I have two battery banks in my boat, one “house” bank which I need to keep control of, and one smaller bank for starting/backup.
The smaller bank is not a dedicated “starter battery”, I can choose bank 1 or 2 or both with the switch, and all equipment can be run of either (or both) banks.
I installed the bmv702 as per instructions, with the shunt between the house bank negative. The other bank was connected to load side of shunt.
I entered the capacity of the house bank (345Ah) and it works. But if I connect the banks together the A and W is wrong, as power is drawn from both banks, but only half through the shunt.
Now I am wondering if I should connect both banks to the same battery side of the shunt, and leave the 345 ah I stated as battery capacity. This way I will have an accurate reading of power consumption at all times whichever setting on the switch, and the only ”fault” will be that there actually is more ah available than what I have told the system (if using both banks). If using only house bank it will be right. Or will the system detect the extra ah’s, when voltage isn’t dropping according to the amps used?
I only need to know voltage on the second battery bank, but I really would like to have control over amps and watts used totally, and also I use both solar and battery charger connected to shore power for charging all batteries. Can I go wrong by connecting all negative batteries to battery side of shunt, and all other negative to the load side? Being aware that the ah capacity won’t always be correct, depending on which bank I use.