12 volt air conditioner

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Eric Currie

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Apr 27, 2023
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Prince Edward Island
I have a 1990 class B based on a Chevy P30. The vehicle air conditioner quit on me but the roof top 120 volt unit works. I'm considering installing a 12 volt parking unit to replace both units so I have A/C when we drive and go off grid. The unit seem fairly cheap and plentiful on the market and there are roof mount models. My concern is how big a battery bank do I need. Currently I have room for 1 battery, I'm also putting a 100 watt solar panel on the roof. I have room for at least 1 more panel but nowhere to put more batteries. Has anyone installed a 12 volt DC air conditioner and how much battery capacity do you need?
 
Because of the high cost of diesel transport trucks are installing battery powered 12 or 24 volt air conditioners so they don't have to keep the diesel idling to run air when they stop to park. Farmers are starting to install them in the enclosed cabins of their large tractors as well. Strikes me as a more versatile way to keep your RV cool without shore power. It will run off your engine generator while driving, not sure how much battery power you need to park.
 
Eric Currie said:
Has anyone installed a 12 volt DC air conditioner and how much battery capacity do you need?
Click to expand...
Guessing these 12V A/C units aren't going to cut it cooling a ~250 square foot RV, they're likely only enough for the cab of a truck.

People have done it though. You need many hundreds of Ah of storage to run A/C from battery. If you figure a typical rooftop A/C unit is drawing upwards of 15A of 120V, that translates to 150A at 12V. People with deep pockets have put together lithium packs that can do this ($thousands). Even with those deep pockets, you'd need some way to restore that charge after a day or so. A 100W solar panel is barely enough to run some LED lights and charge a phone much less kilowatts worth of A/C. Your roof probably isn't big enough to hold the panels it would take to keep up with A/C which is why you don't hear of many folks that go down this road. Far cheaper and more effective to run a genset and power A/C with 120V.

Mark B.
Albuquerque, NM
 
Thank you Mark. The amp and volt thing was what I was confused with. My A/C that cools the cockpit is shot so I may still look at this for driving depending on how much it will cost to have the unit fixed.
 
Even a Class B has quite a bit of interior volume and it heats up quickly in the sun.

A typical 12v a/c unit draws 60-80 amps @ 12v (750-1000 watts), so one size 27 12v battery (100 AH) might last a little over an hour. But lead acid batteries drop their voltage as they discharge, so I'm guessing the a/c would quit due to low voltage after 20-30 minutes. Or maybe less. Lithium batteries would probably do a bit better.

This model claims to be able to operate 6-8 hours using one 480 AH "car battery", but I don't know any car or light duty truck that has that big a battery bank. That's the equivalent of two big size 8D batteries.
 
The ones I have looked at are like 8,000 btu. So about 60% of my roof unit on my 30 foot P30. So first off you'll need two units to replace both dash and roof air.

Power consumption is hard to decipher but range from 300-700+ watts or 25-60amps @ 12V.

One reviewer of a unit claims he gets 12 hours from 600 a/h of LiFePo battery.

I am considering one of these for my teardrop, supplemented by generator power. Like on the boat the most practical use of battery powered A/C was a couple of hours before bed to cool down the sleeping area.
 
If you can find the room, 2 Trojan T105 (6V) paired to make 12V gives you 225AH of usable battery without damage. Usage is between 750w-850w (Amazon units) or about 65 (12v) amps per hour. giving you about 3 hours of use before a lengthy recharge. You might get double the usage if the unit runs intermittently, 15 minutes on, 15 minutes off depending on the startup wattage.
 
Few 12v lead-acid battery banks can deliver 60A for more than a few minutes before the battery voltage drops below 11v. The compressor amp demand increases as the voltage falls (the watt draw is constant) and once it falls below some threshold the compressor can't compress any more and cooling stops. Or the compressor motor burns out due to excessive amps & heat.
 
Going by the listing, these units produce "800-2400W" of cooling. Assuming they mean watt-hours and converting to the more common BTU/hr ratings gives 2700-6800 BTUs. The high end of that range is about the same as a small window air conditioner. RV rooftop air conditioners produce 13,500 to 15,000 BTUs. Automobile dash air conditioners are un the 20K-30K BTU range.

You need energy in to get cooling out, no two ways around it.

P.S. - I like this poorly translated quote in the product description:

"... many drivers worry that the air conditioner will be used all the time when parking, and it will be embarrassing when the car cannot catch fire when driving."
 
I have not run the full series of tests on the Bubba Edison Solar Electric Power Company, ( in the future I will just call it the Bubba System), to much typing.

I did however do a short test run the other day with temperatures of over 102 degrees.

I ran the system for 60 minutes with no outside electricity, (shore or generator). The compressor was engaged the entire time due to high temps. The inside temp was very comfortable, just like shore power.

I did have full sun and the charge controllers were putting out about 100 Amps DC into the battery bank.

The hour run reduced the SOC by 11 % from 100 to 89%.

I had turned off all other 110 volt systems except for the lithium convertor charger in the main panel for the front DC system. The refer, hot water heater, and security system were off.

I will attach this update to the thread on the Bubba system.
 
Compare BTU output between the 12 and 120 volt units. The rest is simply power supply. If they don't have the BTU output, they won't cool the rv
 
John From Detroit said:
Well I won't list all the flags (yellow not red) on that Amazon page nut
1 No mention of amp draw
2 No mention of BTU
And one Red Flag: "No Fuel Consumption"
What do they think makes the 12 volts it runs on? Solar Power?
(Well I guess it could)>
Click to expand...
I think there is a reason it is called a "Parking Unit". Designed to only be on for a few minutes. So the draw won't make a big difference.

I am waiting right now, waiting from inside my Tesla but waiting for the rain to totally stop. Going on a hike. I am typing this on my Tesla screen.

Thunder storm here... Won't last long.

Galena Park, NV (near Carson City)
 
Considering your current setup with one battery and a 100-watt solar panel, it's unlikely to provide enough power to run a 12-volt air conditioner continuously. A single battery typically has a capacity of around 100-150 Ah, which might not be sufficient for your needs. The 100-watt solar panel can help recharge your battery, but it may not fully compensate for the power consumed by the air conditioner.
 
John From Detroit said:
Missed it as it's in the ad section not the specifications section... that's a lot o watts for a 12 volt system.
Click to expand...

Near as I can tell there are a couple of designs. One is a 12V compressor motor and one "dresses up fancily" what is basically an AC motor and inverter.

I gotta believe the AC unit has unacceptable conversion losses.
 
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