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A 12 Volt Behind-Seat Cooler for Model 3


Dec 13, 2018
Los Angeles
For a 6,000+ mile trip in our Model 3 from the Pacific to Atlantic Oceans during the hottest part of Summer 2019, I found this
Koolatron P20 Thermoelectric Digital Precision Control Cooler TC-2.
P20 behind seat.jpg

P20 door open behind seat.jpg

The P20 fits behind the driver's seat - barely. Actually, for the lid to open without interference from the back of the driver's seat, we tilt it rearward perhaps 10 degrees. This still doesn't compress the rear seat cushion. I've got short legs, so fitment may be trickier for some, and compressing the cooler against the rear seat cushion can probably buy a few inches of front legroom. We've always positioned the cooler behind the driver so the front passenger can safely do all the fishing around for snacks - those of you with really long legs might have to locate the cooler behind the passenger.

The P20 is quite roomy - 18 quarts. You could carry a couple of dozen 12 ounce cans, and we traveled with fruit, cheese, and ham as well as drinks. I built a divider out of corrugated plastic which kept the perishable foods closest to the cooling unit and allowed access to those supplies as they were consumed while holding back a full stack of canned drinks.

P20Can fit.jpg

The Koolatron is cooled thermoelectrically. and the manual claims that its typical performance can bring the contents of the cooler to 25C/45C below ambient temperature. So if the P20 is in a 100 degree F space for an extended period of time, the contents will only be able to cool down to 55F. The interior of a car can exceed 140F on a sunny summer day. The Koolatron, like all similar thermoelectric coolers, can't move heat very quickly, so you can't expect it to quickly chill a warm drink to drinking temperature. If you load it with a dozen 100 degree cans from the frunk, the whole interior of the cooler will warm up for a while as the cooler slowly moves the heat outside the cooler (into the interior of your Tesla, which will then move that heat outside the car via the HVAC system). But the system does work just fine. Better, in fact, than those we've used in years past, because of an important quality of the Tesla: Cabin Overheat Protection.

Here's what made the Koolatron P20 work for us:
  • Whenever possible, I pre-cooled the P20 indoors while plugged into an AC to 12-volt DC adapter. The P20 has a carry handle.
    P20 handle.jpg
  • I had the Model 3's Cabin Overheat Protection set to "ON" during our trip (this runs the A/C system to keep the cabin below 105F). This serves to limit the maximum air temperature around the Koolatron, which is pretty well-insulated for its relatively thin walls. Most of the trip, our stops were limited to 10-20 minute Supercharging stops and perhaps an hour-long meal daily, so the impact of Cabin Overheat Protection did not penalize our range.
  • Even when left in triple-digit heat and blazing sun, the contents of the P20 remained cool thanks to insulation. Adding external insulation (a blanket, etc.) would further buffer the contents against temperature change.
  • I carried the Koolatron indoors and plugged in to AC in every hotel room overnight. I used an AC adapter we've had for 25 years that I've used with other 12-volt coolers. (You'll need an AC adapter with a 12-volt "cigarette-lighter" socket and a capacity higher than the Koolatron's 4.5A. Our old power supply was only 5.0A, and it got pretty warm, but it worked every day.)
    AC DC converter.jpg
  • Between the Model 3's console 12-volt Power Socket and the Koolatron, I used an old Igloo Kool Mate Battery Guard. This is a device which prevents accessories from discharging the vehicle's 12-volt battery by disconnecting the accessory below a voltage threshold (i.e., 11.5 volts). Tesla's documentation says the Power Socket is only energized when the touchscreen is on, so I don't think you're going to draw down the Model 3's 12-volt battery by leaving the Koolatron plugged in. But since I had it, I used it.
    Igloo Kool Mate Battery Guard.jpg
Since we were carrying perishable foods, I frequently monitored the temperatures in the P20. The bottom of the cooler nearest the thermoelectric heat sink would stay around 40F, and the top of the cooler might approach 50F. After a night in a cool hotel room, the cooler temp might get down to 38F. It's not a refrigerator (ideal refrigerator temps are below 36F), but as long as you're conscientious or simply want cool drinks, it's fine.

Koolatron's documentation says that the P20 pulls 4.5 amps of current when its heat pump is running. Tesla claims that the Model 3's console Power socket can supply 12A continuous (16A peak). So there's theoretically more current available to run other devices.

NOTE: I discovered the hard way after tripping a virtual circuit breaker in the Model 3 (NOT with the Koolatron, but with a faulty USB adapter) that there is no easy way to "reset" the breaker and restore power. Users are just expected to... wait. It's taken 24-40 hours both times I've tripped a breaker. Subseqently, I've read that performing this Tesla Model 3 Hard Reset procedure can reset circuit breakers immediately, but I haven't had the occasion to try it. (Some may find this procedure too intimidating.)


I'm very pleased to have found an electrically-powered cooler that fits in the Model 3, has good capacity and reasonable cooling power, and can run from the Tesla's 12-volt Power Socket.


Koolatron P20 User Manual PDF
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