Charging Batteries With A Combiner

Big Duck has two separate battery systems.

1) Typical start and house batteries with a 1-2-both-off switch. This includes a dual battery on board charger

2) A Freedom 30 inverter charger with dedicated group 31 battery. The Freedom battery charger is rated at 130 amps. We didn't buy the Freedom 30 for the boat, we removed it when we sold the camper.

I use a Yandina battery combiner to allow both start and house batteries to be charged by the engine alternator without having to mess with the main battery switch.
Yandina Battery Combiner

The group 31 battery is used with the inverter to power the fridge, that's it's only job. The fridge is 120vac only, a dorm model - significantly cheaper than a marine 120vac/12vdc refrigerators and we already had the inverter. The inverter/charger charges the group 31 battery when on shore power or when the Honda generator is running. Up until now, this hasn't been an issue because we run the Honda almost the whole time we're on the boat to power the air conditioner. The group 31 battery holds up fine for the little charging it needs in the summer.

In Spring weather however, we're finding the temperatures quite pleasant without running the air conditioner. This means that the group 31 battery will only keep the fridge going for a few days without running the generator, even though the boat is typically on the move for most of the day.

The solution is another combiner between the starting battery and the group 31 battery. Now the alternator on the engine will charge all 3 batteries when we're on the move, yet they'll all be isolated when charging voltage is not present. And what's more, the Freedom charger will also charge all 3 batteries on shore power or when the Honda is running. We will discontinue using the on board charger altogether.

Let's hope the engine alternator can keep up.