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Author Topic: ac compressor weight  (Read 3888 times)
kyle4501
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PD4501 South Carolina




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« Reply #15 on: July 31, 2006, 08:06:14 PM »

............And our bus engines turn on average at 2400 rpm. this means the small compressors would only be able to put out 1/3 of the cooling that they can produce. Unless someone has an idea on how to spin themfaster on a bus engine??? Let me know! .......

Thanks for bringing up the rpm/ capacity point.

You could belt from the crank shaft pulley to a smaller dia pulley on a jack shaft. Then have a large pulley on the jack shaft belt driving the compressor. (The the belts & pulleys would need to be sized properly for it to last). I like the idea of an over the road A/C that uses an engine driven compressor for additional cooling of the front of the bus while driving.

Most people don't realize that an auto A/C is 3+ tons capacity. My 3 ton home unit pulls 26 amps at 220 volts, so wouldn't that be 475amps at 12 volts or 238 at 24volts. Then you have to add in the efficency losses. The electric power has to come from some where. The advantage of all electric A/C is that you can run it off the genset & leave the main motor alone to push the coach up the mountain.

BTW, I like trying to reinvent the wheel, sometimes you get lucky, but mostly you learn why it is the way that it is.
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I know you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant. (R.M. Nixon)
TomC
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« Reply #16 on: July 31, 2006, 10:14:05 PM »

To talk a little more on car type A/C compressors.  The Sanden SD7H15 7 cylinder compressor is rated at these figures- 1,000rpm-2.5hp and 10,000btu; 2,000rpm- 4.5hp and 18,000btu; 3,000rpm- 6.5hp and 23,000btu; 4,000rpm- 8hp and 27,000btu.  So you can see that the new compressors are not using the excessive horsepower of compressors of yesteryear.  If you used two of these compressors  running at 2 to 1 speed with the engine, it would work well.  For instance, if you were cruising at 1,500rpm on the engine, the compressors would be turning 3,000rpm, using 13hp and producing 46,000btu's total.  You can either run two (or more) compressors on the same circut so long as you size the freon lines accordingly.  Trucks have been doing this for years with the normal engine compressor and then an additional small engine driven compressor when stopped with the help of another electric fan condensor for the truck system that is built in the dash.  The reason you can run multiple compressors is because of the reed valves in the compressor will keep the freon running the same direction, or when one is off, it will block the back flow from the other compressor.  Also, remember that car compressors are rated to turn 5,6, 7000rpm, not because that's where they produce their power, but to be able to with stand those times you kick it down into passing gear.  Even though the above Sanden compressor will turn 6,000rpm, you can see that Sanden only rates it for up to 4,000btu since most car compressors are run at nearly 1 to 1.  And with the relatively low hours we put on the systems, car type compressors will give you many years of service.  Then when you do need a new one, it would be much easier than trying to find the big Carrier type compressor on the road.  Personally, I like the idea of two compressors powering two separate systems-one for the front and one for the back.  BUT-we'll do it our way!  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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