC system keeping the ambient around 20 to 25C. The small heatsink
gets around 50, the bigger one + fan may get down to 40C.

The real issue with both the PRS-10 and the UCCM  is to reduce the temperature
swings. The UCCM will track out long term changes. You just need to protect it
from quick changes. Depending on which PRS-10 you have the temperature 
performance
may be better or worse (per the specifications on the part). A wooden box with
heaters / fans can do this, there are other ways.

A lot depends on just how crazy it gets where you are in Brazil  does it get 
above
40C? ( I looked it up, the record is 44.7C …. yikes … ). Ideally you want to 
keep
the heatsink around 40C. That’s not going to happen if it’s 40 out. Running the
part at 55 C all the time is not a good idea.

More or less, you normally need 10C of “headroom” on any sort of heated device
(like a heated wooden box). You also have a practical problem coming up with
a heatsink that gets to < 10C relative to ambient. The net is that your heatsink
is at “max ambient” + 20C. For a somewhat more practical heatsink, the numbers
are worse …. sorry about that.

What’s a “big” heatsink? Think of something the size of the Rb with a high speed
fan attached. As noted in various posts the magnetic field from the fan will not
make the Rb happy, some sort of ducting to keep it a bit further away might be
a good idea. That sort of thing probably *does* get you within 10C of ambient .

The bottom line is that this sort of gear normally gets used in a location that 
has
heating / cooling. Temperature may swing from 10 to 30, but that’s about it. 
They
generally have pretty big fans moving air around. A cell phone “base station” is
one example of this sort of setup.

Probably enough for now…..

Bob



On Oct 20, 2020, at 7:36 AM, Luiz Alberto Saba  wrote:

Hi Bob

I will try with the toroid setup (as soon as I receive the transformer) and see 
what happens.
I'm really lost in respect of thermal insulation (or cooling).
I'll use a PRS-10 and a Samsung UCCM gpsdo.
A single mass of copper (or alluminium) wil be effective for PRS-10?
I saw in an old trend here people saying that forced cooling is not good for 
the PRS-10.
Closed box or ventilation holes?
It will operate at ambient temperature, in Brazil...
If you or someone has some hints about what to do in this respect, I'll be very 
grateful.

Thanks

Luiz Alberto Saba


Em 19/10/2020 17:35, Bob kb8tq escreveu:

Hi

One weird issue with big caps in a linear supply:

As you increase the size of the caps on the bridge rectifier, the ripple
voltage goes down. The ripple *current* 

Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

> On Oct 20, 2020, at 10:45 AM, Luiz Alberto Saba  wrote:
> 
> Hi Bob
> 
> In a previous tread, someone said that cooling PRS-10 will only make the unit 
> consume more energy, since it has to maintain the lamp hot.
> Is this wrong?

You need to read the entire thread. Cooling a Telecom Rb to a reasonable 
temperature
*is* a good idea. The parts that are not attached to the oven assembly live 
*much* longer
at a lower temperature. Most of these small Rb’s die when this or that weird 
part on this or
that board dies. Caps are usually the first to go, but they can be tracked down 
and replaced.

If it’s a solid state part with no known replacement source …. the unit is 
dead. Also complicating
the repair process is the total lack of any alignment / setup information on 
these Rb’s. If
the part you replace requires realignment ….. you are flying blind. 

Bob


> Before I read the previous tread, I was thinking of electronic thermostat/fan 
> but...
> 
> Em 20/10/2020 10:34, Bob kb8tq escreveu:
>> Hi
>> 
>> Not very well organized message here …. I’m still working on my first cup of
>> coffee …:)
>> 
>> First up: What do I do?
>> 
>> My “lab” is in the basement of our house. There is HVAC running pretty much
>> year round. The temperature “wanders” between about 20 and 25 C over a
>> year. It cycles about 2 or 3 C at roughly a 1 to 2 hour rate. I have three 
>> 5065
>> Rb’s running full time on a rack. I have a couple of GPSDO’s running on 
>> another
>> rack. Various OCXO’s get tested on a bench. All of it is “out in the open”.
>> 
>> I have looked into various approaches to temperature control ( thermo 
>> electric
>> heaters ….). I have a big pile of water pumps, TEC’s, piping, and radiators
>> siting in a dark corner of the room. The more I looked into the power 
>> required
>> to do that, the less I liked the idea ….
>> 
>> I do have a few cardboard boxes and a small pile of “beach towels” that I 
>> use.
>> If the measurement is particularly sensitive, I put a towel over the test 
>> set. If
>> the device is large, I put a box over it. That generally works quite well to 
>> reduce
>> fast changing temperature from drafts in the room.
>> 
>> ==
>> 
>> Are you trying to lock the PRS-10 to the UCCM? If so, don’t bother, the net
>> result is a PRS-10 that is not very stable. Just use the UCCM’s output.
>> 
>> Practically speaking, the PRS-10 is a 0-50C device. It’s no different than 
>> other
>> Rb’s in that respect. It also is no different than the rest in making those 
>> limits
>> really hard to pull out of the data sheet. They talk about 65C baseplate, but
>> that’s not ambient.
>> 
>> The UCCM has an OCXO in it that is (probably) rated too 70C. It depends a
>> bit on what version / vendor you happen to have. In still air the OCXO is ok
>> to 50, in moving air, it should be all right at 70. No idea how the rest of 
>> the parts
>> on the board will do above 50C / moving air. ( = I’d bet there will be 
>> problems
>> above 50C).
>> 
>> The PRS-10 needs a heatsink on it or it will quickly die. It will live a 
>> longer life
>> with a better / bigger heatsink. With a small one, figure 2 years. With a 
>> fan or
>> something large, figure > 5 years of life. That’s all in a indoor situation 
>> with a
>> HVAC system keeping the ambient around 20 to 25C. The small heatsink
>> gets around 50, the bigger one + fan may get down to 40C.
>> 
>> The real issue with both the PRS-10 and the UCCM  is to reduce the 
>> temperature
>> swings. The UCCM will track out long term changes. You just need to protect 
>> it
>> from quick changes. Depending on which PRS-10 you have the temperature 
>> performance
>> may be better or worse (per the specifications on the part). A wooden box 
>> with
>> heaters / fans can do this, there are other ways.
>> 
>> A lot depends on just how crazy it gets where you are in Brazil  does it get 
>> above
>> 40C? ( I looked it up, the record is 44.7C …. yikes … ). Ideally you want to 
>> keep
>> the heatsink around 40C. That’s not going to happen if it’s 40 out. Running 
>> the
>> part at 55 C all the time is not a good idea.
>> 
>> More or less, you normally need 10C of “headroom” on any sort of heated 
>> device
>> (like a heated wooden box). You also have a practical problem coming up with
>> a heatsink that gets to < 10C relative to ambient. The net is that your 
>> heatsink
>> is at “max ambient” + 20C. For a somewhat more practical heatsink, the 
>> numbers
>> are worse …. sorry about that.
>> 
>> What’s a “big” heatsink? Think of something the size of the Rb with a high 
>> speed
>> fan attached. As noted in various posts the magnetic field from the fan will 
>> not
>> make the Rb happy, some sort of ducting to keep it a bit further away might 
>> be
>> a good idea. That sort of thing probably *does* get you within 10C of 
>> ambient .
>> 
>> The bottom line is that this sort of gear normally gets used in a location 
>> that has
>> heating / cooling. Temperature may swing from 1

Re: [time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

What will the output of the box be used for? If low phase noise is an objective,
then one needs to be pretty careful about power supply noise. If low phase noise
is not a “need” in this case, then (good) switchers can be used for everything. 

What’s a “good” switcher? You want one that is reliable ( = does not catch fire
on a regular basis). You also want to get the noise down into the 10 mv p-p 
range.
That generally means filtering the output a bit. Past that the usual 
requirements
of line / load regulation and efficiency come into play. 

Bob

> On Oct 19, 2020, at 10:24 AM, Luiz Alberto Saba  wrote:
> 
> Hi guys
> 
> Planning to build my "reference box" with a rubidium & a gpsdo.
> SMPS will do a good job or the transformer+bridge+capacitor+regulator is best 
> suited for this application?
> In the "test phase" I've used a switched ps for the rubidium and a 
> conventional for the gpsdo.
> 
> Thanks
> 
> Luiz Alberto Saba
> 
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[time-nuts] SMPS or conventional?

[Luiz Alberto Saba]

Hi guys

Planning to build my "reference box" with a rubidium & a gpsdo.
SMPS will do a good job or the transformer+bridge+capacitor+regulator is 
best suited for this application?
In the "test phase" I've used a switched ps for the rubidium and a 
conventional for the gpsdo.


Thanks

Luiz Alberto Saba

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