Q: How does the module work?Ī: The brain of the isolator is a match-box sized potted control box with a microprocessor unit and voltage sensing circuitry. Dual battery or multi-banks battery systems such as four wheel vehicles, RV, hunting vehicles, solar charged batteries, ham radio, etc. (happy customer ) Questions and AnswersĪ: Automatic separation and connection of main (starter) and auxiliary batteries during charging and discharging according to the state of charge of the main battery. Will this damage any parts leaving this connected until I start the vehicle. Can I change the connector on the Yellow wire to a to a clip-on type to avoid needing two people to start the truck. On two occasions I have had to start my truck using the AUX battery and connector. Hello, I have the sbc1120 isolator installed for more than a year now and it works like a champ. This is not necessarily the best place to put it, but it does work. This shows the dual battery isolator/combiner mounted on the negative terminal of a car’s battery. Seventh, no external diodes or current sense resistors are needed, the unit is a self-contained dual battery isolation relay. Sixth, it can be used as a low-voltage cutout to keep the car’s battery from being drawn below 12.6 volts. The starting motor battery will fail quickly if deep-discharged. Fifth, the auxiliary battery can be a deep cycle type designed for running lights, TV, refrigerator, etc. This allows you to give the system a boost in cold weather or if a squirrel snuck into the cab and left the lights on all night. When the engine is turned off the trailer equipment is run from the auxiliary battery Fourth there is an emergency function that will allow the spare battery to feed back to the starting system if the starting battery is dead or weak. While the vehicle’s engine is running all equipment is running from the car’s power.

Third it allows you to run equipment in a trailer or RV from the extra battery without having to remember to disconnect it from the vehicle’s power bus. (There is an emergency function that will allow the spare battery to feed back to the starting system if the starting battery is dead.) In this mode it is a dual-battery relay. Second it isolates the extra battery from the car so it won’t be discharged by the car electronics, and it won’t try to participate in starting the car. In this mode it is called a split-charge relay, or dual-battery relay. It relies on the alternator’s smarts to give it a good charge. The features are as follows: First, it allows you to safely charge an external lead acid battery from the car electrical bus. It can be used as a trailer battery charging module. Big lead acid batteries when they are empty can accept 150+ amps, so rate the wires at the maximum current of the alternator (see the Q/A section below). It will allow the extra battery to be charged at whatever rate the alternator can put out, so it needs big enough cables to do that. Neither will he house battery be used to start the car (unless asked to).

The isolator won’t let the auxiliary batteries be discharged by the vehicle’s gadgets. This battery-isolator is used to control extra battery systems that charge off the vehicle’s alternator. This hybrid system is really the best of both worlds, solid-state control and solid-metal contacts. This almost never happens, but this (to us) is a fail-safe condition, the auxiliary battery will still charge, and to fix it requires only some judicious banging on the relay to get it working again. The worst thing that can happen with a contactor is that the relay contacts will weld together if the big over-current happens while the contactor is trying to open. If you have a 1500 amp spike, the relay’s terminals can probably handle that, whereas MOFETS will simply fail, and when one fails the rest cascade like a waterfall. Seriously, we can design a solid-state battery isolator, but we like the forgiving nature of a big contactor. It uses state-of-the art microprocessor solid state control of the charging and isolation functions, but uses a solid tungsten points contactor relay to control the big currents.

Camper battery isolator relay wiring