Ok, here's the deal: I'm planning to install a 3500 watt system, and I need some help deciding what alternator to get. Here are the choices:
Amps / Amps at idle 220/175 240/165 260/155 280/145 300/135
I want to be able to sometimes play the system with the car parked, but this system will also need as much power as possible, so what would be the best choice?
Well with a 300 amp alt you are going to have to rely on the capacity of your batteries while idle.Once you hit the gas though your alt will charge them much faster with a 300amp ALT,with a smaller alt you are limited.Hey...if you guys like bumpin your music while parked,go for the smaller one ,if you like cruisin and bumpin get an alt that puts out more max amperage .
but the 220 puts out most @ idle on your list! so if u creep without hittin the gas peedle, and like to bass @ the lights.. then the 220/175 will get by just fine! with the help of a good deepcycle batt in the back...
I like to bass @ lights, and creep slow, so I dont use the gas very much.. I like lots of output @ idle... normally the ho should put out atleast half its rating @ idle, if it does less, then that tells u about the manufacturer.. also always choose a large casing... u get more power out of the alt @ idle... my 300a HO does well over 160a @ idle..
B. Where did you get that 300amp alt with 160 idle? If I can get a alternator like that I would consider it more than a smaller one with around that many amps at idle. Thanks.
Then you have to get another alt 
,if you like cruisin and bumpin get an alt that puts out more max amperage .