First thing I did was check the resistor... yep, 10 ohms.j.p.bill said:It may depend on which voltage the PSU monitors for proper operation. In the days of AT supplies it was the +12 line. Usually any small load would make the thing happy - sometimes even a fan.
Your hot resistor is still an iddication that all is not well. It should only be dissipating 2.5 watts, which won't make it more than warm.
I would suggest you lift the green wire you shorted to that black wire. Then, try running the PSU with the resistor connected between +5 and one of the grounds associated with a +5 volt line.
Double check the resistor to be cerrtain it's 10 ohms and not 1 ohm.
I couldn't find the datasheet, but thanks for the suggestion. The supply model is NPS-250GB A, if anyone out there has a knack for finding datasheets!Hero999 said:Search the Internet for the power supply model number, download the datasheet and see what the required minimum is and on which rail to connect it.
Shorting any rail to 0V is never a good idea and is probably what has been causing the problem.
Hey, thanks! Yes, there's a fan inside the PSU (always was connected - I haven't opened the case and hence haven't tinkered with the PSU's fan), and without any modificatons to the PSU the fan won't turn on. Connect the green wire to ground and the PSU fan turns on, but you can't read any voltages on the red, yellow, or orange wires. However...ericgibbs said:hi hank,
Read thru the web notes re-conversion, the only thing I can see thats different is the 10R 10W, mounting.
As you say the Green wire has to be at 0V to enable the PSU.
The author does stress that the 10R gets VERY hot and must be firmly clamped to the frame and to use heat sink compound.
Its just possible as your 10R is gets really hot its resistance is going up, so at some point its not dumping enough current
to satisfy the switcher???
I would use a car lamp as he suggests [in place of the 10R]
I assume that you have got the fan connected and its cooling the PSU?.
Eric
Thanks. No doubt the supplies you mentioned are the most practical solution for some people's projects. That being said, I feel obliged to share with those who have read this far to tell them how I got my used PSU for free!Ambient said:If you want a cheap power supply...
Hank Fletcher said:I think I originally erroneously diagnosed the reason the PSU automatically shut off. I had accidentally shorted one of the red, yellow, or orange wires to ground.
Hank Fletcher said:There's just one more thing I'm curious about though, and that's the different voltage readings I get when I have different loads on the PSU. For instance, with one DC motor connected I might read 11.7V on the yellow wire, but with the fan I might get 11.82V. Is this contrary to what I should expect from a regulated PSU? This difference in voltage is touched upon in that guy's (Andy's?) notes on the mod, but never really explained. Maybe I'm just being a newbie here and not really understanding how a regulated supply works? Anyone want to set me straight?
Thanks very much to everyone who's helping me in this and my other (inadvertent) thread on the subject. Even though I might not have reached the solution directly, all your encouragement and inspiration to continue tinkering is invaluable.
Hank.
Hero999 said:You can probably tweak the output from your supply anyway, you just need to find where the feedback loop is and change a resistor value. This could involve a bit of reverse engineering but it's relatively straight forward is you can find the datasheet for the controller IC.
I've always fancied building a switching power supply, one day I might get my hands on an old PC PSU and rebuild it to a variable supply of my specification.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?