Learn abour Isolators | Modern vehicles vs traditional vehicles

Vehicles have changed over the last 20 years, and with them so too as the standard dual battery isolator.

Why do you need an isolator in a dual battery system?

In the past, the typical dual battery system consisted of a main starter battery and either a secondary battery mounted under the bonnet or in the rear of the vehicle.

The isolator component of a dual battery system acts to separate the main start battery from the secondary battery.

It has always been important to reserve your main starter battery for the purpose of starting the vehicle, however, it is even more important nowadays with vehicles mostly consisting of automatic and push start designs. It's not as easy to just roll start the vehicle as what it was back 10 years ago.

The main starter battery of a vehicle usually consists of a wetcell chemistry. This type of chemistry battery has been designed to allow for cranking ability for starting purposes. A typical wetcell battery is not designed for deep cycle use, such as running a fridge. Using this type battery as a deep cycle will rapidly lessen its life. This particular type of battery is designed to use the top 10% of the battery for short heavy burst of power (starting the vehicle), then it is charged immediately from the alternator as soon as the vehicle starts. Each and every time an individual discharges a wetcell battery past this 10% capacity, the life is heavily reduced.

So what do you do if you want to run accessories from the vehicle with the ignition off?

Simple, install a dual battery system of some sort.

A dual battery system may come in the form of an under bonnet secondary battery, or a more portable option such as a battery box or portable battery pack.

Whatever the user chooses. they will require the use of a dual battery isolator to separate the start battery from the secondary AUX battery.

What types of Battery Isolators are on the market?

The major types of battery isolators are as follows:

  • Voltage Sensitive Relay (VSR)
  • Ignition activated Replay
  • DC Battery Charger (will act as a VSR unless over-ride is fitted)

Voltage sensitive Relay - Explained

The main type of battery isolator is the traditional Voltage Sensitive Relay, VSR. This isolator acts on the voltage of the starter battery to engage and disengage the relay only once the starter battery has reached certain voltages.

The typical VSR will open the charge to the secondary battery once the main starter battery reaches 13.2 - 13.4volts. It will then close the charging circuit when it has detected the main battery has reached <12.7 volts, usually indicating the ignition has been switched off.

What are the problems with using a VSR in new model vehicles?

The issue with new model vehicles is usually due to low voltage outputs. New model vehicles are required to comply with fuel emission targets, resulting in vehicle's being program to reduce their output once the main battery has fully charged.
Battery isolatorDc chargerDc dc

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