Alternator problems (Yanmar 1GM10) Sun Odyssey 24.2

[Rousey0202]

Hello, I'm after advice please to help myself and my marine engineer fix an alternator issue. The original alternator LR135-126 has stopped charging the batteries on my cruiser (1999 Jeanneau Sun Odyssey 24.2)... I have bought 2 replacements (due to the problems I'll explain below). The replacements have a smaller pulley wheel diameter .... when either of the replacement alternators are fitted the engine runs like a dog - it won't rev above idle speed, black smoke exits the exhaust along with oily coolant water. When they are disconnected the engine starts to run correctly but of course no charge goes to the batteries. My engineer has checked the connections to the batteries and checked what he can but all to no avail. Could the issue be due to the smaller diameter of the new pulley wheels? or are we missing something? He has tried to pull the pulley from the old alternator but couldn't release the nut (I think he may have been trying to release the nut anti-clockwise.... I think it may be threaded the other way).
Any advice or guidance would be very much appreciated. Martin

 

[Topcat47]

Two possible problems here. My old Hitachi alternator failed so I bought a Chinese copy. While it was rated the same on the paperwork, it was producing about 70w and the poor old engine couldn't swing it. After testing six the supplier offered to rewind the hitachi, which he did. No problem.

The other is that the smaller pulley drives the alternator at too high an rpm which will have a similar effect. My original chinese copy also had a smaller pull but I was able to remove the OEM from the Hitachi and swap them over. It made no difference, the engine still wouldn't swing it.

It was suggested that I introduce a switch in the alternator circuit so it could be disengaged during starting. I dined't try that.

 

[Rousey0202]

So best option is likely to have the original alternator repaired?

 

[jamie N]

Welcome to the forum.
A couple of things; is it possible to replace the pulley wheel with one that's the same diameter as the original?
EDIT: I see that you've explored this possibility.
"Is it possible to fit a switch to the exciter on the alternator to allow the engine to settle before charging?"
This is how my alternator's wired, I only switch the exciter 'in' once the engine's happy.
Mine's a single cylinder 9hp unit also, so not overly powerful.

 

[Rousey0202]

the engineer tried to get the bolt free from the original alternator... BUT I think he may have been trying the wrong way (do they loosen clockwise due to the way it turns???). To be honest we're scratching our heads (I've no experience of messing with engines)

 

[Tranona]

The suggestion to get the original repaired is a good one. As noted, the 1GM produces virtually no power at start up and low revs. The non original alternator puts too much load on it and it tends not to pick up enough revs to run properly. When the 1GM was fitted with a saildrive they also fitted a relay to cut the alternator out until the engine was running well.

 

[Rousey0202]

The suggestion to get the original repaired is a good one. As noted, the 1GM produces virtually no power at start up and low revs. The non original alternator puts too much load on it and it tends not to pick up enough revs to run properly. When the 1GM was fitted with a saildrive they also fitted a relay to cut the alternator out until the engine was running well.

Thank you.... i'll pass onto the marine engineer

 

[penfold]

Folk have posted before about this problem with GM10s; replacement alternators either being too powerful and/or having too small a pulley. Have the old one refurbed or change the pulley on the new.

 

[andsarkit]

My 1GM with the standard Hitachi alternator has little power left for the prop for the first 30 seconds after starting. I usually run it for a short while before engaging drive.

I can't find any mention of a left hand thread but this picture from the service manual might give a clue if you can work out which way it is being turned.

 

[LiftyK]

I had exactly the same problem and symptoms. I took the original alternator to Just Alternators And Starter Motors near the River Hamble and had it repaired for a reasonable sum.

 

[William_H]

Almost all alternator problems come from bad brushes and dirty slip rings. That is if not external wiring. As said the old one should have been repairable. ol'will

 

[andsarkit]

I don't know where you are based but these people in Plymouth are excellent. Starter Motor and Alternator Company.
They refurbish alternators onsite and can probably give you advice as they were always very helpful for me. They would probably have a suitable pulley from their vast stocks.

 

[Rousey0202]

Hi all and thank you for your guidance to date.... update - I have had the original alternator repaired (and checked again) and now the issue has changed slightly. It's worth noting that the motor still runs well without the alternator attached. However the repaired alternator gets incredibly hot .... nuclear hot... when the engine is ticking over in anything above half revs. The first time i noticed this was when the cabin filled with hot smoke!!! We're at a bit of a loss as the batteries are pretty well charged so there shouldn't be much of a pull on the alt???? Any further thoughts that might assist would be most welcome!

 

[jamie N]

I'd get an engineer PDQ before running it again, I'm afraid. Something's clearly not right, and from what you've written, it could rapidly get even worse with a fire; "No smoke without etc.etc...".

 

[Refueler]

Hi all and thank you for your guidance to date.... update - I have had the original alternator repaired (and checked again) and now the issue has changed slightly. It's worth noting that the motor still runs well without the alternator attached. However the repaired alternator gets incredibly hot .... nuclear hot... when the engine is ticking over in anything above half revs. The first time i noticed this was when the cabin filled with hot smoke!!! We're at a bit of a loss as the batteries are pretty well charged so there shouldn't be much of a pull on the alt???? Any further thoughts that might assist would be most welcome!

Sounds like repairs may have rewired alternator incorrectly ...

 

[Rousey0202]

I'd get an engineer PDQ before running it again, I'm afraid. Something's clearly not right, and from what you've written, it could rapidly get even worse with a fire; "No smoke without etc.etc...".

All the work so far has been carried out or arranged through a marine engineer

 

[jamie N]

There's something wrong. The guy who did the repair might have made a screw up, we all have, but there's something very amiss that really needs addressing before being tried again.
You're absolutely in the right place though for getting the correct guidance on this type of issue though.

 

[Beneteau381]

Almost all alternator problems come from bad brushes and dirty slip rings. That is if not external wiring. As said the old one should have been repairable. ol'will

Its because the donk is so small, a known issue that "marine engineers" should know about. As others have said, some installations come with switched to engage it when the engine is up to speed. They were sometimes switched through the oil pressure switch to ensure that the donk was running at speed before engaging. I suspect the smaller pulley is exarcerbating the situation

 

[William_H]

Re alternator getting hot. Saw a case on an aircraft where the replacement alternator did not have a dedicated earth bolt connection. So engineer fitting new alternator had a spare earth wire so it was fitted it to the spare vacant bolt connection. Unfortunately this was the connection to the centre of windings used for tacho or similar output. ie essentially a short circuit of output of alternator windings. Engine started and alternator and switch on (separate switch) No charge. looked at alternator again wrecked. The entire centre section of iron laminates with pick up coils had been forced to rotate between the end plates enough to break the winding wires. Wouild have got very hot if it did not break the wires.
This makes me wonder if OP has not got an earth short on that centre connection terminal. (or output connection)That would make alternator very hot. ol'will