The simple way to a high power 12V PSU

Most CB transcievers are actually built for use in a car, therefore the supply voltage of +13.8V available in an automobile has become a standard for CB radio units also. If you do not have a better solution at hand, when you use your CB radio from your home a quick fix is to modify a computer ATX power supply. For the standard legal CB radios a cheap ATX power supply is just fine, provides good regulation and plenty of current, all you need to do are the quick hook-ups described below and you’re ready to go.

First of all, take a good look at the large ATX connector and try to identify it with the picture:

atx_pinoutThis is actually the pinout for the older 20-pin models, if you power supply has 24 pins do not worry, everything is the same, there are just 4 extra pins that continue to the right of this picture for extra current support required by newer PC’s.

The first step is to connect the green wire (pin #4) to one of the black wires (#3 for example), so the PSU powers on by itself whenever you connect it to the mains (~220V or ~110V for you other folks out there). Very simple:

atx_1

But because it usually provides many voltage outputs, the ATX power supply will become unstable if you just draw current from the +12V line. Therefore, some kind of consumer will be needed on the +5V line too: a car lightbulb (12V / 21W) or a power resistor will do just fine; i used a 2.2ohm / 20W resistor with great succes but beware, it will get HOT. Just hook it up like this:

atx_2Now you’re pretty much ready to go. Just connect the yellow wire from the power supply to the +13.8V red wire of the CB radio and the black wire to the black wire, power up and enjoy. The output power will be just slightly lower that with a dedicated true +13.8V power supply, but it’s entirely unnoticeable.

This solution is actually so good and simple that i’m using it right now to power the 150W SSB radio. A 50Euro PSU, these mods, some extra RF filtering and some other easy adjustments to the PSU internals and it’s good for 30Amps at +12V.

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