Battery Charging with isolators

by Tom
(Florida)

Hi John, got the latest edition of the Marine Electrical and Electronics Bible, great help.I am considering installing the following charging system, one isolator for each of the two main engines. Each engine has it's own starting battery. The charging output for each engine will go to its respective isolator which will then be split so that one side of the isolator goes back to its dedicated starting battery. The other side of the isolator will be wired to a house battery. This will be the same for the second motor, one side wired to it's own starting battery and the other side wired to the same single house battery. Under this system the house battery would have two charging leads coming in from two different isolators. This system would theoretically charge the house bank if either motor were running. Would this cause problems when both engines are running? What other potential problems are there? What other options are available that accomplish the same task of charging the house battery with either engine. This same system will also have a parallel switch between the two starting batteries.

Comments for Battery Charging with isolators

Average Rating starstarstarstarstar

Click here to add your own comments

Nov 12, 2025
Rating
starstarstarstarstar 		Charging Distribution Options
by: John Payne

Sorry for the delay in responding, been away sailing! Thanks for the kind comments and hope the book helps you. As you would have seen I am not a great fan of isolator switches, the 1-2 Both type that is. If two alternators feed the same battery bank (you say only one battery bank for house power?) one of the alternator regulators will be relatively useless as both see the same battery voltage and one alternator will be almost a "slave". This is a hard situation to overcome. I will consider some options and post any outcomes I can think of.

I like the whole redundancy principle, on my own boat I have one engine but two house banks plus the start battery. I am using a Victron ArgoFET battery isolator which distributes charge between both house batteries and the start battery from a single alternator. These are low loss diode systems. This eliminates the switch issue and you do have an emergency parallel switch is what I also have.

Is a split house bank an option? My setup is that two house batteries supply my electronics loads on one panel and the other service loads such as pumps and so on. This does mean some issues depending on how your switch panels are arranged.

Click here to add your own comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Cruisers Forum.