Low Voltage Disconnects

Starter batteries, also called cranking batteries, are made to deliver quick bursts of power to start the engine. They are not designed to run devices for long periods. If you plan to tour and power appliances often, using a starter battery is not ideal. Doing so can cause damage to the battery.

Before voltage-sensitive relays were common, people connected the starter battery to the auxiliary battery. This setup would continue to draw power even after turning off the engine. To prevent this, you had to disconnect the two batteries manually. This process was inconvenient and easy to forget.

With a low voltage cut-off or voltage-sensitive relay, you don’t need to worry about draining your batteries. These devices disconnect automatically, protecting your batteries from damage. They can be installed between the starter battery and the auxiliary battery. If you use a deep cycle battery with solar or a smart charger, an LVD can go before the fuse box.

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

A Voltage Sensitive Relay (VSR) detects when your car battery is charging. It connects the starter battery to the auxiliary battery, allowing both to charge at the same time. When the car is off, the relay disconnects the batteries. VSRs, battery isolators, and low voltage disconnects (LVDs) all perform similar functions. Some VSRs come with a manual override, letting you connect the batteries even when the car is off, which can help jump-start a dead cranking battery.

A Voltage Control Relay offers more control. You can set the desired voltage for charging. When connected, the batteries charge and discharge at the same rate. These devices cut off power to the appliances or dual battery when the main battery’s voltage drops. For example, if your cranking battery drops to 11.8v, you can set the relay to prioritize charging it until it reaches a healthier level, like 12.5v, before charging the auxiliary battery.

LVDs only stop charging the secondary battery when the car is off. So, if you accidentally drain your cranking battery, an LVD might not be ideal. A Voltage Control Relay gives you more flexibility in how each battery is charged.

Keep in mind, these devices are for cars made before 2006 or those without smart alternators. For newer cars, a DC to DC smart charger is a better option, as it regulates the alternator’s fluctuating charge.

For the best low voltage disconnects, we recommend the Redarc Smart Start range or Baintech low voltage relays. These solutions are ideal for older vehicles without smart alternators, offering a simple and cost-effective way to protect your batteries. If your LVD frequently cuts power, it might be time to expand your battery system. Always check if you're using a 12v or 24v system and confirm the amp rating of your LVD before installing.

What is a low voltage disconnect?

A low voltage disconnect (LVD) is a device that protects your battery from being drained to a level that could cause damage. It automatically cuts off the power supply to connected devices when the battery voltage drops below a set point. This prevents the battery from discharging too much, which can help extend its lifespan and ensure you have enough power left to start your vehicle.

How Does a Low Voltage Disconnect Work?

An LVD monitors your battery’s voltage level in real-time. If the voltage drops below a safe threshold, the LVD will disconnect the battery from all non-critical devices. This stops the battery from losing more charge and protects it from damage. Once the battery is charged back up to a higher, safer voltage, the LVD will reconnect the devices automatically.

Do lithium batteries need a low voltage disconnect?

Some lithium batteries (LiFePO4) come with a built-in Battery Management System (BMS) that provides low voltage protection. However, not all lithium batteries have this feature. In cases where the BMS is not present, using an external low voltage disconnect is essential to avoid over-discharge. Even if your lithium battery has a BMS, some people still prefer to use an external LVD as an added safeguard, especially when running sensitive equipment. This way, if the internal system fails, the LVD will still prevent the battery from dropping to harmful levels and protect your devices.

What is the low voltage cut off for a 12 volt and a 24 volt battery?

For a 12-volt battery, the recommended low voltage cut-off should be set between 11.1 to 11.8 volts. Allowing the battery to drop below this range can reduce its lifespan and increase the risk of permanent damage.

For a 24-volt battery, the cut-off value should typically be set between 22.2 to 23.4 volts. This range ensures the battery is not over-discharged, helping to maintain a healthy charge cycle.

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!