I got a “smart” battery isolator for more charging options with my batteries.

How it Works

The engine alternator charges the engine batteries while the engine is running. The solar panels charge the house batteries. The battery isolator sits on a circuit between the engine battery and the house batteries.

When the engine is running, and the engine batteries reach full charge, then the isolator closes the circuit and and starts sending juice to the house batteries. If the engine batteries run down too much, then the circuit opens, to allow more charge to go back into the engine battery. This way, the house batteries can’t suck up all the charge and drain the engine batteries.

The great thing about this “smart” isolator is that it works both ways. If the house batteries top up from solar, then the isolator can be turned on to top up the engine batteries as well! Therefore, the engine battery won’t run down from inactivity.

I’ve played with this system a bit and discovered that both systems can work in conjunction with each other, to a point. With the solar panels getting full sun, and the engine producing energy, both battery banks fill up rather quickly. Sometimes, though, the charge controller will get confused about why there is so much electricity going into the house batteries, and lay off the bulk charging. So, it takes some calibration.

I installed a switch, for maximum control over when the isolator can turn on or off, too.

Overall, this was a relatively inexpensive upgrade that makes a world of difference.