Yanmar 3YM30 where do I find the tacho sensor point?

[Wotname]

Ahh... the essence of cruising - the art fixing complicated stuff in an exotic location

If the alternator(s) are truly repaired back to original with new internal regulator(s), then yes, maybe returning the boat wiring to original will be the simplest quickest repair given your location and language barrier.

As you can see from the drawing I attached above (which are straight from the 3YM30 service manual), the boat wiring is quite simple, especially if H can get the his electrician on board.

It is only two wires from the instrument panel to the T connector on the alternator.

As soon as you have a charging alternator and connect the P (pulse) wire to the tacho, things should work!

As an academic exercise, it would be interesting to know why this all turned to custard after changing the engine mounts - coincidence ??

Good luck.

[Nautilus2]

Thanks Wotname. I have the manual aboard.
I didn’t understand about the Voltmaster, and H found it yesterday and recognised it as another reg but until I produced its manual he was hesitant to touch it. Then he worked out that power was going in but not out. From this I think he deduced this reg was faulty. But maybe not, just not working because MAYBE there are now new regs in both alternators? Will know today.

So a new day begins! I have google translated your 2 latest gems and sent them to H this morning. It reads well to me and have picked up some new tech terms, but then I am not a fluent speaker of Bahasa. Hopefully that helps him .

[Stu Jackson]

Having followed this, I observe that the situation with those standard Hitachi alternators may have not been mentioned.


If the external regulator does not have derating capabilities, like a Balmar's amp manager and small engine mode, the alternator could be being overtaxed.


Hitachi's own internal regulators are known to cut voltage output based on heat. Maine Sail has written about it.


worname is right about learning to know if both regulators were connected.



Has consideration been given to this?


Good to dig into this stuff, none of us was born an electrician.


Good luck.

[Nautilus2]

hi Stu, Gord and Wotname, mechanic has just confirmed that both alternators were return to the 'as original' with new regulators put in. He has also read and understood Your posts, Wotname ,regarding the internal and external regulators. His question now is: what does it tell us that when he tests the reg in (brown) terminal on Voltmeter Pro, it reads 12v going in. But when he tests the +Bat (red) terminal on VoltmeterPro, it shows 0 coming out. this with engine on and Hitachi original alt WITH the New regulator.

[Wotname]

Originally Posted by Nautilus2

hi Stu, Gord and Wotname, mechanic has just confirmed that both alternators were return to the 'as original' with new regulators put in. He has also read and understood Your posts, Wotname ,regarding the internal and external regulators.

Hmm... maybe I wasn't clear enough - the master volt external regulator MUST NOT be connected to the alternator if the alternator has the internal regulator inside it. You can't have both connected at the same time - bad things happen.

Dependent on how the boat was rewired when the master volt external regulator was first fitted, the outcome will be:

Best case - alternator doesn't charge but no damage done otherwise.
Worst case - internal regular fried and also won't charge.

Answer to his testing question to follow soon!

[Wotname]

Originally Posted by Nautilus2

His question now is: what does it tell us that when he tests the reg in (brown) terminal on Voltmeter Pro, it reads 12v going in. But when he tests the +Bat (red) terminal on VoltmeterPro, it shows 0 coming out. this with engine on and Hitachi original alt WITH the New regulator.

The brown wire is testing correctly.

But the red wire is NOT an output - it is another input to Voltmeter Pro (VP).
It should have 12V on it coming from the 10Amp fuse as shown in the page you posted earlier. It also goes to one side of the field (rotor coil) in the alternator as shown on the drawing. Maybe the 10 Amp fuse is blown??

The VP thens regulates the other side of the field with the blue wire.

I'm sorry to have to say this but this tells me your mechanic (H?) does not know what he is doing with regards to basic electrical circuits and testing. You really need an auto or marine electrician doing this. To be blunt, a second year auto/marine electrical apprentice would know this and have you fixed in a jiffy.

No disrespect to you Nautilus2 but this man is out of his depth.

Nevertheless, we will keep going - the answer is findable

[Wotname]

Sooner later, someone will have to trace or otherwise work out where the two wires on the T connector end up. Currently they will probably be going the red and blue wires on the VP - but this needs to be proven.

If you elect to retain the internal regulator, then the wires on that T connector must go back the panel as per the Yanmar drawings.

[Nautilus2]

ok Wotname. Your advice about insisting on getting electrician is noted. might be a delicate one but I'm on to it.
I am crossing fingers that my/our ignorance in using both internal and external regs together might NOT have stuffed the Voltmeter Pro.


Question: IF i revert to using the alternator and its IC reg, should i be concerned about batteries overcharging if using the motor for long hours?

[Wotname]

Re question: Probably NO unless you plan on running the engine 24/7 for days.

You can safely stop it charging by removing the T connector (when the engine is stopped).

Hope I haven't stepped on any toes...

[Nautilus2]

Not you , but I probably did. As kindly as I could .
Yes have a highly recommended boat electrician coming tomorrow morning. I will prepare notes for him about what has happened so far, including your advices. I live in hope xxfingers!!

Thanks for the last advice. Reassuring re not overcharging.

[Nautilus2]

happiness is...... a charging alternator, tacho working, and no damage to Voltmeter Pro regulator!! a week of frustration with mechanic H trying his electrical best but unable to solve it, ends with 3 hours work with a clever young electrician and EVERYTHING functioning as it should. and there's been plenty of good learning for me too. Though I won't be giving up my day job!!

Thanks Wotname, Gord and all who offered input. specially to Wotname, for sticking with it at all hours - and for giving me the final nudge to get a proper electrician! - it was reassuring to get your enlightening posts.

The electrician was very thorough, referred to my notes and the handbooks, and just patiently worked it through.
His simple explanation to me in the end was it was mostly an issue with the field connector not working properly. not sure what caused this, but it might have been knocked when either the engine mounts were done or when i put in the new batteries.

Absolutely delighted with the outcome , and to be able to now focus on final provisioning, and depart on the weekend. !!!! Thanks CF

[Wotname]

Excellent news!!!

I'm happy all is working properly.

One question though - is the alternator now using the external or the internal regulator?

[Nautilus2]

Me too. VERY.

Using the external Voltmeter Pro. Not using the internal regulator.

Electrician explained that although the internal regulator was in the alternator, it was not connected at all.

If I have his explanation basically correct, he said the blue wire 'Field' would have to be connected differently to connect it. I don't profess to understand it well, but tits reading 14.2 in the batteries with engine on. alternator is charging, and i have RPM, and engine hours accumulating, as i have just run the engine for 1.5 hours with watermaker working.

I think all good. is it?

[Nautilus2]

its. !!

[Wotname]

Originally Posted by Nautilus2

Me too. VERY.

Using the external Voltmeter Pro. Not using the internal regulator.

Electrician explained that although the internal regulator was in the alternator, it was not connected at all.

If I have his explanation basically correct, he said the blue wire 'Field' would have to be connected differently to connect it. I don't profess to understand it well, but tits reading 14.2 in the batteries with engine on. alternator is charging, and i have RPM, and engine hours accumulating, as i have just run the engine for 1.5 hours with watermaker working.

I think all good. is it?

Well it working waaaay better than it was and it sounds like it will stand the test of time.

Maybe worth checking exactly how it is connected when you are next somewhere without the language barrier or perhaps let sleeping dogs lie.

Happy sailing!