The Battery Isolator Relay Delay/E is a reliable approach to charging multiple batteries on a vehicle.

It provides a delay to allow the engine to briefly "warm up" and to recharge the main battery before placing the heavy load of a discharged auxiliary battery on the alternator. It also allows the use of self-exciting alternators.　

How It Works

Isolator Function

The unit operates as an isolator by sensing the level of voltage on the chassis 12 volt system. When this voltage goes above 13.3 volts for approximately 12 seconds, as happens when the engine is running normally (normal alternator output voltage is approximately 14.4 volts), it will close the isolator relay providing charging current to the coach battery. When the ignition switch is turned off, the relay will open immediately.

If the voltage should fall below 12 volts for more than two seconds while the ignition is on, the relay will drop out to feed all the alternators available output to the chassis battery to keep the engine running. This might happen when the alternator is not able to supply sufficient current to all of the loads. When the chassis voltage goes above 13.3 volts again, the relay will again close in about two seconds to retry and charge the coach battery. The resultant flickering of lights would alert the driver of the system overload.