FrankenPower! Building a 12V Power Supply

[Mike Bargman]

FrankenPower!

LeadingEdge Article Written by: Mike Bargman

Being in the IT industry, I never pass up an opportunity to tear up some computer schtuff...Today, I got a PM from my buddy Chris Puckett. He was asking about converting a computer power supply to a 12vDC power supply for his Fromeco Charger and sent me a link to a power supply from Tiger Direct. Being so close to Tiger, I told him I'd throw it together for him and bring it to him at E-Fest.

I thought I'd throw together a "mini-build" thread on putting together a nice 12V power supply if you don't wanna go spend the money for a manufactured supply that can cost upwards of over $100 for a decent supply. Fromeco chargers require at least 10A of output depending on how many outputs you get with the charger.

Chris picked out a pretty killer power supply. It's an Apevia Aspire 500W ATX power supply. Runs about $60.

I'll begin by showing you the components needed to complete this project

- Any ATX PC Power Supply. 300+Watts recommended.
- 10W 10 ohm sandbar resistor
- Binding Posts or Banana Jacks
- If your Power Supply does not have a switch onboard, you must use an On/Off switch to power on the power supply (This will be explained later)

As far as tools required, you'll most likely need the following:

-Sharp Wire Cutters and Wire Strippers
-Phillips Screwdriver
-Soldering Iron
-Solder
-Needle Nose Pliers
-Drill and Drill Bits

Before we start, PLEASE REMEMBER to always use caution when working with electronics. When you are working with power supplies, make sure you never touch any of the capacitors or parts on the circuit board.

Now, let's get to it shall we?

First, open up everything and make sure you've got all the parts required to complete the process. It should only take you 1-2 hours to complete the project if you have everything at hand.

Let's start by taking the top off the power supply. Unscrew the top, and carefully remove it and set it aside.

Now, see all those wires encased in the green mesh? Get rid of all that mess and expose all those wires. You'll need a razor blade and your wire cutters to cut off the zip ties and connectors off the ends of the wires. When you're done, you should have a huge mess of wires that looks like this:

Once you've got all the wires exposed, CUT OFF ALL BUT THE RED, BLACK, AND YELLOW AND GREEN WIRES.

Now, put the top back on the case, and mark where the binding posts should go for your 12V outputs. Since I have a clear acrylic case to work with, it made the process a lot easier. Usually, old ATX power supplies have air vents that will allow you to place the binding posts in correct places. Once you've selected where you want to place the binding posts, drill them out as shown in the second picture.

Attach the binding posts to the top of the case as shown in the picture. Make sure they're tight!

Now, the yellow wires coming from the power supply all put out 12VDC. Therefore, the yellow wires will be attached to the Positive Binding Posts. All the Black wires are Ground and should be attached to the Negative Binding Posts as shown...

Once you have all the connections tight, soldered (or tightened...depending on the type of binding posts you use), you should now locate the green wire from the bundle of wires coming from the power supply. If you're power supply has a power switch on it, you will need to solder the green wire together with a ground (Black) wire. IF YOUR POWER SUPPLY DOES NOT HAVE A SWITCH, USE THE GREEN AND BLACK WIRES ON A SIMPLE ON/OFF TOGGLE SWITCH. IF YOU DON'T DO THIS, YOUR POWER SUPPLY WILL NOT POWER UP.

After you've set up the switch wiring, we'll move to the resistor. ATX Power supplies require a load of some kind to power up. If you do not put a load on the system, the power supply thinks that it's not connected to anything and will not power up. We will use a resistor to put a load on the system. Some people keep some of the leads on the board and use an old hard drive or a fan to produce this load. I don't like it, because it's too much of a pain to carry around a fan or a hard drive all the time. Why not contain it into one package? Right?

When you wire up the resistor, one end of the sandbar should be soldered to a ground (Black) wire and the opposite end should be soldered to a 5V (Red) wire. This will produce the correct load and the power supply should be ready to test.

Make sure you have all your soldering joints and electrical connections covered with heat shrink tubing or electrical tape to prevent arcing or shorting out. Don't put the case on yet! Let's test it first...

YAY! It works! Now let's put it all back together!

Be careful to place the resistor close to an opening where fresh cool air can reach it, resistors tend to get real warm, so if you have room, put it by the cooling fan or near it. See all those unwanted wires??? GET RID OF THEM! Unless you want to save them for a silly reason, remove them so you can put your case back together. I get rid of every other wire that isn't already connected to something else. Now you can start re-assembling your power supply and test it!

Are we still getting 12VDC???

Why, YES we are!! Neat eh? This power supply is capable of up to 34 Amps of 12VDC output! Granted, it IS 500W, but 300W supplies can put out as much as 20 Amps.

[Mike Bargman]

If anyone has any questions, PM me or e-mail me at mike@pitsbros.com. Cheers!

[wizard]

Great thread Mike. I know I have a couple Old ATX supplies around. I would have never thought of using then. I have been using a deep cycle battery under the workbench for charging at home.

[chrisbchips]

Thats awesome Mike! Great tutorial! My Dad and I have tried this before but couldn't quite get it to work so hopefully using your tutorial we'll be able to give it another try.

[Mike Bargman]

Do this, you'll love it. Any old ATX 300W will work...Like I said...any questions or problems, I'd love to help!

[DA2000]

Awesome Mike! Always wanted to try this. Thanks for the tutorial.

[Mike Bargman]

Wow...it's freakin' 2AM here, what is everyone doing up? Go to sleep! LOL. You're welcome, I hope everyone finds it useful. Chris is gonna love this thing...

[wizard]

Same time here. Just watching the snow..

[notorious_benny]

Fantastic!! I just built a new computer and have the crappy old PSU from the old one sitting right here.

Its only rated for 250 watts. Is this enough power to run my Fromeco 4 port charger?

[Mike Bargman]

On the back, side or bottom of it, there should be a sticker that will give you a rating for the +12VDC and -12VDC...if it's over 10 Amps, you'll be fine.

[notorious_benny]

It says + 12V 13A
and -12V (Blue) 0.8A

[Mike Bargman]

You're goood to go!