Alternator fault

[JOHN SLEIGHT]

I have a Bavaria 45 and it has developed a fault in the alternator.
When I was running the engine a battery fault appeared.
When I checked the charge I found that the alternator was charging at 15.8 volts.
I reported the fault to the local boat electronic guy and he removed the alternator and check it.
He reported back that it was ok but that there was a strange pink wire connected at the rear of the alternator.
With this wire is removed the fault disappears. However he can't trace what this pink wire does.
It doesn't appear on any wiring diagram.
Any suggestions???

[SorinCT]

Check if the pink wire goes to the engine panel alternator input. It would give also audible and visible alarm on the panel. If you remove the wire, of course, no alarm but also no indication of fault. Make sure you have a firm connection from the alternator, battery isolator, battery terminals.

[JOHN SLEIGHT]

Thanks for that....I'll check when I go back to the boat.

[SorinCT]

If that voltage is real, you either have a voltage regulator issue or the alternator is isolated from the batteries. 15.8V is too much for lead acid, AGM or LiFePO4.

[JOHN SLEIGHT]

Yes I agree, however the 15.8 volts showed on the 301 panel when the electrician was running his tests.

[Rampage]

I had this fault appear on my Lucas alternator (not the original equipment).  I replaced the regulator in the alternator and that sorted the problem.  I now carry a spare (they’re only £15 or so).  The original alternator was Valero (I think) which developed the same fault: I replaced the whole alternator as I couldn’t find any one to sort the problem where we were at the time.  A regulator for that alternator is also a fairly easy replacement job but more expensive at about £40.
I’d therefore look to replacing the regulator: should be easy enough to source off the internet if you’ve got the details of the alternator.

[Domi409]

Hello, last year I purchased a B45 second hand and had the same fault during our first navigation when restarting the engine at arrival. The seller changed the alternator as warranty for a new one. The next day, same problem.
The seller  could not do more and I started investigating. I can tell you what I did and my understanding of the problem, with my today work around, probably not the final solution but it works for now:

- I have an engine battery and service battery.

- There is a blue box in the engine compartment, the battery isolator (diodes inside, generating a voltage drop increasing with the load current). The alternator delivers current to this box input. The two outputs go to the engine battery and to the service battery.

- The alternator has a pink wire connected directly to the service batteries, mine is connected on the main fuse behind the cushion of the chart table. This wire gives the alternator the real voltage on the service batteries to tell the alternator integrated voltage regulator to raise the voltage to compensate the voltage drop in the diodes and cable between the blue box and the battery (can be a drop of 0,7 to more than 1 volt).
The alternator is built to deliver about 14,2 volts when no pink wire connected.

In my case, the voltage alarm on the Volvo rev counter occurred after sailing when the service battery was low, the engine battery charged. When starting the engine, the battery voltage could go higher than 15 volts; so the alarm. With the alarm ON, on the Bavaria panel, I could read 13,6 V for the service battery and 15+ volts for the engine battery. Only by reducing the engine rev I could stop the alarm.
After navigating at low speed with the engine for some time, when the service battery filled up, I could get again 14,2 volts for the service battery and 14,4v for the engine battery and then no alarm whatever the engine speed.

So when the service battery is low, the 13,6 volts it sees is the level delivered to the alternator to tell it to increase its output voltage in order to see 14,2 volts and it will go to more than 15 volts to compensate the voltage drops, which is also what the Volvo system will measure and report as an alarm.

I tried to clean all cable connections without success and what I did so far is to disconnect the pink wire to replace it by a wire between the engine battery and the alternator. As the engine battery is the reference for the alarm and as the service battery is often at lower charge than the engine battery I do not see a problem.

A longer term solution will be to replace the blue box by a low voltage drop isolator to reduce the issue and keep the pink wire.

Any other ideas will be welcome.

[SorinCT]

You could replace the isolator with ArgoFET, or Cyrix isolator and eliminate almost all voltage drop through diodes. If the "pink" wire goes to the batteries that is the excitation. Most people switch the wire from the engine battery to the house battery in order to optimize charging.

[Domi409]

The pink wire is not excitation, it is a voltage reference to force the alternator to increase voltage in case of voltage drop.
You are right, it should be on the service battery but in my case it caused the issue. If I change the isolator as suggested, I will reconnect this wire to the service battery to optimise charging.

[Yngmar]

15.8V sounds like a broken alternator regulator (on the standard Valeo alternator and most others, this is a replaceable part that slots in the back of the alternator). On the other boat I've seen this fault, replacing the regulator fixed it, although by that time the over-voltage had already cooked the entire house battery bank