12 / 24 volt air conditioner

physics is the limitation, Even if the efficiency is double a conventional rooftop which puts it in the ballpart of high efficiency home units, your still looking at near a 50A draw from 12V, 24V would be around 25A, more tolerable.

If the efficiency is near that of todays RV AC units, double those numbers

Typical RV AC unit at 12A draw is about 1500W=4500BTU AC output is 13K BTU so your running about 3:1, or an Engergy efficient ratio of about 10. (BTU out/wattsin) which actually is a meaningless number, the units don't match. It should be BTU out/bTU in, but then the number is 3x less.

That aside the top AC units approach 20 for a EER, and that still puts you in the 50A range from 12V.

A quick look at the amazon units claim decent efficiency, 750W for 13Kbtu vs the 1400W for a rooftop RV, but still that's around 25A at 24V and it requires 50+A for startup.

Kept in mind if you go with a lower btu unit, it will run more.

So if a 15k btu runs 25% of the time a 5k btu will run 75% of the time...net result is the same number of Amp hours used.

While it's possible, it gets expensive compared to just breaking out the generator. Those that jump thru the hoops usually live with limited use.

^Well put.

ktmrfs wrote:

That aside the top AC units approach 20 for a EER, and that still puts you in the 50A range from 12V.

A quick look at the amazon units claim decent efficiency, 750W for 13Kbtu vs the 1400W for a rooftop RV, but still that's around 25A at 24V and it requires 50+A for startup.

Comparing a 12VDC A/C to a 12VDC compressor refrigerator (they are close cousins), all DC refrigerators that I know of actually take the DC voltage run it through an inverter and generate a 3 phase AC output (3 phase motors much more efficient than single phase).

It can be done, but is it the best solution from a total energy consumption standpoint ?

As pointed out, most mini-splits have a very high EER. There are a few "window shakers" that have similar EER.

theoldwizard1 wrote:

ktmrfs wrote:

That aside the top AC units approach 20 for a EER, and that still puts you in the 50A range from 12V.

A quick look at the amazon units claim decent efficiency, 750W for 13Kbtu vs the 1400W for a rooftop RV, but still that's around 25A at 24V and it requires 50+A for startup.

Comparing a 12VDC A/C to a 12VDC compressor refrigerator (they are close cousins), all dc refrigerators that I know of actually take the DC voltage run it through an inverter and generate a 3 phase AC output (3 phase motors much more efficient than single phase).

It c

an be done, but is it the best solution from a total energy consumption standpoint ?

As pointed out, most mini-splits have a very high EER. There are a few "window shakers" that have similar EER.

even the best units today are around EER=20 or so, vs. about 10 for the typical 13.45K BTU RV AC unit. So 12V or 24V draw is till pretty high. would be nice if rooftop RV AC units were around 15 or so, with decently low LRA so they would easily start and run on a 2Kwatt inverter generator. Best rooftops I've seen are still around 10A vs. 13 or so.

To add to the confusion SEER which is often a higher number than EER

EER is the BTU out/watts in at outside temp of 95F. that's the important one if running off batteries. I've seen units with SEER of 25 but the EER is usually in the 18-19 range.

SEER uses a range of temps from 65F to 95f and units are more efficient at lower outside temps.

If you want to know what it takes to cool the RV when outside temps is high EER is the key and will give you a good idea of the input power needed. Figure a EER of 20 is pretty much best you will get, likely somewhat less.


https://servicechampions.com/blog/difference-between-eer-and-seer/#:~:text=Where%20EER%20is%20calculated%20using,F%20to%20104%C2%B0F.

I have the tools, knowledge and experience to put a mini in my RV. I would not, mostly due to no good spot to place the evaporator, inside unit. The worst part would be if you ever need service, there are not a lot of good mini techs around and the good ones charge a lot more than I think they are worth.

Last year in my Roadtrek I pulled the well running vacuum cleaner sounding Fedders and installed a LG 9500 dual inverter window unit. This thing is sweet, not as quiet as a mini, but still quiet and runs off a Honda 2200 in ECO mode!

If you can fit in a dual inverter window unit would be the way to go!

OP, you mention 2000 watts of solar and LFP batteries. We have 1600 watts of solar and 1030 ah of LFP batteries. The last time we boondocked, we ran the A/C for 5 hours (standard rooftop A/C with heat pump)(and soft start).
1600 watts of solar (with good sunshine) will provide well over half of the amp draw for a standard A/C. So with your planned 2000 watts of solar, the solar panels should provide nearly all the amps that the standard RV factory A/C unit draws.
We have run 2 A/C units before, but when the one without soft start starts, my satellite receiver goes into start up - TV stays on, res fridge also doesn't appear to have any hiccups.

ktmrfs wrote:

would be nice if rooftop RV AC units were around 15 or so, with decently low LRA so they would easily start and run on a 2Kwatt inverter generator. Best rooftops I've seen are still around 10A vs. 13 or so.

Microsair EasyStart solves that problem !

There is no proprietary technology in an EasyDtart, so why don't all RV A/C units have this. Only a couple of $ to build it in ?

jjrbus wrote:
I have the tools, knowledge and experience to put a mini in my RV. I would not, mostly due to no good spot to place the evaporator, inside unit.

I have thought long and hard about this ! The best solution I have come up with is a ceiling cassette. These are much too tall for an RV ceiling. You would have cut a hole in the roof and place a well insulated box over the part protruding.

jjrbus wrote:

The worst part would be if you ever need service, there are not a lot of good mini techs around and the good ones charge a lot more than I think they are worth.

Why do you need a specialist ? The parts are all the same, just maybe a different shape or location.

Some great advice here....as I was only thinking about this for a fairly specific application, using current roof top units would probably work for the temporary situation Im speaking of providing I have enough Solar/Battery capacity. Id go the Mini Split route too if I had a notion of where to put the condenser on the MH but only as an additional cooling unit. Thanks for the comments.