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Old 02-29-2008, 03:47 PM
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Join Date: Feb 2008
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'81 240D total watts on 55 amp alternator

Hey Guys,

I was just wondering, how many total watts (i.e. reciever, amplifier) could I run without killing my stock 55 amp alternator?


Last edited by duolc42; 02-29-2008 at 03:56 PM.
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Old 02-29-2008, 04:03 PM
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Join Date: Nov 2007
Location: UK
Posts: 134
P = V x I, so assuming 12v, 12x55 = 660w total at rated RPM of alternator.

A class AB amplifier is about 35-50% efficient, a class D is about 90%.

Remember that you wont always be using maximum power of your amplifier, and if the load of the amp is more than the alternator anyway, then the power will come from the battery's reserve. The alternator will recharge the battery when the amplifier isn't drawing as much current.

Unless you listen to bass test tones, you dont have much to worry about even with a highish powered amp.

Remember though that when you start using items such as the rear screen defroster, heater fan, headlights etc, there will already be a big load on the alternator.
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Old 03-02-2008, 04:21 AM
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Thanks, i appreciate the input.

Last edited by duolc42; 03-13-2008 at 03:17 PM.
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