900 watts on 70 amp alternator

[bmk6795 10+ year member]

Ok guys im running 900 watts on a 70 amp alt/stock battery. Currently have no big 3 but will soon and eventually extra bats/ho alt. Until then do i need to worry about burning anything up? Big 3 will happen within weeks but the bat/alt wont happen for a few months, just making sure ill be ok until then.

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[southernboom88 10+ year member]

shud be fine. i've currently got over 1k on 70amp alt and stock battery. but do have the big 3 done.

 

[zako 10+ year member]

I would say 70amps of current is not enough if you really need to use those 900watts of power. To give you an example, my PPI P900.4 is a relatively efficient Class D amplifier, rated for 4x225watts at 2ohm. It still consumes over 80amps of current if running at full tilt according to pasmag rest. If you run your amplifier(s) at the lowest resistance supported, a look at their fuses will probably give you an idea how many amps of current they really need. Also remember that the rest of car consumes power as well, so not all of those 70amps will be available to audio system. There are way around this without changing alternator though. Run all amp channels with 4ohm load. Use ported instead sealed box subwoofer. Use Class D amplifier instead of Class A/B. And after all the SPL difference between 400 and 800watts is just 3dB.. not something to lose sleep over.

 

[tc300 10+ year member]

What amp?

 

[lilboom 10+ year member]

get a voltage meter or dmm ant test you voltage at listening level . then report back here.

 

[n2audio 5,000+ posts]

Unless you're planning to blast it non-stop I'd be surprised if you have any problems.

However, there are strange cases where people have issues with set-ups that seem unlikely to be a problem on paper.

 

[Odd-io 10+ year member]

To check it out theoretically:

watts = amps X volts

1008 = 70 x 14.4

That doesnt take into account the charge stored by your battery. Should be fine but there's lots of variables. Good luck and have fun.

 

[jockhater2 10+ year member]

I ran my stock 90 amp alternator and battery on 800-1200 watts. and burned up the alternator within 1 year. Thats when I hopped on forums and started gaining knowledge.

 

[clickclickw00t 10+ year member]

To check it out theoretically:
watts = amps X volts

1008 = 70 x 14.4

That doesnt take into account the charge stored by your battery. Should be fine but there's lots of variables. Good luck and have fun.

I've been looking around for this formula haha.

 

[n2audio 5,000+ posts]

I've been looking around for this formula haha.

It isn't much of a "formula". It is a rough hypothetical approximation of how much power a given alternator might be able to supply in a perfect world.

It doesn't consider the amount of current already being used by the car's stock electrical system. Typically that's 50-60% of the alt's stated output.

It doesn't consider the efficiency of a given amplifier.

You also need to recognize the current demand of any amp will vary significantly based on the type of music played and the volume it is played at.

 

[goingdef 10+ year member]

I ran my stock 90 amp alternator and battery on 800-1200 watts. and burned up the alternator within 1 year. Thats when I hopped on forums and started gaining knowledge.

alts go bad, amps don't help neither do extra batterys on stock alts but when setup right over 1000 on a good agm deep cycle and solid big3 will do fine as long as you keep an eye on voltage at idle. I have ran everything from a crappy Ma hk401sx at .5ohm to a memphis mc2000d and everything in between it's all been on the same 70amp alt for 5 years now with no problems.