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Discussion Starter · #1 ·
I was wondering if anyone can help with a non saab "automotive" query.

We've just had some work done on our boat which included fitting a new alternator (a bog standard Lucas 60amp beast)

When running the battery terminal voltage is somewhere between 14.9 and 15.3 depending on the meter I use. The volt meter on the control panel shows 15 volts.

Is this too high?

I also notice pulsing on the ammeters and lights in the boat pulse up and down at the same frequency. This doesn't happen all the time - it seems to happen when the battery is pretty much fully charged which suggests to me that its the regulator kicking in and out and possibly causing the split charge relay to chatter which would cause both the ammeters to pulse.

Someone has suggested replacing the relay with diodes in each battery line.
 

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Seems quite a bit high. Bosch alternator control units are a nominal 14V, and typical voltmeter readings are 13.8V or so, depending on load.

P.S. I assume you are using lead acid batteries and that marine alternators are essentially the same as car ones.
 

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Discussion Starter · #3 ·
They are Lead acid batteries (admittedly rather large ones) and its not a marine alternator at all. For simplicity (and parts availability) canal boats use automotive alternators.

My big worry is that on a long run (10+ hours) 15 volts is going to start sulphating the plates and also lead to excessive electrolyte loss.
 

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Discussion Starter · #5 ·
High resistance where?

The earth bonding from the engine is fine as is the earth bonding of the alternator to the engine. When its charging in the morning its putting in 40+ amps. The heaters on the engine draw 40+ amps during the startup process and the engine cranks fine. All of which suggest that there isn't an high resistance anywhere

There doesn't seem to be anything getting hot anywhere - I've checked the connections on the back of the ammeters and the battery connections are fine too.
 

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I don't know much about Lucas, but on Bosch alternators the control unit and brushes just screw in in one piece. Very easy to change and quite cheap. If Lucas are similar, it might be worth changing the control unit and seeing what happens.
 

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The voltage control unit may include a Zener Diode which dumps current to earth when the voltage goes over 14.5V, if this diode's path to earth is not to spec the voltage goes too high. A Zener diode is used on permanent magnet alternator, if the magnetic field is from energised coils then the control is of the current in these coils.
 
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