We bought our boat in May 2013 and at the time had a fully reconditioned Bukh DV10 LSME installed. It has a charging generator (see handbook specs below) built into the flywheel however the regulator/rectifier is the original one. Instead of trying to get it working at the time we installed a 40W solar panel with regulator and a new Full River 105Ah battery.

Recently I decided to get a marine electrician to check the wiring and get the generator charging system working, as we are planning an extended cruise which will involve night sailing whilst using a GPS, lights and tiller pilot. The electrician has completed the work and tells me it is all working as evidenced by the newly working charging light going out when engine starts and a battery charging voltage of 13+ Volts that he claims he has seen.

Problem is, I can't see any increase in voltage directly across the battery above the resting voltage of 12.84V with the solar panel disconnected and the motor running for at least 40 minutes at full revs. I am told the charging circuit is weak and I won't see much voltage increase, however the current will still be flowing as evidenced by the charging light going out.
Is it that the battery is healthy and the charging circuit will not make any impact unless the battery was a lot flatter?
I'm at a loss to see any difference at all in battery voltage when the motor is running at full revs compared to how the solar panel can charge the battery even considering it is less than 25% the capacity of the generator.

Bukh Charging Generator;
Charging generator (flywheel-mounted, alternating current)...........SAPRISA 6273
Charging voltage (at 20 C).........................................................14.2 +/- 0.2 volts
Charging output........................................................................210W

keensailor said..

Problem is, I can't see any increase in voltage directly across the battery above the resting voltage of 12.84V with the solar panel disconnected and the motor running for at least 40 minutes at full revs. I am told the charging circuit is weak and I won't see much voltage increase, however the current will still be flowing as evidenced by the charging light going out.
Is it that the battery is healthy and the charging circuit will not make any impact unless the battery was a lot flatter?
I'm at a loss to see any difference at all in battery voltage when the motor is running at full revs compared to how the solar panel can charge the battery even considering it is less than 25% the capacity of the generator.

I can't see how that is actually charging the battery. At 12.84 it isn't charging the battery. Simple. 12.84 is slightly high for a resting voltage, but if your battery is newish and well maintained then you might see that. It's possible that your charging system is keeping it in 'float' charge however, which doesn't need 13.8 volts.

Try disconnecting the solar panel, have the engine off, and run something like some lights. Measure the battery voltage. I'd expect around 12.6 volts. Now monitor the voltage as you start the engine and run it for a bit. Does the voltage increase to 13.5 - 13.8 for a period of time? If so then your battery is being charged. If not then it's not being charged.

HI keensailor
watts (210)divided by volts (13) = amps so you only have a 16.1amp alternator. this is a very small alternator most alternator wont put there max amps out for very long if at all . this could be your problem


my alternator is small too it's rated at 40amps (I have only ever seen produce 28amps).
volts will rise to 14.2 instantly when engine is stared then clime to 14.8 with both house(300ah) and starting battery.

it would be worth checking the charging current in amps with a clamp on multi meter
there is a chance your alternator put's out nothing at idle so check while underway or rev it up a bit

Id some how try to fit a car alternator if it was possible personally
you could try turning a few lights on and see if there's a difference in your alternator charge rate before and after