Special and complex applications are necessary in order to charge the auxiliary battery in vehicles such as trailers, VIP vehicles or boats. The reason for this difficulty is to parallel the main starter battery and the auxiliary battery with one alternator when the engine is running and to separate them when the engine stops so, there is no need for a second alternator for charging the auxiliary battery. And more importantly, even if the main battery is used up, the cranking is not a problem as the auxiliary battery is full.
 

ELO Dual Battery Isolator - Voltage Sensitive  Relay performs this task automatically. The relay measures the voltage of the main battery continuously. When the voltage of the main battery reaches 13,6V for 12V or 27,0V for 24V (fully charged), it also starts the charging of the auxiliary battery. At such time, both batteries are paralleled and charged simultaneously. When the engine is stopped, the voltage of the batteries start to drop from the peak point of 14,2-13,8 for 12V or 27,6-28,5 for 24V. ELO Dual Battery Isolator - Voltage Sensitive  Relay disconnects the batteries when they reach nominal voltage of 12,6V for 12V or 25,0V for 24V in order to ensure the electrical consumption is solely supplied from the auxiliary battery and the main starter battery is kept enough charged to start the engine.
 

There is a delay of 10 seconds before the paralleling process and 60 seconds before the separation process. Thus, in case of sudden changes of consumption, ELO Dual Battery Isolator - Voltage Sensitive  Relay does not perform unnecessary switching operations and the system operates stable. A red LED on the relay flashing frequently indicates that the main battery is full and the auxiliary battery charging will start shortly. If the LED is lit continuously, this suggests that the relay is in operation and both batteries are connected in parallel and charged together. The red LED blinking slowly indicates that the engine is off, the alternator is not generating electricity, and the auxiliary battery will be separated from the main battery shortly.