Hank Fletcher
New Member
Sorry for the newbie question, but I decided to try and modify a computer supply so I could use it as a bench supply. Seemed like a good idea since it didn't cost me anything to get the supply so it seems like a cheap way to get 5V and 12V regulated, and at fairly high currents, too. I searched the net for some ideas on how to do this, and finally followed this guy's notes:
http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM
They're pretty good notes and I tried to contact him with my problem below, but I've yet to hear back.
My problem is with the resistor. I used a 10W, 10ohm resistor as is commonly advised, albeit mine is the green, cylindrical wirewound type. It gets really hot, and although I haven't use any heatsink compound the resistor is well ventilated. The supply works for about ten minutes while the resistor gets hotter and hotter, then shuts down. This hasn't fried the resistor yet, which still indicates 10ohms after it's cooled down. Then you can turn the supply on again and watch the whole thing over... but presumably this is eventually going to cook something permanently.
All this said, I did the absolute bare minimum to test the supply and see if it would work as a bench. I didn't open the supply case. I just shorted the green 5V wire to a black ground wire, and soldered the resistor between one of the red 5V wires and another ground wire. For the ten minutes the supply operates, my multimeter gives all the expected voltage readings from each of the supply's lines. Is it just a matter of getting some heatsink compound, or is more current somehow going through the resistor than theory has predicted? Given the likeliness that someone on this forum has done a similar mod I figured I'd take a chance and throw this out there. Thanks!
BTW, my power supply characteristics:
250W Dell (after the year 2000, so wire colours follow industry standards)
5V, 22A
12V, 14A
5VSB, 2A
3.3V, 18A
-12V, !A
http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM
They're pretty good notes and I tried to contact him with my problem below, but I've yet to hear back.
My problem is with the resistor. I used a 10W, 10ohm resistor as is commonly advised, albeit mine is the green, cylindrical wirewound type. It gets really hot, and although I haven't use any heatsink compound the resistor is well ventilated. The supply works for about ten minutes while the resistor gets hotter and hotter, then shuts down. This hasn't fried the resistor yet, which still indicates 10ohms after it's cooled down. Then you can turn the supply on again and watch the whole thing over... but presumably this is eventually going to cook something permanently.
All this said, I did the absolute bare minimum to test the supply and see if it would work as a bench. I didn't open the supply case. I just shorted the green 5V wire to a black ground wire, and soldered the resistor between one of the red 5V wires and another ground wire. For the ten minutes the supply operates, my multimeter gives all the expected voltage readings from each of the supply's lines. Is it just a matter of getting some heatsink compound, or is more current somehow going through the resistor than theory has predicted? Given the likeliness that someone on this forum has done a similar mod I figured I'd take a chance and throw this out there. Thanks!
BTW, my power supply characteristics:
250W Dell (after the year 2000, so wire colours follow industry standards)
5V, 22A
12V, 14A
5VSB, 2A
3.3V, 18A
-12V, !A
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