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Bench Power Supply for 10$ Computer Power Supply HowTo

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  • Bench Power Supply for 10$ Computer Power Supply HowTo

    This is for some people who have inquired as to how I used a cheap old Computer power supply to run my ballasts in my house.

    It's a great source for a cheap power supply. You can get 5 volts, 12volts in the 10 amp range for very very cheap. They also have short circuit protection so you don't fry them or have to replace fuses

    *Disclaimer* This can be dangerous, the voltages inside can be lethal if power is running through the capacitors, always drain the power supply before working inside of it. If it has been off for some time, it is probably safe. YMMV I've never had problems.

    I just want to spread a little education when it comes to opening your computer's power supply unit.

    I've taken one electronics college class way back in 2001. However, there was an individual who also took the class that was working as a tech who repairs those cabinet arcade game machines. Yup, the voltage running around in there can kill on contact. Yup, same for the computer's power supply.

    This is very simple, all you need are some leads such as these

    Simply take the black lead (black always means ground) and insert the right angle connector into the GROUND connector on an extension cord. Basically you are plugging the lead into the ground of an extention cord.

    Now with the pointed part, sweep it over ALL THE INTERNALS of the power supply. This will effectively discharge all the stored voltage to earth ground. Now you can grab those parts with your bare hands without dying Ya winkles

    I've played around inside my old CRT by doing this. I do think my hand brushed something cause I got 3 little circle "burns" which I have no idea how that happened.

    PS: I am not (repeat) NOT responsible nor liable for any mistakes you make in following my post. This information is provided for educational purposes only.

    There are 2 kinds of Computer PSU (Power Supply Units)

    AT style, used up until pentium 1. This is the cheap kind since it's no longer used. I found 3 for 20$ on ebay... You are looking at the amperage of the 12 volt line mainly. basically any AT style power supply will run 1 ballast fine, 2 ballastst probably. 10 amps is perfect, 8 amps ok, 12 amps great.

    The P8 and P9 connectors determine whether it's a AT or ATX...

    The newer ATX style power supplies have a different motherboard connector, and do not have any switch directly linked to the power supply like the AT do.

    Now you can use either one, but they vary in how you modify them.

    Basically this is what we're going to do, take all of the extraneous wires coming from the power supply and either ignore them, or do what I did and desolder them from the motherboard.

    But there are SOME wires we need to keep, and it depends on which kind of power supply you have.

    Both AT and ATX power supplies have multiple voltages coming out of them. on the standard molex connector seen here:

    I desoldered every molex wire except I kept 1 which I saved the 12 volts for my eventual alligator clip test leads to my ballasts (yellow and black) and I saved the red and black to run the fan so it would be quieter.

    These power supplies are called switching power supplies, voltages can be very dangerous, make sure there is no stored power inside, and NEVER work on them while plugged in. The power supplies need the 5 volt line (red) to have a load on it. I had a turn signal from my car lying around and it worked fine. Without the load the 12 volt line will fluctuate and usually it will not even turn on.

    Before we start taking all the wires off of the power supply, what wires do we want to keep?


    from the above picture the blue/white and brown/black "switch" wires, leave those alone. this will be your switch wires eventually.

    Also leave 1 set of molex wires for your 12volt leads and to load the 5v line.


    On your big 20 pin connector, save the # 14 wire which is green, AND a black wire. this will be your switch eventually to turn it on.

    Also leave 1 set of molex wires for your 12 volt leads, and to load the 5 volt line.

    This list of wires taken from

    Table 1: AT PS M/B Power Connectors

    Letter Signal Color Connector
    A Power Good Orange P8
    B +5v Red P8
    C +12v Yellow P8
    D -12v Blue P8
    E GND Black P8
    F GND Black P8
    G GND Black P9
    H GND Black P9
    I -5v White P9
    J +5v Red P9
    K +5v Red P9
    L +5v Red P9

    Table 2: ATX PS M/B power Connectors

    # Signal Color # Signal Color
    11 +3.3v Orange 1 +3.3v Orange
    12 -12v Blue 2 +3.3v Orange
    13 GND Black 3 GND Black
    14 Power ON Green 4 +5v Red
    15 GND Black 5 GND Black
    16 GND Black 6 +5v Red
    17 GND Black 7 GND Black
    18 -5v White 8 Power Good Brown
    19 +5v Red 9 +5v_VR Purple
    20 +5v Red 10 +12v Yellow

    ATX PS's have a wire (no.14) on the M/B power connector called POWER ON, colored green (see Table 2). If you connect this to the next wire (no. 13 or 15, GND, colored black), the PS will start. So, take another simple switch, affix it on the empty bay cover & connect it to the POWER ON & GND.
    Now some pics to show what I'm talking about. I am using an AT power supply as an example

    Final product, all cleaned up, only 2 wires coming out, I kep the grommet to keep the wires from chafing.

    Your internals may look slightly different, but basically all you care about is keeping the wires you need as in above, the 2 fan wires which we will splice on to the 5 volt line (so it's quiet), and your switch wires. All the other random wires have no purpose for us, and you can desolder or cap them off inside.

    You can see all the wires pretty much are clumped together, 5volt will all come out of one area, 12v the same area, ground another area... I personally desoldered ALL the wires and added 12 or 14 gauge wires, since the stock wires are kinda puny, meant to be shared amongst 12 molex connectors...

    You have saved your "switch wires" either 4 (blue, white, black, brown) for an AT power supply, or your green and black from your ATX motherboard 20 pin connector. Here I put in a Dual Pole, Dual Throw switch in my AT power supply so it connects blue to white, and brown to black at the same time. You would only need a dual pole, single throw switch if you have an ATX wire (since you only have to connect green to black)

    So I don't forget which is "on"

    Here you can see how I soldered wires to a turn signal bulb and connected them to the "used to be" molex plug 5 volt ( red and black) I also have the fan connected to these wires. Some people may not need to load the 5v, it may be 12v or 3.3v, but 90% of the time, it's going to be your 5v line, try it, if it doesn't work try another line.

    Turned on and working:

    That's all I can think of at the moment, feel free to ask Questions if I left something out.

  • #2
    very nice write up, you are the man =D>


    • #3
      I smell a sticky...and good info with pictures!
      2013 Accord V6 coupe 6MT S2000 retrofit done by LightWerkz


      • #4
        people might be curious why you would want to go through such trouble if you can just use a jumper box or battery for a little while... well I made a HID lamp for inside...

        I've also read you can get any combination of voltage out of these, i.e. 12volts - (-12 volt ) = 24 volts, so if you save the right wires off of the motherboard connector on an ATX (they have more voltage rails) you can get 5,8,12,15,18,24 etc... any combination of 12,5,3.3,0,-3.3,-5,-12 you can think of.


        • #5
          Some more clarifications:

          The molex connector looks like this (either male or female):

          These pics only have 2 wires, yours will have 4, but these showed the best picture oncoming...

          If you don't want to open up the power supply,

          if you have an AT power supply:

          You can just connect blue to white, black to brown. or if you have a switch that it came with, just leave it alone.

          Cut 1 molex connector (4 wires) and use your yellow and black for your 12 volt power source, and load the red and black on a light bulb, or a 10-25 watt resistor should also suffice...

          If you have an ATX power supply:

          Connect your Green #14 wire to your Black wire next to it in the big 20 pin connector (or hook these up to a switch).

          Cut 1 molex connector (4 wires) and use your yellow and black for your 12 volt power source, and load the red and black on a light bulb, or a 10-25 watt resistor should also suffice...

          What do I mean by connecting a light bulb to the 5 volt line?

          In this picture there are 3 contact points, 2 at the bottom which lead to a filament, and then the actual chassis of the bulb is the ground. I used a bulb like this, but any bulb of this size should work fine. There is a high and low filament for brake lights, Most bulbs probably will just have 1 contact. I used a thick rosin core solder and heated up the parts and attached wires. It does not matter which goes to thich, but you need to connect 1 to ground and 1 to the filament (bottom) i.e. not filament to filament. Usually bulbs will not have 2 filaments, but this is the worst case scenario if you face one of these, you'll know what to do :-)

          someone asked:

          Also, my PSU says "input 100-120/200-240V~50/60 Hz 5.0/3.0 A" Does this mean that my PSU is 5 amp and 3 amp? I think you mentioned that 10 amp is perfect.
          The "input 100-120/200-240V~50/60 Hz 5.0/3.0 A" just means that at household current in america which is 110 volts at 60 hertz it will take 5 amps. In europe et all... where they have 220 volts at 50 hertz it will only draw 3 amps...

          This is different than your output ratingsn, you should see +12v 10amps or +5volts 20 amps etc... you're looking for the +12v rating specifically, and 5V also is useful to know. most AT power supplies have at least 8 amps for the 12volt and up to 12 amps... any will be sufficient for a ballast. But higher is better, but AT power supplies only come in upto 12 amps or so on the 12v, then you would need to move into the ATX...

          Usually you have to load the 5v with like 10-25% of the max capacity to get a stable load... i.e. if it's 20 amps max at 5 volts, then 10% of 20 amps = 2 amps times 5 volts = 10 watts, so you would need anywhere from a 10 watt bulb upwards. The calculations aren't important, just that you know you need about a brake signal sized bulb.

          It's hard to see in this pic, but most power supplies have a given rating for each DC "rail" or voltage that the have...

          this 90$ ATX power supply at newegg has ~34amps on the +5volt and 22 amps on the +12volt... yours may look a little different


          • #6
            did you allign the filiment.. haha, great work.
            Halogen is for people that can see in the dark. HIDs are for the rest of us.
            Is300 w/ LS430 projectors & LED tails.


            • #7
              Don't forget to make a UV cover for your new HID house lamp.
              '96 BMW M3 Cosmos Blk/Blk

              Bosch bi-xenon projectors w/ d2s 6000k and 6000k HID h1 fogs


              • #8
                very nioce write up ...gj!
                Rock out with your cock out....Bukkake style!


                • #9
                  Originally posted by hamanncheese
                  Don't forget to make a UV cover for your new HID house lamp.
                  I think automotive xenon HID bulbs have UV filtration buillt into the capsule.
                  1994 BG-33P Paradise Blue Integra GS-R
                  Full 98+ conversion
                  E-class bi-xenon projectors


                  • #10
                    haha i work at a computer store and ripped apart one of those to show everyone my hids at work when I got them haha


                    • #11
                      nice writeup
                      2003 350z DB Base


                      • #12
                        Bump for some clarification and some good info...

                        Most people will not have an AT power supply. Most people will find an ATX as they are 100x more common these days.

                        If you have ANY connector at all that has 2 rows of roughly 20 wires... You have an ATX...

                        If you do NOT have a 20 pin connector, you have an AT.

                        If you have an ATX do this:

                        Splice the green wire onto the black on the 20 pin connector, or wire a switch inbetween them.

                        On a MOLEX connector, i.e. the thing your Hard drives and CDRoms plug into, a 4 wire molex connector.

                        Cut that 4 wire molex plug off... The red and black next to it are your load, you need to attach a roughly 10-20 watt light bulb or your power supply will not boot up.

                        The Yellow and black wire next to it are your +12volts and Ground connection, use them as you like.

                        may I suggest Alligator clips and electrical tape any exposed wires you may have. Usually the power supplies have short circuit protection, but that is not necessarily always the case. When you do accidentily short out your power supply, as everyone does, just unplug it and wait a few seconds, it should work just fine.

                        Sticky me! or maybe move me to a better section... I think this has got to be the most important part of retrofits, testing out your lights indoors... dunno, maybe people who live in warm climates all the time don't have this problem, but a cheap bench power supply is a necessary thing in some places!ok, on that 20 pin connector, the green wire... ok, on that 20 pin connector, the green wire...


                        • #13
                          Don't use a Dell's power supply because apparently Dell didn't follow the industry standard. Even thought their ATX PS have the same 20 pin connector, the configuration is different. Save yourself some time and try not to use a PS from a Dell computer.


                          • #14
                            Buahahahah that's crazy!!! The one light you'll probably need for the entire room LOLOLOL. Great write up.

                            It's definitely not for people with zero electronics knowledge...those capacitors if not discharged correctly alone can cause serious harm to an individual...


                            • #15
                              for those of you who wants to use the Dell's PS, the turn on wire isn't the green one. IT's the gray one at the corner, short the gray one to any black one and you should have the PS turned on.