HO alternator output needs (calculation)

Spug

I found out today that the time to replace the alternator in my car has come. Eventually I'm going to need a HO unit when i get the thing road ready and get the system installed that has been taking up room in the closet for quite some time, so I might as well just spring for it now. My question is about the proper "size"/output of the alternator. Is there any sort of formula for determining how many amps I'll need coming out of the alternator to feed the car and the stereo? The highest amperage i've been able to find for my application is 150 amps, I just need to know if it's enough.

Thanks,
Nick

exalted512

what kind of vehicle and what amps do you have? (as well as current draw on anything other than what the car normally runs on. ie. extra lights, etc)
-Cody

neomagus00

i'd figure 50 amps for the car itself (medium size... call it 80 for an expedition, f-150, etc.), AC and so on. your amplifiers' fuse ratings added to that should give a good starting point... i'd tack on at least 15% for safety and a reduced risk of major voltage drops. make sure you look at the rpm/output graph... you don't want it to make its amperage at 5000 rpm, that's pretty useless.

Spug

It's a 90 CRX, the stock alternator is 60 amps. The amps are a JBL BPx1100.1 for the subs (max. current draw is 110A and it has 3x30A fuses) and the other is a JBL Px300.4 (max. current draw is 78A and it has 2x30A fuses). Other than that there's just the headunit (with no internal amp whatsoever) and some driving lights (maybe a 7" monitor in the center console someday).

Nick

neomagus00

hum... that car will draw maybe 35, plus all your fuses = 185.

note that that's full volume with all accessories going strong. i'd get the 150, as long as it makes that 150 at a low enough rpm. no such thing as too much .

Spug

I spoke to a guy at a "local" tuner/stereo shop about pricing (wanted to see if I could get a "quality" unit anywhere near the price of an ebay unit). To my surprise he suggested ebay and told me that a few of their customers had purchased alternators from ebay, the company's name is alterstart ( www.4alterstart.com ), and he said that they were very pleased with them. He also said that they start putting out their real power at aroung 2k rpm, nice and low. Sounds like a plan to me unless anyone has anything to say that'll make me think otherwise. The 150A is only $230 so it's kind of hard to beat if they are as good as I'm told they are.

Nick

neomagus00

go for it, especially with that price and especially at the rec of a dealer.

exalted512

thats where im getting my alternator from...
-Cody

swerve

cody, when i call and order my alternator from there. do i just have to tell them the type of car//engine? i emailed them and asked about a Series II L67 alternator and they replied but i want to be 100% sure it's the right one.

exalted512

its better to give too much information that too little, but if you have the model number of your alternator, im not sure what else they would need...
-Cody