Car Fridge

What makes a car fridge different from other electric coolers

A car fridge is the compressor branch of the electric cooler family, sized and wired for a vehicle. The table on this page keeps only compressor fridges whose maker or listing says they run on 12V DC. That rule drops the thermoelectric coolers, which can only hold a fixed number of degrees under the outside temperature, and it drops anything that needs a wall outlet to work.

What's left is a box that behaves like a refrigerator. You'll see it called a 12V fridge, a 12 volt refrigerator, a truck fridge or an overland fridge. Same idea every time: a compressor, a thermostat and a plug that fits your dash socket. The overview of the whole group, thermoelectric included, is on the electric cooler page. This one is about the vehicle side: the battery, the wiring and the space in the back.

How a 12V fridge works

Penn State's energy course has the cleanest explanation I've read. A refrigerator is a heat mover. Inside the box, cold refrigerant soaks up heat from the food and evaporates. The compressor squeezes that gas, which makes it hot. It sheds that heat to the outside air through the condenser, turns back to liquid, squeezes through an expansion valve, gets cold again and goes back for more. Pushing heat uphill like that costs energy, and in a car fridge the energy comes out of your battery.

The thermostat runs the show. One fridge maker's FAQ says its unit cycles on and off under thermostat control, so the average current is much lower than the maximum. That's the number that matters for your battery. The maximum is what it pulls while the compressor runs; the average is what it costs you overnight.

One compressor design gets a mention because it changes how you mount the box. A maker that uses a swing-motor compressor says its fridges run at up to 30 degrees off level. Other makers want the fridge on a flat, level surface. Check the manual before you wedge one sideways behind a seat.

What to look at when you pick a car fridge

The table shows what the makers or the listings state: DC input, AC power, capacity, zones, lowest temperature, battery protection, solar input, exterior size and weight. For a vehicle, I'd read them like this.

DC input: 12V, or 12/24V

Every fridge on this page runs on 12V DC, which covers car and pickup sockets. Many also take 24V, which matters only if you drive something with a 24-volt system. One maker's manual says the supplied DC cable plugs into the vehicle's cigarette lighter socket, and that the same fridge needs its AC adapter to run at home.

Amp draw is the spec the table can't show you

Draw isn't a table column, because makers state it in different ways. Some list a range, some a maximum, some a wattage. One maker lists a small 12V compressor fridge as variable from 0.66 to 2.75 amps. Another gives its 40-liter chest model a maximum of 2.5 amps at 12.8 volts. A third lists maximum power in fast-cooling mode at 50 to 85 watts across its lineup, and adds that these are lab figures and actual draw depends on conditions.

Quick conversion, if a maker only gives watts: watts divided by volts is amps. So 50 watts at 12 volts is a bit over 4 amps while the compressor runs flat out. Nobody's fridge runs flat out all night unless the lid is open or the truck is parked in the sun. (Exhibit A: every lunch stop where somebody "just checks" what's in there. Usually me.)

Battery protection is the setting that saves your morning

Battery protection works like a low-voltage switch. When the battery drops to a set voltage, the fridge shuts off, and it turns back on when the voltage recovers. One maker's manual lists three levels for 12V use:

• Low: cuts off at 9.4 V, back on at 10.4 V
• Medium: cuts off at 10.9 V, back on at 12.0 V
• High: cuts off at 11.6 V, back on at 12.7 V

Higher cutoff means the fridge quits sooner and leaves more in the battery to crank the engine. The same maker says to set the level for your vehicle battery and recommends medium. Its FAQ recommends the low level when the fridge runs from an external power bank, since there's no engine to start. A fridge with no battery protection listed is one you unplug when the engine stops.

Capacity: measure the cargo area, then pick quarts

The table shows capacity in quarts. Because no space goes to ice, a car fridge can be a size smaller than the ice cooler you're used to. Every extra quart is also extra box to keep cold, and in a car that comes out of the battery; the FAQ below has one maker's sizing advice.

Then the tape measure. Exterior size in the table is length by width by height. Measure your cargo floor, and measure the height with the lid open, because a car fridge you can't open is just a heavy footrest. (Renee would like it noted she said this first. It's noted.)

Weight: it rides full

Weight in the table is the empty fridge. Add the food and drinks, and that's the load on your tie-downs, on a fridge slide and on your back lifting it over a tailgate. If one person has to unload it alone at the cabin, read this column before the capacity column.

Zones, temperature and AC power

A dual-zone car fridge splits the box so one side freezes and the other chills. One maker's dual-zone models let you set either side anywhere from 50°F to -8°F. If the stated low is 0°F or colder, the fridge can work as a portable freezer on the drive home.

AC power means the fridge can run from a wall outlet at home or at the cabin, which gives the vehicle battery a rest. That's also the easy way to pre-chill it the night before you load the truck. Unplug the DC lead first; at least one maker tells owners never to feed its fridges from both sources at once.

Solar input still needs a battery

A yes in the solar column means the maker or the listing states the fridge works with solar. In a vehicle that means a panel on the roof or the hood feeding the second battery described below, never the fridge itself. Panel setups are covered on the solar cooler page.

How to power a 12V fridge while camping

This is where a car fridge is won or lost. A charging-gear maker spells out the problem: once you stop, the fridge keeps drawing power from the car battery and drains its charge.

You have four practical setups:

1. Starter battery only, while driving. Fine for road trips with daily driving. Set battery protection to high when you park. The same maker notes that a fridge set a little colder than needed can often ride out a night unpowered.
2. A second battery. A dedicated battery runs the fridge while the starter battery stays reserved for the engine. The charging-gear maker recommends at least one secondary battery for a 12V fridge setup.
3. A DC-DC charger. It charges that second battery from the alternator while you drive, per the same maker.
4. A portable power station or battery pack. It keeps the fridge off the vehicle's electrical system entirely; use the low protection setting.

My one opinion on this page: if the fridge runs overnight, run it from a second battery, not the one that starts the truck. The reason is right in a fridge maker's FAQ: a single battery also has to start the car. A dead fridge loses you some milk. A dead starter battery at the end of a two-track road loses you the morning hunt.

Quick math for battery run time

The charging-gear maker's example uses a 110 Ah battery and a fridge drawing 5 amps. Discharging only to about 50%, which it says reduces stress and extends battery life, that's about 10 hours. Its sizing table for three days at 60% discharge suggests roughly:

• 35 to 52 liter fridge: about 100 Ah
• 50 to 65 liter fridge: about 120 Ah
• 65 to 85 liter fridge: about 150 Ah

A fridge maker adds the worst-case method: divide your battery's amp-hours by the fridge's maximum draw. Real run time is longer because the compressor cycles, and shorter on hot days with the lid opening every hour.

Jess's take, written in the margin of my wiring diagram: "Amp-hours are a budget. The lid is the spending." She's right, and she charged me nothing for it.

Mounting a car fridge in a truck or SUV

A loose fridge in a moving vehicle is a heavy passenger with no seat belt. Mount it like you mean it.

• Tie it down. Use the fridge's tie-down points and real straps, not a bungee.
• Pack it securely. One maker's manual says to arrange the contents securely when the fridge rides in a moving vehicle.
• Give it air. One slide maker's fitting instructions call for 50 mm (about 2 inches) of ventilation on all sides of the fridge.
• Mount slides to something solid. The same instructions say the mounting surface must support a fully loaded fridge with the slide at full extension.
• Look before you drill. Check under the mounting surface for fuel lines, brake lines and the fuel tank first, per the same instructions.
• Leave the drain reachable. If the fridge has a drain, mount it so you can open it without unloading the whole truck.

If you get a voltage error the moment the compressor starts, one maker's manual blames small wiring imperfections that cause a voltage drop at start-up, and suggests trying a lower protection level and measuring the battery voltage. Translation from an electrician: the socket and the wire between it and the battery matter. Trust the wiring, but measure it.

Car fridge safety

Have a second battery or hardwired circuit installed by a qualified auto electrician, as the charging-gear maker recommends. One fridge maker's manual says its supply line is protected by a 15-amp fuse inside the fridge, and that a damaged power cord must be replaced by qualified personnel.

Who should skip a car fridge

If you drive to a cabin with a working refrigerator and stay put, the drive is the only part a car fridge helps with, and an ice cooler covers that. If your trips are day trips with a stop for ice, a thermoelectric cooler or a hard cooler costs less in every sense. And if you live in an RV, a fridge designed to stay put is on the RV fridge page.

For everybody else: battery first, protection level second, tape measure third. And yes, the fridge gets its own seat belt. Technically, it's a strap.