Multiple Charging Circuits
I returned to the boat with a new fuse for the bow thruster circuit. Once connected I measured the voltage at the bow thruster with the Travelpower providing 240ac to the Victron Multiplus inverter/charger. All is well there. Further tests at the domestic battery bank revealed the domestic alternator was not supplying any current.Time for a bit more wire tracing. With the help of the Beta Marine engine manual I found the cable that normally connects the domestic alternator D+ terminal had been cut at the engine end. This meant that the alternator will not start supplying current until it reaches quite high revs.
Alternator fact: The alternator only needs a current to energise it at low revs. At high revs the weak magnetic field already present in the rotor will generate enough current to energise the alternator.
I think it was disconnected to avoid having the alternator and Victron compete to charge the batteries. I'm going to reconnect it because the domestic alternator is essential for recharging while cruising when the Travelpower is not running. The two charging systems will only compete in as much as the one with the lowest voltage output will shut down and leave the field clear for the other. I'd rather have the two systems running than none at all as we had when the Travelpower drive belt broke.