Battery problem

[spartan3956]

This is a bit technical but the electrical wizards might help. The standard set up on my motorhome is two 85amp batteries that are seperately connected to the control panel for charging and supply. I have increased both banks to 2x 85amp batteries so i have 4 in total. Two of the batteries (1 bank) supply the Inverter the other is left for 12 volt usage. The inverter Batteries also supply the 12 volt. When camping for a few days and extended use of the inverter i noticed the batteries on the 12 volt supply are also dropping voltage so they appear to be feeding the inverter batteries to equalise the voltage. Is there some way to isolate the two sets so that i have a good 12 volt supply even when the inverter batteries are exhausted. I still want both sets to charge via the Alternator/ control box charger when on hook-up. but one set only to supply. Is there anything i can fit in the wiring from the batteries or will i have to place a switch to isolate the one bank and remember to switch it back on when on the move. Pete

[Clive]

If you wish to operate the two banks independantly then you require a second split charging relay. This way the batteries will only be connected in parallel when the engine is running and the alternator is generating. Have a look at http://www.motts.dsl.pipex.com/SPLIT%20CHARGING%20SYSTEM.htm for a technical description of split charging. You just need to double up. BUT If you permanently parallel all four leisure battereies you will actually get more out of them as they will share the duties and individually be working at a lower discharge rate which actually allows a slightly greater effective ampere hour capacity.

[spartan3956]

Thanks for the info Clive I assumed that the two feeds had seperate relays but this is now unlikely. I didnt connect all four batteries together as two were old and the other new. I can see the logic in lower output per battery when all connected. What rating should the relay be?. Pete