Alternator Question

[Fishhawk]

Last summer I installed underdrives and a 100 amp alt. on my 85 GT. This winter I installed an electric fan that pulls about 13amps. I've noticed at idle the volts go down to 10.5 to 11. The other night after a 3 hour drive with about an hour stuck in a construction zone I notice a white corrosive build up around the positive terminal on the battery. Am I frying my battery? Please tell me I don't need to now shell out $300 for a 3g.
Also I have two amps driving the stereo with subs.
PS ... I would have thought a 100 amp alternator would have been enough.

And what's so different about a 3 G from any other 130 amp Alt.

 

[TRWXXA]

A 100 amp alternator with an underdrive pulley is probably not putting out any more amps than a stock 75 amp alternator with the stock pulley. At idle, that's barely enough to run the ventilation fan at it's highest setting, much less any lights or other accessories.

Losing the underdrives will help you a bit, but you'll still only be putting out about 30 amps at idle.

You can get a 150 amp, 3G alternator for about $125 from Alterstart, and a wiring upgrade kit from PA Performance for about $50. Then you'd have about 65 amps at idle.

 

[Fishhawk]

I didn't have this charging problem until I installed the electric fan. I'm thinking of changing the alternator pulley, if that doesn't work, having the alt. rebuilt to around 160 amp. Just found out about a guy in my area that does that for the local PD, FD and EMT's for their vehicles. Hopefully cheaper then buying a new alt.

 

[Dbeck002]

I had the same problem. I have a 3G Alterstart alternator and it was damaged because it tried to hard to pump juice at idle with underdrives. Its being repaired though.

Solution: Overdrive your alternator.