Hi
I have 24 v House bank (lithium) on my boat and have used Solar so far to charge it. The Solar yield is not sufficient, So I have purchased a 24 volt 80 amp alternator to be able to top up when needed ( see schematic in the attachment). My plan is to connect the Alternator directly to the BMS and use the Relay on the BMS to activate/deactivate the Alternator. Is this not feasible or am I missing anything in this setup?
24 v Alternator.pdf (201.5 KB)
The best source of info would be the alternator wiring diagram.
The D+ connection normally only provides a small current at start up to the field to get the alternator producing some voltage. The alternator then provides its own voltage and current to the D+ terminal and field. Therefore, if D+ is not connected then the alternator may well.not start, but once the alternator is running, disconnecting D+ after start up will have no effect.
Additionally, some alternators retain enough magnetism to self excite even if D+ is disconnected, especially when the engine is revved up.
You have to disconnect the field wire to one of the brushes which means internal mods. The field current will be too high for the BMS relay and will burn it out or weld it on, you will need to go through a power relay, and then avoid surge currents from the second relay coil, see FAQ linked below.
Finally, I see you have an external voltage sensing on the alternator, you have connected that to the wrong side of the BMS and fuse, it should go on the alternator side of the BMS and fuse. If the fuse blows or the BMS contactor opens without shutting down the alternator, the alternator is disconnected from the battery, so the battery voltage will drop to say 13.7V, which the alternator will see, so it will keep increasing the voltage at its output. It may have a secondary limit built into the regulator to stop it going too high, check up on this. If it does have then you may consider leaving the sense wire where shown.