Alternator and charging problem

[paulhagedorn]

In my car, I have a 55 amp Bosch alternator. It fits in the stock position without any modifications. I am thinking it came from a later Bus, but not sure. Tomorrow, I will post the part number, but hopefully someone can help me in the meantime.

Did the Bus use a different Voltage Regulator?

I had the alternator checked about a year and a half ago, and the place that looked at it said the brushes looked fine and it was doing what it should be doing(they hooked it up to their machine and put a belt on it, spun it and it worked fine).

Problem is, when the car is running, there is only 12.7 volts going across the battery...not enough to really give the battery a charge.

What alternator would be a 55 amp alternator that would fit in the stock position without modification? What else besides the voltage regulator cause it to have a lower than normal voltage?
What other alternative alternators give more than stock amperage(35 amps)? I am worried about not having a big enough alternator for the stereo system I have in the car. I have a 4*40 watt amp up front powering two 4 1/2 or so dual JBL's and two 5 1/2's or so Infiniti Kappa's.

Someone please help.

TIA,
Paul

[Dave at Pelican Parts]

First of all, I trust that you measured the voltage across the battery posts themselves, and didn't use the center-console meter, right? And that you've cleaned up all of the connections, particularly on the battery + and - posts and clamps. And finally, that you've gone through the charging system troubleshooting guide that Jim Thorusen wrote, available in the Tech Articles section of this site.

The original mechanical-style voltage regulators can get old and "tired" eventually. You might try replacing it, possibly with a newer solid-state version that is available from some auto parts stores.

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[John Rogers]

There seems to only be one voltage regulator now, the solid state one which is for busses and 914s, etc. There are two alts that will fit, the 55 that you have and a big one (90) that is from camper vans and 1976 914s that had a/c installed. The connectors are swapped on the big one and require a different harness or redoing the connectors at the relay board (swap DF and D+) or you'll get 18 volts at the batt, NOT good. I just went through this problem a month ago and I fell the best thing is to get a new regulator, rebuilt Bosch alt, a sealed batt and new 3 ga wires which will be good for several years. Good luck.

[paulhagedorn]

Thanks John and Dave.
Yes, I did measure the voltage across the battery terminals. What is really causing me concern is that the alternator was tested and found to be good. It could be on its way out, yes, but my feeling is that there is a problem somewhere else. The battery was checked by an uh-oh zone person, and it seems to be good, but with a low charge.

Damn, this is really aggravating me. I don't want to throw money at the problem unless I know what to fix. I still haven't had time to get the number off the alternator so someone might be able to tell me where it came from, but I would bet it is off a bus.
Maybe I just need to look at the wires that come from the alternator to the relay board/voltage regulator and the others. It might be time to replace the positive lead from the battery...anyone know how much resistance I should get for that wire.
I know it is dependent on if it is solid or not, the cross sectional area, and the length...but I don't have those numbers...someone just take a WAG.

I also have a couple of voltage regulators I could put in the car and check to see if the regulator is the problem.

Hopefully I will have time this weekend.

[paulhagedorn]

Does anyone know the distance between the two bolt holes on the alternator? Also, does anyone know the part number for the bus amp that is a direct bolt on?

Thanks

[John Rogers]

The part number is AL-108X and is the 70 amp Bosch
alternator. I have been told by several people that the D+ and DF connectors are switched on this
model which is probably why I got 18 volts to my batt when I tried one? Good luck.