Details on the Power Supplies bought from All Electronics 10/00
---------------------------------------------------------------

Catalog # PS-185 (Compaq # 172417-002 (172432-001))

This dirt-cheap power supply ($7.50 + $1.50 for standard IEC power
 cord, power supplies from Digikey with similar outputs cost $200)
has a collection of useful output voltages:

+5 V   @ 18 A,   \ (useful for digital electronics 
+3.4 V @ 12 A,   /  and some stepper motors) 
+12 V  @ 6 A,    (useful for driving many DC motors)
-5 V   @ 0.15 A, useless?
-12 V @ 0.15 A   negative supply for op-amp circuits

(185 W output power max)

[ Warning: at these high currents, be careful to avoid shorting
  power to ground or wires WILL melt and burn! ]


The one major drawback of this power supply is that, as with
 most switching power supplies, it is not stable (and will not
 work) unless one of its outputs is loaded at
 at least 5% of capacity (roughly).
This means you need to be continuously drawing at least 1 amp
 from the 5V supply or 300 mA from the 12V supply.
One way to do this is to hook a power resistor from 5 V to ground
 or from 12 V to ground, wasting some power as heat but ensuring
 that the power supply works.
Some other load such as a light bulb or fan could also be hooked
 up permanently, as long as it draws enough power.




Detailed instructions on using this power supply: 
 (pinouts for the various connectors are below)

1) Make sure the black pushbutton (hanging off the power supply 
   on a pair of white wires) is off (the "out" position)

2) Make sure the switch right below the power jack is set
   to "115" (meaning running off standard U.S. 115 Volts AC, 
   not European 230 VAC).

3) Connect a load resistor from +5V to ground or from +12V to ground.
   A resisitor of 5 ohms or less from +5V to ground,
or a resistor of 40 ohms or less from +12 to ground should work.
   Think about power dissipation! P = (V^2)/R, so make sure your
   load resistor is for at least that much power dissipation.

4) While looking at the fan, press the black pushbutton. If 
   everything is connected correctly, the fan should spin up
   and run at a constant speed. If the fan does not turn on,
   or turns on briefly and then shuts off, something is wrong:
   check that the load resistor is properly connected.
   If the fan pulses continuously, turning on, off, on, off,
   then it is almost working, but the load resistor needs to be 
   smaller: the power supply is not sufficiently loaded.




Pinouts for the power supply connectors:

When labeling the colors of the wires used in the power 
 supply connectors, I will use the following letter codes: 
 R = red, O = orange, W = white, B = brown, K = black, 
 P = purple, Y = yellow, L = Blue, G = grey

+--------------+
|  R  K  K  O  |
+--------------+
   5  0  0  12

+--------------------------+
|  Y  W  B  B  G  K  K  Y  |
+--------------------------+
   0  3  3  3  0  0  0  0

+-----------------------------------+
|  O  L  W  K  K  K  R  R  R  W  P  |
+-----------------------------------+
  12 -12 -5 0  0  0  5  5  5  5? 0



Max Davis, 10/00