I've come across a number of 'make your own power supply from a computer power supply' thread. All seem to require a fair bit of tinkering. What i'd like to know is: What would happen if I were simply to find the 12V rail on an old computer power supply and connect my charger to this? Anyone electrically minded sees a problem with this?
Thanks in advance
-Michael

Most computer power supplies will work if you do this, but some of them need to be tinkered with for various reasons. I have had one working, it could not put out much more than 10 amps with all of the 12v leads working together. It is a good tinkering project.

Most should work fine depending on the amps your charging your pack. I tried using one before and I can pull atleast 5amp on a 250 watts power supply. Goodluck and be careful

i used to use an 18 volt power supply for a PC, to charge my starter box batteries, 10xD cells, 12volt, and it had no protection or any mods, i just plugged it in and it pumped a continuous 2.3 amps into the battery,
the battery was acting as its own voltage regulator, it souns dodgy but if you had seen my starter box you probably wouldnt question it.
it worked fine until one day i plugged it in backwards and blew the supply

Most computer power supplies aren't regulated so you need to have a small load on them to stabilise the output voltage / current.

I personally wouldn't recommend simply plugging your charger into one without doing the mods you see in various forums. It may work, but it could be risky, both to you and your charger!

Safety disclaimer:

If you are interested in making your own - remember that it is possible to do all the wiring and mods without actually opening the psu - so it's quite safe that way, but if you dont know what you're doing then I suggest you don't attempt it!

Hi all we get our from 24 Hour Computer Center the power supply 12 v @ 16 amps

www.24hcc.com.au

steve

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I was fortunate enough to pick up a computer power supply for cheap from the club.

Some suplies only regulate the 5V rail so as you load the 12V rail the voltage will drop...

mmm I'm playing with one at the moment and can only get 9.9v out of it - what am I doing wrong ?

I had to load up the 5volt line with 2 brake lights (both elements) to get my 12v line up to 12 volts under load.

If I only put one light bulb on the 5volt line, the 12volt dropped to 10ish under load, which wasn't enough of course.

Be very careful with this stuff guys, specially if you're playing inside the power supply. It can kill you. Dead. Kaput.

Obviously 12volts is safer, but.. still...

-Scott

Heavy - Those instructions were the ones I used On that site here they also tell you what resistors you need if you dont want to use light bulbs)

If you aren't getting enough volts on the 12v rail then you need to increase the load on the 5v rail.

This means using a lower ohm resistor or higher wattage light.

As an example, when I made my first ps I used a 5.8 ohm resistor on the 5v rail. This gave me 12.1v under no load but dropped to 11.86v under load when charging. In this case if you were to use a 5 or 4 ohm resistor then this would increase the voltage on the 12v rail.

On my newest version I used a 12v 50w halogen bulb on the 5v rail and now I get 12.2v without load and 12.05 under load

Whoops, almost forgot - make sure you have a big enough power supply too start with - 400w minimum.

So the jest of it all is that unless I put a load/resistor on the 5V rail, I won't get 12V out of the 12V rail. But sticking a charger on the 12V rail will not having any adverse impact beside the fact that the Voltage may drop to a useless level... Does that sound about right?

Yeah that's right except you may also damage the charger because many modern computerised chargers don't like being plugged in to unregulated (ie switching) power supplies.