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Old 30-09-2015, 04:15   #1
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Bad alternator? NOT!

I hope this might be helpful to others.

Nothing like the smell of burning wires.

Four years ago updated the charging system, including a new alternator from Electromaax. On our annual two week trip to the North Channel of Lake Huron this year I noticed the batteries were not charging while motoring. When I opened the engine room to check the alternator I was greeted by a face full of smoke. All of the wires connecting to the alternator were burned back about 8 inches.

Change of plans. We sat for three days at a small town marina while they sent the alternator away to be rebuilt. A new wiring harness was ordered from Electromaax . I kept asking “WHY DID THIS HAPPEN?” but did not get an answer. I learned later that John Stevens at Electromaax had also urged them to find the root cause, which was not likely to be a sudden alternator failure.

After this (expensive) repair, and five hours motoring into the return trip the same thing happened. We noticed it this time when the engine alarm went off. The oil pressor sensor wire had burned through and shorted out where it contacted the freshly burned wires from the alternator harness.

So, very obviously, something other than the alternator was at fault.

We spoke with John again who arranged for another alternator to be delivered that day, and also repeated his advice to find the root cause elsewhere in the electrical system. It took the marina staff at my home port a full day of head scratching and testing to determine that there was a ground fault in the 30 year old fuel lift pump. HUH?? I don’t understand how a fuel pump with a ground fault could continue to work, but replacing the pump solved the issue.

Here is the really embarrassing part. An external regulator can significantly improve charging performance so I also purchased one from Electromaax, intending to install it on our next trip. “Not if there is any chance you’ll wreck it” said my wife. “No chance” said I. I think you know what happened. By the time I was done it would not charge on either the external or the internal regulator.

Back came the same little town marina staff who, over the course of the day told me the battery isolator was the problem and installed jumper wires, told me that the power to the back of the alternator was the problem and installed a jumper wire, and finally told me it was charging perfectly and everything was fine. This was not free. We continued our trip. It was not fine.

We went for the next two weeks with no engine charging capability. I figured I’d have to take both the alternator and the regulator out to have them bench tested. When I disconnected, bundled up, and reconected all the wires to make this removal easier when we got back to the dock… it started charging!! I still don't know what happened but I assume there was a missing or bad connection that had gone unnoticed by me and the marina staff.

So what I learned through this is:
  • Alternators are a pretty simple and robust machine and are not likely to die an early death on their own.
  • An apparent alternator problem does NOT mean the alternator is bad. It is more likely the connections or the belts. The cause could be far removed in the electrrical system.
  • Beware of technicians who evade yur questions.

For troubleshooting advice John Stevens at Electromaxx was extremely helpful.
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Old 30-09-2015, 04:53   #2
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Re: Bad alternator? NOT!

Greetings and welcome aboard the CF, Aloha.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 30-09-2015, 11:55   #3
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Re: Bad alternator? NOT!

Loose/bad connections are the source of most fires and "hot" wires. Fuses won't necessarily stop it as the problem is not too many amps for the wire/fuse but the heat generated by the normal current through basically a resistor. Usually it only happens with high current devices although any size wire/circuit can cause it. Yours was a real world example of coincidental happenings. Really hard to understand why a short in a fuel pump could cause a big alternator wire to get hot though. In any case, make sure you have all wires fused on your boat. Many don't have them but I highly recommend fusing the alternator positive cable too.

Glad you got this strange situation sorted out. I hate it when you can't find the "smoking gun", i.e. something works later and you never really know why.
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