View Full Version : how to slow down a 120v motor
12-31-2008, 12:36 PM
Can anyone help me I need to slow down a 120v radial arm saw. It is an older model with 6 brushes. The saw runs at 5500rpm and I need to go under 5000rpm.
12-31-2008, 12:55 PM
Run it at a lower frequency. A VFD would be a logical choice, or replace the motor.
12-31-2008, 03:03 PM
As long as its a brushed motor you can use the cheaper versions of speed controls out there. Harbor Freight has one that I believe will handle 15-20 amps. You didn't mention the amps that your motor draws, should be on the same plate as the 120V info. Whats nice in this situation is you only need to drop a small amount of RPM's. The more speed you have to drop the more torque you will loose with this type controler so I believe in this case you will be OK. The controller should be in the $20 category. Just check to make sure you are in the right amperage range of the controller. Kurt.
12-31-2008, 03:11 PM
There is no name plate on the motor itself. The unit is just plugged into a 120v circuit which is protected by a 20amp breaker. I did see a controller on e-bay for 16.95 the looked like it would fit the bill. It mentioned a 20amp capacity as well. Since this is a radial arm saw the motor is a intregal part of the saw and can't be replaced. We are attempting to use an abrasive wheel on the saw after our 10" saw died today. Found a 12" old Dewalt saw and thought it would be perfect but wasn't thinking the max rpm for a 12" abrasive wheel is lower then for the 10" we had. Also the new saw has a 1" arbor whereas the old 10" had a 5/8" so we can't just put a 10" wheel on the 12" saw.
12-31-2008, 04:46 PM
Well, you certainly have a dilema there. Its very important that you don't go over the recommended speed. You don't want a wheel comming apart at 5K rpm! I suppose if you have a tachometer you would be sure. Aside from that it would be a crap shoot and not too safe. Good luck, but stay safe!
12-31-2008, 05:29 PM
I do have a tach. It was fresh out of my frozen truck and the display wasn't working very well probably do to frozen batteries but it appeared to be going 5500rpm. I will retest Friday and figure out what to do.