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Old 26-01-2012, 14:29   #1
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Yanmar 80A Alternator Upgrade

Just installed a brand new 80A Hitachi on our Yanmar 4JH-T(B)E and it powered just fine on test, but after a 4 hour motor trip up the coast it quit supplying power like the previous one. New to us boat, and not sure what to look for, if anyone has resolved a similar fault, would like to hear how.
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Old 26-01-2012, 15:57   #2
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Re: Yanmar 80A Alternator Upgrade

Could you describe in more detail how you knew it quit supplying power? voltage, current, state of charge of the batteries. Heck, it's supposed to stop supplying power when the batteries are full!
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Old 26-01-2012, 18:55   #3
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Re: Yanmar 80A Alternator Upgrade

I don't know anything of that alternator or what regulator that may be in use, but it could be by design. A good regulator will normally cut the charging after a while to allow the batteries time to stabilise, and then monitor the voltage.

The system may also have a temperature sensor on the alternator or batteries and reduce or shut down charging to avoid damage.

In either case, if the batteries still need more charge, then charging would restart automatically in a few minutes. If it's a temperature sensor issue, batteries will take longer to cool down.
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Old 26-01-2012, 19:06   #4
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Re: Yanmar 80A Alternator Upgrade

Quote:
Originally Posted by cwyckham View Post
Could you describe in more detail how you knew it quit supplying power? voltage, current, state of charge of the batteries. Heck, it's supposed to stop supplying power when the batteries are full!
Ditto!
Did your old alt. quit completely? And did you have it tested?
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Old 01-02-2012, 11:14   #5
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Re: Yanmar 80A Alternator Upgrade

Thanks for the responses. Installed the new upgrade alternator before departing seller's marina, and when we test ran the engine, the volt meter showed a solid 14.5 volts. During the 4 hour motor trip to our new marina, meter showed constant decline in volts to 12.2, mostly drained by the refrigeration system. The old alternator is in the shop for troubleshooting/rebuild, bet have not heard from them yet. When multiple 12V uses engaged, alt. still does not kick in.
Big bonus was finding another brand new, Made in Japan (!) alternator in one of the boat's lockers, but need to figure out why the replacement stopped charging.
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Old 01-02-2012, 11:20   #6
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Re: Yanmar 80A Alternator Upgrade

STOP!!

Something's wrong for sure, and before installing that spare alternator you need to find out why the other two alternators stopped working properly.

It is possible that a wiring fault could be present wherein the connection between the alternator's output and the battery is intermittent or broken.

It is also possible that someone turned off the battery switch while the engine was running, which would likely blow one or more of the alternator's diodes. Another possibility is an intermittent wiring fault in the wire supplying field current to the alternator...at the switch, at the connection to the alternator, within the wiring harness itself, etc.

There could be other problems as well which would cause flaky operation of the alternator, related to the batteries, the regulator, or the wiring thereto.

It would be worthwhile (read much less expensive) to hire a competent marine electrician or a mechanic familiar with alternator wiring to find the problem. Probably wouldn't take more than an hours' time, and could save you a lot of $$$ and a lot of grief.



FWIW,

Bill
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Old 01-02-2012, 11:56   #7
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Re: Yanmar 80A Alternator Upgrade

If you do this, you'll never have to worry about fried diodes ever again:

1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

I agree with Bill, you need to do more research.
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Old 01-02-2012, 12:07   #8
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Re: Yanmar 80A Alternator Upgrade

My wild guess is the alt gets disconnected from the battery and the regulator burns.

I would look for a lose wire - maybe the neg between the engine and the batteries, or neg or pos the clamp on the battery. Or a faulty 1/2 both off switch? Something that momentarily disconnects the alt when the boat is moving, etc..

Which part of the alt fails? Is it the regulator?

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Old 02-02-2012, 17:44   #9
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Re: Yanmar 80A Alternator Upgrade

Dumb question: Which battery bank was the voltmeter on? Which bank is the alternator charging? Was the switch turned at some point? Have you tried putting a voltmeter on the alternator output itself? Have you tried "full fielding" the alternator (google it, I haven't done it so can't explain well without maybe introducing dangerous errors) to see if it's the regulator or alternator that's having issues?
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