Alternator Issue

[Rsponsford]

I need help with an electrical issue. I’ve been dealing with an alternator problem for almost four years now. I’ve gone through four alternators (Leece-Neville 160amp DUVAC) now and I will spare everyone the history. I’m sure I haven’t been buying multiple faulty alternators and something must be mis-wired. I had a chance to go out to the RV again yesterday and do a little more troubleshooting. I didn’t have the time or materials with me to change out the key switch wire or sense wire, which I think will be necessary to ultimately troubleshoot the root problem. Here is what I observed:

The coach has sat for a month without starting the engine or generator so batteries were a little low.

Battery voltages measured at Isolators with engine off & no generator or shore power and no electrical loads:
-Voltage at the alternator sense wire is 12.27v (same as chassis voltage)
-Voltage at alternator key switch terminal is 0.0v with ignition key off
Chassis Batteries: 12.27v
Alternator: 0v
House Batteries: 12.07v
Generator Battery: 12.32v

Battery voltages measured at Isolators with engine running (idling) from front run box & no generator or shore power:
-Chassis voltage at the sense wire drops to 6.7v at idle
-Voltage at key switch terminal is 7.7v at idle. (There is no voltage at the Key Switch terminal with the ignition key on and engine off.)
Chassis Batteries: drops to 11.87v
Alternator: 6.9v
House Batteries: 12.07v (no change)
Generator Battery: 12.28v
Alternator output increases to around 10.8v as RPM is increased


Battery voltages measured at Isolators with engine off & generator on:
Chassis Batteries: 12.55v and charging via Echo Charger
Alternator: 0v (65mv)
House Batteries: 14.28v
Generator Battery: 13.68v and charging


I plan to bring the coach to the house on Monday for more testing and to install a new 200 amp Leece-Neville DUVAC alternator. Clearly, the alternator voltage output above is a problem. It seems the key switch wire is at least part of the underlying problem. I was thinking of replacing the key switch wire and installing the new alternator with minimal wiring, including no jumper, and seeing what it does. Attached is a photo of the current wiring at the back of the alternator and a photo of the DC panel and isolator where I measured voltages. (I also measured the same voltages directly on the alternator.) Input is much appreciated!

1990 CC Concept
Detroit 6V92TA
3000w Xantrex Inverter with 150a DC Three Stage Converter/Charger
630AH Domestic Battery Bank, 6-6v GC’s in Series/Parallel
2-8D Lead Acid Chassis Starter Batteries
Sure Power 2402 (240amp) Battery Isolator

[deandec]

Everything I know about testing the alternator comes from the Electrical section of my Gillig Service Manual.

It provides some very detailed guidance on how to test for over voltage and under voltage situations.

But, I am not sure it will guide you to the answers you need.

Might be worth a review if you have not done so.

[Rsponsford]

Originally Posted by deandec

Everything I know about testing the alternator comes from the Electrical section of my Gillig Service Manual.



It provides some very detailed guidance on how to test for over voltage and under voltage situations.



But, I am not sure it will guide you to the answers you need.



Might be worth a review if you have not done so.

Thanks! Not sure why I didn’t think to look there. I did look over the attached diagram last night and It did answer a couple questions. I’m pretty sure I have a bad isolator so I have ordered a replacement. I haven’t yet identified each wire and their function.

[Rsponsford]

Just realized I forgot to close the loop on this thread. The coach is fixed and a four year old ongoing problem is resolved. The 160 amp alternator installed was not properly wired which goes back to previous ownership. There were four problems with the wiring:
1) The ignition switch wire did not have voltage regardless of key switch position.
2) A jumper on the back of the alternator had been installed from an AC terminal to the ignition switch terminal. The voltage on this wire was apparently being used to turn the alternator on/off since there was no voltage on the ignition wire where it should have been.
3) There were two wires on an AC terminal which turned out not to be connected to anything at all.
4) Worst of all, there was a wire from an AC terminal connected directly to ground. This shorted out and destroyed the alternator. How this didn’t kill the alternator more quickly I have no idea.

I installed a 200 amp alternator from AJ Electric and corrected all of the wiring issues above. I also had to replace the battery isolator. Thank you everyone for your input and a big shout out to Jim Ferrari at AJ Electric for his patience and sharing his expertise to help me understand the system and getting this finally fixed.

[JohnRR]

Thank you for the update they are important for those who may do a search of the subject in the future.