Yanmar 3GM30 alternator and charge warning light issue

[mikedefieslife]

I have a Yanmar 3GM30 and control panel A.

Recently my alternator stopped producing output. It was connected to a Sterling Power alternator to battery charger. When I disconnected the alternator my charge warning light showed on the panel as it is supposed to.

As the alternator was of unknown age and history I bought a new one. However it too doesn't appear to be working (no current or voltage when running), even when connected directly to the batteries. The odd thing is the charge light on the panel no longer comes on either.

I believe that this alternator is the type that needs to be excited before it will start producing. For this purpose there is a connector L R that leads from the alternator to the panel and via the charge warning light. I have tested the warning light bulb itself and it works when 12v is applied.

I have tested the L R connectors that lead to the alternator. Both appear to be positive, and tested to ground i.e. the alternator case or engine case, they read nominal 12v. I have also checked continuity all the way from the lamp to the L R connector. It is good too.

I'm at a bit of a loss now as else could be the issue.

Any suggestions?

[Cat36Mahalo]

Could you clarify connect to Sterling Power Alternator?? Do you mean connected to output of Sterling Battery Charger.

I’m also confused when you say no voltage output. Heavy Red wire should always have voltage when the Battery Switch is on.

How are you measuring Amps?

[mikedefieslife]

Ignore the Sterling. It's connected directly to the battery now.

The alternator is not putting out any additional voltage i.e. the voltage I get from the big red wire (in this case 50mm2) is the same regardless of whether the engine is running or not.

Current is measured in two ways. 1) With a clamp meter. 2) by monitoring the battery monitor

[JimsCAL]

I see two main choices: (1) new alternator is not connected correctly, or (2) it's defective. Could have wiped the diodes by running without the alternator connected to the batteries.

[mikedefieslife]

Was thinking it might be faulty was DOA. It's never been run not connected to the batteries. With the old one, when I failed I just removed the belt, so it didn't spin.

This new one has never worked from the start, but even with the engine running and the alternator belt off so the alt doesn't spin, the charge warning light doesn't come on which it should. In fact the the charge warning light should come on with ignition, which it used to, but doesn't now.