AC/DC variable speed motor

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Old 04-26-09, 12:45 PM
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AC/DC variable speed motor

Hey I new to the forum and I know very little about converting AC to DC and what I would need to do so. Im looking to get a DC motor that would have enough torque to lift about 5 pounds. I would like to run it off 120V AC plug. I need a DC motor because it will have to be a variable speed starting at very low speeds. Could someone please post on what I would need to accomplish this and how to put it all together to make it work.

Thank you.
 
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Old 04-26-09, 02:45 PM
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Welcome to the forums.

Is there a reason why you can't use an AC motor and controller?
 
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Old 04-26-09, 03:00 PM
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I may be wrong but I believe AC motors have very little torque when run at less the 1/3 speed as well over heating issues when run below 1/3 speed. If I am wrong please correct me. I would use an AC motor if it has no risk of over heating at very low speed and still have the torque I need as I would be using it for about 45 min. straight per use.
 
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Old 04-26-09, 03:12 PM
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Another solution is a continuously variable pulley set up. I repaired a few of these 30 years ago but can't remember the exact name. Cone shaped pulley halfs are pushed in and out by electro mechanical means to very pulley diameter. An idler pulley keeps the built tension. You can adjust speed while running.
 
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Old 04-26-09, 03:32 PM
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Well if you're going to use a d/c your will need a variable speed drive. I'm not sure what you're needing to for but most of the time you would also have a gearbox with the motor. The gearbox will give you the torque and better control at lower speeds.

jim
 
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Old 04-26-09, 03:34 PM
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Never seen one do you think I can pick those up at your local hardware store or should i hit up a electric motor repair shop?
 
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Old 04-26-09, 03:37 PM
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I agree with Ray, I think you need a pulley or gear set up to do the work. The motor will only provide the movement. Once geared or pullied correctly, the motor can run wao all the time and you can control the lift, etc via the workhorse set up. If this is a school project, change your theory from the motor itself to a method of lift.
 
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Old 04-26-09, 03:51 PM
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Originally Posted by sparky76 View Post
Never seen one do you think I can pick those up at your local hardware store or should i hit up a electric motor repair shop?
Hardware store not likely. but you might try a motor supply store or Grainger. If this is a school project your going to need a government grant unless daddy is rolling in it.
 
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Old 04-26-09, 06:04 PM
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check out the surplus catalogs

Look for a 90v DC gearmotor, and a line connected controller board. The board takes 120vAC directly and expects a potentiometer control. I'd expect under $100.
Since you are lifting, the gearmotor should allow power off and not let the load fall, within limits...
 
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Old 04-26-09, 06:49 PM
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Thanks alot I was just going to say i think i am going to go with a gear motor. Would it be more cost effective to go with a bridge rectifier and a capacitor and wire in a 5amp speed control before the rectifier? or with a line connected controller board? or is that the same thing?
 
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Old 04-27-09, 04:48 PM
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Unless you really want to fiddle, i'd go with an off the shelf controller. There are plenty of them out there. If you do your own, there is no need for a capacitor, since the motor back EMF smooths the voltage. Also, the commercial boards allow easy motor reversal, which is just a output polarity change.

The other, much different idea, is to use a stepper motor. Totally different design, both motor and controller. I'd try for the 90v gearmotor first, maybe a 20:1 reduction, but it's not critical.
 
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Old 04-28-09, 10:00 AM
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You might experiment with a Milwaukee " Right-Angle drill if you can couple the driven load to the drill chuck.


This drill operates with a "series"-type motor where a reduction in motor speed will increase the torque. The slower the speed, the higher the torque .
 
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