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Lab Power Supply


This entire time I've been using the PC power supply just by sticking wires in the ATX plug. Not a great solution as the wires have a habit of popping out. To turn on an ATX type power supply you need to short the green and ground (black) wires. ATX powers supplies are the most common type. The only other one I know of are Dell's, which have a special configuration for the 'ATX' plug. Same style of connector, completely different voltages at each pin. This is why your nice new motherboard explodes because you used your old Dell power supply when building a new computer. My friend knows this from personal experience.

Lab Power Supply Formerly of PC

I have managed to take that old PC power supply and make a proper lab power supply out of it. It's a rather simple setup. You can find out how to do this yourself on http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/step2/Planning/ and you can find all sorts of other odd do it yourself projects on Instructables. I took several binding posts and attacked each seperate set of wires to a seperate post. The wires are:

Orange = 3.3V
Red = 5 V
Yellow = 12 V
Blue = -12 V
Black = GND
Grey = PwrOK
Purple = Stby
Green = PwrON

The grey wire you use to indicate, using an LED, that the power in on and the purple wire is hooked up to another LED for stand by power. Stand by power is the power that is still left inside the capacitors. If this LED is on then it is dangerous to touch anything inside the power supply. 

There is also a power resistor in there as most power supplies only work correctly when constantly loaded. In this case I have a power resistor on the 5V rail. In the picture below there is a variable 0 to 500 Ohm, 25W, power resistor (set to 10 Ohm). I later replaced it with a 10 Ohm 10W resistor. I also kept the two 12 V rails seperate. If you make a lab power supply you may or may not have an extra 12 V rail. 

For the ON/OFF switch I had to make a 0.5 inch diameter hole in the case. For this you need a step drill as regular bits typically are not that large. Also, regular drill bits make ugly holes and leave burrs. Canadian Tire has a step drill set that goes on sale for $10 bucks down from $35 every now and then.

Lab Power supply opened.
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