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Date:         Wed, 19 Apr 2000 12:36:05 -500
Reply-To:     ehall@TOGETHER.NET
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Ezra Hall <ehall@TOGETHER.NET>
Subject:      Re: A/C compressor Power usage
Comments: cc: Jim <jrasite@EONI.COM>
Content-Type: text/plain; charset="iso-8859-1"

Folks, Well, I probably should have saved this thread for Friday!

Thanks for all the responses! The consensus is, approx. 5HP is needed, way too much power for a reasonable sized motor per the below note and my browsing through MSC and Grainger. I suspect practical cooling levels could be obtained with fewer HP (not as many cooling BTU's), but even a 2HP motor is large!

Another suggestion, use an A/C compressor from a houshold unit. This may be a possibility, but not without problems. I am not sure if the refrigerant and oil used for Houshold compressors is a close enough match to R12 for compatibility. Perhaps the oil could be flushed and changed. Bypass valves may need to be added to the Freon lines to select which compressor to include in the loop. Best case, one could add an external compressor connecting to the low and high side ports. The valves on the existing compressor would prevent backwards flow of refrigerant when the added compressor is in operation, and vice versa preventing the need for selection valves. An interesting and possible implementation, but not one I will persue since I don't have the equipment to work with freon...

In summary, I will not be trying any of these options, and will instead make sure all our screens are in good shape! Thanks for humoring me! Ezra

Jim wrote: >Wow, an off-the-wall question that I have experience with!!! >We have a stationary crane where I work. It has an automotive >a/c unit run by an electric motor. It is geared 2:1 (2 turns >of the motor to 1 turn of the compressor) We use a 1725 rpm >motor. I currently has a 5 hp 3 phase motor on it and come >summer, it will, no doubt burn up yet another motor. This >year I'll up the hp in hopes of precluding another melt down >to a 10 hp motor. A 10 hp THREE PHASE 480v motor draws about >20 amps. (Guessing... the NEC* is at work.) AFAIK they >don't even make a 120v 10 hp motor. If they did, it would >draw about 80 amps. That's a lotta juice, my friend. Not >really practical. > >Wait, I just found the 1999 NEC*... 10hp single phase, >120v motor draws 100 amps. That's 4 ga. wire to feed it. >About the size of your jumper cables. Definitely more than >your local campground will have available.

Jim


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