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Old 28-12-2007, 20:25   #1
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Internally Regulated Yanmar alternator

I was looking at my engine wiring diagram the other day, and came across the, "Huh, why did they do that?" part of the diagram for me.

I haven't been able to find an alternator/regulator diagram for a Hitachi (assuming I have one on my 3GM30F) on the web, and Calders book talks mostly about external regulation .


There is a 2 wire plug on the alternator. (I'm not talking about the main out or ground connections here.)

One wire appears to be the excitation circuit as switched power (from the key) goes through the charge lamp to the blue/black wire on the alternator.

The other wire out of the alternator is red/black. It goes to the coolant temp warning light. The other side of the light goes to the temperature switch to ground. So it looks like the alternator wire is a 12 volt output to supply power to this warning lamp, but why? Why just the coolant warning lamp? Or is this schematic flawed? I haven't tried to trace it out on the boat yet to see if it matches the schematic.

Thanks, John
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Old 29-12-2007, 18:40   #2
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I think I found my answer. I've been looking at a diagram in a Clymer manual. I finally remembered that there is a diagram in my Yanmar operators book. The Red/black wire is consistently used as the switched power. The hot side of the coolant warning light is connected to switched power and the alternator. I think Clymer missed a connection because Yanmar uses the line drawn in a semicircle around a crossing wire to indicate no connection, but are inconsistent as to whether they use a dot or a simple cross to indicate a connection where wires cross.


So the mystery wire is likely the sense wire to the alternator to tell the regulator how much to turn on the alternator. Some alternator setups can use the battery output to sense the voltage, but then whatever voltage drop there is in the wire misrepresents the voltage at the battery so undercharges the battery.

Someday I'll get around to upgrading the whole charging system.

Half way down this page is a diagram of an internal regulator and alternator, which I now assume is similar to the one on my boat. It shows the sense circuit and the excitation circuit.

Automotive Electricity and Electronics - Google Book Search

The funny part is, I found an error in the Yanmar diagram. The tach sensor is shorted to itself.

John
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Old 29-12-2007, 20:26   #3
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"but are inconsistent as to whether they use a dot or a simple cross to indicate a connection where wires cross. "
John, manuals aren't infallible. No one wants to pay an engineer to proofread them, and if they aren't using an electronics CAD program, it would be all too easy to forget to draw the "dot" on top of a connection. Using lines that simply cross, instead of having the semi-circle to clarify there is no connection, is of course again faster and cheaper. (sigh)

You might be able to extract some information directly from Hitachi-US but if I'm remembering right, they don't like to talk to end users. A lot of boat systems omit the sensing wire or tie it back to the output, since "just one" sensing wire will always be hooked up to the wrong place in a multiple battery bank system.

One of the little books (the 12 volt bible?) has diagrams for an awful lot of alternators, aimed at showing you how to bypass the internal alternator and use externals. Apparently there are many ways to skin a cat and almost as many ways to design integrated alternators and regulators. If you can find out for sure what alternator you have, you might find the diagram in an auto shop manual at a library. Try some generic Japanese car manuals, they are usually Hitachi or Denso.
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Old 30-12-2007, 03:25   #4
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