Electric motor to power car a/c

This is a little bit off the beaten path...please delete it if it is too far off. I am converting my van into a camper and would like to relocate the a/c unit to the rear of my van - I plan on putting a steel box in the rear, against the side wall and putting the compressor and coil in it - using the parts from the van. I was thinking of getting a 24v electric motor to power the compressor - 24v so that it would be able to run off the solar panel on top of the van. Would 2 hp be big enough? What kind of motor would work?

This website is good,
http://www.surpluscenter.com/Electrical/
Looks like now they got more stuff they are selling.

Much depends on the model compressor, but I don't think 2HP is enough. typical AC compressors take 5HP off the engine at highway speeds.

But an Automotive compressor isn't a very efficient. It's designed to work over a very large RPM range without having a dramatic impact in the available output in a very wide range of operating temperatures and conditions. So many sacrifices are made to it's efficiency ratings in the name of consistency and durability.

A home AC compressor is designed to run at a constant RPM in a fairly stable environment, and so it's design is far more efficient.

I recently tested a 6000BTU home window unit and found it pulled 350 watts most of the time. you would lose ~10% or so converting your 24vDC to the 110AC needed to run it, but you're still looking at a roughly 1/2Horsepower needed to run a unit designed to cool a volume of around 1000-1500 cubic feet compared to 5hp to run a unit designed to cool 200-300 cubic feet.

I paid $50 for that window unit, used. That's likely less than the cost of just the refrigerant needed to refill your Van's unit once you install it in it's new box.

Drunkskunk said:

I paid $50 for that window unit, used...

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As an immediate practical matter, I'd go the window-shaker route too. But maybe something can be put together with a vehicle AC unit and renewable energy.
I haven't even begun to work out the details, but the quality of being engineered for variable input speed could be employed. I've wondered about using a windmill with the proper gearing to directly run the refrigerant compressor. The system would avoid the losses from the energy conversion of mechanical to electrical energy, and the inconsistency of the wind could be compensated for by making the system larger than necessary and using thermal mass in the ACed room.
Of course, windless days, are sometimes the hottest, so the system does have some shortcomings.

Thanks! I would prefer the window unit also. Is there some way to take apart the parts of a window unit? Separate the compressor and condensor - put it in one place, and put the rest in another, about 3 feet away? The bigger picture here...I want to put a 5 cylinder diesel engine in my van but it is longer than the v6. It I replace the engine driven fan with an electric fan, and can move the a/c to some other place, there would be a comfortable amount of space for the new engine. It seems that home a/c units are not belt driven by a motor but the motor function is built into the compressor

In the past I've seen a few DIY electric car conversions on the internets that used a separate electric motor to run the existing air-con compressor. You might be able to find details of the size of motor used. From memory we're talking at least a couple of HP.

pengyou said:

Thanks! I would prefer the window unit also. Is there some way to take apart the parts of a window unit? Separate the compressor and condensor - put it in one place, and put the rest in another, about 3 feet away? The bigger picture here...I want to put a 5 cylinder diesel engine in my van but it is longer than the v6. It I replace the engine driven fan with an electric fan, and can move the a/c to some other place, there would be a comfortable amount of space for the new engine. It seems that home a/c units are not belt driven by a motor but the motor function is built into the compressor

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If you are capable of swapping those 2 engines (in a van, no less), then you should also understand the basic principles of AC. Theoretically, the components could be physically separated, but in practice, it would be more trouble than it's worth. You would have to cut the lines, evacuate the system, extend the lines, and refill the system.
I know a girl in Arizona, USA, who mounted an AC on the roof of her van for the comfort of a bunch of dogs she often carries. I don't know the details of her setup.

As Nehmo points out, it can be done, but it would be complicated.

I made my suggestion on the window unit based on cheapest and most efficient use of materials. However, there is another choice. Roof mounted RV air conditioners. They work at efficiency levels similar to window AC units, and many can run off DC power. They are designed to fit on the roof of a van or camper, and already aerodynamically shaped.
However, they aren't cheap.

Hit up the junk yards, there used to be a RV junk yard near the regular one in my area. But I think it was a little shady. Im sure they are out there, I just havent looked.
Great idea about the RV a/c unit on the roof. Could also scoop up other stuff you need, raised roof, air vents, windows, beds, matresses etc.

Yes rv are good but they add 8" or more to the height of the van, something I am trying to avoid

back window?

Second generation Honda Civic Hybrid:

An internal electric motor is added to the air-conditioner, so it can be powered by either the engine, an electric motor, or both. At a stop, the compressor powered by the battery keeps the cabin cool. An additional compressor that is powered by the petrol engine also engages if rapid cooling is required. When the interior temperature is stable, air conditioning is provided by the battery solely.

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https://en.wikipedia.org/wiki/Honda_Civic_Hybrid

I am currently thinking about doing something similar. I want to be able to use my van ac system off an extension cord or generator. I was thinking about adding a second electric compressor to the existing system in parallel with some type of valve to switch refrigerant flow between the two compressors. What does everyone think of this idea?