12V Power Supply
last updated 2-12-2012
completed power supply

Do a search on ebay for a Dell Poweredge 2850 power supply or model NPS-700AB. I found mine from a computer business that replaces them after so many hours then sells the pulled power supplies as used. With shipping you should be able to get one for $20.

NPS-700AB pinouts

Power On: To turn on the power supply you need to solder B1 to A1 and run a wire to B6.

Fan control: Solder a 1K resistor from C1 to B2, solder another 1K from B2 to A2
B2 controls the fan speed. At 3V you get full fan speed.
C1 is ground
A2 is a variable voltage that increases as more current is drawn from the power supply.
The two resistors are a voltage divider to divide the output of A2 (current) to B2 (fan control).

12v charger connections. PB1, PB2, PB3 are ground. PB4, PB5, PB6 are +12V.

shows completed soldering