Originally Posted by

**Richard Clark**
guys the math is really very siimple------4000 watts is 4000 watts and watts is always volts x amps-----so in a 12 volt system it would be 333 amps and at 15 volts it would be 266 amps--------now if we have to pass that wattage through a lossy system (like an amplifier) we have to account for efficiency losses and add a percentage----ie if the efficiency is 50% we have to double our starting amperage since the voltage is still the same------so a 50% lossy device outputing 4000 watts would draw 8000 watts-------at 13 volts this would be about 615 amps--------class AB amps range about 50-60% at full output and class D amps range about 60-80% at full output------NOW for the biggest factor-------if we are playing music we can automatically divide these numbers by 1/3 or more for short term values due to the crest factor of music and for long term values we can divide by even more-----there are pauses between songs and at the end of the disc where the current demands are VERY low and these affect the long term average quite a bit-----and---sooner or later you are bound to ride by a cop and might have to turn it down a bit-----its not likely that a long term value of more than 10% can be needed for actual power requirements in a real system-------so for that 4000 watt system most any stock alternator will do just fine since it is a rare system that requires more than 50 CONTINUOUS LONG TERM AMPS.............RC

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