# ATX computer Power supply



## charliehorse55 (Sep 23, 2011)

To use a computer powersupply as a DC-DC converter you can simply plug the HVDC directly into the input terminals. As it is a switched power supply, it can run from either AC or DC. The maximum DC input voltage should be 1.5 * rated AC voltage. 180V for 120V units, or 360V for 240V units. 

To get the output to be 13.8V instead of 12V you need to modify the feedback circuit that controls the +12V rail.


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## Fatboynotslim (Oct 25, 2011)

thanks for that, I assume the 13.8V is a good voltage to charge the battery. Sorry if I sound dumb I am new to all this. Do I need to control the charge current , trickle current?


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## charliehorse55 (Sep 23, 2011)

Fatboynotslim said:


> thanks for that, I assume the 13.8V is a good voltage to charge the battery. Sorry if I sound dumb I am new to all this. Do I need to control the charge current , trickle current?


If you are using a lead acid battery, no.


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## JRP3 (Mar 7, 2008)

Fatboynotslim said:


> Do you think you can use this for a cheap DC to DC convertor ? Is 18amp sufficient for a vacuum pump and to charge the main battery?


Not if you intend to use your headlights or the fan.


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## Duncan (Dec 8, 2008)

charliehorse55 said:


> To use a computer powersupply as a DC-DC converter you can simply plug the HVDC directly into the input terminals. As it is a switched power supply, it can run from either AC or DC. The maximum DC input voltage should be 1.5 * rated AC voltage. 180V for 120V units, or 360V for 240V units.
> 
> *To get the output to be 13.8V instead of 12V you need to modify the feedback circuit that controls the +12V rail*.


OK how do I do that?

Does this apply to all PC power supplies? - I have a couple of old ones with a switch for 110v - 230v - will they take DC as well?


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## Coulomb (Apr 22, 2009)

Duncan said:


> Does this apply to all PC power supplies?


There is always a sense line that goes back to a controller chip somewhere. If you can find that (usually easy, but you can't guarantee it in general), then you can just change the voltage divider and it will aim for a higher voltage. Whether it gets there is another matter, depending on turns ratios and details of the design. But generally, a small change like 12 V to 13.8 V is often possible.



> I have a couple of old ones with a switch for 110v - 230v - will they take DC as well?


Yes, usually, but the minimum voltage they will operate on varies a little, and you will definitely not be able to use an old power supply if you run 96 V or less. See DC - DC converter 80 - 140 Volts 8 - 10 amps  (AEVA).


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## skooler (Mar 26, 2011)

Is this of any use?

http://www.mp3car.com/power-supplies/31652-car-power-supply-battery-charger-from-old-pc-supply.html

Basically says to relace a resistor with a pot and 'tune' for the right output voltage.

So I assume all that is required to be done is the above link and a DC input?

Cheers,

Mike


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## Fatboynotslim (Oct 25, 2011)

Thanks Mike, this is very usefull.


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