A 70-amp isolator will set you back in the neighborhood of $50 or more.Ī fairly new entry to the battery isolator field is the “smart isolator.” We recently installed and began testing the Battery Doc isolator from WirthCo Engineering ( Like other isolators, this electronic isolator prevents SLI and house batteries from depleting one another. You’ll need to get an isolator with a rating equal to or larger than your alternator output. If you’re a boondocker relying on your alternator to recharge your house batteries, a solid-state isolator will be a penalty.īattery isolators of this nature are rated by how much current they can carry. That may not sound like a lot, but to quickly charge batteries, more voltage is important. Solid-state isolators are not 100 percent efficient-they tend to add a little resistance to the circuit, reducing the effective amount of voltage to the batteries by over half a volt. This prevents either battery from drawing down the other. This keeps the SLI battery charged up, and the house battery too, without either one of them “seeing” each other.

Current can flow from the vehicle alternator back to the RV, but not from the SLI battery. Solid-state battery isolators utilize electrical diodes, which act like a one-way valve. These isolators are relatively trouble free, but like any mechanical device are subject to occasional failure. The solenoid doesn’t use any power in itself, other than a tiny amount when the ignition system is switched on. Another wire connects the relay to the positive post of the SLI battery, and another runs back to the RV. You simply need to find a source of power from a circuit that’s only hot when the ignition system is “on,” and run it to the relay. The solenoid isolator is relatively inexpensive-it’ll set you back less than $20. Turn the ignition system off, the relay switch opens, preventing current to flow from either the chassis to the RV, or vice versa. When your vehicle is running, current throws the switch closed to allow current to flow from your vehicle charge system back to your RV. Somewhat comparable to a vehicle starter relay, the solenoid is a big electrically operated switch.

The simplest battery isolator is nothing more than an electromechanical relay.

It used to be there were just two kinds of isolators now there are three. At the same time, the isolator allows your house batteries to charge up by drawing on your chassis or tow vehicle alternator. Without such isolation, your house battery and SLI battery will seek to maintain the same charge level-and if that’s too low to start your rig, you’re left in the lurch. The RV had “stolen” power from the truck battery, leaving us wandering around with a set of jumper cables, looking for a hot jump.īattery isolators do just what it sounds like: They isolate your RV “house” batteries from your vehicle’s SLI (starting-lighting-ignition) battery. After our first night on the road, a chilly one where the furnace ran during the night, we found we couldn’t start the truck up. On one of our earliest RV adventures, we learned the hard way about the importance of a battery isolator system.

Battery isolator relay diagram