concern over battery banks

[davidbrady]

Yes, the ignition switch 'on' also energizes the 'aux-bat' constant-use solenoid connecting the chassis batteries to the house batteries and allowing the 50DN to charge both banks.

Yes, as soon as the ignition switch is turned to accessories the house batteries will connect to the chassis batteries immediately pulling the chassis batteries voltage level down to that of the house batteries. When the engine starts the alternator takes over charging both banks.

It's good that at idle the alternator is only generating a fraction of it's rated output so we're probably not going to overwhelm the 200A constant use solenoid. It's bad that when the key is switched the chassis batteries dump lots of current into the house bank and in the process create an inrush which probably briefly overwhelms the solenoid - certainly creates a big-ass spark at the solenoid high amperage contacts.

In cases like this I always start my generator to get the 240A of BULK charging going to help bring the house batteries up before starting the engine. A complete solution would have some sort of differential voltage sensor and battery isolator isolating the two banks if their voltage deltas are extreme. BB tried to do this with the M450. You may find this thread interesting.

SpongeBob has two completely separate systems: an alternator and battery bank for the house, and an alternator and battery bank for the chassis. I do have a dash switch to temporarily connect them for the case of dead chassis batteries, but the solenoid is never energized automatically by the ignition switch.