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paulktreg

Custom Built Power Supply Load - Updated

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My original posting from DIY-Street:

 

Ever thought about building a power supply load to properly test your ATX power supplies. Well I have finally finished mine and I thought I would just tell you briefly how I went about it.

 

I am using aluminium clad wirewound resistors as the loads.

 

resistors_small~0.jpg

 

These resistors come in a range of wattage (power handling) ratings from 10W to 200W. The circuit diagram of my load is here:

 

loadmk1.jpg

 

I have designed it to give me a choice of three loads for each of the 3V3, 5V0 and 12V0 DC lines. (I have initially repeated the 12V0 resistor bank 4 times so that I can load up 4 seperate 12V0 lines). I calculated all my resistors for various loadings and tried to keep it to 100W resistors and below. There is quite a price jump if you use 200W resistors.

 

Just as an example lets say you wanted to pull 5A (I) from the 12V0 (V) line.

 

Resistance R= V/I = 12/5 = 2.4R (ohm).

 

The power handling rating of this resistor in Watts W= V*I = 12*5 = 60W.

 

You would need to connect a 2.4R 60W resistor across the OV (Black) and 12V (Yellow) lines on your power supply.

 

You will not get a 2.4R as they come in standard prefared values, the nearest aluminium clad wirewound resistor you can get is 2.2R 100W. (This partly explains why my circuit diagram looks a bit complicated. It was a mix of trying to get certain values of resistors and keeping them below 100W to try and keep costs down). The wattage ratings of these resistors is somewhat misleading. If you buy an 100W resistor it is only safe at about 50W unless it is bolted to an heatsink to help dissipate the heat they generate. Hence:

 

psuload01.jpg

 

This is two large heatsinks bolted together with the fins on the inside. (I have to say I was lucky enough to find these on ebay. New they would have cost a small fortune). This photograph shows the power resistors mounted with heatsink compound to the sides:

 

resistors_small.jpg

 

The final wired load is shown here:

 

psuload06.jpg

 

Note the addition of a small 12V power supply. This powers my fans so that it doesn't affect the loading on the power supply (although it's only a few watts) and more importantly I can keep the cooling on after the power supply is switched off to cool the beast down.

 

So now I have a custom built ATX power supply load which gives me the following options:

 

A 3V3 load of 3.3A, 9.7A or 16.5A

A 5V0 load of 5.0A, 10.6A or 17.5A

A 12V0 load of 2.5A, 8.5A or 12A (x4)

A fixed -12V0 load of 0.4A

A fixed +5VSB load of 2.3A

 

Selecting my loads carefully I can now load up basically any power supply to a level of approximately 1000W continuous and possibly 1400W for a limited time period.

 

I think 750W-1000W will provide sufficient load to test power supplies upto and at a level used by 99% of PC users out there. I have measured the load on my own PC system and I was surprised to find it at only 180W. In the future I can if necessary add two more 12V load banks (12V0[5] and 12V0[6]) which will take the load up to approximately 1400W continuous.

 

I have had a OCZ Stealth X Stream 600W running for 4 hours this evening at a loading of 650W. The load did get hot to the touch but I think theres a bit more in it yet!

 

Hope you found this slightly interesting.

 

Regards

 

Paul

Edited by paulktreg

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That may be the nerdiest thing I have ever seen :)

 

How quiet are the fans? :D

 

How hot do the resistors get?

 

Seriously, more pics and closeups.

 

Don't be a pic teaser.

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In the famous words of internet geeks all across the internet, MOAR!!!

 

Pix or it didn't happen, k thx.

 

;)

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Is it just a whole bunch of large wattage resistors sinked to a metal heat tunnel? Cool project.

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Hello

 

How about this for a custom built load?

 

I can load power supplies up to about 700W with this but it does get rather warm!

 

 

Hey Paul give me a PM if you want the code for your whole thread, I can pull it from DIY yet and we can just get that posted up here since it's interesting as all hell to us nerds. :)

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Hey Paul give me a PM if you want the code for your whole thread, I can pull it from DIY yet and we can just get that posted up here since it's interesting as all hell to us nerds. :)

Doo eeeet! :)

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I now have the original entry from DIY-Street and I will post it here later today. This includes photographs and specifications, etc,etc.

 

Regards

 

paulkter

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