Voltage Sensing Relay (VSR) 140A

Voltage Sensing Relay (VSR) 140A

A battery to battery charger allows you to charge your leisure battery while you drive.



Voltage Sensing Relay (VSR) 140a Split Charging

12V, 140A rated voltage sensitive relay for split charging applications in camper vans, motorhomes, 4x4s and boats. Allows charge to flow into one battery (or bank of batteries) only when a charging voltage is detected at the other battery (dual sensing operation).

Dual sensing operation

Charges from starter battery to leisure battery when alternator is running and charges from leisure battery to starter battery when mains charger is connected.

  • Relay connects when sensed voltage reaches 13.7V or higher,
  • Relay disconnects when sensed voltage drops to 12.8V or lower,
  • Maintains battery isolation when not charging, so starter cannot be drained by leisure use and vice-versa,
  • Ignition protection to UL1107,
  • Fully automatic operation,
  • E Mark approval,
  • Virtually zero voltage drop,
  • Protects sensitive electronic equipment from harmful engine start-up spikes,
  • Well proven design with 1000’s of units operating in the field,
  • Terminal connections marked on inside of unit for easy installation.

Note: The benefit of this type of relay is that it does not require a connection to the alternator or any modifications to the existing vehicle electrical system. Simply connect the +ve terminals on each of your batteries to the terminals on the relay and the black relay wire to a common -ve point.

An LED indicates when the relay is ON (contacts closed). Fixing holes in the body allow the unit to be mounted to a bulkhead and body cut-outs offer various cable routing options.

Fully encapsulated electronics make this unit splashproof and particularly suitable for harsh environments (marine use, vehicle engine bays etc.)

Sold individually.


These relays are not suitable for vehicles with ‘smart’ or ‘intelligent’ alternators. As a guide this applies to vehicles having engines that comply with Euro5 emissions standards and onward, often also incorporating regenerative braking (if in doubt please consult your vehicle manufacturer to confirm). If your vehicle has a smart alternator then you will need to use a battery-to-battery charger instead of a VSR.

Additional information

Weight 1.3 kg
Dimensions 18.6 × 13 × 7 cm

Batteries and Solar

Input Voltage


Output Voltage






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