The amps you get depends on the power supply you use. The
power supply will show the amps rating somewhere on the
label. The one I did does 10 amps at 12V and 25 amps at
5V.
Not really hard to make.. just need an old AT power
supply (it can be done with an ATX supply, but a lot more
wiring is necessary since these get power on and power good
signals from the motherboard), some 10 ohm 10 watt
"Sandbar" resistors, and an automotive 12V bulb. If
your PS is less than 200 watts you only need 1 resistor. For
larger wattage supplies 2 is sufficient.
First thing you do is unplug the PS and let it sit for a
bit as there are some large capacitors in there that will
give you quite a whack if they're not discharged
completely! (I let mine sit overnight.. an electrical
engineer could probably give a more accurate time.)
Next, open the box and remove the circuit board. Disolder
all the computer wiring from the board remembering where the
red, yellow, and black wires were. The red are the 5V+ wires,
the yellow are the 12V+ wires, and the blacks are grounds.
There are also 12V- (blue if I remember) and 5V- (green?)
that could be used to get 24V or 10V when used with their
positive counterparts, although not much current there.
Anyway, I only used the yellow, black, and red circuits on
mine. I wired in one piece of 14AWG to the board where the
yellows were connected, one 14AWG and 2 18 gauge wires to the
grounds, and 2 18 gauge wires to the 5V (reds). I hooked the
2 10 ohm 10 watt resistors in parallel and connected them
with the auto bulb to a 5V 18 gauge wire and the other side
to one of the 18 gauge ground wires. The remaining 18 gauge
ground and 5V wires will connect to the binding posts that
will be installed to the case. The 14 AWG wires will connect
to the binding posts for 12V out. (As an aside, you could
just wire in 2 binding posts for 12V only if you don't
need the 5V out.. I found that the 5V works great for running
in brushed motors though!)
Mount the binding posts on the case (make sure they
don't ground to the case! This will shut down the PS if
your lucky and if not it will ruin it!) and connect the wires
to them and reassemble the PS.
That's it.. you've now got a power supply capable
of running field chargers and (if you wired the 5V in)
running in new motors/brushes! If you want to get real fancy
you could paint the case as well and label the outputs. I
haven't done this yet but plan to. I've used mine for
many hours since I made it (almost on constantly since then)
and it's still working like a charm!
The only thing I noticed is that if you're running in
a motor on the 5V line it's better to shut off the
supply, connect the motor, then turn it back on. Sometimes
the sudden hit of the motor can temporarily shut down the PS
(usually 20 seconds or so and it powers back up). This can be
built in less than an hour for less than $5 (USD) and will
work as well as if not better than most commercial 12V only
supplies.
Here is a little draw of the long text… (click on it for the large version)
And here is a photo of the final product…
