Voltage Sensitive Relay (A Smarter Version of Old Split Charge Relays)

Sale price£53.60

Customer Reviews

Based on 1 review
Fraser Campbell
VSR - Not suitable for engines with smart alternator

I have one of these in my T6 Caledonian Conversion. Due to the engine having a ‘smart alternator’ it just doesn’t deliver enough of a consistent charge to be compatible with a VSR (voltage sensitive relay). This means you can drive for hours to your destination and arrive to find your leisure battery at the same charge as when you left, or even worse! The only way around this is to get a DC - DC charger, which I’m now upgrading to.
Imagine it works fine with old fashioned engines and alternators but they’re no just for those with a modern vehicle, wanting to go off grid and reliant on engine charging.

Fraser, Thanks for highlighting this. We do indicate that the product is not compatible with T6 vans. Please return it to us for a full refund.


This item is rated at 140Amp, which is ideal for campervan conversions.

It's a clever little bit of kit which makes charging your Leisure Battery really easy. The unit senses the voltage of both batteries that it is connected between. If either battery is receiving a charge, the VSR will activate paralleling the two battery banks.

The VSR is compatible with situations where a battery charger or second charging source is attached to the leisure battery. They are so reliable many are fitted to blue light emergency vehicles.

When the engine is started and the van battery reaches 13.7 volts, the VSR engages, allowing both batteries (van and leisure) to be charged simultaneously. When the voltage drops below 12.8 volts (eg the engine is stopped), the VSR disengages, separating the batteries. This system eliminates the possibility of draining the starter battery and protects sensitive electronic equipment powered from the house battery from harmful engine start up spikes.


This is not compatible with VW T6 vans.


Advantages of fitting a VSR over conventional charge (diode isolators):

  • Easy 3 wire connection at the battery
  • No need to bypass existing alternator wiring
  • VSRs have no volt drop. Conventional diode isolators incur a minimum of 0.6 volt drop
  • Compact size - No large heat sink 
  • Cost effective solution 
  • Dimensions: 69L x 69W x 50H mm (2.7L x 2.7W x 2H inches)
  • LED lights to show when connection is made
  • Simply attach your car and leisure battery positive terminals to the two lugs, and connect the small black wire to a ground source and that's it.

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