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Dual Power Supplies


A few days ago I was sitting here at my desk reading all the e-mails from all the readers concerned that I was gonna fry my power supply with my cigarette lighter modification. And I'm thinking (probably shouldn't do that, that's usually the beginning of a few days work!)  I still have the old power supply left over from an upgrade to my 350 watt sparkle. There has to be some way to fit an extra power supply into a mid case, hmm,..

WAIT, this is the disclaimer! I am not responsible if you stick a drill in your eye. I am not responsible if you cut your fingers off with a jigsaw. Its not my fault if you are electrocuted and it burns off all you body hair. I am not responsible if you burn your house down. This is electricity you are going to be playing with, its dangerous. This article is written as a novelty item only. I am not liable for anything you do. I am not an electrician, nor am I trained in electronics. I imply no expertise in these fields and may very well burn down my own house. That I will probably be held responsible for. Unless I can find someone else to blame!

Equipment List

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You are probably asking yourself why I would go to so much trouble to keep this case. Its small. Also its a mid/full ATX. If you don't know what a mid/full is, count the drive bays. This old thing will hold 4 up top, and 5 down below. Not to mention, its small.

The first thing I noticed was really how limited the choices were. There was only one possible place, under my 3.5 inch drive bays. After thinking about it for a while I decided that I really didn't want a power cord hanging out the front of my case or heat blowing into the case from the power supply exhaust. The only thing I could think of to make this work the way I wanted it to would be to remove the power connector and the on/ off switch for the power supply, hard wire a power supply cord into the box, run it to the back of the machine. And then reconnect all the wires, restoring the original functionality of the switch and plug. This is how I did it.

Fist of all you need to isolate and cut the the green wire and one ground wire from the rest of the wires leading to your atx mobo connector, make sure they are at least 6 inches long from the back of the psu case, and cut them. All of the other wires are not needed for this. You can bundle them if you have room, I chose to cut and cap them. Inside the psu box you will find the backs of the power connectors, take note which are which, I left the voltage selector switch where it was. I don't think ill be traveling abroad with my machine any time soon. After removing the screws for the connectors pull the plugs out a little bit so you can cut the wires, leave enough room so you can reconnect them later.


You will need to measure how long the power cord from the back of the case to the power supply needs to be. Don't forget to add a few inches so it will reach in the psu box, also it doesn't hurt to add another few inches to be safe. The wire will be in the bottom of the case so it wont be in the way of anything after you are done. Cut the cable to the desired length and strip back the outer casing about an inch and a half (for inside the power supply) on one end, and 3/4 of an inch on the other end. It should look something like this.


Inside the power supply you should have 3 cut wires, I had green brown and blue. Inside my power cable I had green, blue and white. I substituted the white for brown and matched the other two colors. I suggest solder on this job. Twisting and tape just aren't safe. After you finish soldering tape up the connections really well. If you decided to cut and cap the extra wires it should look like this.

Molex Connector

Next make your relay to molex connector. How long you want it is up to you. I ran mine to the top of my case. Cut off the red wire and the ground for the red wire. All you are going to need are the yellow and ground for the yellow. I extended the wires using the wire from the motherboard connector. Then tape off bare wires. I also used a little shrink tube to tidy it up.


    Still with me, good. Now comes the tricky part. :-) Hopefully you have been able to find the relay without too much trouble. DO NOT COPY THE PHOTOS!!!  

#1. They are wrong!

#2 The relay switch is upside down in the photo!

I made a mistake the first time! Don't worry, I made the mistakes so you don't have to. ;-) Strip 1/8th to 1/4 of an inch of the insulation off the green and black wire that you set aside earlier. The connectors on the relay perform the following functions

85 Trigger, this is where I soldered my yellow to the molex connector

86 Ground, this is where I put the black wire from the molex connector

87 Ground, this is where I put the black wire from the power supply

30 This is where I put the green wire from the psu

87A Ignore this one, you don't need it

Try to do a clean soldering job, you don't want any strands of wire to be loose and touching other connections. After the soldering is done it should look like this.

Next I ran the power cable through the grommet leading out the back of the power supply unit. Replacing the cover of the psu I slid the relay switches bracket between the cover and the bottom of the unit. Then I replaced the screw. There that wasn't so bad, was it?


Cutting Holes

The next step was to cut holes! I think the easiest way is to use chipboard and make templates for the power supply,  the original switch and psu power cord connector. Make sure you know which screw holes you're gonna use on the psu! This is pretty straightforward so I wont go into detail.


After you've finished with the templates (hopefully you have removed all the components from you computer! metal shavings ya know!) Mark out the locations where you're going to be cutting. Remember, its easier to remove more metal than it is to replace metal. Measure twice, cut once.

I was unpleasantly surprised to find that exactly where I wanted to mount my psu the manufacturer of the case had been considerate enough to drill some holes for ventilation. So much for a clean, professional looking job. I just did it anyway. I started to cut with my jigsaw, it promptly died, bummer. DREMEL TIME!! Anyways, the tool for this job is the jigsaw. Take it slow. After your done with the cutting, use the file or a dremel to take down the sharp edges.


Repeat the process for the power connector and psu switch on the rear of the case( keep these as close together as possible, those wires are short).

Drill the holes for you screws and mount the power supply ,power switch and power connector .Mount the power supply and the receptacle and the switch.


Finishing Up

Now we need to connect the power switch to the receptacle, it should be just restoring the red wire between the two. Next, solder the power cable we mad to the receptacle. Take note which wires you had substituted. I used green to green, blue to blue and white to brown. After you finish soldering tape everything up nice and clean.


LAST STEP,. we hope ;-) Now after you get your machine all put back together you can test it. I plugged 1 cdrom into the new psu, just for testing. Plug the molex connector into your primary psu. Power up. VOIS LA! Hopefully after doing this your cdrom light comes on. Now power down, does the secondary psu power down also? If so congratulations. You have just successfully installed a second power supply in a mid or mini atx case. If the power supply stays on then you need to go back and look at the connections to the relay, something is probably crossed. If the relay is fine but you have no power, make sure your power switch you just installed is turned on. And last but not least, if sparks shoot out, catches your dog on fire who then runs  into the curtains which promptly burst into flames and burns down your house, please re-read the disclaimer provided above. ;-)



Every thing is working fine. All my cd roms and the lighter run on the secondary power supply. My mother board and my hard drives run on my primary, sweet.

 Now, what are we gonna use all this power for? hmm,..... ;-)