Simple Alternator Question. Car stereo related. please look.

[kinggrimwood]

Does anyone know how many amps the stock alternator on my 1991 LS400 is cranking out?
the auto parts stores sell one at 90 amps, and another at 100 amps.

I am building a good car stereo, and my mono amp at 500wRMS powers my subwoofer of 500wRMS, and i'm going to do another 2channel amp spitting out 300wRMS for my component speakers(150 each side).

Does anyone know how many amps all this is going to be using? what the stock amp rating is on the alternator, and if it is enough? I know the 175amp alternator sold on lextreme is tempting, but i don't have $400 for it.

Also, will buying a better battery help? My current battery is very weak i think.

Any help and answers to my questions would be greatly appreciated.
thanks,
Jeremiah

 

[Peewee]

Stock alternator is 100A. (Some say its 120A but I'm not 100% sure)

I highly doubt you'll have any problems, but get a decent battery anyway.
Mine is 550CCA and is the stock size.

You've got 800WRMS listed there, but I'd be highly surprised if it draws more than 500WRMS peak, and about 300WRMS sustained.

 

[kinggrimwood]

I think i have a weak battery. Not labled well, so i don't know it's specs. Would it be a good idea to pop for a good battery. i.e. 850CCA w/ 120 min reserve?

Also if i do have problems, would you recommend a capacitor? Some people think their worthless, and others are true believers.


On a seperate note, does anyone know anything about the starter being disabled if there isn't enough volts coming from the battery? Sometimes if i leave me headlights or stereo on for even a little while without the engine running, the car won't start ( yet there is still power to run the accessories). A jump start ALWAYS works, and i figured the starter disables if not receiving ample power as to not damage it. This is my speculation, i'm wondering if i'm correct.

thanks,
Jeremiah

 

[Peewee]

Its not the starter being disabled, is that you don't have enough power left in the battery to turn on the starter.
If the battery drops below 12v (maybe 11v), the relay wont be able to stay on, so the starter cog won't be thrown.
Other things like the radio, cig lighter will work down to about 10.5v

850CCA is a huge overkill, but it means you can run the stereo for longer without the motor on, and still be able to start the car.

Becareful though, if you drain a lead-acid battery flat more than about 3 times, you will pretty much kill it.
I had a battery die 4 months after I bought it because I drained it too many times.

As for a capacitor, on a single sub system, its not REALLY needed, but it can help.
Put an ANALOGUE voltmeter across the amp power terminals, and see how low the voltage drops.
If its drops a fair way, you need a cap.

 

[kinggrimwood]

Thank you very much for you help. I appreciate it. I'll consider dropping to around 700CCA, but the price difference isn't that much, so i might just go for the big guns.
anyway, thanks again.

 

[Lextreme II]

I have 1000 CCA in my LS400. Its in the trunk.

 

[kinggrimwood]

where'd you get a 1000CCA battery?

 

[Celsiorous]

If you are worried about power to the amps id say go with the caps for sure, how much power the battery and alternator can supply isnt as important to car audio as how fast they can supply it. When a large bass note drops it will drain alot of power and when the next bass note hits the car cant give the power fast enough to the amp. I dont know all the technicalities around this but I have heard the difference when caps have been added and usually its huge considering the price of caps.

 

[stevechumo]

where'd you get a 1000CCA battery?

When running subwoofers with amps, or hi-power speakers, using the biggest battery that fit in place and a good capacitor is always the answer. I'm using 920 CCA battery with a 1.0 farad capacitor to feed a pair a 10" Polk blowing roughly 500 RMS, plus a secondary amp blowing 4 tweeters, without any light dimming problems or whatsoever, not to mention a pair of fog lights lighting at the same time. For the high CCA battery, you can get it at many auto part shops including the Optima battery, especially at hi-performance car parts & stereo stores.