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1999 Beneteau 50
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91 Posts
Discussion Starter #1
Can someone explain to me the difference between the R and L terminals on a Yanmar 4jHE Hitachi Alternator?

I just replaced the alternator on our Yanmar 4JHE; the old one had a stud work its way loose and cause internal damage.

I want to make sure that it's charging properly. When I start the engine, voltage at the gauge remains at about 13V; I would expect it to increase.

The ground is good as well as the battery terminal. I also get voltage at the R terminal, but not the L terminal.

I'm a little confused on the difference between the R and L terminals in this application. The tach signal comes from a separate sensor in the flywheel housing. According to the manual, the L terminal runs through a lamp, and supplies the excite voltage; the R terminal goes to the regulator. The lamp should be energized until the alternator begins to supply voltage. When the engine starts, the lamp does shut off.

What's odd is that when I disconnect the R-L plug from the alternator, the lamp on the panel remains on. Makes me wonder if it's actually a oil pressure light and not a charging lamp.

I have to admit, I find the wording in the manual as well as the troubleshooting steps, a little unclear.
 

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1999 Beneteau 50
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91 Posts
Discussion Starter #2
So I called Catalina and as usual they were very helpful, but recommended that I reach out to Yanmar directly. The Yanmar technician was also very helpful and explained that the L terminal supplies the excite voltage to the alternator. It is powered from the ignition switch and will either have an in-line resistor or charge lamp to provide resistance. He said I could try jumping the l-terminal to positive voltage, to see if that caused it to load up.

I'm not quite comfortable doing this, since there would be no resistance and unsure of what it could do to my alternator.

Here's the interesting part. I decided to trace the wire and check for resistance along the way. It runs through a harness that connects to a plug at the back of the engine. From the plug, the harness goes to a terminal on the wall of the engine compartment. After pulling back the insulation, I discovered that the excite wire (blue with black stripe) goes to nowhere! You can see it coming out the harness pointing to the left.

I assume that means my alternator has never been charging, for the five years that I've owned the boat. I can't believe it's taken me five years!

I'm not quite sure what to do next. I didn't find a similar wire on the other side of the terminal. I also didn't see a resistor near the ignition switch. So I'm not sure where this wire went to originally, or even if the terminal was original, or an afterthought.

I guess I could wire it into the ignition switch but I'm leery of doing it, not knowing how the original system was designed.



136045
136046
 

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Registered
1999 Beneteau 50
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91 Posts
Discussion Starter #3
Problem solved!

A member from the Catalina 42 Association pointed out that a 1990 boat didn't come with a Yanmar 4JH3E - that it must have been re-powered. That explains the terminal in the engine compartment. When they re-powered it, they failed to reconnect the excite wire from the alternator; not sure if this was deliberate or by accident. I wired it to the ignition switch connection on the terminal and the alternator is now charging at just over 14 volts. I looked at the survey I had done in 2015 and sure enough, it does state that the engine was replaced in 1999. I'm surprised that this problem was allowed to persist for so long (self included). I know that I've seen the alternator charge at < 14 volts at least once, which is a bit of a mystery.
 
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