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'[EE]:loading a power supply for testing purposes'
2004\01\19@121551 by al smith

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I have a couple of power supplies that I want to create a test jig for, and
to simulate a load.  What we are talking about is 40A @2.5V and 10A @1.25V,
so putting a resistor(s) out there might not be the best solution.

Any ideas?

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2004\01\19@123006 by Jonathan Johnson

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A  wirewound rheostat should do the job, you can get these in large
wattages.

Cheers

JJ

-----Original Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of al smith
Sent: Tuesday, 20 January 2004 4:14 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: [EE]:loading a power supply for testing purposes


I have a couple of power supplies that I want to create a test jig for, and
to simulate a load.  What we are talking about is 40A @2.5V and 10A @1.25V,
so putting a resistor(s) out there might not be the best solution.

Any ideas?

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2004\01\19@130951 by Edward Gisske

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Al,
A trick that I have done is to make the load resistor out of thin-wall
stainless steel tubing, which has reasonably high resistance. I then run tap
water thru the tube for cooling. You are only talking a hundred or so watts
here, so the water cooling might be overkill. I have used the trick for a
load bank for an electric engine dynamometer to dump about 100 hp pretty
painlessly.
Edward Gisske, P.E.
Gisske Engineering
608-523-1900
gisskespamKILLspamoffex.com
{Original Message removed}

2004\01\19@133516 by Zipwize

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When we tested power supplies for spacecraft, we used the Macintosh Audio Amplifier (Vacuum tube) as the load. We injected both sinusoidal and square wave signals into the amplifier to test the regulation response time. You would have to use several audio power amplifier outputs in parallel to get the load you need.

Best Regards,

Fred Bailey
Thermal Dynamics
West Lebanon, New Hampshire

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2004\01\19@150954 by John N. Power

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> From:         al smith[SMTP:.....micro_eng2KILLspamspam.....HOTMAIL.COM]
> Sent:         Monday, January 19, 2004 12:14 PM
> To:   EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject:      [EE]:loading a power supply for testing purposes

> I have a couple of power supplies that I want to create a test jig for, and
> to simulate a load.  What we are talking about is 40A @2.5V and 10A @1.25V,
> so putting a resistor(s) out there might not be the best solution.

> Any ideas?

The December 2003 issue of Nuts & Volts has a construction article beginning
on page 48, titled "Variable Resistive Load" which describes a power load. It
can absorb up to 50 volts and 10 amps, but not both at the same time. Total
power is limited to 250 watts, which is pushing it, but 100 watts should be
reasonable. It is a constant current sink, with two ranges: 0-1 amp, and 0-10
amp. It uses a MOSFET with large heat sink as the variable element, and
has a digital readout for voltage and current.

John Power

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2004\01\19@152825 by David VanHorn

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If you want a constant current, I've used LM338K and it's equivalents as a constant current sink.  Dissipation becomes a problem, but you can parallel as many as needed, and heat your fishtank. :)

Simply tie adj to ground, and add a resistor to the output set for the current you want it to take, at 1.25V (check reg spec on minimum output voltage)

Dissipation will be (Vin-1.25)*I watts.

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2004\01\19@174920 by John Ward

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I've successfully used a bank of "buz XX" mosfets before, having driven them
with an opamp and sensing output load current via resistors to form a "sort"
of current limit.

This also adds the advantage of being able to simulate load variances in
steps, so that you can determine PSU ringing etc.

That also works well on a jig as one can then use a pic as we did, and do RC
filtered PWM to put load onto PSU, and then have a basic failure
testing/logging subsystem

One of the Elektor magazines ( about a year ag or so ) had a circuit ( voltage
driven variable load) which was so similar to ours that i thought we had spys
in our midst :)

J

On Monday 19 January 2004 19:36, you wrote:
> A  wirewound rheostat should do the job, you can get these in large
> wattages.
>
> Cheers
>
> JJ
>
> {Original Message removed}

2004\01\19@181652 by David VanHorn

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At 12:48 AM 1/20/2004 +0200, John Ward wrote:

>I've successfully used a bank of "buz XX" mosfets before, having driven them with an opamp and sensing output load current via resistors to form a "sort" of current limit.
>
>This also adds the advantage of being able to simulate load variances in steps, so that you can determine PSU ringing etc.

At some point in the future, I intend to do this with the PMD1208lS analog outputs, so I can do a varying current output.

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2004\01\21@142336 by Peter L. Peres

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Look for 62 and 125 miliohm shunts (2*62 will do for you) rated 100W (or
50A). These are not so hard to find. You can dyi using large cross section
manganin or constantan wire (as used in toasters etc).

Peter

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