Low-voltage cut-off settings explained

Many compressor fridges have a built-in battery guard. Its job is to stop the fridge draining the battery too far, and the setting you choose decides how early it steps in. Here's how to read it.

What it does

• It watches voltage. Dometic says the system monitors the incoming DC voltage and turns the cooler off if it senses low voltage¹.
• Why it exists. It's designed mainly to stop the fridge draining the vehicle's starter battery and leaving you stranded².
• Three levels. High, Medium and Low¹.
• It comes back on by itself. Once voltage is restored, the fridge restarts³.

Which level to pick

ARB's advice, set out as a list:

• High. Use it when the fridge runs off the vehicle's starting battery. This preserves enough voltage for the vehicle to start after the fridge has switched off³.
• Medium. ARB says it suits a conventional dual battery set-up³.
• Low. Use it only if the fridge has its own dedicated power source, separate from the starter battery. Dedicated battery or solar are the examples ARB gives³.

Dometic's advice differs a little. It recommends High or Medium when the fridge runs from a starter battery, and Low for an accessory or dual battery². That's a good reason to read the manual for your own model.

The voltages behind each level

These numbers are ARB's, for a 12V fridge³. Other makers use other values, so look up your own model in its manual.

• Low. Switches off at 10.1V and restarts at 11.1V³.
• Medium. Switches off at 11.4V and restarts at 12.2V³.
• High. Switches off at 11.8V and restarts at 12.6V³.

Notice that each restart voltage sits above its switch-off voltage. The battery has to recover a little before the fridge comes back.

Why a full-looking battery can still trip it

• The fridge checks the voltage under load. Dometic explains it uses the voltage while the compressor is running, not the resting voltage².
• So a battery reading 12.8V at rest can dip when the compressor starts². That dip is what the fridge sees.
• Extra connectors make it worse. Dometic warns that splitters, pigtails and extensions can add line loss, meaning voltage drops along the cable². Don't use them.

If it keeps cutting out

• Try one level lower. Dometic says if the protection is on a recommended setting and the fridge still won't start, try one level lower, for example High to Medium².
• Think first. A lower level lets the battery sink further. On a starter battery that's the very risk the setting is there to prevent. If the fridge keeps tripping, the battery or the wiring may need a look from a licensed auto electrician.

Batteries have their own limits

The fridge's cut-off is only one guard. The battery maker sets its own limits.

• Follow the battery maker's manual for charging and storage limits.
• Lithium-ion batteries can be a fire or explosion hazard because they contain flammable electrolytes⁴. High temperatures or mechanical damage can make the reaction inside a cell run explosively⁴. Don't keep using a damaged battery.
• Don't charge or store a battery outside the limits in its manual.

Safety

Changing the setting is a button press. Cables are another matter.

• Isolate the battery before a battery, fuse or fridge lead is joined or taken off. No exceptions.
• Work from the manual for your own fridge and battery, since the steps and warnings differ between models.
• Hesitating? A licensed auto electrician is the person to call. This isn't routine DIY.
• Mains-side jobs such as permanent wiring or a grid connection need a licensed electrician in Australia. Don't attempt them yourself.

To turn all this into hours of running time, see how long a battery will run a fridge.