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Author Topic:   I/O alternator not charging
kwik_wurk posted 05-02-2009 05:33 PM ET (US)   Profile for kwik_wurk   Send Email to kwik_wurk  
Well. I bought another boat, and it isn't a Boston Whaler, in fact it is at the other end of the spectrum. But for the price, it was what i wanted. (I looked hard for a good Revenge, but I wasn't happy with what I found.)

As part of that great price, came an engine with an alternator that is not providing charge to the batteries. (No noticeable change in battery voltage.)

I have only started the engine once, and it is still at the sellers home. I intend to go back with a smart charger to charge both batteries.

I want to make sure I have a good list of troubleshooting items to check before I decide to drop it off at the mechanics.

The engine is a 5.7l I/O (Indmar), but still the standard 5.7l GM block; it is a replacement engine with a couple hundred hours. Everything has been replaced and during 2006-2007, and the receipts definably showed a ton of parts and labor.

What I have done during the brief sea trial: I have checked the battery isolation/combiner switch - no problems. The auxiliary motor is fine, and does not have an alternator - no problems. All the wiring coming from the I/O alternator looked good.

The batteries read 11.6 with everything secured - too low. The voltage with the engine running is ~11.48, so obviously something buggy.

I did not find any shorts in the electrical system, but there are some non-OEM wiring that I haven't traced completely. I was going to reset the alternator breaker (50 Amp); but I decided not to. I didn't want to blow something up due to a short.

I don't think the batteries are bad, they are new (1-2 years), and have water.

I know several things to check, but I am hoping to add to my list, so I can hopefully save a few hundred bucks.

Any troubleshooting suggests for dealing with the alternator.


And here is the boat:

jimh posted 05-02-2009 07:46 PM ET (US)     Profile for jimh  Send Email to jimh     
With an automotive type alternator the usual configuration is for everything to be integral with the alternator. The rectifier diodes and the regulator are built into the alternator assembly. If the connections to the alternator are good, and there is no sign of any charging, you will probably have to remove the alternator assembly from the motor and have it repaired.

Some of the newer GM alternators have more sophisticated electronics in them than previously used. I just got a replacement alternator for one of my GM cars. The instructions were very specific on how to connect it to the wiring harness, as an error in the sequence of connections could cause the alternator to fail. Too modern for my tastes.

By the way, just about every GM car I have ever owned has needed the alternator replaced after about five years. The GM alternator seems to be able to provide about 0.01-Coulomb of extra charge, and anything unusual about the load will cook the alternator.

The INDMAR marine motor may have a specialty alternator with a rating to be qualified for inboard motor use on a boat.

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