Running Xcvr from a Second Battery

[WA2WMR]

I would like to install a Yaesu xcvr rated at 23 amps in transmit in my new car. The cigarette lighter sockets inside the cabin are only rated at 10 amps. Getting through the firewall is problematic (read not acceptable). I do have storage locations where I could keep a second battery. What I am looking to do is charge the second battery from one of the cigarette lighter sockets. Is it possible to set up something that would charge the battery from the cigarette lighter but when transmitting draw only from the battery?

[W3TDH]

The radio would draw from both the battery and the charger adapter so you would have to have a current limiter in the adapter line. That would prevent the radio from overdrawing from the charging circuit and opening its fuse.

Check your owner's manual to see if there is an unused fused output in the cabin fuse holder which is usually located under the dash or in the side wall of the driver's foot well. The cabin fuse holder is often supplied by a pair of large gauge conductors that will readily handle the 23 amperes of current drawn by the radio during transmit. It is fairly likely that you will find a unused fused terminal that will at least handle the charging circuit. For any battery type with the possible exception of Lithium Iron Phosphate the charging can be done by a circuit from the alternator but you need to use a battery isolator which will prevent the Starting, Lighting, and Ignition loads from drawing current from the radio battery. With an isolator in the circuit no other load in the vehicle can draw current from the radio battery. Depending on the chemistry of the radio battery you may need a charge controller to prevent the battery being charged at too high a current. That will avoid the charging circuit damaging the battery.

If you have more questions please ask.

Tom Horne W3TDH

240-688-8590

Edited September 25, 2023 by W3TDH
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