Isuzu alternator not charging

[Midnight]

Lady boater moored near asking for help.
A new auxilliary alternator was recently fitted. Whilst running the engine to charge the batteries the aux red light came on and the buzzer sounding. No loose wires. Looks to me like the new alternator has failed but anyone any ideas what else it could be or what to check? Its a twin alternator setup.

[Tony Brooks]

Drive belt loose /off? I kind of assumed that you checked that.

 

if it only has one charge warning lamp it might be the engine battery alternator, but of two lamps that will not be the case.

 

In theory, a short on the warning lamp wire between amp and alternator, but unlikely.

 

 

[Midnight]

Yes checked the obvious stuff. The panel has two lamps one for each battery / bank. I'm not great on electrics but put a multimeter on both, the domestic alternator voltage increased but the starter alternator voltage stayed same when the engine was started.

It's the left side buzzer and light that comes on. Not the aux

[Tracy D'arth]

 Is there a tacho, --  working?  Looks like a failed alternator then.

[Midnight]

1 minute ago, Tracy D'arth said:

 Is there a tacho, --  working?  Looks like a failed alternator then.

 

Not working 

[Jon57]

I’ve got some jump leads on board for a temporary fix from the good alternator to the leisure batteries. Give me a call.

[Tony Brooks]

10 hours ago, Jon57 said:

I’ve got some jump leads on board for a temporary fix from the good alternator to the leisure batteries. Give me a call.

 

It is easier to simply jump between the engine and domestic battery's positives, the negatives should already be linked. Remember to remove the jump lead as soon as the engine is stopped.

Edited October 1, 2023 by Tony Brooks

[Jen-in-Wellies]

16 minutes ago, Tony Brooks said:

 

It is easier to simply jump between the engine and domestic battery's positives, the negatives should already be linked. Remember to remove the jump lead as soon as the engine is stopped.

Beware if there is a current monitoring shunt in the house battery negative though. Some might be overloaded by an engine start. Jumper cables +ve to +ve and -ve to -ve on both the house bank and engine battery would be safer.