# Computer Power Supply as DC to DC Converter



## etischer (Jun 16, 2008)

The problem is these PC power supplies are not designed for the vibration and heat associated with automotive use. That being said, the cheap EV DC-DC converters aren't much better. I already had one IOTA short out. 

http://www.diyelectriccar.com/forums/showthread.php/possible-problem-iota-dc-dc-converter-42424.html


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## CrunchTime (Feb 13, 2009)

Also see this thread on modifying a Thermaltake Power supply...

And don't forget that if you're using an MR2 power steering pump, you'll need 50-70A (depending on which one it is)...


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## madderscience (Jun 28, 2008)

The other problems with a computer power supply as a DC-DC:

some of them can be quite sensitive to input voltage variations. I had one burn up because the input voltage (DC) was too low, oddly enough.

Also, to charge a 12V battery (which ought to be there for backup if the DC/DC fails) you really need an output voltage at least 13.6V if it is a sealed battery and 14.something if it is flooded. The computer power supply wants to put out exactly 12V. might be possible to tweak it, but the adjustment range is probably not much as these things are designed very task-specific.

I am successfully using a small switching power supply as a dedicated DC/DC for my homemade BMS head end unit so it can be done, but I tried several different models before finding one that worked well on about 72V to 160VDC.


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## Max57TBird (Mar 22, 2010)

Snakub said:


> Has anyone considered the option of using a computer power supply as a DC to DC converter. A lot of them run on DC as well as AC and they are a lot cheaper than even the least expensive "EV" DC converter. A good 650 watt power supply can produce 12 volts at 30 amps more than enough to power all the accessories.


 
Gavin Shoebridge in his book, Electric Conversion Made Easy has a chapter on converting a computer power supply, including a schematic and modification to adjust the voltage. Evidently, it worked for him.


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## Tesseract (Sep 27, 2008)

madderscience said:


> some of them can be quite sensitive to input voltage variations. I had one burn up because the input voltage (DC) was too low, oddly enough.


That's the "constant power" behavior... so the power supply draws more input current to maintain the same output power as input voltage declines. Most power supplies are smart enough to not draw so much current they burn up, though...


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## madderscience (Jun 28, 2008)

funny part is the burning up happened under no load. The PS in question was an older laptop "brick" power supply.

the power supply I had success with is a Meanwell S-60-12 which came from Fry's. its about 4" square by 1" tall and rated for 60 watts, which is enough to run my BMS (which uses maybe 10-15 watts). Not enough for a whole car DC/DC but enough for a dedicated supply like I did.


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## TX_Dj (Jul 25, 2008)

Check the web for "bench top ATX power supply" or similar. There are plans out there that show you how to convert an ATX supply to provide a variety of voltages from 3.3v up to 24v. 3.3v is native to the newer supplies, but 24v is a combination of -12v and +12v. Some of the better new supplies come with single 12v rails capable of up to 80A peak, but are more expensive than some true DC converters.

It is quite possible to build an ATX supply to drive 13.x-14.x V, but it's not an optimal solution for reasons others have pointed out.


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## Stunt Driver (May 14, 2009)

I have gone the simplest, but maybe not most efficient way - took IBM laptop power supply, which gives out 8-9 amps at 16v, so I inserted couple diodes in series to drop voltage. All I loose id 9A*2v=18 watt of energy, which is misarable. I may add second unit when brake boosted installed, or if i'll drive more at night.

With no steering pump or light on - 9A in combination with aux 40AH battery is enough. Good thing about laptop PSU - it's sealed and durable. Mine runs off 75-90v DC for last 5 months with out trouble.


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## few2many (Jun 23, 2009)

Heres a good link to check
http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply


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## barnabyportelli (Jun 28, 2012)

Hi,

I was planning to use an ebay 400W 13.8V switching power supply for my conversion project. something like :
http://www.ebay.co.uk/itm/400W-13-8...5162&pid=100011&prg=1005&rk=1&#ht_3081wt_1185

The problem is that there seems to be a switch between 110Vac and 240Vac a I was planning to use a 144Vdc battery pack. Which voltage setting should I used?

thanks

Barnaby


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