7 replies so far
#1 posted 07-20-2017 05:18 PM |
HI- I have a router speed controller and a palmgren 8” grinder. ==the speed controller is used for a single speed router when I need it- and never tried it for another purpose- but will see if I can get you the answer you need. |
#2 posted 07-20-2017 05:23 PM |
I have generally read the advice that you should not use a speed controller on an induction motor. Most of the speed controllers are made for the screamer type motors which work differently. Most grinders have induction motors, so do do that right you would need a VFD, and a way to cool the motor when it was running slower than designed. Brian -- Part of engineering is to know when to put your calculator down and pick up your tools. |
#3 posted 07-20-2017 05:25 PM |
Lighting dimmers are not the same thing as motor speed controllers, they work differently. You will harm the motor by using a lighting dimmer. |
#4 posted 07-20-2017 05:28 PM |
There are variable-speed AC induction motors I’ve got by for years using a 3400 rpm |
#5 posted 07-20-2017 05:30 PM |
“Poles and Speed The number of poles, combined with the ac line frequency (Hertz, Hz), are all that determine the no-load revolutions per minute (rpm) of the motor. So, all four-pole motors will run at the same speed under no-load conditions, all six-pole motors will run at the same speed, and so on. The mathematical formula to remember in helping make this calculation is the number of cycles (Hz) times 60 (for seconds in a minute) times two (for the positive and negative pulses in the cycle) divided by the number of poles. Therefore, for a 60-Hz system, the formula would be: 60×60 x 2 = 7,200 no-load rpm ÷ number of poles. For a 50-Hz system, the formula would be: 50×60 x 2 = 6,000 no-load rpm ÷ number of poles. Using this formula, you can see that a four-pole motor operating on the bench under no-load conditions runs at 1,800 rpm (7,200 ÷ 4 poles). Note that when an ac motor is loaded, the spinning magnetic field in the stator does not change speed. Instead, the rotor or moving part of the motor is restrained by the load from “catching up” to the field speed. The difference between the field speed of 1,800 rpm in this example and the rotor speed of approximately 1,725 rpm is called the “slip.” Slip varies with the load over a narrow operating range for each motor design.” source: http://www.achrnews.com/articles/84983-how-to-determine-speed-for-an-ac-induction-motor |
#6 posted 07-20-2017 08:07 PM |
Thanks everyone. Mine was just a thought, and I will gladly put that brain fart in the trash. |
#7 posted 07-20-2017 08:18 PM |
what Loren said. Also, single phase induction motors use a starting capacitor to get the motor rolling. To use a VFD on an induction motor to control speed, you have to have a 3 phase induction motor (you can create the three phase power with a VFD that runs off of single phase as the output is electronically created, but the motor must be wound for 3 phases). There is not starting capacitor on a 3 phase motor. Instead, the three rotating phases (120 deg apart) create the starting torque to spin the motor up from a dead stop. -- Matt -- I yam what I yam and that's all what I yam |
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