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Old 04-01-2009, 09:50 PM   #731 (permalink)
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A/C motor control would probably see a higher demand then the one you designed too. If I remember correctly, AC motors are much more adaptable to regen braking.

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Old 04-01-2009, 09:55 PM   #732 (permalink)
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I think Roger means Air Conditioner motor rather than Alternating Current Motor. I have no clue how to make a controller for an AC motor. hehe.
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Old 04-01-2009, 10:12 PM   #733 (permalink)
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Cool! All I need it to do is for it to ramp up to speed. This motors full load speed is 4000 RPM. I'll have like a 3:1 pully reducer to connect it to the compressor. Its a brushed PM DC motor, not a series motor live the traction motor. So, it has lower torque. What might work good is to use the 5K pot input like on the standard controller, so I still have speed control in case I need to turn it up or down a little bit. All we need is say a 3-5 second ramp up to speed. I'm sure I can put together the output stage. I'll be very conservative on the ratings of components, so I get nice long life and no temperature issues.

Even though this can easily be done with the little 8s, if your going to standardize on the 16s for the PCB layout, lets just go with them. You can always sell 8s on EBay :^)
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Old 04-01-2009, 10:27 PM   #734 (permalink)
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Sounds good, Roger! Oh Heck, they were only like $1.80 each anyway, including shipping! hehe. I like the idea of manual control over the A/C. May as well have hardware current limiting too! The hardware current limiting parts are like $2! You can even use the same PCB layout, just with a different resistor value before the 383 comparator, to set the current limit to something more reasonable (like NOT 500 amps. unless it's a really really hot day).

Oh Dear! I need to order some ATMega16's! All the digikey and mouser stuff came today, but I forgot to order the ATMega16's. I'm such a whippersnapper sometimes.
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Old 04-01-2009, 10:33 PM   #735 (permalink)
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Quote:
Originally Posted by Roger Heuckeroth View Post
What I would like to do is adapt your design to run an accessory motor for the A/C. I have a 2 HP DC motor that I will connect to the A/C compressor.
Are you over-volting this motor to give it more horsepower? Even with a reduction ratio of 3:1 I'm not sure 2 HP will provide enough oomph to pull the compressor, unless it is a fairly weenie one. I don't remember how old-school my A/C learnin' is, but I remember at the GM school an instructor saying that a compressor under full load can require as much as 20 horsepower...

...of course I haven't checked to see how successful other conversions have been at this, so the point may be moot...
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Old 04-01-2009, 10:45 PM   #736 (permalink)
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20 horse power! No problem! Current limiting set to 500 again! hahaha!
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Old 04-01-2009, 10:56 PM   #737 (permalink)
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Quote:
Originally Posted by Intrigued View Post
Are you over-volting this motor to give it more horsepower? Even with a reduction ratio of 3:1 I'm not sure 2 HP will provide enough oomph to pull the compressor, unless it is a fairly weenie one. I don't remember how old-school my A/C learnin' is, but I remember at the GM school an instructor saying that a compressor under full load can require as much as 20 horsepower...
Outside of commercial/industrial applications, an A/C compressor is not going to use 20HP of power constantly. Even a large central A/C unit is only 4HP or so at most. It would not be unreasonable for a compressor to use 20HP for a split second on startup, however. Therefore, you'll actually need two current limits. One that acts instantly if the current exceeds LRA (Locked Rotor Amps) and another with a time delay of a few seconds that prevents the current from rising above FLA (Full Load Amps) for an extended time.

Also, belt drive for A/C compressors is long obsolete. Direct drive is the way to go. (Indeed, modern A/Cs even direct drive the fans.)
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Old 04-01-2009, 11:02 PM   #738 (permalink)
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Intrigued,

It's the same thing like someone saying your going to run that big car on that little 20-30 HP electric motor. People try to compare engine HP knowledge to Electric motors and they don't understand how John Wayland's White Zombie with two little siamese 8" motors blows away the Corvette in the other lane.

Seriously though, 2 HP is plenty. This motor is designed to do 2 HP continuously. A typicall 6000 BTU window air conditioned has about a 1-1.5 HP compressor. This motor will be spinning the compressor at 1,330 RPM, which shouldn't be too much load. If it does bog down too much I'll drop it to a 4:1 ratio.

Compressors normally follow the rule that if you double the speed you quadruple the HP. So maybe your instructor was right. If the compressor was running with the engine revving to high RPMs, maybe it could pull as much as 20 HP.

One side note. Some people have tried treadmill motors to run A/C compressors. They are about half the size of this motor, and they don't quite have enough torque. However, they will work fine to run power steering pumps.
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Old 04-01-2009, 11:40 PM   #739 (permalink)
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Also, belt drive for A/C compressors is long obsolete. Direct drive is the way to go. (Indeed, modern A/Cs even direct drive the fans.)
HUH??? Am I getting too old school here? I've never met a car that had a direct drive A/C. What do they drive it off of, the timing chain???
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Old 04-01-2009, 11:49 PM   #740 (permalink)
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Quote:
Originally Posted by Roger Heuckeroth View Post
...People try to compare engine HP knowledge to Electric motors and they don't understand how John Wayland's White Zombie with two little siamese 8" motors blows away the Corvette in the other lane.
Guilty! Yeah, I still have problems with electric horsepower being unequal to gas horsepower...

Also, yes, it was only during high load times that a compressor would pull 20 horsepower. I'm thinking the class I heard this in was the V-5 GM compressor, which varies displacement according to load. They were going on about how these compressors would use so much less horsepower when it wasn't needed, to help with fuel economy. This was about 20 years ago, so I'm guessing they've come up with more efficient compressors...

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