Alternator not charging

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Jun 25, 2006
63
Hunter 34 Bayou Chico - Pensacola
We recently replaced the original alternator on the Yanmar 3GM in our Hunter 34 with a high output version (I think it's a Hatachi). The wires all seemed to match up with the exception of an extra single yellow wire on the back of the alternator. It doesn't appear that we are getting any juice from the alternator but when we took it to an auto parts store for testing they demonstrated that it would generate nearly 15 volts. The yellow wire showed up as a "stator wire (optional)" on the diagram that the auto tester showed for our style of alternator. A voltage test at the alternator shows 12.5 volts before start-up and drops to 12.4 after start-up which I assume represents the drawdown from the starting process. Any ideas on what we're missing?
 

zeehag

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Mar 26, 2009
3,198
1976 formosa 41 yankee clipper santa barbara. ca.(not there)
have you spoken with your local yanmar dealer?? he should know for sure what to do...the one near me installed mine and is awesome....mine is 80 amps output......
 

druid

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Apr 22, 2009
837
Ontario 32 Pender Harbour
One thing I learned was at least for SOME Alternators attached to Yanmars, you need to ground them separately (ie they don't ground through the mounting bolts like most alternators do). Have you hooked up a ground (it will need to be big enough to handle the alternator's output)

druid
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
If the alternator was well painted you'll want to scrape some away at the foot mount to be sure you have a solid ground path. Most of these alts are case grounded. You can also run a separate ground as Druid mentioned. A picture of the connection side of the alt may help..
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Optional stator wire

If the alternator does not have an internal regulator you will need to get one. With that said the stator is the part that the regulator uses to turn on the alternator and since it is optional that would imply that the new one has internal regulation.

Did the folks that tested the unit use the optional stator wire to make it work?

I'd dito the grounding of the unit. Given that all the wires got connected (presumably correctly) the only thing could go wrong is the connections are not electrically sufficient to make the unit work.

Check all your connections for low resistance. 99.44% of all boat electrical problems are corroded connections.
 
May 11, 2005
3,431
Seidelman S37 Slidell, La.
Hitachi Alternator

The Hitachi alternators have a funny little double plug on the back. Looks like a small T shaped indention, with two small spade lugs. There is a special plug that fits this receptacle. Costs less than ten bucks from an alternator shop. When I installed the larger Hitachi, I was getting 16+ volts from it. The little plug fixed it. Find yourself an alternator shop that knows their business, and they can fix you up.
 
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