Computer power supplies cost around US$15,but lab power supplies can run you $100 or more! By converting the cheap (free) ATX power supplies that can be found in any discarded computer, you can get a phenomenal lab power supply with huge current outputs, short circuit protection, and very tight voltage regulation.
In this instructable I will show you how to quickly convert one of those many computer power supplies into something that you can use to power your electronics projects, for electroplating, for electroetching, for heating wires for foam cutting, etc.
The voltages that can be output by this unit are 24v (+12, -12), 17v (+5, -12), 12v (+12, 0), 10v (+5, -5), 7v (+12, +5), 5v (+5, 0) which should be sufficient for most electrical testing. Many ATX power supplies with a 24-pin connector for motherboards will not supply the -5V lead. Look for ATX power supplies with a 20-pin connector, a 20+4-pin connector, or an AT power supply if you need -5V.
PLEASE, YOU ARE WORKING WITH AC VOLTAGE!!! IF YOU ARE NOT SURE OF WHAT YOU ARE DOING - DO NOT ATTEMPT THIS.
These instructions were originally posted by me on http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
I finally had to package the PSU in a nicer box. The wooden book was from a local craft chain called Michaels which I lined with foil and then packaged the electronics in. I also added back the 3.3V terminal as this was useful and I missed not having that in my previous version.
In this instructable I will show you how to quickly convert one of those many computer power supplies into something that you can use to power your electronics projects, for electroplating, for electroetching, for heating wires for foam cutting, etc.
The voltages that can be output by this unit are 24v (+12, -12), 17v (+5, -12), 12v (+12, 0), 10v (+5, -5), 7v (+12, +5), 5v (+5, 0) which should be sufficient for most electrical testing. Many ATX power supplies with a 24-pin connector for motherboards will not supply the -5V lead. Look for ATX power supplies with a 20-pin connector, a 20+4-pin connector, or an AT power supply if you need -5V.
PLEASE, YOU ARE WORKING WITH AC VOLTAGE!!! IF YOU ARE NOT SURE OF WHAT YOU ARE DOING - DO NOT ATTEMPT THIS.
These instructions were originally posted by me on http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
I finally had to package the PSU in a nicer box. The wooden book was from a local craft chain called Michaels which I lined with foil and then packaged the electronics in. I also added back the 3.3V terminal as this was useful and I missed not having that in my previous version.
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Signing UpStep 1: Harvesting the ATX power supply
1) Unplug the power cord from the back of the computer. "Harvest" a power supply from a computer by opening up the case of the computer, locating the gray box that is the power supply unit, tracing the wires from the power supply to the boards and devices and disconnecting all the cables by unplugging them.
2) Remove the screws (typically 4) that attach the power supply to the computer case and remove the power supply.
3) Discharge the power supply by either letting it sit unconnected for a few days, or by attaching a 10 ohm resistor between a black and red wire (from the power cables on the output side). Using a resistor will only take a few seconds to fully discharge the power supply.
4) Gather the parts you need: binding posts (terminals), a LED with a current-limiting resistor, a switch (optional), a power resistor (10 ohm, 10W or greater wattage, see Tips), and heat shrink tubing.
2) Remove the screws (typically 4) that attach the power supply to the computer case and remove the power supply.
3) Discharge the power supply by either letting it sit unconnected for a few days, or by attaching a 10 ohm resistor between a black and red wire (from the power cables on the output side). Using a resistor will only take a few seconds to fully discharge the power supply.
4) Gather the parts you need: binding posts (terminals), a LED with a current-limiting resistor, a switch (optional), a power resistor (10 ohm, 10W or greater wattage, see Tips), and heat shrink tubing.
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This will not work if the device really needs 0V (ground). For example, if it is connected to something else which is at 0V from another power supply. Hope this is not too confusing!
I am looking for something to power an electrolysis tank for rust removal. I basically need like, 12V with about 2 Amps. A lot of people will try and go with as many Amps as possible but the more seasoned guys say 2Amps works well, it just takes a bit longer. I used me 12v car battery charger set to the 30 Amp "Quick" Charge setting but after 3 Hrs. it shut its self down. Most people leave these going for 8 hrs. or more depending on size of items being cleaned or amount of rust... in the three hrs. I ran mine on the 30 amp setting, its got almost all the rust off and old vise. So Im thinking if I can run this at 12v with anywhere in the 2 amps and above, it would be good. But then Im seeing all these PSU's being turned into bench power supply's and now, not only do I want to make this for the Rust Removal, but I may as well use it for a bench power supply too.. lol its just confusing, all these Volts and numbers and - / + and stuff... Like the pin outs on this PSU, some wires are +12v or +12VC DC or +12 VB DC or VA DC or worse, +12 VD DC / SE... lol
I read mauve and it says somewhere else purple too, I got things mixed around
I liv e in Europe and using 220V AC input.
Do I have to change the 10 ohm 10 W resistor with some different resistor or is it good using the same?
I need 6 amp out in the 12V line!
Thanks a lot!
Sam
Most of the PSU are compatible with 100-240V input so you could use it in most countries.
I have a question. My PSU has +12V 8A and -12V 0.5A. If i use 24V, how much current (A) i can get? tnahks
- sleepyjz
anyway this project it's very nice and got the chance to reuse many psw that i got at home...cause of my job and passion
Otherwise, your question is not quite clear...
[This is a little old, maybe you have long given up].
In my case, with a 10ohm resistor (pulling 0.5amp) + a small lightbulb (pulling 0.3amp) I'm getting 12.35V. That might be the upper limit of this power supply, but I will check sometime with a bigger load (like 1ohm) to double check. But my 12.3V stays stable under load.
From what I've read,
You might also have a problem if your voltage sense wire isn't done properly. In my case there was an brown wire that went into an orange cable in the biggest connector of the original cables (the 24pin output). I had to make sure that brown wire was again shorted to the orange cables. Whether the brown cable exists an is shorted to the 5v or 3.3v (or in some cases even 12v) line depends on a number of things, so I just had to go through the trash to find the 24pin connection that I cut off and see what the case is.
When you say "it settles at 11.88v" I'm wondering what you mean by settles. Do you mean no-load voltage is 11.88v? The more likely problem tends to be that no-load voltage is "12.xx" V, but under load the line drops to 11v or something like that. That is primarily what the resistor is supposed to help with.
I would also try and see if you can add another 10ohm resistor in parallel, or a small incandescent lightbulb, just to see if increasing the load helps. That will double the amount you pull from the 5v line (from 500ma to 1amp).
So 1) i would try adding another resistor (in parallel, not series)
2) Is there anyway you can work around your 12.6 or 12.4v requirement?
The 12v rail is giving 12.4v (no load), the outputs of these psu's arn't regulated right?
If i use a high current voltage regulator i'l get a fairly large voltage drop, and that wont give me the full 12v i need.. the only v reg i have right now is a sharp pq12rd11, since it has low Vd, the output i get is around 11,9v.
What do you think, should i use this one and some transistors to handle more current?
Need some tips guys =)
anyway, ill powerup the stirp using just the regular 12v output
Otherwise, your question is not quite clear...
[This is a little old, maybe you have long given up].
Brilliant instructable I am new in electronic engineering and wanted a lab power supply will you please tell me that how Can we add a potetiometer(voltage regulator),rheostat, voltmeter and ammeter to calculate and vary voltage and current?
Thanks
You could do the potentiometer (variable resistor) but would need a beefy one if it isfor high current.
I actually constructed a little box (about 1x1x2 inches) with a knob on it to control voltage. This was based on an LM317 chip (check on google). Two input wires from this cube were connected to any voltage source and two output wires went out to whatever I was powering. The knob varied the voltage. Only limitation was that the maximum current needs to be less than 1 ampere and the maximum voltage was input voltage minus about 1.3 V.
So if you connected it to the +5V of the lab power supply you would get any voltage from 1.2 V to 3.6V. If you connected it to +12 V you would get a variable voltage from 1.2 V to about 10V.
Let me know if you are interested and I can post an instructable about this little cube.
I get the desired voltages in the designated ports according to my multi-meter. I can do a small load with an LED light and small computer fan and the power supply operates as it should.
But anything larger (rc motor, motor dyno) the power supply immediately shuts off. I cannot find a reason for this at all. Any ideas?
Current (in Amps) = (Horsepower x 746) / Voltage.
A 1/4th hp motor will require 15 Amps from a 12 V supply. Or, 37 Amps from the 5V supply.