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Topic: Alternator question (Read 313 times) previous topic - next topic

Alternator question

For the past year or so we've been dealing with the alternator "dropping out" and then coming back. I first noticed it last year on our way to Texas. Voltage had always been pretty stable at around 13.5 volts as shown on the VMSPC. On that trip voltage was somewhat lower, and sometimes would drop down to around 12 volts, then come back. I had MOT check it out, and they concluded that the alternator was failing, so they replaced the alternator. We headed north, and barely got out of town when the voltage dropped to 12 volts. We returned to MOT and they poked and prodded but found nothing. Headed out and same thing in the same spot. Came back and Keith drove the coach while a tech had a test instrument connected to something in the engine compartment. I was watching the computer. We all sang out at the same time and at the same place in the highway where the problem appeared before. After we returned to MOT Keith found that the excite wire for the alternator was connected to a point that also supplied the 12 volts to the radiator fan controller. When the fans came on the alternator wasn't getting the 12 volts. Keith fixed that and also properly wired the fan controller so that the fans now shift from low to high.

The problem was partially solved, but not completely, in that the voltage would still occasionally drop down, sometimes only a bit, sometimes down to 12 volts, but it always came back. Today, while replacing the Trik-L-Start I noticed that the ground wire from the isolator was loose, so I tightened it up.

Question: might that have been the issue all along?

Re: Alternator question

Reply #1 –
Loose connections can cause all kinds of problems.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins
 

Re: Alternator question

Reply #2 –
Quote from: red tractor –
Loose connections can cause all kinds of problems.
Even  the tight connections can cause issues. Because we are unable to see most electricity it is difficult to see the problems. A test light across the suspect connections and other non suspect connections may show a voltage drop. (Resistance) A voltage meter will show the same but the test bulbs make for rapid visual testing. I would guess the ground wire on the isolator would be to dissipate static noise. The isolator is big power diodes and is just restricting the flow to one direction or another similar to check valves. I would even check the alternator case to chassis ground. Testing circuits under a load helps to isolate them. Always good fun chasing down gremlins
Scott