Question about Saws
Motor stopped working. When I turn it on, the motor hums but the belt does not turn. Could the problem be the Starting Capacitor?
Assuming the motor shaft is not frozen and the rotor turns freely by hand
All single phase induction (No brushes) motors require energizing a "starting" winding for a second or so to get the thing turning.
Once the armature in turning the "run" windings take over and the start winding is turned off. If power is left on more than a few seconds without the motor starting, the starting winding will be permanently damaged. It can tolerate power for only a few seconds.
The momentary connection to the start circuit is controlled by any of several different methods. The most common system is a switch located at the opposite end of the motor from the output shaft. The switch is in the end cap and there is a flyweight on the armature that opens the switch when the motor gets up to speed. If the switch fails to make contact when stopped the motor won't turn. The contacts can be worn to the point of not contacting or it may have sawdust or other matter between the contacts. Whatever the reason the contact is not making connection to the start winding.
Another method use is an "Inrush" relay. This may be located in the motor or anywhere else like the manual switch box or another box exclusively for the relay. Radial are saws frequently use this system. When the motor is powered up the current is several times the current that it takes to keep it running. This high current (inrush) is detected by the relay and snaps closed until the current falls to the lower running condition. In this design the relay is open at rest and closes for a small amount of time at power up.. In the first design the contact is closed anytime the motor is at rest and opens when up to speed.
Look for a fault in these areas.
There are many other ways to start single phase induction motors, but these are by far the most common.
Posted on May 12, 2013
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Posted on Jan 02, 2017
SOURCE: My very old Craftsman 10"
Go to searspartsdirect.com and put in your model number. Look at the motor and wiring section. Look at item 16. The motor overload protector. (probably your reset button) WIth saw unplugged, unwire one sid of this switch and test with an ohm meter. You should read through the switch. If it is open then that's why the saw doesn't work. Many of this type of oveload requires quite a push to reset as you're flexing a klixon disc back to make contact. If is open and you can't reset, it's available there although a bit high priced.
Posted on Aug 13, 2010
Testimonial: "Thank you so much, I really appreciate this information and advice."
by seized is it burnt up or are the bearings just bad, the bearings are minimal but the field/armature would be more. Give me the model number and I will try and find a breakdown and let me know what we are looking for and I will try and help.
Posted on Oct 01, 2009
Testimonial: "Thanks Rowdy, The motor model is RM871. The table saw is 137.248481. It actually hasn't seized, it still turns very slowly, but makes a terrible noise"
You can try Sears but they can be a bit pricey. I use to send out motors for a factory I worked in to a rebuilder who would even do new windings. Check in your area for a rebuilder, As for the replacement being a Sears unit they may have a similar motor in stock. Good luck.
Posted on May 08, 2009
SOURCE: I have a 10' Craftsman
If this is anything like my table saw, you shouldn't need to remove the motor, just lower the blade all the way, reach in from the back and place the belt over the pulleys while holding the motor all the way up. If the belt is too short, it might be the wrong one. They shipped me the wrong one twice, I finally went out and purchased a universal belt (constructed kind of like a bicycle chain) from a local woodworking supply shop. Its been working great for 2 years.
Posted on Jun 20, 2009
On the motors I deal with there is a series of numbers that identify the shaft size, hp and all other requirements. I would try and contact a local Grainger and see if they can help, if not try in the yellow pages for a motor repair shop in your area and sometimes they can get you one. Good luck
Posted on Jul 18, 2009
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