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[NikonD3 10+ year member]

Running 3000-4000 Watts in my ride how big of an HO ALT do I need

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[Cruzer 10+ year member]

im a noob but i would guess any HO alt would work, obviously the larger the better

 

[chillin 10+ year member]

im gonna say its gonna be more about how many batteries your gonna need and you will probably be better off posting in the electrical section

 

[audioholic 5,000+ posts]

Listener preference will be a much larger factor than the number of batts. Even if you have a stretch-van filled with batts, if your stereo is capable of drawing more than your alt produces, and you never listen with the volume low, and never recharge your batts 'offline', eventually the batts will run dry as well.

4000 watts at 80% efficiency (avg efficiency for amps at full tilt) is gonna be more like 4800 watts the amplifier(s) draws. And since watts = amps x volts, we know it will be 4800 = amps x 13.6. (13.6 volts is the avg between 12.8 volts and 14.4, which is the batt voltage and alt voltage) So max amperage draw will be (approx) 350 amps of current draw. But, this would be if all your amplifiers drew 100% power at the same time. This wont ever happen, unless you enjoy listening to pink noise at full volume, so you can safely assume the realistic max current draw will be something less than that. Then you can also factor in that if your average current draw over time is less than your alt's max output, the batt(s) will absorb the largest spikes that exceed the alt's potential. But just remember, because a lot of people dont consider this... if you rely on your batt(s) to handle a substantial portion of the load, at best you will have a system voltage issue, at worst you'll have a dead battery some day when you least want it.

Long story short, its impossible to say exactly what sized alt will fit your needs. Maybe you own a 100,000 watt stereo, but never turn the volume up past 5%. Or maybe you're the type of person who, if the engine is on, the stereo is on, and the h/u volume is set at max the entire time. These two examples would obviously have different alternator requirements, even if their stereos are identical.