I have an '86 Iroc with a 305TPI.

The original Chevy alternator was a big cased 108AMP Alternator.

I fought for years trying to by alternators from the local auto stores for $100 instead of getting one from Checvy for $300.

They never lasted and caused me to destroy numerous batteries.

Finally I bought a Stinger 150AMP for >$500.

This worked great for a long time until I accidentally shorted it while the car was running. I had it rebuilt by stinger and it was running fine but the car has been sitting for four or five months.

I took it for a drive last saturday and it started on its own. By Tuesday night, it didn't have enough juice to crank.

I started charging it and it was charging slow.

I decided to check the AC voltage across the battery terminals with the car running.

DC Voltage was right at 14.4Volts.

AC Voltage was around 28~29 Volts.

Seems like the Alternator is bad (diodes shot).

The next day I played a little and while the car was running, I opened the knife type battery disconnect switch on the positive terminal and measured voltages again.

Just battery:
DC Voltage = 12 Volts
AC Voltage = 28~29 Volts

Alternator / CAR Side: (battery out of circuit)
DC Voltage = 14.4 Volts
AC Voltage = ~35 Volts

I feel like I must be loosing it. I know that any AC voltage when the car is running is bad. (My alarm installation manual said anything above 1/10th of a Volt AC was bad for the alarm and the car) But the battery is measuring AC voltage when it is totally isolated (well just nothing connected to the positive terminal).

I'm afraid I have toasted another battery.

Any help or suggestions would be welcome including suggestions for a high AMP replacement alternator. Since the Original Case was bigger, the brackets are setup for a large alternator body and most replacements ahve to be custom fitted into the space.

I had considered a Phoenix Gold Alternator when I got the Stinger. I also looked on Jegs.com and saw a MSD Ignition Alternator in both 130 and 160 AMP versions that would work.

I really feel like I need an extra (safety) voltage regulator / diode rectifier bridge to protect the car and battery from these failing alternators.

Here is the alternator I was looking at:
http://www.jegs.com/cgi-bin/ncommerc...21&prmenbr=361

Thanks in advance for any help.

 

It's impossible for your battery to read 28vac when isolated. Some multimeters are auto ranging, you sure it's not reading 28 millivolts? That is just noise and no big deal. But if your alternator is really reading 35 vac, sounds like a shorted output rectifier is allowing unrectified ac into electrical system.

 

I'll double check everything again but when I work on electrical for cars, I usually prefer to use an analog meter unless there is a specific reason to go with digital.

I have both.

I like the analog meter because I like to see the needle swing.

Since I was using the analog meter, I was approximating the exact voltages. I had said 28~ 29 volts. I didn't look that close to try to find it exactly.

When I wanted to see if the alternator was charging the battery, I looked real close and it looked like 14.4 Volts.

If I had used a digital meter, I would have put in the exact numbers in my message.

I'll check it again.

 

I had my system checked at the custom shop that ordered the alternator for me.

They said it was fine.

Apparently, using an analog meter is no good. Must be digital.

Now I just have to wonder why the battery died a couple of days after I ran it which is what prompted me to test it.