Re: [volt-nuts] Load Testing a PSU

[Joseph Gray]

Tom,

I'm guessing that Stan meant that you use the shunt as a load resistor.

Joe Gray
W5JG


On Tue, May 17, 2016 at 11:07 AM, Tom Miller  wrote:
> You are mixing the terms "shunt" and "load" I believe in error. The shunt is
> not a load. It would be in series with the load.
>
>
> - Original Message - From: "Stan, W1LE" 
> To: 
> Sent: Tuesday, May 17, 2016 12:47 PM
> Subject: [volt-nuts] Load Testing a PSU
>
>
>
>> Hello The Net:
>>
>> Every test bench needs an assortment of current shunts.
>> Some of mine are: 100 Amps will give a 50 millivolt drop across it at 100A
>> load..
>> Another is a 50 Amp shunt that gives 50 millivolts across it when
>> loaded to 50A.
>>
>> Then use a DVM to measure the voltage drop.
>>
>> Also have a FLUKE current probe "clamp on" using a Hall effect technique,
>> to measure AC and DC current.
>>
>> A Ebay search should give some cost effective results for a current shunt,
>> just for an idea.
>>
>> Stan, W1LECape Cod   FN41sr
>>
>>
>>
>>
>> z
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>
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Re: [volt-nuts] Suggestions for 10 milli Ohm 0.04 % 100 W resistor

[Mitch Van Ochten]

Hello David,

This seller is offering a lot of ten (10) 0.1 ohm 10W 1% wirewound resistors.  
These resistors are quite stable and have a fairly low temperature coefficient. 
 I believe you could fabricate a 0.01 ohm +/- 0.04% resistor (after trimming) 
that could easily handle 9W and do the job.

http://www.ebay.com/itm/1-Ohm-10W-1-Wirewound-Precision-Resistor-Lot-of-10-Dale-Silicon-Coated-/261291077744?hash=item3cd6297070:g:r18AAOxy~ilSPKbj


Best regards,

mitch

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Dr. David 
Kirkby (Kirkby Microwave Ltd)
Sent: Tuesday, May 17, 2016 4:59 AM
To: Discussion of precise voltage measurement
Subject: [volt-nuts] Suggestions for 10 milli Ohm 0.04 % 100 W resistor

I have an HP 6674A power supply with option J06,  which means that the PSU is 
70 V @ 30 A rather than the standard 60 V @ 35 A .

I've replaced a couple of bits in this and will need to replace some more, so 
it would be prudent to get this calibrated.

The service manual calls for a 8.5 digit 3458A, which seems a bit over the top 
given the displays for voltage and current are only 4 digits. I think my 6.5 
digit 3457A will be good enough. This is a 2.1 kW PSU, not a precision 
measuring instrument. But I don't have any ammeter that can read
30 A, so I can not just use an external ammeter if I want to know the current.

The service manual also calls for a 0.010 Ohm 0.04 % 100 W resistor, with a 
recommended resistor of a Guildline 9230/100. I am wondering how practical it 
is to make such a resistor and verify its performance on the 3457A.
Some versions of this PSU have a lower output voltage (56 V) but higher current 
(42 A). With the 30 A PSU I have,  the maximum power that could be dissipated 
in a 0.01 Ohm resistor is obviously 9 W.

Any suggestions about what I can use that will not cost a fortune?

Looking on eBay, Guildline resistors are several hundred USD each. I can't 
justify that given the cost of a Keysight calibration of the PSU is $199 in the 
USA.

I much admit that I have never really much attention to calibration of a PSU. 
It seems a bit of a waste of money when you can use a decent multimeter if you 
really want to know the voltage or current. But with a PSU of this size, I 
don't have an ammeter good enough.

The other tricky bit about calibration of this PSU is the need for loading it 
to full power (2.1 kW) then dropping the load to 50% and measuring the recovery 
time. It should recover to within 100 mV in 900 us. Likewise it should recover 
the same if switched from 50%  of load to 100 %. The manual calls for an 
electronic load,  but I suspect a FET switch and some big resistors in water 
will do. I don't see any need for such resistors needing to be very high 
precision, but obviously something decent is needed to calibrate the ammeter.

Dave.
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[volt-nuts] Suggestions for 10 milli Ohm 0.04 % 100 W resistor

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I have an HP 6674A power supply with option J06,  which means that the PSU
is 70 V @ 30 A rather than the standard 60 V @ 35 A .

I've replaced a couple of bits in this and will need to replace some more,
so it would be prudent to get this calibrated.

The service manual calls for a 8.5 digit 3458A, which seems a bit over the
top given the displays for voltage and current are only 4 digits. I think
my 6.5 digit 3457A will be good enough. This is a 2.1 kW PSU, not a
precision measuring instrument. But I don't have any ammeter that can read
30 A, so I can not just use an external ammeter if I want to know the
current.

The service manual also calls for a 0.010 Ohm 0.04 % 100 W resistor, with a
recommended resistor of a Guildline 9230/100. I am wondering how practical
it is to make such a resistor and verify its performance on the 3457A.
Some versions of this PSU have a lower output voltage (56 V) but higher
current (42 A). With the 30 A PSU I have,  the maximum power that could be
dissipated in a 0.01 Ohm resistor is obviously 9 W.

Any suggestions about what I can use that will not cost a fortune?

Looking on eBay, Guildline resistors are several hundred USD each. I can't
justify that given the cost of a Keysight calibration of the PSU is $199 in
the USA.

I much admit that I have never really much attention to calibration of a
PSU. It seems a bit of a waste of money when you can use a decent
multimeter if you really want to know the voltage or current. But with a
PSU of this size, I don't have an ammeter good enough.

The other tricky bit about calibration of this PSU is the need for loading
it to full power (2.1 kW) then dropping the load to 50% and measuring the
recovery time. It should recover to within 100 mV in 900 us. Likewise it
should recover the same if switched from 50%  of load to 100 %. The manual
calls for an electronic load,  but I suspect a FET switch and some big
resistors in water will do. I don't see any need for such resistors needing
to be very high precision, but obviously something decent is needed to
calibrate the ammeter.

Dave.
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