alternator warming

[timv]

Hi I have a phantom 38 and last time I took the boat out after just one night without shore power the port engine wouldn't start until I started the genny after which it started within a few minutes .This suggests a duff battery but they are only 12 months old and on return to the marina my mechanic noticed the alternator was warming up when plugged into shore power. I know nothing about electrics but my mechanic has suggested we take the alternator to be checked suspecting a fault there, which seems logical to me. I just wondered if anyone had had a similar experience or had any ideas. Many thanks for any thoughts

Tim

 

[Alex_Blackwood]

Hi I have a phantom 38 and last time I took the boat out after just one night without shore power the port engine wouldn't start until I started the genny after which it started within a few minutes .This suggests a duff battery but they are only 12 months old and on return to the marina my mechanic noticed the alternator was warming up when plugged into shore power. I know nothing about electrics but my mechanic has suggested we take the alternator to be checked suspecting a fault there, which seems logical to me. I just wondered if anyone had had a similar experience or had any ideas. Many thanks for any thoughts

Tim

Difficult to say without knowing your setup. However if you have a battery master isolator (of any description) which has been left "ON" you could possibly get a current path through the alternator which will cause your fault. Or even a faulty diode in a split diode charging system, maybe, or a faulty VSR. Think you need to check more than the alternator as I would suspect something along the lines of the above rather than the alternator itself.
Also worth checking that the ignition switch isn't faulty. Maybe none of the above. But!
Edit 10:04 110525. In theory the diodes in the alternator would be expected to block any back voltage so don't discount the alt. Just trying to say look at everything.

 

[timv]

thanks for the advise , I will look into it

 

[PaulRainbow]

In a basic installation the alternator B+ is connected to the battery positive on the starter solenoid. The alternator is therefore always live and doesn't normally get hot when not in use.

With the exception of alternator diodes, the other suggestions in post two cannot cause the issue (sorry Alex).

An ammeter on the cable to the alternator will almost certainly show a current draw to the alternator, in which case it obviously needs fixing, any half decent auto electrical place can do that.

Turning the main battery isolator off should stop the current draw, if not disconnect the battery. Do not leave the power on as the alternator can get very hot, potentially starting a fire.

 

[timv]

In a basic installation the alternator B+ is connected to the battery positive on the starter solenoid. The alternator is therefore always live and doesn't normally get hot when not in use.

With the exception of alternator diodes, the other suggestions in post two cannot cause the issue (sorry Alex).

An ammeter on the cable to the alternator will almost certainly show a current draw to the alternator, in which case it obviously needs fixing, any half decent auto electrical place can do that.

Turning the main battery isolator off should stop the current draw, if not disconnect the battery. Do not leave the power on as the alternator can get very hot, potentially starting a fire.

yes we have turned the battery isolator switches off - many thanks

 

[volvopaul]

Hi I have a phantom 38 and last time I took the boat out after just one night without shore power the port engine wouldn't start until I started the genny after which it started within a few minutes .This suggests a duff battery but they are only 12 months old and on return to the marina my mechanic noticed the alternator was warming up when plugged into shore power. I know nothing about electrics but my mechanic has suggested we take the alternator to be checked suspecting a fault there, which seems logical to me. I just wondered if anyone had had a similar experience or had any ideas. Many thanks for any thoughts

Tim

That engine start battery is also your domestics so it's quite normal , it's how Fairline built it , crazy idea I know . You don't have a problem as long as the other engine battery is good condition.

 

[Alex_Blackwood]

In a basic installation the alternator B+ is connected to the battery positive on the starter solenoid. The alternator is therefore always live and doesn't normally get hot when not in use.

With the exception of alternator diodes, the other suggestions in post two cannot cause the issue (sorry Alex).

An ammeter on the cable to the alternator will almost certainly show a current draw to the alternator, in which case it obviously needs fixing, any half decent auto electrical place can do that.

Turning the main battery isolator off should stop the current draw, if not disconnect the battery. Do not leave the power on as the alternator can get very hot, potentially starting a fire.

Paul, I agree with you. Perhaps got a bit convoluted in my post. What I was trying to say, put simply, was. Don't dismiss anything, check your whole system.
Never say Never Once again it doesn't help not knowing the actual setup, in this case not really a criticism.

 

[timv]

That engine start battery is also your domestics so it's quite normal , it's how Fairline built it , crazy idea I know . You don't have a problem as long as the other engine battery is good condition.

thanks Paul, enjoy your holiday mate