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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 01-30-2009
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Alternator Light ON

Hi,

We have a 1984 Endeavour 33, original Yanmar engine. We have had it for two seasons, and at the time of purchase the alternator was rebuilt.

This past season the alternator light on the engine cockpit panel was always ON.

Also, the man who did our engine maintenance this fall replaced the alternator belt which he said was the wrong size.

We usually daysail or only go out for one night at anchor (we did two night twice). I know the light was always ON this year, but I don't know about last year (our boating IQ is slowly going up). I am wondering if it ever worked.

I would like to ask the maintenance man to look into this, but I could not find any info about what this could possible mean- I'd like to have some idea of what might be the problem, etc.

Any insight would be very much appreciated....

Thank you, SaltyPat
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Old 01-30-2009
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it could be that your alternator is shot. without shorepower, try measuring the battery voltage 1st, then start the engine and measure again to see if the volt has gone up some (by 1volt at least). If yes, alternator is ok, if not its diodes are probably fried.
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Old 01-30-2009
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That light is supposed to go out when the alternator starts producing voltage higher than the battery's voltage. I would do a few things that are relatively easy before calling a mechanic. I would look at the alternator to see if the belt is on, or whether it's very loose. I would check the alternator terminals to see if a wire came loose. If you have a volt meter on your boat's instrument panel, I would note the voltage before I start it and then see if it goes up after I start it and rev it up. If the voltage increases up to around 13.5 to 14 volts, that would indicate a lot of work ahead of you to figure out why the light won't go out.
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Old 01-30-2009
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Even simpler than the suggestions above, WalMart sells a $15 gizmo that goes into a cigarette lighter outlet that tells the whole story. It shows if the alternator is putting out and the state of the battery charge.
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Old 01-30-2009
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This happened to my boat last year and it was because the aleternator belt was the old kind without the groves that the newer ones come with - it was slipping when there was anytype of load on the alternator and the light would always be on inless my batts were completely topped off. I would check that and see how loose it is - also check it with the engine running to see if its spinning properly.
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Old 01-30-2009
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Get a wee multimeter, set it to voltage DC, and stick it over your battery terminals.
Start the motor.
You should see the battery voltage rise abruptly, then do a slow rise until it is about 14V.

If the alternator warning light is on all the time, it certainly suggests that you are not charging at all.
.
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Old 01-30-2009
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Pat, if you pick up one of the books like "12 volt doctor" or "12 volt bible" you can probably troubleshoot this yourself for the price of the book and a $20 multimeter (Target, Walmart, just as good and half the price of Radio Shack or Home Depot).

The light usually means a charging system "failure".
That can translate into:
-Loose or corroded wire anywhere in the system
-Internal regulator failing in the alternator ($25-100 part)
-Diode failure in the alternature ($25-100 "diode frame" assembly)
-Loose belt, glazed belt, other belt tension problem

And if you have a typical V-belt, the best way to properly set the tension on it is with a tension gauge, pretty hard to fund except used these days since v-belts have been obsolete for over a decade. You can estimate tension with your fingers and a rule, but a gauge will give you better belt, alternator bearing, and sometimes water pump bearing life as well.

If you don't measure at least 13.8 volts between the alternator's charging post and ground (at the alternator mount to the engine) at low idle, there's an internal alternator problem or a belt problem. Better alternators will put out 14.3-14.4 volts at all speeds, including idle. Which is what you should see at "cruising" speeds, too.

You can also unbolt the alternator and take it into most of the auto chains like Advanced or Pep Boys, and they will load test on a machine for free. If it needs a diode set or regulator--I'd spend the money on a good remanufactured (not just rebuilt) replacement, and then take your time getting the repair parts and fix the old one, to keep as a spare.
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Old 01-30-2009
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Lots of good suggestions

Thanks to all for the good suggestions- all the replies really helped.
I have a suggested book I can get and a lot of good troubleshooting ideas.

If I get lucky, it will be the previous bad-fitting alternator belt which was causing the problem.....

Thanks again, I feel like I can now better work on a solution.

Just waiting for spring on the Chesapeake.

Best to all, SaltyPat
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Old 01-30-2009
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okay here is something else, there is a wire off the back of the alt, if that wire has a bad connection. you might want to pull that wire and pull the engine panel and check the connection and put a ohm meter across the wire
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