Do I REALLY need a big alternator?

[sdmustangrider]

66 Mustang.

Do I really need it? I do have an upgraded ignition, couple gauges, and a small amp with these specs:

• 4-channel car amplifier
• 50 watts RMS x 4 at 4 ohms (75 watts RMS x 4 at 2 ohms)

I use to have a sub amp pumping 300+ out but took it out now. So my question leads, do I still really need my 100+ amperage alternator? Just trying to make things simple, and hook all my wires up back to OEM specs. I loved the single wire alternator, but been having electrical issues.

[JohnnyK]

Well the simple answer is. What does all your stuff draw?

[22GT]

I doubt it. I'm using a stock 42a alternator and I have AC. I doubt your radio draws more power than AC. What it your voltage reading at 2000 rpm, with the radio on?

[sdmustangrider]

Not sure what it reads but the last time I really had charging issues was when I had the stock alternator which is (35A?) I believe when I had my system put on. Then I added the 150a alternator and never had an issue. But now, i want to keep things simple by putting a 65a alternator in, knowing the only thing I have drawing power would be the ignition system and that amp I indicated above. Also I have 3 gauges which I hardly think would draw much power. Other than that, I think a 65a should work without any issues. If you're using an AC, then I should DEFINITELY think I would be good. Thanks GT.

[JohnnyK]

Well, yes, it is a small amp. It should say what it draws though.

Make and model?

[sdmustangrider]

It's an Alpine MRP-F300. Where would I see how much it draws? I have the specs up right now.

[supershifter2]

you can get a 65 amp small case G1 alternator.

[sdmustangrider]

I found a couple 65 amps from Oreilly. Since I'm going to change back to external voltage regulator, I'm going to change out the original one to an electronic regulator. Before
I did the 3G alternator swap, my battery kept dying with the original alternator which was still good. So I'm wondering now if the regulator was the problem back then, and a 3G alternator was really necessary.

[gman]

I read once an msd ignition control mod takes about 15 amp/hour to run. After you add in headlights and brake lights your oem alt. is tapped out. They didn't leave much head run. Then again I don't think the factory coil took 15 amps. 65amps should cover everything but this depends on how much the radio/amp draws. Keep in mind at idel you may not be making 65 amps, I'm not sure what rpm that rating is at.

[sdmustangrider]

I got one of those ready to run distributors, but no box. Not sure if that doesn't use a whole bunch of amperage. Don't do much night driving. I'll use my truck for that. As for the radio and amp, I figured with just pushing less than 75 watts on my amp, I can't see me using so much power from my alternator. But I think a 65 amp is a WAY bigger improvement over the stock 35 or 45 amp alternator I had before I added on the 3G alternator.

[Kelly_H]

Think you'll be fine with the stock alternator for what you're running. I succeeded in running all of my stock components plus extra speakers, a fancier radio, A/C, and EFI on a 38A alternator with no problems. Swapped up to a 95A from PA Performance just to give myself extra insurance - didn't want to have to pick between electrical components if something drew too much.

[Joe]

Factory ignition draws ~5A.
I = E/R
I = 14v (alternator on line) / {1.4 (coil primary impedance) + 1.4 (resister wire)}