help converting a motor to run on AC

Thread Starter

wazeer

Joined May 30, 2010
11
Hello all, checking in with a project that I need help with.

I am building a turn table to turn aluninum wheels on so that I may use a buffer to polish them. I need it to be a variable speed so I can start slow and finish up at a higher speed.

Here are the specs on the motor I found:


SPECIFICATIONS
  • Speed 250 RPM
  • Voltage 130 DC
  • Amperage 0.5 Amps
  • Power 1/12 HP
  • Torque 10 in - lbs.
  • Gear Ratio 10:1
  • Rotation Reversible
I want to run this motor on 120 vac and need to be able to control the speed from 0 to 250 rpm. I have been studying on it and realize I need a full wave rectifier, however I am not sure what else I would need to complete this.


I am curious how some of you would design this?


Thanks in advance.
 
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Thread Starter

wazeer

Joined May 30, 2010
11
Ok, If you dont mind me asking, what would be involved in building that?
From what I understand I will need a transformer that will take the 120 volts to 130 volts,
then a full wave rectifier to change from ac to dc
A potentiometer to adjust the voltage / change the speed
I have read that a capacitor could be used to smooth out the voltage, however it may not be needed because it running a DC motor
 
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jpanhalt

Joined Jan 18, 2008
11,087
It appears your interest is in polishing aluminum wheels, not developing a motor control. I suggest you look at a low cost (<$100) commercial solution.

Check out:

http://www.driveswarehouse.com/Drives/AC+Drives/?gclid=CObQyOmo_KECFRdSagod3X-jDQ

http://www.kbelectronics.com/catalog_chassis.htm

Your 130 VDC motor is a bit odd, but maybe at such a low HP rating, it is not. Even with a 1:10 gear reduction, I wonder whether it will have enough power to rotate against the buffer. But then, that is another issue. Since the price difference between a 0.5 to 1 HP controller and a 1/12 to 1/6 controller ( if made) is probably pretty small, I would go with a slightly larger and possibly cheaper controller just in case you have to get a more powerful motor for the turntable.

I have found ebay to be a relatively cheap source for DC motor controllers, once you have narrowed your choices. You will find new KB drives for less than $100 and used for $30 or so in the 1 HP and less range. As usual, beware of "removed from operating machinery, condition unknown" ads. That may mean that the machinery was just fine, it was the controller that started to smoke.

John
 

Thread Starter

wazeer

Joined May 30, 2010
11
Thanks for your replies. My interest is in building this turntable, but I am also interested in having something with a practical use. This is why I want to build as much of it as I can. I realize this motor might be a little undersized, however all it has to do is turn the wheel so I can polish the wheel evenly.

I think the wheel, once up to speed, will act as a flywheel and help to keep the wheel spinning.
If I could chuck it up in my lathe it would work perfectly.

So if you guys think building a power supply is too hard or not practical, I will scrap the idea. If it is something that can be built, then I would really like to bo it.

Can 120 vac operate this motor without using a step up transformer? If the transformer would make it operate better then I will go that route. If I understand it correctly, a full wave rectifier will operate the motor with out a smoothing capacitor.

I really appreciate your guys replies, and I hope I am not being a nuisance.
 

jpanhalt

Joined Jan 18, 2008
11,087
Without knowing what type of DC motor you have, one cannot say whether it will operate on AC. I suggest you read these links:

http://en.wikipedia.org/wiki/Brushed_DC_Electric_Motor

http://en.wikipedia.org/wiki/Universal_motor#Universal_motors_and_series_wound_DC_motors

For the second link, scan down to the section on universal motors.

Can you post a picture of the data plate for the motor? What was its originally intended use? Is the motor reversible (easily)? Does it have permanent magnets? These characteristics may give a clue as to whether it can run on AC. I suspect that if it has just a DC rating that it is not a universal motor.

In any event, just hooking a bridge rectifier between the motor and the mains is a dangerous suggestion. Where did you get that idea? If the mains are 120V and you simply rectify it, the maximum rectified voltage will be more than 130 V DC.

John
 

jpanhalt

Joined Jan 18, 2008
11,087
From the link given in post #9:

Protech right angle permanent magnet gearmotor.
It won't run on AC. As previously suggested, you need a real power supply -- not just a bridge across the mains. If you want variable speed, then PWM is the way to go.

John
 

Bernard

Joined Aug 7, 2008
5,784
Based this on GE SCR Manual, 5th ed, 1972, fig 10.9. It is simple & if using NTE 5646 TRIAC, the DIAC is built in. Caps 300V, 100 ohm-1W, diodes 2A, 300V bridge or even 1N4004's.
 

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Thread Starter

wazeer

Joined May 30, 2010
11
I just looked on fleabay and all the PWM's were for 12 to 40 volts. So you think that maybe I should look for another motor?

I want something that will stay between 0 and 200 rpm. I assumed that DC was the only way to go. What about an AC motor. Does anyone know of an ac motor that will do this?

Once again I really appreciate all the help
 

Thread Starter

wazeer

Joined May 30, 2010
11
I finally have made it back to this project. A coupla changes. I found a 90 volt DC gear drive motor It has more HP than the other motor I was looking at. Now for a coupla questions.

I have a motor controller that came out of a treadmill which also had a 90 volt motor. Is a motor controller the same thing as a power supply?

Providing the amperage draw is the same for both motors, Wouldn't this controller be all I need to run this motor?

Lastly, the circuit has a 5.5 mh choke wired in series with the motor. Is this how the voltage is converted from AC to DC? I read where a choke is designed to block High frequency AC currents but allow lower frequency currents, DC, to pass. In laymans terms, what does this choke do?

Thanks for everyones replies, I will eventually get this thing figured out.
 

R!f@@

Joined Apr 2, 2009
9,918
choke is to prevent or eliminate interference.
it's not an AC to DC converter.

Showing what u have will help
 

Thread Starter

wazeer

Joined May 30, 2010
11
choke is to prevent or eliminate interference.
it's not an AC to DC converter.

Showing what u have will help
7

So I'm guessing the choke was to stop interference from the motor to the digital display that was on the treadmill.
 
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