Induction Motor with no cap/switch

Thread Starter

cooljjay

Joined Sep 1, 2021
1
I'm needing help, I have an old Craftsmen table saw with a direct drive motor...n it's driving me nuts!

First the original motor, as you can see....I had to take it apart to clean it, done multiple times.....I reassembled it back, to the lovely smell of burning something and smoke....took it apart twice after that, got it working....put it back in the saw, attached the blade and now it grrrs and the shaft locks tight and trips the breaker....there is only a start n run winding, no capacitor...no centrifuge switch and no brushes..as can be seen in the next photos..there is just something called a "motor relay" believe its like an old mercury switch...if the table falls, locks the saw...

So now, I found a used motor, identical to this but uses a start capacitor as well as the "motor relay", now this was sold to me as used working....I went to power it on and it just didn't seem to have the power.....after a second, burning saw dust smell and smoke that wouldn't stop...so powered it down, went to another outlet and same thing...powered it off....came inside, removed the breaker/power switch from the control box....powers on now, no smoke but still not sure if it has the power needed....

Can anyone help explain to me, about these induction motors? Are the windings just on death's door because of a poor design and I am just pushing em over the edge or is there a fix etc? Really driving me bonkers...
 

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MaxHeadRoom

Joined Jul 18, 2013
23,899
If it does not have a switch, it most likely has a current relay that is in series with the start winding and opens up once the current drops after starting.
 
The capacitor shown in your image (based on it's value) seems to be a start capacitor. That capacitor needs to be removed from the start winding when the motor attains about 75% of it's rated speed. Failure to do so will release the smoke stored in the windings. The switch that Max mentioned, if working correctly, will do that.

There are three ways to open up the capacitor/start circuit. 1. centrifugal contacts on the motor (which you don't have, and would be bad in a dusty environment). 2. current relay (usually a sealed unit out side the motor, or 3. electronic disconnect, (does the same as the current relay, but no actual relay, just electronic components}.
If the start relay fails, open, the motor won't start, but it will hum, and eventually release smoke.
If the start relay fails, closed, the motor will spin up, draw lots of current, then smoke, quickly. Sparks and fire will follow quickly too(or your breaker will trip).
Here is more information (disregard the run capacitor in the included diagram in your case)
https://eepower.com/capacitor-guide/applications/motor-starting-capacitor/

In the past I have replaced failed centrifugal contacts with electronic, externally designed switches, small enough to embed inside the motor housing (it was a larger motor, about 60 years old).
Here is an EXAMPLE only https://store.eurtonelectric.com/univeralmotorstartmoduleupto3hp-3.aspx

If you go this route, you should buy one based on the current draw of your starter winding.
I've never heard of a mercury switch on a table saw. I do know they make heavy duty merc switches but other than minimizing contact ware I don't see the need on a table saw.
 
Single phase induction motors that use a Current Relay sometimes have no internal spring, and absolutely need to be oriented correctly with gravity, to operate properly. If not the start winding won't operate, and you'll never come up to full speed; or it won't give full torque, and instead just overheat after several minutes.
 
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