Yanmar 4jh2e charging issue

[mrangry]

I have a Yanmar 4JH2E (1992) and found that the alternator isn't charging. I believe it is an 80 amp Hitachi unit, but cant see any model number, just Hitachi on the casing.

It has a heavy live cable going to the unswitched side of the engine isolator and a heavy black cable earthed onto the engine block. There are also two spade terminals, one of which I believe is a charge warning lamp but unsure of the other. I dont have a charge warning lamp and nether of these two terminals were wired when I got the boat. There is also a wire coming from the side of the casing which I think is for a tachometer. This is unused as the engine has a sender for this.

I am getting 12.6 volts across the live and neg terminals with the engine both off and when running indicating the alternator is not charging.

Looking online I am wondering should one of the spade terminals be an ignition live feed? Does the alternator require this for it to charge?

 

[andsarkit]

If it worked before and there is no change to the wiring then it is probably an alternator fault. It could be the brushes or a failed diode. Unless you are competent to pull it apart and check it with a multimeter it is probably easiest to take it to an auto electrician that specializes in alternators.
If you want to check it yourself this book may help. Alternator handbook

 

[mrangry]

If it worked before and there is no change to the wiring then it is probably an alternator fault. It could be the brushes or a failed diode. Unless you are competent to pull it apart and check it with a multimeter it is probably easiest to take it to an auto electrician that specializes in alternators.
If you want to check it yourself this book may help. Alternator handbook

I should have added that I have 300 watt solar panels charging the batteries ( 4 x 110ah agm house bank and 1 x 110ah lead acid starter battery). I have never tested the alternator output before now and it is possible that it hasn't been charging all along since i got it and the solar was adequate for the power usage up until now.

It only really came to light after being on anchor for two nights with six people in cloudy wet weather that the Ctek app showed the house bank at 67% state of charge

 

[VicS]

I have a Yanmar 4JH2E (1992) and found that the alternator isn't charging. I believe it is an 80 amp Hitachi unit, but cant see any model number, just Hitachi on the casing.

It has a heavy live cable going to the unswitched side of the engine isolator and a heavy black cable earthed onto the engine block. There are also two spade terminals, one of which I believe is a charge warning lamp but unsure of the other. I dont have a charge warning lamp and nether of these two terminals were wired when I got the boat. There is also a wire coming from the side of the casing which I think is for a tachometer. This is unused as the engine has a sender for this.

I am getting 12.6 volts across the live and neg terminals with the engine both off and when running indicating the alternator is not charging.

Looking online I am wondering should one of the spade terminals be an ignition live feed? Does the alternator require this for it to charge?

I would expect to see a direct feed from the ignition switch to the spade terminal labelled R , and a feed via a "no charge" warning light to the spade terminal labelled L.

There should be a wiring diagram in the owners manual.

There are also wiring diagrams in the Service manual which you will find at YANMAR 4JH2E SERVICE MANUAL Pdf Download | ManualsLib See pages 314 et seq

If you really don't have a "no charge" waning light the direct feed from the ignition switch to terminal R will give the alternator the initial excitation needed to start generating but it seems odd not to have the warning light