Flashing "Charge light" when batteries fully charged

[gspeak]

I have twin Yanmar 3GM30F on our Lagoon 380. House bank of 480AH, plus start batteries for each motor. All are combined.

Two weeks ago while trying to track down a phantom load on the starboard start battery that seemed to lose charge overnight, I found a relay that was hot all the time. I traced the wires from the relay & all appeared to go to a connection box that used to be connected to the old motor driven refrigeration compressor system. This old motor driven compressor system was removed ages ago. I removed the wire that went to the relay from the +terminal on the alternator and the phantom load to the battery has gone.

However, now I notice that when both the port & starboard motors are running AND the batteries are fully charged AND with no electrical system loads on, the starboard "Charge Light" flashes on the dashboard panel. If I shut down the port motor it stops flashing, or if I apply a load to the electrical system eg. turn on a pump, with both motors running it also stops flashing.

The alternator is definitely charging as the battery monitor shows amps & volts when the starboard motor is running, the same with the port motor.

The light never flashed previously.

Any ideas why this is so, or if it is doing any harm to run it like this?

Thanks in advance for any input.

Dave

[smac999]

because all your batteries are combined into one bank. and you have 2 sources of charging on the same bank. once everything is full they will fight each other and one is turning off as it's not needed. previously you had a load on the batteries all the time (which was draining them) so the alts would stay working. like they do when you add a load now manually.

the solution to this is external regulators with a field balancer. or replace the combiners with something like an isocharge. (though this still may cause the same issue not sure)

not going to harm anything. just means one alternator is not charging, but it's not needed at that time. if you had a tach that runs off the alternator you would see the problem worse because the tach would stop working as well.

[gspeak]

Originally Posted by smac999

because all your batteries are combined into one bank. and you have 2 sources of charging on the same bank. once everything is full they will fight each other and one is turning off as it's not needed. previously you had a load on the batteries all the time (which was draining them) so the alts would stay working. like they do when you add a load now manually.

the solution to this is external regulators with a field balancer. or replace the combiners with something like an isocharge. (though this still may cause the same issue not sure)

not going to harm anything. just means one alternator is not charging, but it's not needed at that time. if you had a tach that runs off the alternator you would see the problem worse because the tach would stop working as well.

Thanks for your reply. I forgot to mention that the three banks are combined with two Yandina 160 Combiners which I understood to only "combine" when the voltage was over a certain amount. Not that that makes any difference to what you are saying because it is only occurring when charging.

The question I was really concerned about is, is it going to be doing any harm running like this anyway, if that alternator isn't contributing when its not needed? Will it hurt the alternator or any other systems? Just wanted confirmation that all is OK.

Thanks again.

Dave

[colemj]

No, it will not do any harm. Ours also operate this way - the alternator light comes on when the batteries are fully charged and the alternators are not supplying current.

This will happen regardless of having a combiner, duocharge, isocharge, field balancer etc. The cause is that current is no longer needed, so the alternators stop supplying it.

If it is bothersome, just turn on a load.

Mark