No! Wait! Cut the GREEN wire!

So, you need to power your radio...

That was my problem.  I had radios, but nothing to power them with in the house.  So I went into scrounge mode.

When it comes to computers and electronics, I tend to save things.  Probably longer than I should.  But you never know when you're going to need something.

I looked online, and found the purpose-built radio power supplies to be out of my price range.  But as it turned out, I had several "used" computer power supplies at my disposal.  Now they are definitely *not* purpose-built for ham radio.  And rather than just one voltage, they output several voltages at various amperages depending on the wattage of the power supply.  Current available for each voltage is usually listed on a label attached to the unit.  Those voltages are +12 -12 +5 and +3.3.  I was only interested in the +12.  Of course ideally I'd want something that output 13.8, but most radios are tolerant enough to accept 12 volts.

Computer power supplies have a *bunch* of multi-colored wires coming out of them.  That in itself can be a show stopper for some folks.  Plus all modern computer power supplies have a *feature* that makes them pretty much unusable for the average consumer.  There's no on-off switch.  Or if there is, it doesn't seem to do anything when it's removed from the computer case.

The feature in question is that the computer motherboard controls the on-off function.  So when you tell your computer to shut down, as a final act, the motherboard tells the power supply to go into a suspend mode.  It doesn't actually turn off, but it does draw very little power.

So what to do?  Well, first have a look at the connector of a computer power supply:

Looks like a mess doesn't it?  If you look at one of these closely, you'll find that among all the wires, very few wires have colors that aren't repeated.  To be specific: Brown, Blue, Green, White, Violet, and Gray.  All of the other wires are either Black, Red, Yellow, or Orange.  So?  Well one of those wires is responsible for turning the power supply on and off.  Interested?  I was.  Turns out it's the green wire.  If you connect the green wire to one of the black wires (ground), as long as the power supply is plugged into mains power, it will magically turn on.

*** I'm inserting the usual disclaimer here.  Working on power supplies is potentially life threatening.  Make absolutely certain you have removed the connection from the mains, and done your best to drain the unit of any residual power.  The capacitors inside these units can keep their charge for months.  Use extreme caution.  Additionally, if you choose to purchase one of these to modify, opening the case or cutting any of the wires *will* void your warranty.  Please consider all this information carefully before you proceed.  End of disclaimer ***

So now what?  There are two choices.  If you are planning on dedicating this power supply to something other than computer use, then I would recommend removing all the extra wires and putting in something that will handle the current of the project you are working on.  In my case, I opened up the unit and removed all but one red, yellow, orange, and black.  Of course I left the green and an additional black to provide the on-off function.  In addition, I had some very flexible 8 gauge wire that is generally used in sub-woofer amplifier installations.  So I attached that to 12 volts and ground.  Buttoned everything up, and viola!  A re-purposed power supply.  Here is a picture of my re-purposed supply:

In the foreground you can see the rocker switch attached to the green and black wires.  Since I use this power supply for experimentation as well as powering my radios, you can see banana plugs on a couple of the wires.  The large red and black wire connect inside as described above and terminate in a Deans power connector.  Those of you that are involved with electric radio controlled models will recognize the connectors.  I probably should have used the Anderson Power Pole connectors, but I didn't have any of those and I *did* have the Deans connectors.  I can always make an adapter later.

The other choice is to take the connector that mates with this one off a dead computer motherboard and make your connections there.  I did that for a smaller unit I had that I didn't want to carve up.  The subject of removing parts from printed circuit boards is covered in detail in other places on the web.  I used the hot air method.  Provided by a scrapbooker's embossing tool of all things.  Think of it as a baby paint stripping heat gun.

Don't have any spare supplies lying around and still trying to save a buck?  Look on E-bay, Amazon, Tiger Direct, Newegg, the possibilities are endless.  I've actually purchased them from Newegg for as little as 12.95 with free shipping.

Well, that's enough for today.  Who knows what tomorrow will bring?

73
Steve
KDØWSW