Yanmar charging light

[mikemonty]

I hope the answer to this is not so simple that I look like an idiot:
The charging light on my 1GM10's panel is on constantly.
I've had the alternator at an autoelectrician who told me there was nothing wrong with it.
Not know for my trusting nature I did a rough test, and yes there is over 14 volts at the battery when running the engine, which drops when the engine is stopped.
I've had a look at a circuit diagram (the one for the small panel - late models), this shows a diode on the alarm circuit which I think allows a voltage across the lamp when the voltage from the battery is higher than the voltage from the alternator thus a light shows when not charging.
I haven't had time to trace the circuit for loose connections but my first gambit would have been to check if the diode has blown.
But I can't find the dam* thing! anyone know where this wee beasite normally hides in a yanmar wiring loom?
regards,
Mike

 

[William_H]

I can only describe in general terms that alternator lights usually provide power to the field coil via the regulator for that time before the alternator fires up to provide it's own field coil power. This normally doesn't require a diode in the light circuit.
So if you monitor the battery voltage (ie charge) and remove the lamp and you find the battery charge drops then the alternator is not providing its own field poower. Indicating a faulty alternator (they often have 3 separate diodes for generating field power.)or if it has a seperate regulator then bad wiring to the regulator.
I hope this helps olewill

 

[boatmike]

Its usually built into the panel. Do you have a series of warning lights built into a block with a printed circuit board on the back? If so it's there. check the continuity of the wiring first though. if it goes to the alternator via a wiring loom plug and socket at the engine end of the loom, check the continuity of that. I HATE those damn things. Very often I have found this sort of problem down to corrosion in the plug contacts and on every engine I have ever had on my boats have hard wired past this plug and eliminated it. OK it takes longer if you have to remove an engine but I don't mind that!

 

[mikemonty]

I had another look at the wiring diagram in the light of this and yes, I have made myself look like an idiot.
The diodes in question are in line with the buzzer, their only connection with the charging light is that the diagram shows the buzzer power being taken off the charging light supply.
I'll try your "charge light circuit" test next time I'm at the boat.

Best Regards,
Mike

 

[boatmike]

Totally correct Olewill. There are some that have a backflow diode though due to common power being supplied to the lights by a single cable with loads of electric-ery on a PC board. I usually rip em out and wire direct as I dont like poxy printed circuit boards. Had one recently where the alternator was getting its field coil current via the wire to the preheater circuit. Clue was that the preheater light stayed on until the engine revs picked up. Damn short in the circuit board! I tend to think these things are made to eliminate conventional wiring as much as possible but rely too much on printed circuits that you can't mend. If there was a conventional hard wired set up what you describe would be literally true indicating a blown diode in the alternator which it still might be although he says the alternator has been checked. Sometimes now however they are not even bulbs that you can take out and are LEDs moulded into a block of bloody resin!
Pees me off that something as inherently simple and reliable as a diesel should be controlled from a panel with PC boards all over it and wired through mickey mouse plugs and sockets that are never waterproof..... But then I am a dinosaur.....

 

[mikemonty]

Hi,
The lights are mounted on the panel and simply wired to - no circuit board and no obvious diodes (Although this looks like a red-herring now - see above).
The engine was new last year and the connections are clean (not to say they are tight though).
I can JUST about get to the block connectors through the companionway, but given that fact - I'll try to check continuity almost anywhere else first!

Best regards,
Mike

 

[boatmike]

You are fortunate then. Thats good and Olewills test is valid. You can check continuity with a lead run from the bulb direct to the alternator external of everything else. If it's not directly connected check that damn plug before wasting any more time!

 

[steve28]

Does the buzzer sound at the same time ?, i had this last week on another yanmar and it was the plastic two wire plug on the back off the alternator.

 

[mikemonty]

Hi Steve,
No it doesn't.
As I play my exchanges with the autoelectricians back in my head it sounds more and more like I've been fobbed off.
Day 2 "Have you looked at it yet?"
No - We'll do it today.
Day 3 "Did you look at it this morning?"
No - we'll do it this afternoon.
Day 4 "Did you look at it yesterday afternoon?"
No - We'll definitely do it this morning.
"Did you look at this morning?"
No- We'll....
"Look, I need to know before this weekend etc."
Day 5 "Did you...."
Yes Sir - There's nothing wrong with it.
"Oh thats...unexpected...I'll ....take it back then.... must be a problem elsewhere....."
Subtext - We got fed up with you so we spun it and saw a voltage and decided to fob you off.

Mike