sabersaw30

iTrader: (10)

My alternator went out I was using a overdrive pulley on the alternator to keep my volts up.Will the 145 amp truck alternator keep my volts up without using the overdrive alternator pulley? Looking for a alternator that will keep the volts up.Seems like I am defeating the under drive pulley using the overdrive pulley.

99Bluz28

iTrader: (35)

10% or 25% UD crank pulley, and what's your current idle speed ?

b0b

iTrader: (1)

My alternator just did the same thing to me, I wasnt using an overdrive though. Are you A4 of M6? Dont worry about defeating the purpose of you underdrive crank pulley. The best thing to do is set your idle speed up rather than alter your alternator setup, you shouldnt need an overdrive unless you just want extra insurance. Mine shows a little low at idle, but I have a 500 rpm idle, stock alt, and 25% udp. Driving it is well above 12-13 volts. Adjusting your idle seems to be the best/simplest solution.

99Bluz28

iTrader: (35)

The problem with a 25% UD pulley on a A4 is that the idle speed is already 150 rpm lower that with a M6, and in gear 250rpm lower! So with figuring a factory P/N idle of 550, and a in gear idle of 650 I'd raise the idle at least 100rpm. This will bring the alternator within 5-7% of stock idle speed, but still be able to keep the battery topped off. So a stock alternator should be just fine with adequate rpm.
Btw, a overdrive alt. pulley with a stock Dia. or 10% UD pulley can cause it to over speed the Alt. possible damaging it.

02'Andy

iTrader: (3)

I keep my idle rpm set around 800-850, keeps the voltage up just fine, even with the AC on. I've got a 25% UD pulley, A4 car, stock alternator.

bww3588

iTrader: (49)

A 25% under driven crank pulley and a 25% over driven alt pulley will not drive the alt any faster or slower than stock at any given rpm.

In my experience with a 7200 rpm rev limit, I was killing alt's all the time. I never did switch to the truck alt but found a good one o'relieys. I have a feeling I'll kill it at some point. The ones I picked up at autozone would die the first time I took it over 6500.

99Bluz28

iTrader: (35)

Thanks for the correction, I've seen this happen numerous times when someone has a big stereo and uses a OD alt. pulley to get their idle amperage up, but then still takes the rpm up high and trashes the alt..

NVR_SPDS

iTrader: (39)

Like was said, stock alt, higher idle. I have a 25% U/D on both our cars. Mine is a H/C/Stalled Auto, and my wifes is Cammed/799s 6 speed. Think the idle in my car sits around 850.

sabersaw30

iTrader: (10)

Yeah it is a a4. Check this out took my alternator to have it checked at advance and it checked out good. My battery is showing 12.5 volts with the car not running. Could I have a bad cell in the battery not letting it charge? My volts with the car running is around 13.2volts it use to stay steady over 14 volts.I was getting a whine thru my speakers and my volts are not going up with the car running. I guess it is my battery.

sabersaw30

iTrader: (10)

Thanx for the help messed around with the idle it is charging a little better know.