Chapter 1:

Building a Home Brew


Power Supply


Illustration 11 An old Power Supply, lotsa cables coming out!

Well, most Prototypes involve electric Motors, Electronics and Rechargeable Batteries, and here's your chance to build an useful Gizmo with a discarded PC Power supply, a good'ol Soldering Iron, some Jacks, Alligators and Binding Posts.

Old PC's, pre-PII, Version:

Basically, the PC output is 0V, and +5V at 20 A, +12V at 8A, -5V at0.5 A, and -12V at 0.5 A (See picture below).

Illustration 12 See the warnings on the right? Better follow them!

But that means, disregarding for a moment the Amps, that combining a -12V and a +12V, you get 24V!

What's best, as the output's a bunch of wires, you can have multiple independent 5V / 0 outputs, for example, not the same with a cheapo multi-voltage transformer.

Here's the wire colors and their respective Voltages:

*The orange wire, inside the box, which you can open at your own risk, seems to be +3.3 V on ATX Power Supplies, but this one's a 386 PC Power Supply that we won't open!!

It's best to have as many rows of outputs as you could get from the number of independent cables available, but I'll only show 2 for this example.

In total, without opening the box, it's best, here's the possible outputs:

That can and must be extended if you're considering the Amperage, and you must do that, as some Electronic components won't take something like 20A without hissing and smoking, and going out of business!

The experimental approach, and a good Multimeter, would have solve that problem, but if you make some calculations, and know that two different Amperages in serial go down to the lowest Amperage, you get:

Here you can roughly see what can be done, the small box is the PC Power Supply, the white spaces are where the 9 outputs are shown;

Remember, you can use the PS power plugs, use some thick copper wire soldered to the wire you unse on the binding posts, to make a "jackplug" of sorts, to pluck into the plug's holes, that way you can internally re-arrange the outputs at will!

Leave one of those plugs sticking out if you like, so as to check Hard Disks and CDs and what not, OUTSIDE your PC...

I think it's better to spend some cash on binding posts, and have the outputs clearly printed on top of these 9 pairs of posts, than to have only 5 posts, an output table, and a lot of opportunities to make mistakes!

Illustration 13 The asterisk marks THIS last 17V 0.A is from the White wire output.

So why use posts at all, not some pairs of wires sticking out?

Because this way, you still can use the first table, and have the best of both worlds.

A tip from Amuron, from the Inventors Garage,, you still don't have to open the box, all it takes, in his own words is that,

“You need to address the power enable pin #14 being pulled low for it (ATX) to function”.

ATX version:

Notice the Green wire? PS-On! Also, a Polyswitch current limitation will help the thing not going kaput, although using a weaker fuse than the ones you'll find on the ATX may fix that. See the wire color values? New voltages, and different Amperages! Yes, you've guessed right, it needs a completely different set of tables!

Here's the values for the wires, Volts and Amps, and now the 20(!) different possible outputs, some of them giving identical outputs, but with different wires, all here...

Please note the lower row of outputs is just a lot of 5V and 12V outputs, so as to take advantage of the many wires available.

Not shown here, but you can leave one of those 4 Pin PC Plugs sticking out, good for some occasional PC Peripheral, (HD, Floppy Drive, CD, etc.) testing!

Take some time, dismounting the Power Supply out the PC so you can use the PC's own on/off switch, do some wire cutting and soldering, check and re-check the outputs with a Multimeter, here you have it, a Power Supply for next to nothing.

Of course you can use the inside wires to use the Led wires, on ATX PCs Power Supplies, you can do a lot of Pazzazz, but if you know that much, you'll know how to, this one for most people, that can cut a wire and solder it, build a box, pierce some holes on metal plate, and not much else!

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