Yanmar 1gm10 alternator wiring question

[Wotname]

Originally Posted by four winds

Have you ever cut the key switch off without first killing the engine with the fuel stop lever?

Hmm... this shouldn't cause any problem if using the stock Yanmar wiring harness.

[twinboat]

Originally Posted by Wotname

Hmm... this shouldn't cause any problem if using the stock Yanmar wiring harness.

That's right. Let's not add anything more here until there is power TO the alternator.

Same with pulling it off to have a shop check it. They will put power to it, on the red wire.

Will it test good, don't know. Will it work without a battery connection, NO.

[four winds]

Originally Posted by Wotname

Hmm... this shouldn't cause any problem if using the stock Yanmar wiring harness.

I thought this would blow the diodes in the alternator. No field current with alt spinning.

After a long overnighter, got to anchor very tired and absentmindedly hit the switch before killing the engine (3gm30f). Said, "Oh sh*t" and went to bed. Next day the alt light was on.

Sorry, not trying to complicate helping the OP. Just thinking out loud. You guys guys got his back. I'll stay out.

[Wotname]

Originally Posted by four winds

I thought this would blow the diodes in the alternator. No field current with alt spinning.

After a long overnighter, got to anchor very tired and absentmindedly hit the switch before killing the engine (3gm30f). Said, "Oh sh*t" and went to bed. Next day the alt light was on.

Sorry, not trying to complicate helping the OP. Just thinking out loud. You guys guys got his back. I'll stay out.

FYI, the diodes generally blow when the output is disconnected while running rather than the field current. Usually occurs when the battery switch is turned off while the engine is running.

Disconnecting the field current just means the alternator stops producing an output.

Can't really say what happened in your instance - sorry!

[four winds]

Thanks Wotname, it was a very old original alternator. And apparently a coincidental malfunction. I have misinterpreted posts about this issue it seems.

However, it's worth pointing out, if the OP infact doesn't have a proper connection at the B terminal then the alt diodes may have blown. Since that would be the same effect as switching of the battery switch. Assuming it's wired the most common original way.

Curious the outcome, but promise lurker mode only now. Feels a little weird to post more than once or twice in a thread anyway. Have received invaluable help on the forum and like to give back. Hopefully without the "well you're the expert" admonishment once received .

[twinboat]

Disconnecting the battery from an alternator output terminal is not an automatic diode destroyer.

People have been testing alternators, for ever by pulling the battery cable to see if the engine keeps running.

If the alternator was spinning fast and producing near rated output, there is a good chance it would blow but at idle speed, most likely, not. It just can't make enough power to hurt it self.

[Blue Crab]

Quote:
Originally Posted by four winds
Have you ever cut the key switch off without first killing the engine with the fuel stop lever?

Originally Posted by Wotname

Hmm... this shouldn't cause any problem if using the stock Yanmar wiring harness.

Whew. Made my heart skip a beat for a moment.

[bill good]

Check the 30A fuse & fuse holder while you are at it.

Regards

[johnlikesail]

Thanks to everyone for your assistance! I have made some progress and have new info to share:

The 30A fuse is good
There is appropriate power at the back of the Alt at the "Batt" terminal (13.17)

The problem (old info but since there have been a lot of posts):

The voltage on the batteries themselves (2 NEW deep cycle batteries in my system) does not change (go up) when i run the engine or when I increase engine RPMs, etc. The battery light also stays on.

I have a way that I can test the alternator directly now as I run the engine...should the "batt" terminal on the alternator show an increased voltage as I run the engine? What should it rise to? I will probably consider any rise a working alternator and this would mean that there is some disconnect between the alternator and the batteries.

Thanks all for your help!!

[four winds]

I said I would lurk, but I lied. lol.

If you have good voltage at the alt bat terminal, which you do, then the charge path to the batteries is connected and good.

The voltage is a little too good, maybe you checked with an auxiliary charge source connected or immediately after engine shut down. 13.17 suggests a fully charged bank being held in float charge.

A resting battery bank fully charged should be about 12.7, 12.8 volts.

If I was going to test your setup. I would turn on some lights and listen to music for a while to discharge the bank some. With no charger connected, important. Maybe the voltage drops to 12.5 or so insuring charging is needed.

On my boat, same alternator, if I started the engine the voltage would rise to 13.7-13.8 immediatetly. The alt would whine and the engine would sound loaded. Over the next hour or so the voltage would slowly rise to about 14.2 and remain there until shutdown.

I never run long enough for a full charge, but after many hours I believe the voltage would slowly drop as the batteries top up.

[bill good]

Red light "on" alt not charging or lamp not connected as per diagram. (1) take alternator to be tested. (2) lamp is connected at the alt by the 2 pin plug on the alternator blue/black goes to "L" Red/black to "R".
The plugs & sockets on the Yanmar are poor quality.
Regards Bill

[johnlikesail]

So then if I have already run the motor and tested the voltage on the batteries directly, and confirmed that no charge is reaching them...

and now I have confirmed that there is a good path to the batteries since they show up when I test the voltage at the "batt" terminal on the back of the alternator...

can I say for sure that I have a bad alternator? It sounds like I can...

[four winds]

Are saying the voltage did not rise after you started the engine?

Are saying the voltage at the battery was the same before and after starting the engine?

Your batteries have good voltage, why is that?

[johnlikesail]

Are saying the voltage did not rise after you started the engine?

---Yes

Are saying the voltage at the battery was the same before and after starting the engine?

---Yes

Your batteries have good voltage, why is that?

---I recently charged them with shore power and they were on "float" charge. However, it was an earlier date when I had used them up a bit before I started the engine and tested the voltage at the batteries to see if it would rise. I hope I am making sense...

[four winds]

OK, yes makes sense. I think it's time to take your alt to a shop.

Look for a traditional starter/alternator repair shop if you can find one. A rebuild may cost around $200.

A chain parts store can test it maybe but won't be able to order a replacement most likely.

Yanmar price will be high. Online clone price will be one quarter of Yanmar.

I have an original and a clone that have been abused for six years as my only charge source living on the hook. Recently had both disassemble completely on my salon floor. So I could test and select a combination of components that would make a good one. Up and running again but no spare now.

I say that to say, in my opinion, there is no need to shy away from an aftermarket clone. Others will disagree but typically only use price as their yardstick.