have to start lathe motor by hand

[Trojan62]

hi
i have an old lathe from 1980 that i bought about 2 months ago, recently i noticed that there was an auful clanging noise from the motor and presumed that the fan had come loose. when i opened up the motor this was the case.
anyhow, i fixed the fan back and it was running ok, but since i put the motor all back together again i can only start it by giving the belt wheels a quick helping hand spin. when i turn the lathe on it sounds as though is wnats to run with a humm noise, but then i have to spin it to get it going.
im not sure if im right, but is this trouble with the capacitor, if my motor has one.
the only thing is, is if it is the capacitor its not the type on the outside of the motor and must be inside somewhere.
if this is the case, im a bit loath to open up the motor again.

any ideas......

thanks......

 

[footprints]

Very long shot, but worth checking first is the polarity of the wires correct where you disconnected the motor? Might make a difference if the capacitor is connected the wrong way. Always works in Star Trek and other sci-fi films!!

 

[davelx]

Very long shot, but worth checking first is the polarity of the wires correct where you disconnected the motor? Might make a difference if the capacitor is connected the wrong way. Always works in Star Trek and other sci-fi films!!

http://www.youtube.com/watch?v=-VYyoJu0I70

 

[JohnW2]

Very long shot, but worth checking first is the polarity of the wires correct where you disconnected the motor? Might make a difference if the capacitor is connected the wrong way.

I don't think that AC usually knows or cares much about 'polarity' . However, it's obviously possible that the OP disturbed the connection to the capacitor (assuming there is one), or the capacitor itself, when he had the motor opened up.

Kind Regards, John

 

[footprints]

Worth checking for Tribbles too!

 

[nickjb]

Certainly sounds like the starting capacitor. Mine went pop when it got a bit full of metal swarf. It needed a hand to start up at high speed. New capacitor and it was good as new. Cost about 80p from Axminster, who supplied the lathe around 20 years before.

 

[conny]

Worst case scenario is your start winding has burnt out if there is no internal cappy.

Is the fan internal or external with a small cowl over it? If external then there would be no need to touch any of the wiring.

Can you post a piccy of the terminal board? It may be that if you have disconnected anything you may have put it back wrong.

 

[eveares]

As others have said, it is most likely the start capacitor.

The start capacitor provides the motor with a current inrush to the start/aux winding of the motor what allows the motor to initially start turning by providing a phase shift in the start/aux winding against the main winding.

When the motor if first turned on, the start capacitor is in the circuit until the motor reaches around 3/4 of its rated speed, the start capacitor is then removed from the circuit what is usually done with a centrifugal switch built into the motor.

Your problem is most likely either.

1) A blown start capacitor (They blow if left in the circuit for more than a couple of seconds as they are not designed to be in the circuit for long.)

2) A stuck centrifugal switch in the running position, resulting in the start capacitor never being brought into the circuit initially to start the motor.

3) A stuck centrifugal switch in the start position, resulting in the start capacitor being blown after being being left in the circuit to long.

4) A wiring fault.

5) A damaged motor/winding of the motor


Also if you have multiple capacitors, your start capacitor will likely be the one with the higher capacitance and also possibly larger in physical size.