AC Motor Speed Controler-Help Needed

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Old 08-09-09, 09:22 PM
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AC Motor Speed Controler-Help Needed

So, here's my story. I purchased an " Expander Wheel" to use on my bench grinder. Basically, it is a 6" rubber wheel that you slip an abrasive belt onto. When the wheel spins, it expands, holding the belt in place. Problem is, it is only rated for 2800 R.P.M. All my bench grinders are 3650 R.P.M. I tried it on a 1750 R.P.M. motor, but it's too slow.


Well, I found a motor speed controller on the internet, but it states " For all motors 3 H.P. or less, with brush type motors". So, now I wonder, do bench grinder motors have brushes? Another search tells me that todays grinders use "induction" motors. Another search and I find that this means they are brushless.


Wondering if anyone knows where I can get a speed controller for an induction motor. Also, I have a large exhaust fan in my shop, and I had an electrician install a speed controller on it. I don't recall seeing him climb up and check to see if it had brushes or not. The controller is made by Bamville, who according to their website, make ceiling fans. Would ceiling fans have brushes?
 
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Old 08-10-09, 12:07 AM
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Originally Posted by bunsorama View Post
So, here's my story. I purchased an " Expander Wheel" to use on my bench grinder. Basically, it is a 6" rubber wheel that you slip an abrasive belt onto. When the wheel spins, it expands, holding the belt in place. Problem is, it is only rated for 2800 R.P.M. All my bench grinders are 3650 R.P.M. I tried it on a 1750 R.P.M. motor, but it's too slow.
A. If you have belt driven grinder it very simple change the pulley arrangement to achived correct speed where you want to be at it.

Well, I found a motor speed controller on the internet, but it states " For all motors 3 H.P. or less, with brush type motors". So, now I wonder, do bench grinder motors have brushes? Another search tells me that todays grinders use "induction" motors. Another search and I find that this means they are brushless.
A. Most modern grinder motor are brushless type aka induction motors expect small or very cheap grinder will have brush motor and geared or belted down the speed to where it need to be at it.

Wondering if anyone knows where I can get a speed controller for an induction motor. Also, I have a large exhaust fan in my shop, and I had an electrician install a speed controller on it. I don't recall seeing him climb up and check to see if it had brushes or not. The controller is made by Bamville, who according to their website, make ceiling fans. Would ceiling fans have brushes?
Most modern motor do not have brushes unless you have DC motor it will have brushes on it and the exhaust fan you are describing that is induction motor and in the shop you may have three phase supply and if that the case what they will do is add a varibale frequicey drive or adjustable speed drive both funtion the same what it do is change the HZ { Hertz } to change the motor speed like example at 60 HZ which it is a normal North America supply and for 4 pole motor it will spin little under 1800 rpm useally about 1730 to 1750 RPM is common speed range and if you want to slow down to half speed what the VSD will do is change the HZ down to half like 30 HZ the motor speed will drop down to about little under 900 RPM.

Keep in your mind this part the VSD will work very well with three phase motor but single phase motor it is very limited with it due the starting winding in there and yes there is speed control for single phase motor but not very wide spread unless you have super small motor or PSC { perment split capaitor motor } then the speed can be change with voltage or HZ and somecase ceiling fan motor controller may work for that useage but one warning here they are designed when first turn on it will go high speed mode first then ramp it down it oppoiste of dimmer switch.

If you know what brand name motor or grinder let us know maybe we know a good speed controller you can use.

Merci,Marc
 
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Old 08-10-09, 10:21 PM
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All my bench grinders are direct driven, no belts. Typical Harbour Freight cheap grinders, totally enclosed. The motors have very limited specs on the tags. Just RPM and voltage. Some have horsepower ratings, some just list amp draw.


My shop is single phase and the speed contoller on my exhaust fan does just as you described. It starts on high speed, then you turn it further clockwise to reduce the speed. I think this would work on my bench grinder as it only runs full speed for a millisecond if you turn the knob quickly.

I don't think the motor would know if it was turning a blade or turning a wheel. Unless there is a specific load that needs to be on the motor for the speed reducer to work.

Here is a picture of the controller for brush type motors. I was hoping to find something similar for induction motors. You just plug it in. But, I do recall my exhaust fan controller has a heat sink on the outside, so that might be a problem.




 
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Old 08-13-09, 10:14 PM
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Well I decided to try a ceiling fan controller to see what would happen. It is a Leviton "Trimatron", Model # 6616, rated at 5 amps. It works extremely well on one of my grinders, not as well on another, and not at all on two more. The one it worked well on , the motor did not get hot, made no strange noises and the controller did not heat up either. So, I 'think' I am good to go.


Strange thing is that this motor speed controller was $12.00, but they want $19.00 for an incandesent light bulb dimmer, which I think would be a top seller.
 
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