Make yourself a 12V power supply from a computer PSU

by RCRookie | May 22, 2012 | (10) Posted in Tips

Here is a quick howto, how to make yourself a power supply for your LiPo battery charger. You will need a used or new computer power supply unit. In a computer power supply you have multiple voltages, but we are interested in the 12V one. There are a lot of wires of different colors, we are looking for yellow ones, which give out 12V.

CAUTION: You will be dealing with some serious voltages. Until the current goes through the DC converter, you have some 220V AC so watch out. Always unplug your cable from the house power socket. If you don’t know what you are doing, buy yourself a power supply. 

Here is what you do:

Take some yellow wires and wire them to a connector. This will be your 12V. Do the same for some (the same number as yellow) black ones, that is your negative. These are the connectors you will then plug your charger on. Because, in a power supply unit the 12V voltage is not the primary voltage, we have to wire a resistor to the 5V wire, which is the red one. One easy trick to do here, is wire the red and a black wire to a 12V car light bulb, which will act as a resistor. Now we are almost done. Just one more step, so the power supply starts. You have to short wire the gray and one black wire together. This is the signal which tell the power supply its on. The color of this wire varies from power supplies, so check that the signal is PS-ON. You probably have this written on a sticker on the power supply. Now, when you click the switch, the power supply unit should start: The fan starts to spin and the bulb lights. Check the connectors with a multimeter that you really have 12V.

See the pictures below.



Reinaldo Moreira on October 23, 2012
Great idea.
I did some couple of "power box" for my friends on the club.
Just using a cheaper 10$ 220w computer font. I use one resistor of 10 ohm x 10 watts in the 5 volts wire.
Works great and I can put on charger 4 LIPO batteries with 2.2A each and no problem.
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Josh Bixler on May 22, 2012
I have this at home and LOVE IT! Thanks for posting!
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silverknight on August 2, 2012
One extra tip is to put a rated potentiometer in series with the 12v (yellow) line and now you can make it a variable output if you want to charge smaller batteries also. You could also put an inline (or series) digital voltmeter as an easy display so when you adjust the pot you know the voltage output easily.
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Non Action Man on August 2, 2012
Wire wound pots are not always able to carry too much current. Try an LM317 voltage regulator. With a few simple components you can make a 2~2.5A*
regulated output with thermal overload protection.

*current output depends on a few factors, mainly the amount of voltage you want to drop.

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whowhatwhere on May 24, 2012
I have one that I built some years ago, but without the resistor. Why is the resistor needed? Is it to reduce the current?
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ronhollenbeck on May 30, 2012
The resistor is needed to step the voltage up a bit. The ones I have tested will only put out about 11 volts unless the resistors are used.
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Astroman on May 23, 2012
Does this work on 4s + batteries also charging at over 3A?
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puregame on May 30, 2012
It could, depending on the power supply, most are 180-200watt, this rating is to the components inside. This means that you can draw ~ 15 amps from them (180/12). One thing to watch out for though, there are 3 different, "rails" on computer PSU's, +3v, +5v, and +12v. It will have a rating for each rail, if not assume 75% or to be safe 70% of the total output. Therefore a stock (crappy) PSU, assuming 180w, can handle (75% of 180 / 12) = 11.25 amps.

Also I suggest putting two +12v wires in parallel, that way it doesn't stress the wire as much.
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RCRookie on August 2, 2012
Thank you all for your replies. I will soon be posting an article about a more powerful (360W, 30A) and relatively cheap (40-50$) DIY power supply, stay tuned.
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Crispim.joao on August 1, 2012
a few lil' details: the "ps-on" wire is more often green than grey... (but I did get one with grey!)

other detail. some PSU's have a brown wire shorted out to the 3.3V line on the ATX plug. this is to "measure" the voltage dropout on the main power line (3.3V) btw: most of the power supplies control the 5V line as the main one but the main line is supposed to be the 3.3V

I have at least 2 power supplies of this kind and they are very useful! its just a shame we can't trick them to put out 13.8V mines often only give out 11.5V with little or heavy load (and with load on the 3.3V and 5V lines)
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Make yourself a 12V power supply from a computer P...