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Car batteries or cranking batteries are not designed to run devices or appliances for a long time as they are wired to produce a lot of power very quickly to the starter motor, so if you do plan on touring and using electrical devices often, using your car battery is not recommended. Before voltage sensitive relays existed, people used to connect their main battery to the start battery and run devices like this, but soon realised this would continue to draw power from the cranking battery as well. To counter this when they would turn off the car and use their appliances, they would have to remember to switch off the connection between the two, which is still just as annoying and inconvenient. So, to avoid having to pop the hood and disconnect manually, a voltage sensitive relay or low voltage cut off is the way to go. They can be installed anywhere after the cranking battery and before the dual battery, or if you are just running a deep cycle battery, perhaps off a solar panel or smart charger, an LVD can be installed before the fuse box/appliances. 

But what’s the difference between a Voltage Control Relay, a Low Voltage Disconnect, a Battery Isolator and a Voltage Sensitive Relay?  

Voltage Sensitive Relay = a device that will detect when your car battery is charging, this device will engage and connect your starter battery to the auxiliary battery to charge together at the same time. When the vehicle is switched off it will disconnect from the main battery. Essentially a Voltage Sensitive Relay (VSR), a Battery Isolator and an Low Voltage Disconnect (LVD) will do the same thing. Some Voltage Sensitive Relay’s will come with a manual override switch that will connect the two batteries even when the car is off, meaning if you are in a real jam there are voltage sensitive relays that will allow charge to be reversed so that you can jump start the cranking battery from the auxiliary. 

A Voltage Control Relay is slightly more advanced with the capability of setting your desired charge input in some cases. It’s important to remember that when batteries are connected, they will discharge and charge at the same rate equally. Put simply these devices can cut off power supply to an appliance or dual battery when the main battery drops. A Voltage Control Relay allows you to a pre-set it to a voltage input of your choosing, even when the car is turned off. For example, if you accidentally leave your headlights on and drain the cranking battery to the dangerously low charge of around 11.8v, you’ll want to make sure as you drive, your starter battery is prioritized. Setting your Voltage Control Relay to around 12.5 volts will give your main battery a chance to charge to more favourable state, before allowing the connection to the auxiliary battery to start. A low voltage disconnect will only stop charging the secondary battery when the car is off, so in the case of accidentally discharging your cranking battery an LVD may not be the most ideal choice. A voltage control relay will essentially allow you to have more flexibility in how you charge either battery. The super important thing to remember is that all of these devices are designed to be used in cars prior to 2006 or any car without a smart alternator as the design was changed to fluctuate charge depending on the temperature and output of the engine, in which case we recommend looking into a DC to DC smart charger which can regulate the output of smart alternators when hooked up to a dual battery system. 

If you’re looking for the best low voltage disconnections Australia has to offer then we highly recommend the Redarc Smart Start range of low voltage relays, low voltage cut outs, battery isolators, battery isolator switches, or even some of the low voltage control relays we stock from Baintech. A lot of older vehicles that do not have smart alternators will use this method as it is a simple and relatively cost-effective way to protect cranking batteries. If your Low Voltage Disconnect (LVD) is often cutting off power to supplies, it’s a good sign you might need to expand your battery system. Always remember to be aware of whether you are running a 12v or 24v battery system and how many amps your low voltage disconnect is rated to before installing. 

Why Buy Your Low Voltage Disconnects from Outback Equipment? 

  • A Huge Range of Stock 

  • Aussie Owned and Operated 

  • Battery Chargers Delivered to Your Door 

  • Plenty of Payment Options 

Order Your Battery Isolators For Your Vehicle Today 

Secure the life of your batteries when running a dual battery system on your vehicle with Outback Equipment. Browse through our huge range of low voltage disconnects and battery isolators online today!