Battery Isolator
A 12V 140A battery isolator is an automatic power management device, typically a Voltage Sensitive Relay (VSR), designed to manage the charging of two separate batteries in a vehicle or marine system while ensuring they do not drain each other
Function and Operation
Purpose: The primary function is to allow a vehicle's single alternator to charge both a main (starter) battery and a secondary (auxiliary or house) battery. It prevents power draw from accessories (like fridges, lights, or winches) on the secondary battery from draining the main battery, thus ensuring the main battery always has enough power to start the engine.
Automatic Operation (VSR): Most modern 140A units are "smart" and operate as Voltage Sensitive Relays.
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Connects for Charging: When the engine is running and the main battery reaches a preset voltage (typically around 13.3 volts), the isolator automatically engages and links the two batteries so the alternator can charge both.
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Isolates When Off: When the engine is turned off and the voltage drops below a certain threshold (typically around 12.8 volts), the isolator automatically disconnects the batteries, isolating them from each other.
Zero Voltage Drop: Unlike older diode-based isolators which can cause a voltage drop and generate heat, VSRs are designed to have zero voltage drop, providing more efficient charging.