Lagoon 400 Yanmar issue with electric system.

[CatNewBee]

Hi therej just got a stupid error I am trying to track down and fix, but cannot understand it yet.

After stopping the engines, i restarted them again 10 minutes later.
One engine has the a permanent buzzer, the charge control light remains on and the rpms are not displayed at the gauge. However, the engine is running fine and can be used.

My inital thogth was, i lost the v-belt, so no drama.

Then I opened the engine compartment and the v-belt was in place and ok.
Next assumption was, the generator is damaged.

However, i wanted to check the start battery, and on the panel the aux battery was disappeared. I took the circut diagrams out and found, the board measuring the voltage is connected to a device called "325 fusible mesure tension batterie moteur et ventilateurde cale tribord" and according to the plan it is installed under the walkway between the engine compartments behind the air intake hoses together with the fan and a relay. Not serviceable without tearing out the hoses, that are glued to the hull below. What a stupid place to put electric devices in.

It must be a single device, that causes problems, however here my questions

Why is the rpm gauge not functioning when the generator does not output power?

Why is the battery voltage is measured at the engine intake air fan, what is this french device all about, and not showing anything if the alternator is faulty? The starter works flawlessly, so it must be something else, not a regular fuse.

I used a voltmeter to confirm the generator does not charge, indeed there are only 12V in contrast to the other engine with 13.5V. But it can be the field power or any other error.

The errors seem not to be related, but come at the same time.

Any hints and thoughts are welcome. My next step will be to get a spare alternator and replace the one to see if the error persists. Very strange, the panel does not show the battery voltage any more, but the battery is working.

[CatNewBee]

Here the electric circuit diagram in question

[CatNewBee]

And here the place where they should be installed. I am suspecting, there is only the fan and nothing else, because the cable going behind the tubes has only 2 wires... All the other stuff must be somewhere else on the boat. Anyone an idea where to look at?
The Yanmar manual does not provide any meaningful troubleshooting information either, besides contact yanmar service.

[CatNewBee]

Hi all,

Found it finally under the berth, the fuse is zip-tied near to the main positive breaker switch. From there one cable is going to the panel and the other to the engine compartment, where it goes to the relays and the blower. It also connects somehow to the alternator field coil, so even there is ignition and the starter is working and the panel has power, it does not provide energy to create a magnet field in the alternator and therefore the alternator has no power output, resulting in a error in the panel with beep and battery light lit, it also affects the rpm display, that then shows no rpm.

Replaced the fuse and everything is back to normal now.

I hope, this post helps one day someone with the same issues.

[Whomda]

Thank you, as always, for following up with the fix. I'm sure you will be saving someone a huge hassle someday.

[Dtm67]

Agreed. Appreciate it as well!

[Ulstue]

Hello CatNewBee
I don't want to say: wonderful that you have had this problem, but wonderful that you found the defect! For me your thread is an extremely big help. I have the same problem, but I am not on the boat. I'd like to bring the appropriate fuse with me when I get back on the boat. It would be fantastic if you could write down the specifications or part number of the spare part, or maybe even a photo of the place of installation. Would be great if that were possible!

[CatNewBee]

It is a standard automotive red 10A fuse.

I digged a little deeper into the issue to find the reason why it burned, seems the blower fan under the walkway behind the air intake hoses is weared or has corrosion on the bearings, it makes some noise sometimes when starting.

I assume the friction leads to a higher power draw when powering on the engine and eventually burns the fuse. It happened again after 5 or 6 successfull starts with no issues, so it seems to be on the edge for replacement or repair. However it is a PITA to get it out it is deep inside between the hoses and the compartment for the life raft, and we are sailing at the moment, so it will have to wait for the next bigger maintenance window. I am also thinking about moving it to the engine room for easier service next time.

I have now replaced the 10A standard fuse by an automatic 15A fuse as a redneck solution to buy me some time until a propper fix can be done - and as push-button fix just in case it trips again under way, I know, not the right way for fixing things, but the amp draw is only a short peak, when the blower starts and the cabling can take the 15A in the meantime too as far as I can see, so not too dangerous.

[CatNewBee]

This thing...

[Ulstue]

Thanks!