Originally Posted by btrayfors
Or, better, use a Xantrex EchoCharge (15A maximum current flow) or a Balmar DuoCharge (30A max). These work by sensing a charging current on the house batteries, then diverting a portion of it -- up to 15A or 30A, respectively -- to the other battery bank to be charged.
The banks are kept separate, no significant voltage drop, no in-rush current when the batteries are "combined", etc.
Both devices work very well...we've installed both on many clients boats. And, they're "smart"...they won't overcharge your batteries.
Thanks Bill. The concern I have with the duo charge is that I already need that to charge the engine start battery from the alternator. My understanding, which of course could be way wrong, is that you can't use the duo charge to charge three banks. We already are going to have it set up so that the thruster battery gets charged on the Xantrex echo charger (it will be charging the house with the primary, and there are two additional echo chargers, one for the engine and one for the thruster). The problem is that we rarely will be running the battery charger when the thruster is in use, and I'd really like to have the altnernator propping up the thruster battery.