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I have been told that a CDM1250 operating at 45 watts draws about 10 amps.

I was just told that the way to calculate amperage @ 12 volts is to do this:

45 watts divided by 12 Volts = 3.75 amps. IS THIS CORRECT?? I am confused.

danny20 wrote:I have been told that a CDM1250 operating at 45 watts draws about 10 amps.

I was just told that the way to calculate amperage @ 12 volts is to do this:

45 watts divided by 12 Volts = 3.75 amps. IS THIS CORRECT?? I am confused.

There are 2 reasons for the extra current. The power amplifier is much less than 100% efficient so you need more than 45 W input to the power amplifier to get 45W out. You also have to power all the other circuits in the radio.

So, 10A sounds about right for the total current to operate a 45W radio when transmitting.

Yeah, that's about right.

PA's are about 50% efficient at best.

I was always told for moto mobiles to double the watts and divide by 12 to get the approx. fuse rating.