How do I charge a third battery bank underway?

[JohnV8r]

Hey Everybody,

I just splashed Shambala after finally getting the Aqualights installed. I need to wire them into the electrical, and intend to put a third (house) bank of 6V batteries in and wire my bait pump, refrigerator, interior lights, spreader light, inverter, and underwater lights into that battery bank so there is no way to I can run down the two starting banks while I'm at anchor or drift fishing.

To accomplish the charging for the third bank, I sent my Lewco 20 amp 2-bank charger back to Lewco and had them upgrade it to a multi-stage 3-bank charger that is now capable of charging wet cell, AGM, and Gel Cell batteries. So that takes care of charging at the dock when I'm plugged into shore power.

The next question is how to set up the charging for a third bank of batteries while I am under power. In other words, how do I split the charge of one alternator from one of the engines to charge two banks. I have found something at West Marine called a Balmar Digital Duo Charge (page 379 of the '07 catalog). The basic concept behind this unit is that you connect the alternator to the house bank and once the house bank reaches 13.3 volts, a regulated 30 amp current then charges the starting battery. My only concern with utilizing this type of pecking order in the charging is that I do not intend to rewire all the electronics, radar, etc, that draw current off the starting banks when I am underway. My plan was to wire everything that I might use at anchor or while drifting to the third/house bank so that I could run that bank down without ever having to worry about not being able to start the engines. Conversely, everything that might be used while underway like electronics, nav lights, etc, would remain connected to the starting banks. The biggest concern I have with using the Balmar Digital Duo Charge is that I don't want to create a situation where the house bank may be charging while the items used while under way end up draining a starting battery bank while it is waiting for the house bank to get to 13.3 volts and switch the charging over.

So what is the preferred method for charging two starting battery banks and a house bank in a Bertram 31?

Thanks in advance.

JohnV8r

[Skipper Dick]

The best way I found is to install an isolator. I installed one that has two inputs (one from each alternator) and three outlets and they charge each bank separately and equally. I forgot how much it was, but I'm sure it was between $150 and $200. It was easy to install and does the job while underway just as an A/C charger with three ouputs does back at the dock. The great thing about an isolator is that each bank is independant from one another.

Dick

[In Memory Walter K]

The key is an isolater. It allows the alternators to charge the banks, but does it only in one direction. by that I mean it will only allow your third bank to drain itself, but not any of your other banks. A lot has to do with how your batteries are set up with your switches. You could have each engine charge its own starting battery, choosing one of them to also charge your third bank. Walter

[JohnV8r]

Thanks guys. I appreciate the help!

[randall]

my house switch is on off....but the two starting batteries are 1, 2, all....so i run with the house on ...one starter on 2 (starter and house) and the other on 1....

[merlin]

look for a Guest battery isolator. It seems like a common choice for marine.
I just installed a large one myself for about $200.

2 inputs, 1 from each alternator and 3 out.

Merlin

[mikepelham]

In Nigel's book he rerferances osolators the advantages and disadvantages. He recomends one from Wells Marine. I spoke to them and ordered one, very friendly http://www.wellsmarinetech.com/products.html

It also has a temp parralel swithc where you can combine all batts for starting. I have 4 batts on board, or will, after I am done re-wiring