series stacking of pc power supplies

[DragnsBane]

I found this in a text book I recently picked up at the local Goodwill. which by the way is an excellent source of cheap electronic stuff.

I found a pic of the power supplies wired in series but can't post the pic. will try later

[DragnsBane]

found out the file size was to large to be uploaded. trimed it down a little. i realize it shows 15 volts but just replace the 15 with 12 and the 30 with 24. do you think this would work and would the 5 volt output still be available?

[arvidb]

It depends. If the ground (-) outputs on your supplies are internally connected to frame (safety) ground, then it won't work. Plug in both power supplies (in a grounded receptacle if that's where they're supposed to be used), connect a 10 kOhm resistor between the 1st supply's ground (-) lead and the 2nd supply's 12V lead. Then measure the voltage over the resistor with a multimeter.

If you get 0V or very close, then you can connect them in series. If it shows 12 V, then it won't work.

Supposing it works, you can pick +5V from the power supply whose ground lead (-) is connected to the other supply's +12V lead.

Arvid

[DragnsBane]

from what i can tell in the grounds are comung offthe board inside the power supply. will run to radio shack later and get some 10K resistors and hope that murphy doesn't rear his ugly head. one more thing what would happen to the amperage output. would it double as well or would be cut in half since the voltage is doubled?

[arvidb]

The amperage will be the same as the smaller power supply can deliver. So if one can deliver 7 A @ 12 V and the other 10 A @ 12 V, when you connect them in series then you can draw 7 A total @ 24 V.

This is because since they're series connected, the current will have to pass through both supplies. And since one supply can only take 7 A, that will be the limiting factor.

Arvid

[ESjaavik]

Yes, and when it limits, the bigger one may start driving the smaller with reversed voltage. Please stand back, it may get interesting as the caps discover what's happening!

And if it's for driving motors, stepper or servo, PC power supplies (switchers) are not a good choice anyway.