voltage question

[ben1x]

I need some advice on probably a simple question.I have a handheld CB radio which will take either 8 nicad at 1.2 volts or 8 AA batteries at 1.5 v0lts.These are in series which comes to 9.6 and 12 volts.I have checked the AA batteries new and they come to over 13 volts.My question is -could I remove the AA's and hook it up to a 12 volt car battery without damage.Also,would a small amp fuse help?I have done this to other devices without problems, but this radio is more expensive and Japanese made.Thanks for your help.Ben

[torbjorn]

It will most likely work well under steady-state conditions in the car. But beware that equipment that is not designed for in-car use may get damaged from the transient overvoltages that regularly occur in a car's electrical system (for example, when starting the engine, switching off ignition and so on). If the car's entire electrical system is in as-new state, then it will not be a big problem. But on older cars where the battery might be aging, maybe there are loose or corroded connections in the charging circuitry etc, transients might be very much worse.

I think you should connect the radio via a fuse in the + line, properly chosen according to the radio's current consumption. Either try with a 1 A fuse or measure the current consumption when transmitting and choose the fuse for about 1,3 - 1,5 times the actual current. On the radio side of the fuse, connect a transient protection diode, i.e. 1.5KE22 or an 18 V 5 W zener in parallell to the radio. Then the fuse will blow in case of a severe transient in the car's electrical system.