12V 140A Automatic Dual Battery Isolator Voltage Sensitive Relay Kit

12V 140A Automatic Dual Battery Isolator – Voltage Sensitive Relay (VSR)

The 12V 140A Automatic Dual Battery Isolator is a compact Voltage Sensitive Relay (VSR) designed to manage charging in dual-battery vehicle installations.

Ideal for vehicles fitted with a separate leisure or auxiliary battery, the isolator automatically connects the starter and auxiliary batteries when sufficient charging voltage is detected, allowing the vehicle's alternator to charge both batteries. When the engine is switched off and battery voltage falls, the batteries are automatically disconnected, helping prevent accessories connected to the auxiliary battery from draining the vehicle's starter battery.

With no manual switching required, the VSR continuously monitors starter battery voltage. At approximately 13.3V the relay engages, connecting the auxiliary battery to the charging system. When voltage falls below approximately 12.8V, the relay automatically disconnects after a short delay.

Features

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  12V automatic dual battery isolator

  
  


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  Heavy-duty 140A continuous current rating

  
  


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  170A intermittent current capacity

  
  


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  Voltage Sensitive Relay (VSR) operation

  
  


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  Automatically connects auxiliary battery at approximately 13.3V

  
  


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  Automatically disconnects at approximately 12.8V

  
  


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  Approx. 5-second switching delay

  
  


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  Helps protect the starter battery from auxiliary electrical loads

  
  


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  Allows alternator charging of an auxiliary or leisure battery

  
  


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  Fully automatic operation – no manual switch required

  
  


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  LED status indication

  
  


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  Compact design for convenient vehicle installation

  
  


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  Suitable for cars, vans, motorhomes, campervans, 4x4s, utility vehicles and other suitable 12V applications

  
  

Specifications

Voltage: 12V DC

Continuous Current: 140A

Intermittent Current: 170A

Cut-In Voltage: Approx. 13.3V

Cut-Out Voltage: Approx. 12.8V

Delay: Approx. 5 seconds

Operation: Automatic Voltage Sensitive Relay

Operating Temperature: -30°C to +105°C

Dimensions: Approx. 67.5 x 67.5 x 53.5mm

Weight: Approx. 200g

How It Works

When the engine is running and the starter battery voltage rises to approximately 13.3V, the isolator automatically connects the auxiliary battery, allowing the alternator to charge both batteries.

After the engine is switched off, system voltage begins to fall. Once it drops below approximately 12.8V, the isolator disconnects the auxiliary battery, helping preserve the starter battery for reliable engine starting.

This makes it ideal for dual-battery installations powering equipment such as lighting, refrigerators, inverters and other 12V accessories from a separate auxiliary battery.

Important: Designed for suitable 12V charging systems. Compatibility with smart/variable-voltage alternators and lithium battery installations should be checked before installation. Correct cable sizing and suitable circuit protection must be used according to the application.