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PC PSU question - convert 12volt wires to between 18 to 24 volts.


- i want to convert one of the 12volt wires up to between 18 to 24 volts. is there a simple "up-converter" that I can use? a jiggy that i can attach to do this?

using a standard PC PSU.

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jeff-o6 years ago
Hmmm, how much current do you need?
altomic (author)  jeff-o6 years ago
about 1.8 amps -give or take.
jeff-o altomic6 years ago
Ah, too bad; the -12V line can't supply that much current.

I wonder if two power supplies would do the trick? You'd connect them up much like a pair of 9V batteries to get 18V. In this case, you'd get 24V. I've never tried this before, does anyone know if it would be safe to do?
altomic (author)  jeff-o6 years ago
could I connect a 12 and a 5 and get 17?

I'm doing this on a 20" g5 Imac. the original power supply died. reports have shown that 17" g5 imacs work fine with a slightly altered PC PSU at 12v. however the 20" have a reported flicker to the screen at 12v.

the screen usually needs 24v.

So I'm wondering if there is anyway to bump up 12v to something a bit more and see how it turns out.
jeff-o altomic6 years ago
OH! Thanks for clarifying what your intentions are. At the risk of killing the rest of the computer, I'd advise against it. Get a new power supply, and use the old one for other purposes.

And yes, if you connect something across the -5V supply and the +12V supply, the total will be 17V. But, you still won't get enough current out of the -5 (if the iMac PS even has one) and then the ground for the screen will be 5V less than the rest of the computer (not so good!)
altomic (author)  jeff-o6 years ago
Thanks Jeff-o

the old Imac PS has just one cable. its a 22 pin cable that looks basically the same as an ATX power cable.

I'm going to try standard PSU with appropriate re-wiring (shifting around some wires) and see how it pans out.

new Imac PSU's are around $100.

Its not really worth it for the performance of the computer.


jeff-o altomic6 years ago
OK, I hope it all works out! Remember to fool the ATX PS by attaching the green wire to ground, or it won't turn on.
You might be able to extract it from the +12 and -12V supply, but your ground connection will have to float then. You can't have more current than the -12 will supply though.

Steve
altomic (author)  steveastrouk6 years ago
hey, I keep hearing that magical word "float". what does that mean?
"Float" here means that there is no direct connection from the low voltage point of your circuit, which you call "zero volts" or ground, and what is nominally "real" ground, the reference to which all our mains circuits etc etc take a reference.