I need to upgrade an alt.

 

Why - what's the problem?

Keep in mind that for us the IDLE rating is what's important - not the max current rating (which is usually rated at like 2000 RPM).

PM Lysmachia - she just had hers rebuilt at a place that makes it do almost full output at idle, and it wasn't much money.

 

Gonna have some high current draw soon from two amps.

 

How many watts we talking here? Will you spend a lot of time idling, or mostly driving?

I ran about 6000W off one Streetwires 150A alternator with 2 batteries and 3F of cap. When I would really get on it in competition, I would adjust the idle speed up (since it was a 22R, this was REALLY easy).

IMHO, multiple alternators are not worth the trouble. If you do, I would recommend that you keep the two systems TOTALLY separate - one for the car, one for the stereo, lights, etc.

 

I usually am driving fast when I have the tunes cranked. I keep it low in town so I don't bring unwanted attention from cops and criminals alike.

Subs will be 2000x1 RMS @ 2 ohms from a T30001bd. 300 amp fuse
Front stage will be 600x2 @ 2 ohms from (maybe) a T15002. 250 amp fuse

The RF sheet for the 30001 claims 2990 watts as the actual RMS power at 2 ohms. The T1500 is around 750x2 @ 2 ohms.

I'll use RF's high side of 4,500 watts so not to have too little power.

 

Let's make all the calculations at 12V to be conservative (when the alternator is working, you have 14.5V) So your peak current draw will be about 400A. Your typical power draw will be about 1/3 that, or about 133A ('cuz we're deaing with sine waves here).

So, you need about 150A of alternator and ideally 37.5F of capacitance (some of which is built into the amp) very close to the ampifiers. (Power stored by a capacitor is 1/2*capacitance*voltage^2.)

Without the caps, the battery will have to supply the extra "surge" capacity, and they react slowly and are usually too far away to do it really effectively. The one battery should be able to handle it, (assuming ~800 CCA), but if you're going to be playing the system for any significant period with the engine off, another battery would be a good idea.

I'm sure the EE's are going to chime in and say you don't need all that, but here's my $0.02

 

I called around to check on some and found all high prices. (At least I thought so.)

I traded in my core to NAPA and got $50 or $80 off the one I bought from them.

 

Did you call places local to you, or online places?
There is a place not too far from me that will make it into a HO, but I am not too sure on the price since it varies. It is much much much cheaper than the online places.