depends on the vehicle. some cars have alts that have a little headroom over what the car actually needs. but some imports have alts just big enough to get by.
ex: the vehicle itselft needs 50A to operate well, but it has a 100A alt. you would have 40-50A of head room (400-500watts)
My stock alternator can't even handle 488wrms!! It's only 70 amps. It's fine when I don't have the defrost and heat on, and driving lights. It's either freeze and have the sub loud, or warm and have the sub low. I have no money either to upgrade, at least not yet.
My truck has a 105amp alt and I'm running two vega exl 1000s.. I've also got an Optima Yellow Top plus the stock battery... each amp is getting 14.4v but as soon as I turn it up to full potential the current draw is going to be 180 for the amps so I need an alt.. Hit 145.6dB with a factory alt though..
alot depends on the car and the alty itself. You can put a "bandaid" on the ordeal with a cap, battery upgrades or extra one, and the Big 3 but its only temp. A HO alty or really just a stepped up, well built alty will do. I have a local place who did my friends alty and upgraded it from a 105amp Delco alty to 120amps and the thing makes the lights brighter when you step on the gas. Alot will have to do with the quality of the build of the amp. i think a Honda 55-70amp alty handles like 400rms before you start to really see a problem, my 80amp Mitsu alty takes 1440rms with some dimming, my 105 GM Delco took 1440rms no problem with little sign of dimming.
I have a 500rms class A/B kicker amp powering my subs, a 250rms class A/B amp powering my speakers, a 1.2 farad cap, a Duralast gold battery, and an 85 amp alternator. When everything is cranked at night, most times the volts stay above 13.5 but sometimes It drops to 13 with everything full blast and everything running in the car. The thing is my lights dim pretty bad even at 14 volts. What is wrong there? I might upgrade to a 600rms class D amp down the road (draws same power but puts out more). Any suggestions?
I have no clue what size my alt is, but I'm running 1700W in it. I can get my HU up to about 35/40 before it starts dimming. I was pleasantly surprised.
i have 2 jl 1000/1 and 1 jl 450/1 hooked up to my stock alt right now. i am waiting to hear from nate about the ho alt. in the meantime my lights dim at around 15/30 volume. but it is so loud in my car at that volume. at 18/30 it is really loud and the voltage meter i have reads 12.4v at that time.