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Table saw - single phase motor burnt out

r8hil

Plastic
Joined
Jan 13, 2023
Location
Aylesbury - UK
That was as I figured.... bad start system, so run winding is the only one getting current, and it fries due to the motor not starting.

No sign of any other possible switching for the other (start/run) winding suggests that either there was an open capacitor, or some other interruption of the circuit to it (bad connection, etc). Also possible that a stall when using the saw led to excess current, since the capacitor may not allow enough current to burn the winding.

Cause is not the first issue, which is to get a good motor, or fix that one
Is there a way to check if current is passing through both windings, when wired up, with the multimeter? Since I replaced the capacitor it can't be that, so the problem might lie with the switch?
Thanks
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
Is there a way to check if current is passing through both windings, when wired up, with the multimeter? Since I replaced the capacitor it can't be that, so the problem might lie with the switch?
Thanks
At the moment, it won't matter much what originally caused the problem, since the fried winding is completely unreliable, even if it sorta works now (which I doubt, actually). Eventually, you will want to keep whatever it was from happening again.

Direct answer... set to ohms, connect to each end of the winding in question. The one with the capacitor, you need to connect to the wire after the capacitor, which will be one of the wires you connected the capacitor to.

We do not know the old capacitor is any good. So, yes, it could have been the capacitor. Currently, one winding is fried, so problems are quite likely.

As for the switch, it clearly connected power to the run winding, so it worked. For the type of motor it seems to be, power would have been connected to both, and the switch appears to have done that.

It could have been a stall of the motor, maybe a piece of lumber closed up on the blade, etc. Could have been a bad connection somewhere. Odds are the capacitor did not pass enough current to fry the winding, so only the "run" winding fried, but maybe the connection to the "capacitor winding" was bad. Can't tell from here.

I agree, the motor does not look that odd. Is there any sort of nameplate on it? Odd shaft sizes can be fixed with a lathe, or with an adaptor sleeve if too small. Make it fit the pulley.
 

r8hil

Plastic
Joined
Jan 13, 2023
Location
Aylesbury - UK
Forget the other readings I said. I was measuring the resistance with the jumper plate on so it was false! I've taken readings with the wires away from the terminals, run winding shows 4.5ohms and start winding shows about 12ohms. Does that sound normal?
thanks
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
Those numbers are possible, but the one winding looks not just overheated, but black with bubbled insulating varnish.

If that is actually true (it was just one view of the end where I think I see that) then the motor is not reliable, and may not be operational or even safe.

What power is the motor? I do not think we have that piece of data.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
That does not look at all unusual, aside from having the switch inside, possibly size, and any special size shaft. It appears to be a standard foot-mounted motor. I would think it can be replaced with a similar motor fairly easily, although the shaft might need to be machined to size (don't know if it is smaller or larger than standard for the size).
 








 
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