Yanmar 2gm shutting down with battery selector on.

[andrewgswitzer]

Hey all!

I'm new to the forum. Thanks for having me.

I have a Pearson alberg 35 that has been repowered with a late 90's diesel yanmar 2 gm. The motor runs great. However, once the motor is fired up and put into gear, it bogs down and dies if the battery selector for the boat is on. It runs fine with it in the off position.

It is my belief that this is an alternator problem? I have not done any testing yet as I wanted to get some more opinions first.

What do you think?

 

[Davidasailor26]

Welcome to the forum!

Depending on how things are wired the engine really shouldn’t be run with the selector in the Off position. Doing that will (usually) separate the alternator from the batteries and damage the diodes in the alternator. It’s possible that your alternator was rewired in a way that avoids that problem. If that’s the case then I guess it’s possible that there’s an alternator problem like you say, but more testing would be needed. Still, I’d be surprised if the alternator could support a large enough load to actually kill the engine. If the alternator is 80 amps that’s only going to siphon about 4 hp off the engine, so it should be able to handle that. Unless you also have a very large aftermarket alternator.

 

[andrewgswitzer]

Interesting. Do you you have another theory on why a battery selector switch could change the load on the motor?

 

[kappykaplan]

Try having someone watch the alternator / front of the engine when the battery selector is rotated. What is the condition of each battery?

 

[Stu Jackson]

Try having someone watch the alternator / front of the engine when the battery selector is rotated. What is the condition of each battery?

Except you do NOT want to turn the switch off while the engine is running. Until you know more about how the boat is wired, if you do so you could blow the diodes on the alternator rendering it useless.
Better check are to turn the cockpit panel key switch off and see what happens.
Why? Because the switch interrupts the alternator output, while the key switch only turns the field signal off.
Usually.
That's why it's better to learn how it's wired and about alternators first before you go fiddling.
Of find someone who does know to help you.
Good luck.

 

[kappykaplan]

Except you do NOT want to turn the switch off while the engine is running

Stu, he's already done it.

 

[kloudie1]

Welcome aboard, Andrew.. Lots of good info here..
I think you have a good idea about the alternator, next step might be to remove it and bring it to an alternator shop for testing.. I'd suspect the voltage regulator as a prime suspect .. Take a picture of the wiring on the rear of it so that you can ask the alternator people if it is wired correctly .. It may be that the wires aren't correct on the boat side of things.. The Yanmar wiring diagrams are in the ownwe's resources section under General Downloads, I think.. Good luck with it!

 

[Stu Jackson]

Stu, he's already done it.

I understand. I was trying to get him to avoid doing it again. And to learn how alternators work.
I know, still doesn't answer the original question. That's still a head-scratcher.

 

[kappykaplan]

I know, still doesn't answer the original question. That's still a head-scratcher.

Yep!

 

[jviss]

Hey all!

I'm new to the forum. Thanks for having me.

I have a Pearson alberg 35 that has been repowered with a late 90's diesel yanmar 2 gm. The motor runs great. However, once the motor is fired up and put into gear, it bogs down and dies if the battery selector for the boat is on. It runs fine with it in the off position.

It is my belief that this is an alternator problem? I have not done any testing yet as I wanted to get some more opinions first.

What do you think?

I think it could be the alternator load, but could use more info.

Are you at idle when this happens?
What's the idle speed?
Have you tried increasing the engine speed as it starts to bog?

 

[Benny17441]

Running the engine and alternator disconnected from the batteries will likely burn up the diodes in the alternator. That alone will not cause the alternator to shut the engine down. Verify all the connections from the alternator and also the battery switch. Is ithe engine dying at idle? Check that the idle is not too low. (750-850 RPM). If it dies at higher RPMs then the alternator could be locking up. Remove the belt and spin the alternator by hand, at first with the battery switch on and then with the switch off. If the amount of force required to spin the alternator increase dramatically then the alternator is likely shot and is being energized by a stray short or connection. Are the alternator bearings making any noise? Take the alternator to an electric shop to be tested and rebuilt if necessary.

 

[andrewgswitzer]

Still trouble shooting this. I only get to get to my boat a couple days a week. The batteries are brand new 31 series agm's so bad batteries are out of the question. No systems are hard wired to the batteries. If I catch it as the rpms drop I can increase the amount of fuel and power through but it is definitely still bogging. You guys are probably right, I had crappy Batts when I bought the boat at the end of our last season here in upstate NY. I experienced this problem last year. Which is most likely due to the fact that I had poor batteries not alternator. Therefore, turning the batt selector off has now burned up my alt. I'm pulling it now.

 

[heritage]

My 2gm20f bogs down when at low rpm when the dc to dc converter is switched on. The converter is only putting a 20 amp load on the stock alternator. I didn't think that that light of a load would have much impact, but it does. The engine smooths out at about 1200 rpm. Your new AGMs may be having a similar effect on your engine.

 

[jviss]

If it still bogs down I bet your alternator is OK.