Country of Origin: United States
I have a small RV camper van and it did not have AC from the factory. I have purchased a used aftermarket evaporator assembly and a new condenser. I already have a Zexel DKS-15 compressor that I plan to use.
Here's where the wacky idea is: I plan to use a 120V electric motor to power the AC compressor. The idea is that when plugged in to 120V it can run with the engine off, and when just driving the large 140A alternator and 2000W inverter will power the motor. I can't use a roof AC unit because it won't fit with my pop-top. It will be like a Prius; I have checked out those compressors but the electronics required to power it is too costly.
For refrigerant I'm thinking of using HC-12a. I know there is a lot of debate about this but my compressor and evaporator are designed for CFC-12, and this seems the best way to go.
The motor/compressor will be mounted under the van, probably direct drive. Currently my thought is to use a 2 horsepower 3500 RPM motor. Is that enough horsepower? How about RPM? Will the compressor being physically lower than the condenser be a problem?
I would appreciate any thoughts! Thanks!
Not a workable solution with the items at hand.
a "140 amp" alternator is maxed out @ 140 amps, and will not run at that output for long periods. 140a x 13.5v = 1890 watts. Your vehicle will need about half of that. To be generous, you have 1kw to work with.
A 2hp 115 volt ac motor draws 20 amps running, so 20 x 115 = 2300 watts at the motor. Starting loads are much higher. Your "2000w" rated inverter is not big enough to run the motor, and starting it is completely out of the question.
Now for the compressor. I don't have tha capacity chart for a DKS15 in front of me, but a small compressor can soak up as much as 6kw in shaft input at full output. That puts your 2hp motor at about 25% of what is needed to drive the compressor at full output.
By the time you add in the losses for all of the electrical conversion, this gets much worse. FYI, the toyo pious is a sauna in the desert heat.
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
Thanks for the reply! I appreciate your input!
I did some tests the other day. The alternator outputs 90A @ 14.1V at idle and 130A @ 14.0V at speed. I plugged in a 1500W toaster oven and it consumed 120A @ 14V = 1680W, so the inverter is 89% efficient. I let that run for about 10 minutes at fast idle and the inverter wasn't even warm.
I plugged in a 12,000 BTU portable air conditioner rated for 950W input and it started up and ran for a few minutes, blowing cold air. After a few minutes it stopped running and made a loud humming sound until the inverter kicked off. At the time of the loud sound the inverter pulled over 250A. For some reason the portable air conditioner does not like being driven from an inverter... It is not a full sine inverter.
Any more thoughts? How much horsepower does the Zexel DKS15 require?
Is it possible to use two compressors in parallel? I saw the Highlander (I think) hybrid works like this. There is an electric compressor attached to a belt driven compressor. Either one or the other is used depending on if the engine is running or not.
My idea would be to use the engine compressor while running, and when plugged in it would use the hermetic type compressor.
Yes that's potentially workable. The major problem I see with it is getting the oil to flow properly. There's a risk that all the oil might end up trapped in the wrong compressor, the one that is not running so it doesn't need it. Also, large hermetic R-12 / R-134a compressors are hard to find in junkyards. Nearly all electric air conditioners run R-22, and I suspect the performance of these compressors would not be optimal with a lower pressure refrigerant.
How about using a large 12v dc motor? I think treadmills use them. That would eliminate the need for an inverter and the problems of converter efficiency and inductive ac load.......
I have decided to move the large alternator to the stock alternator location and install a regular belt driven A/C compressor, for now. In the future I would like to explore adding another compressor.
Maybe you can help me understand how the oiling of the compressor works. This is my guess, the oil will tend to settle in small spots, like little nooks where the tubes are soldered, extra space around hose fittings, a film on the hose wall, etc., where there isn't a lot of refrigerant flow; this oil won't lube the compressor. It collects in the condenser, dryer, etc. This oil is compensated for by adding more oil to the system so that there is enough flowing around with the refrigerant when running. Does that sound right?
Adding another compressor would act like another 'oil trap', although unlike the other oil traps there isn't refrigerant flowing around it all the time. So possibly the hoses leading to the second compressor and the entire compressor could fill up with oil and starve the running compressor. Perhaps if the compressor could 'drain' back to the main refrigerant hoses it might trap a controlled amount of oil... If anyone has any thoughts on my theories feel free to share.. Thanks.
I did look into 12V motors, however to power the 12V motor from 120V while plugged in at a campground I'd need a large power supply. Also that 12V motor could still need to be 5 horsepower or something unreasonably large.
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