Running Vehicle Air Conditioners on Batteries

[mhiscox]

There are a lot of advantages to being able to air condition a camper cabin using battery power. In fact, I can do it--for just an hour or two--in my Sprinter with a small AC and over 600 amp-hours of AGM batteries. A lot of cost for a fairly modest accomplishment.

But if you'd like to have a better analysis of how batttery-powered AC could work, the equipment available, and some idea of the appropriate component sizing, you'll likely find this twelve-page writeup by the people at Dometic Truck to be useful:

http://dometictruck.com/pdf/L-2523.pdf,

With an increase in anti-idling restrictions and widespread recognition that idling a big diesel just to provide sleeper AC is expensive and hard on the engine, considerably more options have been made available. Most common to date are Auxiliary Power Units (APU's) which fit in a big box on the truck's frame and operate off a modest-sized diesel generator. They still burn diesel and still make noise, but both the noise and fuel consumption are much reduced. Dometic's newly-expanded product line has the system running off AGM batteries that have been charged the truck's oversized replacement alternator during routine operation.

Anyway, I found their document to be a pretty good summary of what you could expect to accomplish using batteries to power the AC for both trucks and camper cabins. You might, as well.

 

[convict]

Re Aircon ..see "Powermaker"

..do a search "for powermaker John (whatcharterboat) has written a very good post on them".

or Check out "Powermaker" site, a very nice and flexible toy, it has a little Yanmar(?) donc in it, ..John (whatcharterboat) has written about pros and cons of Aircon issues on this site and he is always worth a very close read.

As you say, when you go beyond 850-950 BTU batteries are a stretch, and dollar for dollar ..APU vs a 'Powermaker' type of unit, the alternative options really open up.

..don't get me wrong I do like APUs, just a thought.

 

[whatcharterboat]

Check out >> http://www.dcairco.com/products.html (not just the truck air con either. Some of the satellite communications hut AC looks interesting too)

and do a search for "viesa" dc air con / cab coolers. All really expensive for the amount of cooling capacity though. Only made for truck /sleeper cabs and probably not big enough to do a large camper. Still allow a flexible installation and they are all very tough and can certainly handle the rough going of an expedition type truck.

We sometimes deal with a guy here who custom builds DC air/con but no one has ever made a really magic break through in cooling efficiency. No one >>> so basically if you want to AC a large area then it'll still take a lot of your hard earned electricity or fuel to make it happen. So as Mike says "A lot of cost for a fairly modest accomplishment."and that usually means noise and vibration too.

Thanks for the comments convict and thanks Mike for the link >> nothing like a bit of light reading on a Saturday night. Lol.

 

[alan]

Here's some pic's of 12v or 24v airconditoners they say the large unit will do a small camper/caravan ok.

 

[Bogo]

I haven't looked in the past year, but 4 100Amp hour AGM batteries should run an efficient unit that would cool a well insulated camper van for 8 hours assuming 50% duty cycle. The battery pack would be about 325 lbs figuring 75lbs each for 4 group 31 AGM batteries. This assumes the camper is already cooled down. That was using a DC Airco unit. In my search I figured Kool Rig was likely the most efficient, but it is also very costly. The guy wants to sell it as a package including Li-Iron Phosphate batteries. The Kool Rig unit also works as a heat pump for heating as well as air conditioning.

Another thing I determined is 24VDC units are around 8 to 10% more efficient than 12VDC ones. This mirrors what is seen in inverters also. 12/24VDC refrigerators also see a similar boost in efficiency.

Given 24VDC is often more efficient and one should up the size of the alternator for charging the large house battery bank. Also given that the DC powered air conditioners are more efficient than direct engine powered ones while driving. I figured that ripping out the engine mounted compressor, and replacing it with a 100 to 200 Amp 24 VDC truck alternator was the way to go. That would charge a 200Amp Hour 24VDC house battery bank. That battery bank would supply power for the air conditioning while driving. I figured at most 30 Amps would go into air conditioning and the rest would go into recharging the battery bank and other loads. I would still leave the 12VDC alternator and battery system in tact for running normal 12VDC vehicle systems, but I would switch over as much as reasonable to 24VDC and the house battery bank. I haven't done anything with this idea yet as I expect DC air conditioning units to drop in price as volume ramps up and the air conditioner compressor in my truck is still working well. There is still a very heavy demand from the trucking industry as one can save thousands of dollars of fuel a year in the average long haul semi. There is no reason they should be priced over $1000 for roof top unit given that I can get a high powered 120VAC powered rooftop RV air conditioner for $800. Last I knew they were still around $3,000 plus battery bank and engine alternator modifications.

 

[LukeH]

This is a question that's been playing on my mind for a while now too.
I hope to be able to build a generator free camper, but with three important luxuries:
Washing machine
Dishwasher
Aircon
(hey it's for going on holiday right? so why would I want to do the dishes on holiday when I don't do them at home?)

The first two are going to need an inverter and a big battery bank, on to the third.

DIRNA are quite popular in Europe in the retrofit market: http://www.dirna.com/compact30-ing.php
A supplier in France quoted me 1500 euros for a 2000W unit.
Doing the maths with their figures, worst case (for the 3000W unit) 24 amps x 8 hours = 192 Ah
So a battery bank of AT LEAST twice that could handle the cycling ok - I'm aiming for 500Ah at 24 volts. But to handle even that level of cycling I want traction batteries.
(weight isn't a problem - yet)
I have found that when you're well inland evaporative cooling units do a great job of making life comfortable; they don't work on the coast because it's already humid. So by installing one of each you save a bit on battery life when inland.
But if you're stopped for more than a day you're going to need some serious static charging capacity.
Solar rather than wind - because if there's enough wind to run a turbine, you're not going to need AC.
So in order to be able to run the AC the following day you need 576watts coming from the roof. As solar panels are rarely going to run at 100% rated output power that's 1000W of panels on your roof!!! (looking at an inclining roof like the japanese two story thingy - might help reduce the solar needed too)
I have the space, do you?
The best price I've seen in Europe is around 2 euros per watt for no name panels, and then it depends on the size.

That's one hell of an investment for the whole system!
I don't have that kind of cash kicking around just yet, but then once I've got the box mounted on the chassis, I should be able to see clearer through the build maze.

Also given that the DC powered air conditioners are more efficient than direct engine powered ones while driving. I figured that ripping out the engine mounted compressor, and replacing it with a 100 to 200 Amp 24 VDC truck alternator was the way to go.

the word "efficient" is really popular these days, and often misused. While it may be true that a manually controlled engine driven AC saps more from an engine than a fully automatic electrically driven unit, we're comparing apples with pears. The reduction in power consumption thanks to the electronic management, not the way the compressor is driven.
Generating electricity to use it up in rotating machinery (compressor) is inherently less efficient than using the rotation directly to drive the compressor; especially when it's all under the same hood, and the heat generated has to be evacuated somewhere. This heat usually flows around the cab that you're trying to cool.
Having written that, it's probably exactly what I'm going to do as my truck doesn't have AC, so bolting a (couple of) Dirna unit(s) on the roof with some heavy cables is way simpler than plumbing in a whole system. If you do go all electric, why bin the compressor?
You could use it to feed an on board air setup which is really nice to have.
My truck is already 24V and has air brakes, so the tanks and OBA are already there.

Gosh and all I wanted to do was subscribe to the thread :Wow1:

 

[Bogo]

This is a question that's been playing on my mind for a while now too.
I hope to be able to build a generator free camper, but with three important luxuries:
Washing machine
Dishwasher
Aircon
(hey it's for going on holiday right? so why would I want to do the dishes on holiday when I don't do them at home?)

Yep, but I currently use paper plates to avoid that chore.

My only worry is current small RV dishwashers are really to small for cooking pots. Also they require being level.

The first two are going to need an inverter and a big battery bank, on to the third.

DIRNA are quite popular in Europe in the retrofit market: http://www.dirna.com/compact30-ing.php
A supplier in France quoted me 1500 euros for a 2000W unit.
Doing the maths with their figures, worst case (for the 3000W unit) 24 amps x 8 hours = 192 Ah
So a battery bank of AT LEAST twice that could handle the cycling ok - I'm aiming for 500Ah at 24 volts. But to handle even that level of cycling I want traction batteries.
(weight isn't a problem - yet)

If weight isn't an issue, look at electric forklift batteries.

{snip}
That's one hell of an investment for the whole system!
I don't have that kind of cash kicking around just yet, but then once I've got the box mounted on the chassis, I should be able to see clearer through the build maze.

Neither do I.

the word "efficient" is really popular these days, and often misused. While it may be true that a manually controlled engine driven AC saps more from an engine than a fully automatic electrically driven unit, we're comparing apples with pears. The reduction in power consumption thanks to the electronic management, not the way the compressor is driven.
Generating electricity to use it up in rotating machinery (compressor) is inherently less efficient than using the rotation directly to drive the compressor; especially when it's all under the same hood, and the heat generated has to be evacuated somewhere. This heat usually flows around the cab that you're trying to cool.
Having written that, it's probably exactly what I'm going to do as my truck doesn't have AC, so bolting a (couple of) Dirna unit(s) on the roof with some heavy cables is way simpler than plumbing in a whole system.

OK, the reason engine mounted AC systems are not as efficient is because the compressor is not rotating at, or even near, ideal speed. Often they are compressing allot more freon than is needed. They are over sized so they are still able to provide reasonable air conditioning output while idling.

If you do go all electric, why bin the compressor?
You could use it to feed an on board air setup which is really nice to have.

First, my engine compartment is small, 1994 Toyota Hilux, and the air conditioning compressor spot is a convenient place to put a big alternator. Second, I already have a portable 12VDC powered air compressor. Third is I plan on adding air bags to the rear suspension to handle the greater constant weight. When I do I'll install a DC powered compressor system plus tank. Fourth is once you hack up an air conditioning compressor for use compressing regular air it has a limited life due to lack of proper lubrication. Yeah there are some models that work better than others, but the Toyota one is not one of them.

 

[WHERE2]

solar air cooler, [SOLAR CHILL] a thought?

I believe their is a 12vdc and a 24vdc solar "air conditioner". solarchill, maybe.

This is a question that's been playing on my mind for a while now too.
I hope to be able to build a generator free camper, but with three important luxuries:
Washing machine
Dishwasher
Aircon
(hey it's for going on holiday right? so why would I want to do the dishes on holiday when I don't do them at home?)

The first two are going to need an inverter and a big battery bank, on to the third.

DIRNA are quite popular in Europe in the retrofit market: http://www.dirna.com/compact30-ing.php
A supplier in France quoted me 1500 euros for a 2000W unit.
Doing the maths with their figures, worst case (for the 3000W unit) 24 amps x 8 hours = 192 Ah
So a battery bank of AT LEAST twice that could handle the cycling ok - I'm aiming for 500Ah at 24 volts. But to handle even that level of cycling I want traction batteries.
(weight isn't a problem - yet)
I have found that when you're well inland evaporative cooling units do a great job of making life comfortable; they don't work on the coast because it's already humid. So by installing one of each you save a bit on battery life when inland.
But if you're stopped for more than a day you're going to need some serious static charging capacity.
Solar rather than wind - because if there's enough wind to run a turbine, you're not going to need AC.
So in order to be able to run the AC the following day you need 576watts coming from the roof. As solar panels are rarely going to run at 100% rated output power that's 1000W of panels on your roof!!! (looking at an inclining roof like the japanese two story thingy - might help reduce the solar needed too)
I have the space, do you?
The best price I've seen in Europe is around 2 euros per watt for no name panels, and then it depends on the size.

That's one hell of an investment for the whole system!
I don't have that kind of cash kicking around just yet, but then once I've got the box mounted on the chassis, I should be able to see clearer through the build maze.


the word "efficient" is really popular these days, and often misused. While it may be true that a manually controlled engine driven AC saps more from an engine than a fully automatic electrically driven unit, we're comparing apples with pears. The reduction in power consumption thanks to the electronic management, not the way the compressor is driven.
Generating electricity to use it up in rotating machinery (compressor) is inherently less efficient than using the rotation directly to drive the compressor; especially when it's all under the same hood, and the heat generated has to be evacuated somewhere. This heat usually flows around the cab that you're trying to cool.
Having written that, it's probably exactly what I'm going to do as my truck doesn't have AC, so bolting a (couple of) Dirna unit(s) on the roof with some heavy cables is way simpler than plumbing in a whole system. If you do go all electric, why bin the compressor?
You could use it to feed an on board air setup which is really nice to have.
My truck is already 24V and has air brakes, so the tanks and OBA are already there.

Gosh and all I wanted to do was subscribe to the thread :Wow1:

 

[Bogo]

I believe their is a 12vdc and a 24vdc solar "air conditioner". solarchill, maybe.

One of the makers that makes them for trucks has as an option a solar panel set for on top of the trailer.

There are many 12VDC and 24VDC air conditioners available. Most could have some solar power as an option. The problem is without a large roof area there isn't enough roof space for the solar panels.

 

[Fish]

Swampy

I use a Swampy 12 volt swamp cooler in my shell when I'm trying to sleep back there. Mine is one of the smaller ones that only holds 1/2 gallon of water, though I do have the water kit. That typically lasts a couple of hours, which is enough for a nap if I've been up all night.

I'm typically someplace hot and dry, so the Swampy works great. The slightly larger one might work a little better, but I've got what I've got.

Swampy

 

[NeverEnough]

I've yet to find a DC air conditioning unit available in the US market that doesn't cost at at least 4 times what a conventional AC unit costs. I finally gave up and decided I'd rather put the money into my batteries, charge controllers, and panels.

I came close to ordering a 12V DC TurboKool evaporative cooler, but after learning more about how it works, decided it wasn't quite ready for off-road adventures and I was concerned about it's water usage. I'm leaning towards the Coleman PolarMach "RuffNeck" low profile. It's a heavier duty version of their standard RV unit.

 

[mhiscox]

I'm leaning towards the Coleman PolarMach "RuffNeck" low profile. It's a heavier duty version of their standard RV unit.

Depending on how big the area is that you need to cool, the Coleman Polar Cub (9200 BTUs) is worth considering. I had one on the Mog Camper and it worked well into the upper 90's, though it was overmatched in the triple digits. But that was cooling quite a large cabin (14x7x6).

One reason for mentioning the smaller unit is that I was generally (not always) successful starting and running it off of a single Honda eu2000i generator, which is a feature.

 

[Bogo]

I've yet to find a DC air conditioning unit available in the US market that doesn't cost at at least 4 times what a conventional AC unit costs. I finally gave up and decided I'd rather put the money into my batteries, charge controllers, and panels. .

Right now it is supply and demand. The trucking industry is soaking up them fast as they realize the benefits. In a long haul sleeper cab used only twice a week it pays for it's self in less than a year in saved fuel alone.:Wow1: Even in a cab that is only driven in, there is much savings to be had. They typical engine driven air conditioning compressor is very wasteful of energy. Switching to DC based air conditioning units can help increase fuel economy while driving.

In reality the DC powered units shouldn't cost more than $1000 if the volume of production can be achieved.

 

[TomH]

You may be interested in this build by K-9 Sprinter, who had Sportsmobile build a kennel vehicle, which he calls the Dobervann, for him. His house battery consists of three 8D batteries to power the AC for his dogs.

http://www.sportsmobileforum.com/viewtopic.php?f=15&t=5616

http://sprinter-source.com/forum/showthread.php?t=13275&highlight=Dobervann