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Electric Motors/Motors capable of variable speed?

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QUESTION: Hi, I am wondering if either of these motors I have are capable of variable speed. Motor 1 has 3 speeds, but I want a motor that I can slow down to a range of about 1/2 a rotation/second to 10 rotations/second. If these motors wouldn't be damaged by lower voltages, would a standard house light dimmer be an acceptable way to implement variable speed?

I can do simple things like add a 5 or 15 watt or more single-value resistor (potentiometers that can handle wall power cost as much as one of these motors). I wouldn't have any idea what ohms would be appropriate, though.

Motor 2 came attached to a capacitor. Motor 1 did not. Would I want to get a capacitor for it before using it? If so, do you know what specs it should have?

Thanks for any help you can give!

ANSWER: Unfortunately you reduce speed by varying voltage.
Both motors are induction single motors designed to run at 1050RPM and 1650 rpm respectively
Reducing the voltage will not reduce the speed. It only weakens the magnetic field and thus reduces the torque and HP.

You need to use a gear box with a DC motor to have the speed ratios.

---------- FOLLOW-UP ----------

QUESTION: Thanks! What are motors called whose speed can varied with voltage (other than "non-induction")? I only need minimal torque and don't need any faster than 20 revolutions per second. (It will spin something that weighs a few ounces.)

Also, is the capacitor soley for reducing start-up amps? Can you suggest what I can Google for to find out how to calculate what specs I need for motors? (I have a third motor that might need its capacitor replaced, but its markings are illegible).

Answer
Correction. In my previous answer it shoud have said: "you CANNOT' reduce speed.......

You need a permanent magnet DC motor which will vary speed by varying voltage.
The capacitor increases the start up torque under load and also reduces the running current.

cant use the 3rd motor since it is a cap start motor.  

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Harcharan Singh Diocee

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Electric motor winding redesign, AC and DC. Troubleshooting, motors controls generators. Vibration analysis, dynamic balancing, root cause analysis: electrical and mechanical.

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thirty five years electro-mechanical and Senior Management

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Journeyman Motor Rewinder, Millwright, Industrial Electrician, Vibration Analyst level II. Certified Electrical Technician ASTTBC, FSR Class B, in BC. Laser alignment specialist. Marine machinery repairs. Business Management Certificate. Last 19 yrs as Plant Manager

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