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IamIan

Since the biggest thing holding electric cars back is battery technology, EV converters need to be careful in how they use the power they have. As a result many EV converters avoid having air-conditioning since the power draw has a noticeable effect on range, others decide the small sacrifice in range is worth it for the increase in comfort. Here are several options for keeping the occupants of your EV cool and comfortable:

No Air-Conditioning: Air-con uses the same amount of power in an ICE car or a EV it is just less obvious in a normal car. Once the drain of air-con is realised many people decide that having the window open or using the fan alone are sufficient enough cooling for them. If range is a big priority and the temperatures of your area don't get excessively hot then this is the simplest and best option.
Dual Shaft Motor: If having AC is a must for your conversion then the option that is most similar to AC in a normal car is to run the AC compressor off the rear shaft of a dual shaft motor. The advantages are simplicity and similarity to standard cars but the AC will only work when the motor is spinning. This Saab is an example of using this approach.
Accessory Motor: Another option is to run a small 12V accessory motor which is attached to the compressor. This approach allows AC to be used when the car is stationary and means that there is no direct drain on the power to the drive motor but adds weight and complexity. This Honda is an example of using this approach.
Ice: Rather than storing electricity and using it to lower the temperature of the car it may be easier and cheaper to store a direct source of cooling; ice. Blowing air through an ice water mix is a rather effective form of cooling and might be sufficient for your cooling requirements. A DIY example can be seen here, or you may prefer Mr Sharkey's no nonsense approach here.
Compressor with integral motor: A more recent option is a compressor with a motor built in like your home AC unit. Some of the newer hybrids use this technology such as the Prius or this conversion which utilizes a variable speed control to maximize efficiency. With this option you also have more freedom as to where to locate the unit and you don't have a lot of mounting hardware to fabricate. http://www.evdrive.com/BMW_project/AirConditioning.html Extension of the above is DC powered complete unit. Expensive , but compact. DC-Breeze is an example. ~$2,500 for 5,000 BTU / hr cooling all in a ~50 pound package... just plan for the ~580 Watt load to run it.

JRP3 · #2 06-01-2009, 06:42 PM

I wonder about the suggestion to use a 12 volt motor for the A/C compressor. The vehicle linked to uses a 180 volt motor running from pack voltage. I don't know if a 12 volt motor would have enough power, or draw too many amps, plus you get conversion losses from the DC/DC converter.

eric-ev · #3 06-02-2009, 01:21 PM

I'm pretty sure the only 'right' way to retain AC is to use a dual shaft motor (one with a shaft off both ends), and hook the pully up to that. Practically lossless, unlike DC converted from the pack!

JRP3 · #4 06-02-2009, 07:54 PM

Well there has to be some loss from the belt running around the pulleys and clutch even when disengaged, though I'm not sure how much. Also the A/C stops when the vehicle stops unless you hold the throttle, and not all motors, (like mine) have dual shafts. I think a pack voltage motor might be a good solution.

eric-ev · #5 06-03-2009, 06:10 AM

I suppose there would be some loss from spinning the clutch and pulley, I imagine it would be less loss than converting that many amps to 12v though.
The plus side would be the converter you can just switch off.

Personally I wouldn't be concerned about the pump not running at stop signs or whatever, whenever the car was in motion it would be spinning the electric motor through the drivetrain, powering the AC, and actually capturing a bit of power via 'regenerative braking via air conditioning'

A motor on pack voltage would be the 'correct' way too, provided it was sized correctly.

Anybody have any idea how we'd select the right rpm/power motor for the AC?

JRP3 · #6 06-03-2009, 06:49 AM

I haven't found solid numbers on A/C hp requirements, I've seen between 3-12 hp mentioned which is a large range. I think some people have used treadmill motors but don't know if they are appropriately sized.

rmay635703 · #7 06-23-2009, 11:24 AM

Although not the strongest why not use circa 1920's technology?

Passive AC does work but would present an aerodynamic issue. (a big 2' tall 4'x4' dome) There is a place here in Wausau WI working on selling passive portable refridgerators for developing countries, I would assume this same technology would work on a car, insulate the roof, put on a big screen magnifier over a nice set of black AC lines. THe sun compresses the refridgerant and cools the other side.

I doubt it would be strong cool but it would gently cool the roof area.

Now lets see if I can find the joints name, at the moment they are still in the business incubator. Their initial designs were marketed toward large scale business AC, minimal energy needed to make the hi-tech version operate.

Cheers
Ryan

few2many · #8 06-25-2009, 11:07 AM

When you drive an ice car with the ac on, and then turn off the motor, do you occasionally hear a sound from under you're dash or hood? That's the sound of the ac system equalizing pressure through the expansion valve. The high side, high pressure liquid is vaporizing in the evaporator and settling on the low side. the evap will usually be able too cool for a minute or so after the engine shuts off. On an e car, I would run the ac off the traction motor, install a larger receiver to hold a little more liquid freon and a larger accumulator for added low pressure space. When you're motor is off, at a traffick light, there should be enough to keep the ac going for a few minutes. You want someone to carfully calculate the charge, as this is a high pressure system and if you're accumulator is too small, you'll hammer the compressor with liquid, which destroys it. Remember, not only do you have to somehow power the ac compressor(seperate motor, traction motor, or motor compressor packaged unit) but you also have to run the electric fan that pulls air throught the condenser, these usually draw a lot of amps. Ac is a luxury and in arizona, it'll have to be a reality!