**UPDATE** I've posted Rev.1 of the record, see below (Sunday Feb 6 2005) I'm actually writing up a record of the steps I took in converting an 250w power supply to have 6 banana jacks/plugs to power a project circuit, or whatever need be. This conversion has been going on for three weeks on-and-off, but this thread made me get off my duff and start to type it up. I'm about 80% done and it should be up in a day or two (extremely busy with school and life right now) . Here's Proof:
First off, credit to this guy who gave me the idea to make my own project power supply. Disclaimer: If you do anything to hurt yourself, others, or damage any property, it’s your fault . Not mine . This is a record of the steps I took in building the power supply, and wanted to share it with everyone at bit-tech . Notes: I’m sure there are a few spelling mistakes, run-ons, fragments, and just ugly english altogether in this write up. I’m just trying to make this as clear as possible for everyone to read. A power supply will not run if there is no load connected across it. The fellow above (lets call him “Andy”) used one 10ohm 10watt resistor as his fake load for the 145W power supply. The power supply that I used has 250W of power, so to be safe I doubled up on the 10ohm 10watt resistors and placed them in series (a picture of this is below). These two resistors came together for $2.59 cdn. Here I opened the case and tried to take out the screws holding down the PCB. This was a little hard, so I bent the side a bit and unscrewed them. I did this because not all of the wires will be used. Seeing how I don’t need eleven ground connections, I cut five of them clean off the board. You can see the marks near the bottom left of the PCB. This also applies with the +5v lines too. Out of the six available, I saved three. Again, notice the marks near the bottom right of the PCB This is a shot of the various connectors I will use for the different voltages. I drilled some holes for the fake load into the lid of the power supply. The two 10ohm 10watt resistors will sit here strapped to the case with zip ties/zap straps/ plastic ties/whatever you want to call them. In order to try and maximize heat transfer, I sanded down this area with some scrap sandpaper. Between the resistors and the case I applied some heat sink compound that was kicking around. I was initially not going to use the compound and just let the resistors cool off from the fan, but after I had seen how weak the fan was the compound was the next available option. Here you can see the compound was applied and the heat sinks tied down. In this picture, I had already drilled the holes for the plugs/connectors/banana jacks, the switch (which I later removed, because it was momentary) and the red LED w/ built in resistor. Here is the top of the cover. This picture shows the wires soldered on to their plugs. The red LED has its own ground and +5v line, and the resistors in series also have their own ground and +5v line. Some people may say that the yellow and black wires are soldered together, but they’re not . That black wire goes with the green wire for the switch, and just happened to be there when the picture was taken. By this point, I screwed the PCB down again, and left a few wires grouped together (but the bare ends covered with electrical tape) for potential use later on. Here’s a list of what the coloured wires mean: **************************************************** Black Ground (0v) Red +5v Orange +3.3v Yellow +12v Blue -12v White -5v Green Power on (used to switch the power supply on/off) Gray Power OK (this wire was tied off) Purple +5v standby **************************************************** Here is the PSU buttoned up and ready for testing. (I left the case looking like that...can't forget the ghetto factor )
Here is a list of final voltages for the power supply: THEORETICAL VOLTAGES +3.3v +5v +12v -5v -12v ACTUAL VOLTAGES +3.36v +5.1v +11.68v -3.8v -9.76v The actual voltages surprised me a little bit, but fully expected from a power supply made by a company that I’ve never heard of. I’m sure that if a top notch power supply were to be converted, the actual voltages would be much tighter to the theoretical voltages. The green wire. Some people may be thinking: “green wire…what’s that for?” The PSU wants to know that everything is OK (a.k.a POST) before turning fully on, and that’s what the green wire is for. I picked up a little SPST switch for $2.15 cdn. and then soldered the green wire and a ground wire to this. I could have easily just soldered the green and black wires together and used the switch at the back of the power supply, but I prefer it this way The brown wire. There might also be a brown wire kicking around in the power supply, and that is used to monitor the +3.3v orange line. Should things start to get a little nutty with the 3.3v line, I’ll crack the case and play with the brown wire and update this post . The gray wire. There was also a gray wire in my power supply, and it’s not required to run the power supply. Its only purpose is to tell the motherboard that the correct voltages are available, and it can start the computer boot process. This wire should not be grounded or tied to any load at all. Final words…for now Overall, I’m quite happy with the conversion and available voltages. +15 volts can be used (11.6+3.3 =14.9), -13.56 can be tolerated with chips, as well as +5 for practically anything. It’s pretty handy in testing out a pre-lab and working out bugs at home, then in the priceless two hours that we get in class. All I have to do now is go in, build the circuit and test, show the teacher and head out, all in half the time! If anyone else decides to pull something like this, post your make of power supply and actual voltages! Oh, and thanks for reading!
With the more powerful supply they could be in parallel to give a heavier 5 ohm (1A) load, may give better regulation. Still fine at 10W rating. Also consider a single 4.7 ohm 25W aluminium-clad, they cost a bit more but look cool as shlt.
This is cool. I have been meaning to do it for a while now. Probibly should get round to it! That can only provide one voltage at a time, but a PC supply can give 5 (12, 5, 3.3, -5, -12) different voltages, plus it's free from an old machine you don't use. _C
It's an old AT PSU it has 5V, 12V, a switch to turn it on/off and a LED that tells you if the PSU is on/off. It's the best to try things before putting them in my rig, if I short something or blow up something, it's just going to be an old AT PSU.
