Voltage Sensitive Relay 12v 140A For Leisure Battery Charge

Truck ElectricsSKU: 280020

In stock


VSR Voltage Sensitive Relay - 12v 140A

This simple device allows the charging of two separate battery banks from a single charging source such as vehicle alternator with no risk of flattening your battery bank.  By sensing the main battery voltage, the VSR (voltage sensitive relay) will only connect the secondary bank to the source when the first bank is fully charged. This ensures that the secondary bank can never drain the main bank.

Dual sense allows the unit to sense the voltage of both batteries that it is connected between. If either battery is receiving a charge the VSR will activate. This allows the charging of the second battery from an external battery charger or second charging source.

The VSR can handle charging currents up to 140A with zero voltage drop, no moving parts and encapsulated design makes it suitable for marine applications as well as split charging systems in vehicles.


  • Continuous Rating : 12VDC/140 amps
  • Sense: Dual
  • Engage Voltage: 13.7VDC
  • Disengage Voltage: 12.8VDC
  • Ignition Protected: UL1107
  • Stud: M6
  • Ground : Negative, 0.5M/18 AWG wire
  • Weight: 0.2Kg
  • Dimensions: 68mm x 68mm x 49mm
  • Mounting Screws: 4.8 x 50mm and 3.5 x 13mm
  • Direct alternative to the Durite 140A VSR
  • Complete with E Mark approval
  • Not suitable for vehicles fitted with smart alternators

vsr electrical drawing


How It Works:

The VSR allows two batteries to be charged at the same time.  When the engine is started and the start battery reaches 13.7 volts the VSR engages allowing two battery banks to be charged at the same time.  When the voltage drops below 12.8 volts the VSR disengages, separating the two batteries.  This system eliminates the possibility of draining the wrong battery and protects sensitive electronic equipment powered from the house battery from harmful start up spikes.

Once the start-up battery voltage rises to above 13.7 VDC the VSR switches to charge both batteries in parallel.  When the voltage drops below 12.8 VDC the VSR disengages.  A buzzer-like sound may be heard as the relay quickly switches in and out.  Disengagement can occur at idle or if the house battery is at a low charge.  An increase of the engine's RPM will increase the alternator output and hold up the voltage.



Truck Electrics serving Ireland, UK and Europe. To browse and purchase more products and view our current for sale and clearance offers please go to the truckelectrics.com home page.


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