How to best use a 12V fridge
Over the course of a year testing fridges for the Spring issue of Overland Journal, I started to notice the most important performance variable from one sample to the next had nothing to do with the fridge itself, but how it was used. I was also surprised to discover just how many overlanders didn’t maximize their 12V chiller’s full potential. Below are a few tips for the best results. Some are painfully obvious while a few others, perhaps not so much.
The cool down
The largest power load levied against any fridge comes during the initial cool-down as the unit struggles to bring its contents to the target temp. If you load your refrigerator then hit the road for a day’s drive, that power draw may be of little consequence. If however, you drive intermittently, stopping frequently causing your battery to shoulder the load of the power draw, you’ll risk exhausting your electrical storage capacity.
Pre-cool the fridge and contents: The most power efficient thing to do, if possible, is to use a 110V power source to cool your fridge and its contents before hitting the road. This is clearly not possible for those on extended travels, but for most of us weekend warriors, that solution is easily achieved.
Hyper cool the contents: With my unit plugged into a wall outlet prior to a trip, I often set the target temp to just a hair over the freeze point. I may even add a few frozen items before departure like my favorite libation, a quart of pre-mixed margaritas frozen hard as a brick. Once underway, I will often raise the thermostat to my preferred 40ºF. Should I stop frequently, which I’m prone to do, the fridge will often not even kick on as it’s being cooled internally by the hyper-cooled contents.
Keeping your cool
There are a handful of tricks one can employ to help your fridge maintain a low temp without an excess of power draw.
One out, one in: As stated above, cooling contents demands more power than maintaining the temperature of already cooled contents. If you pull a 12 pack of beers out of a fridge one by one over the course of a day, the fridge slowly becomes empty of its cooled mass. When you then plop a full 12 pack of warm cans in it, the fridge has to work extra hard to cool that warm mass. If you can, replace each cold item with a warm one; One beer out, one beer in. The large volume of pre-cooled beers, and other contents, will help cool the newly added warm beer.
Pack smart: In our extensive fridge and cooler tests using all manner of sophisticated thermal measuring instruments, we learned there can be as much as a 5-8ºF disparity in temperature between the top inch of a fridge and the bottom. For this reason, I always stack dense items, fluids mostly, as low as possible in the unit where the coldest air sinks. In that position, those fluids are able to cool fastest and they’re not as impacted by the warmer temps at the top of the unit.
Placement in the vehicle: Once again our extensive testing over the year illuminated interesting nuances in real-world performance. The same fridge used in the same manner, had variable performance outcomes depending on the vehicle it was paired to and was even affected by different placements in the same vehicle. Although not convenient or practical, anecdotal testing showed that placing a fridge in the center of a cargo area, away from as many windows as possible, could modestly improve thermal retention and efficiency. This isn’t rocket surgery. Avoiding sunlight on your fridge will naturally help keep it cool.
Insulated covers: Not all refrigerators are created equally and this also applies to insulated covers. Our controlled testing proved telling. Some fridges benefit greatly with the addition of an optional cover. Others, not nearly as much with the unit’s own thermal properties the largest contributor to thermal retention. If a particular model has marginal insulation but a thick and effective cover––it’s worth having. Covers also play into the aforementioned issue with solar heat. If you are forced to place your fridge by a large window where it’s likely to get cooked, covers can go a long way toward bolstering thermal retention.
Keep it closed: I did my best to quantify the impact of opening a fridge multiple times over the course of an hour, but it proved a tough metric to repeat and measure accurately. Suffice it to say, even with cold air inclined to sink in the unit and not spill out as it would with a front opening door, most units lost a considerable amount of cold air any time the lid was opened and subsequently closed. I could literally feel a rush of chilled air being expelled with each closing of the lid. My best summary would suggest that a premium $2,000 fridge opened repeatedly during the day will not perform as well as a cheap $500 fridge opened just two or three times a day. That’s an obvious no-brainer, but worth mentioning.
Dense contents work best: All refrigerators are designed to do more than maintain a cold interior space. They’re engineered to actually cool the contents to a specific internal temperature. Cooling 40 cans of beer requires more energy than cooling and equal volume of loosely packed bags of leafy greens. Once cooled, the fluids will hold their thermal value much longer, thus making them work to the advantage of the fridge’s efficiency. This somewhat leads us to the next and last point.
Keep it full to keep it cold: If you keep your fridge continually full by always replacing chilled items with warm items, it will work less to maintain your target temperature. When my fridge starts getting empty at the tale end of a trip, I often fill it with containers of water and chill them while I drive. If I arrive home with mostly cold water in my fridge, I’ve done well to eek out maximum efficiency. If all I have in my fridge on the last two days is lone beer and a baby carrot, the fridge will work hard to keep the interior of the fridge cool.