I want to travel with my dog and many times I have to go into a store where I cannot take my dog, but would worry about the heat in the summer building up while I am absent with the car turned off. Is there some sort of unit that is available to turn on with the car OFF while I run into a store or restroom, etc. thanks to all that respond, p

  • Not that I know of. Take the dog in the store as a service dog... – Moab May 25 '18 at 22:38
  • There are solar powered fans that clip over your door window. Better than nothing. – mike65535 May 26 '18 at 1:53
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    Don’t leave the dog in the car... – Solar Mike May 26 '18 at 4:55

Consider the power needs of an A/C unit. The Prius one is about 1 kW and runs off the high voltage traction battery. It would require 90 amperes if run from a 12V battery, but it doesn't because it has a higher voltage.

A 50 Ah battery could in theory provide 600 watt-hours, meaning 36 minutes of runtime. However:

  • There is Peukert's law meaning you get less capacity with increased current draws. The 50 Ah capacity is valid at 10 or 20 hour rate, not at 36 minute rate! At 36 minute rate, flooded batteries with alpha=0.33 have 3.3 times less capacity at 90 amperes when compared with merely 2.5 amperes, i.e. the intended 20-hour discharge rate.
  • Lead-acid batteries don't like deep discharge. Thus, you should be using only at most 20% of the battery capacity, i.e. 7.2 minutes without Peukert's law effects, and 2.2 minutes with Peukert's law effects.

Is 2.2 minutes of runtime enough for you? If it is, you could connect a 12-volt A/C unit to the 12V battery without damaging the 12V battery. Remember to use thick wiring rated for 90 amperes!

For me, I would say 2.2 minutes isn't enough to be of any use. The car won't get very hot in 2.2 minutes. For a duration of 2.2 minutes, the dog won't suffer even without any A/C.

From experience, I can say that in my 2016 Toyota RAV4 hybrid, the A/C compressor won't run for long using the 1.6 kWh traction battery. It occasionally needs to start the engine, i.e. the prime mover. The battery is just a temporary energy storage bank.

Solar power would be a relatively good choice for air conditioning. Air conditioning is needed whenever sun is shining and thus solar power is available, and the electricity produced from solar power should be barely enough to remove the excess heat caused by the same solar power. However, cars have relatively small roof area and large windows. You would need to cover the entire roof and also probably the hood for the solar power powered A/C to work.

Most solar power units are just ventilating units designed to circulate air. Better than nothing, but not enough to leave a dog in a car! This should be evident from the small size of their solar panels.

Edit: justification for solar power: commercial polysilicon cell efficiency is about 17%. At the same time, EER is about 12 for a very efficient air conditioner, meaning COP is about 3.5 (i.e. 3.5 kW of cooling for 1 kW of input). Thus, 3.5 * 0.17 = 0.595, meaning 59.5% of heat per square meter can be removed per each square meter of solar cells. So, you would need 1/0.595 = 1.68 times the cell area when compared with the area you need to cool. Barely possible, if you cover the entire roof and hood with solar panels. And this assumes good polysilicon solar cells and very efficient A/C system. With multijunction solar cells, you could achieve over 40% efficiency, but then again those are used only in space applications, so they have a huge price and are very hard to find.


They make small portable "air conditioners" for cars, they have a fan and are powered by plugging into the cigarette lighter/power port.

These units are not "air conditioners" in the way you may be thinking of, because they do not have a compressor driven refrigeration cycle like your car air conditioner. They are a fan-driven heat exchanger that use ice as the refrigerant. They work about as well as your car unit if set to the lowest setting and only work as long as you have unmelted ice.

I don't like linking to specific products but have made an exception here. Use google-fu or search the ubiquitous on-line shopping website.

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