Modded PC power supply for charging

[BrianG]

People have asked how to use a relatively cheap 12v power supply for their battery charger (Hyperion 7i, Multiplex, etc) in the past, so I thought I'd make a little "how-to". Many battery chargers require a 12v DC input to power them up. A car battery works, but it's nice to have something that can be plugged into the wall. The power supply in a computer can be used as a 12v power supply if it has enough current on the 12v line, and is an ATX style (which is in all computers for at least the last 5 years or so). Older power supplies have a 12v line but are not as robust.

You should be able to find a computer power supply that can deliver around 15A @ 12v for about $40. Then it takes a little modding to convert it.

WARNING: The internals of a PC supply contains hazardous voltages in the range of 160-180V DC. Make sure power cords are disconnected and let the unit sit for about 10 minutes to discharge the capacitors before you open the case.

1. First, you have to figure out how much 12v current you'll need. The Hyperion 7i charger requires up to 150 watts. This equates to about 13A @ 12v. The Thunder Power 1010 requires up to 350W, which is about 30A @ 12v. It might be tough to find a generic computer power supply capable of 30A, so then you might want to stick with a heavy duty supply for best results. Note: These figures reflect charger efficiency losses and a safety margin.
   
   
2. Next, you have to make sure the supply will turn on like it should. Plug the supply in and turn on the switch in the back (if there is one). Take a piece of wire and short the green wire to any black wire. These are located in the large motherboard connector. If the internal fan turns on, you are all set. If not, this particular model probably needs one or more of the voltage supplies (either the 12v, 3.3v, or 5v) loaded somewhat for the circuitry to work. You can still use this, but you'll have to use a loading resistor or something, and that is beyond the scope of this post. This is not really common nowadays so you should be fine. Also, many current power supplies actually contain two 12v supplies in one unit and you shouldn't simply tie these together, and you have to make sure at least one of them can supply 15A+ by itself.
   
   
3. A picture is worth 1,000 words, so:
   
   Before
   
   
   After
   
   
   Actually, these are different supplies, but they looked similar when I started. You get the idea. I got fancy and shortened unecessary wires, re-braided the wires I wanted, and then added a Deans connector for each set of wires. I also left the 5v (red) and 3.3v (orange) supplies usable in case I wanted to use them, but all that's needed are the 12v (yellow) and ground (black) wires. All you really have to do is connect the green wire (in the large motherboard connector) to any black wire to turn the supply on.