[sdiy] Load testing dual PSU

Oren Leavitt obl64 at ix.netcom.com
Mon Nov 3 20:41:13 CET 2014


Some years back, I scored a couple of 8 ohm 300W power resistors from 
Allied Electronics for about $17 USD a piece. They were clearance sale 
items because they are non-ROHS.
These have been very handy for load testing power supplies and audio 
power amplifiers.

In addition to the resistive loading, I like include some large 
capacitive load in parallel. By including the C, you can see how the PSU 
behaves with inrush current at power up.

- Oren

On 11/3/2014 11:54 AM, Rob Spencer wrote:
> I'm having a look at these resistors and weighing the costs...
>
> 10 individual 2 ohm 20W are about £2 each.
> 1 variable 47 ohm 100W is £22.
>
> I'm tempted just to get the variable one and connect a meter up. This way I can ramp the current up with out having to switch off, plug in next resistor, then switch back on.
>
> Cheers
>
> Rob
>
>> On 3 Nov 2014, at 15:28, blacet at blacet.com wrote:
>>
>> A few calculations with Ohms law will do the trick. R=EI
>>
>> W=EI will give you the minimum resistor wattage. I tend to use cheap ones
>> from Mouser in the white ceramic housings. I also use 2X the minimum power
>> to avoid them getting really hot.
>>
>> I will string a few of them together as required to get the necessary ohms
>> and watts.
>>
>>
>>
>>> Hi Roman,
>>>
>>> Thanks for the confirmation. In fairness I probably just need to get some
>>> higher power resistors. For some reason I had it in my head that they
>>> would be hugely expensive. I think I was picturing massive heavy ones that
>>> I remember from college. I'm sure they aren't as expensive as I thought.
>>>
>>> P.S. Friend request sent. I'd like to see the photos of that's okay.
>>>
>>> Cheers
>>>
>>> Rob
>>>
>>>> On 3 Nov 2014, at 12:49, Roman Sowa <modular at go2.pl> wrote:
>>>>
>>>> hi,
>>>> actually I use both :)
>>>> A string of 1 ohm 20W resistors, about 15 of them, so I can adjust load
>>>> resistance with banana cable by clamping part of the string. And there
>>>> is also G4 socket with soldered across part of the ladder, so I can see
>>>> if there's heavy current flowing or not witout looking at power supply
>>>> Amp meter. This is usable when testing switching circuits. I plug there
>>>> 5W, 10W or 20W bulb depending on needed load capacity.
>>>>
>>>> It get's hot, no matter what you do, just learn to live with that. Not
>>>> really pssssst hot, the resistors get nicely warm/hot after some time at
>>>> 3A.
>>>>
>>>> Your temperatures will stabilize in manner of minutes, not days, so
>>>> unless you are doing burn-in test, there's no need to leave it on for so
>>>> long.
>>>>
>>>> Roman
>>>>
>>>> PS for my Facebook friends, few hours ago I posted a picture with the
>>>> load fixture described here.
>>>>
>>>>
>>>>
>>>> W dniu 2014-11-03 13:24, Rob Spencer pisze:
>>>>> Hi,
>>>>>
>>>>> I've recently developed a +-12v PSU, with +5v and post voltage
>>>>> protection and am looking to do some load testing. I know I could
>>>>> stick a low resistance across it but that's going to get very hot
>>>>> very quickly. The other thing I'm thinking is to place some 12v light
>>>>> bulbs across the rails and leave it running for a few days with
>>>>> temperature monitoring in place on the voltage regulators.
>>>>>
>>>>> I'm wondering how other people have tackled this in the past.
>>>>>
>>>>> Cheers
>>>>>
>>>>> Rob _______________________________________________ Synth-diy mailing
>>>>> list Synth-diy at synth-diy.org
>>>>> http://synth-diy.org/mailman/listinfo/synth-diy
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