If you use a car battery to power your two-way radio, please wire it straight to your battery terminals -- but through an inline fuse, of course!
Most radio transceivers these days are built to work off a 12 volt DC power supply, which is the voltage found in all modern cars and motor vehicles — except for military vehicles and large trucks which run 24 volt DC power. This means it is pretty easy to run a two way radio, be it a CB radio, a licensed commercial transceiver or an amateur radio transceiver directly from your 12v car battery or from your car’s electrical system.
For temporary use, it is a simple enough matter to clip a pair of crocodile clips to your car’s battery terminals or to the vehicle’s cigar/cigarette-lighter socket. This is the quick and dirty approach, because it is fast and easy but it does have a couple of disadvantages.
When a fuse blows, it has just prevented your wiring from catching fire… so always use a fuse in the power leads and make sure it is rated for the correct number of amps (Amperes) for your 2-way radio.
The cigarette (or cigar) lighter socket cannot handle a heavy power load (measured in Amperes or amps). In fact it can handle a load of around 12A to 15A (those are amps) maximum before it blows a fuse — Otherwise it will probably set fire to the car’s wiring. This is why it is important to have the right sized fuse in your power-line, between the battery’s positive (red, +) terminal and the equipment.
Your car’s lighter socket is okay for a little 27 MHz CB set (or even an Australian UHF CB set), because they don’t use high power. Most CB sets that transmit 5 watts AM only need a 2 amp power supply, but even a single-sideband CB radio that transmits a 12 watts PEP signal can manage to send okay from a 4 amp power supply.
Commercial and amateur radio HF radios can transmit 100 watts PEP, and sometimes more. They need a power supply capable of delivering the 12 volt (it is often 13.6 volts or thereabouts) at 22 amps. Medium-to-high -power VHF and UHF mobile radios usually transmit a 25 to 50 watts signal, and this can burn 10 amps of power or more each time you press the transmit button on the microphone. Some VHF radios can even transmit a 75 watt signal.
Your 12 volt wiring between the battery or power supply should also be thick enough to handle this many amps. (Ask your local auto-electrician if in doubt.) And for any radio transceiver capable of more than, say 5 watts output (the same as a 27 MHz AM CB), you should run the power wires directly to the car battery terminals, with a fuse on the red (+, positive) side wire. Make sure the fuse it rated for the same number of amps that your radio will require, i.e. 2 amp, 5 amp, 10 amp, 15 amp, 20 amp, 30 amp etc.
Many hams will put a fuse in both the positive and the negative power-supply wires. It is also a good idea to make sure the radio is grounded to your vehicle’s chassis.Oh yes. There is one last pointer that is important. If you plan on using your two-way radio a lot, make sure you don’t run your car’s battery down too much or you won’t be able to turn the engine over when you need to start the car again.
Emergency and military vehicle often have a special auxiliary battery (a second battery) just to run the auxiliary electronic equipment. That way the starter motor battery will remain fully charged. Many 4-wheel-drive enthusiasts and ham radio buffs do so as well. It costs money, but its better than being stuck in the middle of nowhere, well out of cell phone range to a tower, and find you have no battery power for the radio or for the car!
73 de David, vk2dmh
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