Engineering:Voltage-sensitive relay

A voltage-sensitive relay (VSR) is a relay used for automotive, truck and marine applications.

A VSR senses the input voltage generated and automatically connects or disconnects the appliance or circuit at pre-set voltages for a variety of applications. It is typically used to prevent over-discharging of a car battery and is very common in a dual-battery system.

A VSR is usually classified into 12 V – 24 V range with varying electric current. A single-sense relay only detects voltage at one pole while a dual-sense relay detects voltage at both poles.

An ignition-protected voltage-sensitive relay can withstand repetitive engine cranking transients without significant effect.

VSRs are inexpensive and offer little or no voltage drop. However, the relay may chatter (repeatedly open and close at very short intervals) if the voltage is not stable.