Advice needed on single phase motor

[DaveyLe_Spark]

Hello all, if anyone is kind enough to offer some advice on this it will be hugely appreciated. I am a registered spark working mostly on domestics and commercial but i have a family member with an odd fault on a single phase motor running a pillar drill (I don't normally work with motors but i'd love to know more!). It sometimes goes backwards for no reason. I have not seen the switch assembly, i have only the motor.

I have tested this evening the coil(s). In the enclosure where all the connections are made, there are two ends of the coil, tested them up to find 14.83 ohms resistance. The motor is rated btw at 350w, 3a, 230v. On the other side there is the starting cap, 80microfarads, the coil these are connected to show 1224ohms.

I can only assume that the cap is wired to a starting coil with larger resistance and once spinning it is the other coil which turns the motor?? (i've looked for literature in my college stuff and google doesn't understand a word i say...lol).

Whichever way i look at it, the maths don't add up and i still can't think why it would randomly run backwards.

Any ideas??

Dave

 

[Knobhead]

Have a look at http://www.electriciansforums.net/commercial-industrial-electrical/43777-motors.html I'm not goimg to write it all out again.

 

[Inteificio]

Tony's stuff is definitely worth reading, spent ages going through that.

Not really sure, but a long shot for me is the cap is blown leaving only the main winding in circuit.
with only one winding, the direction of starting might be off.

Not done much with motors, but thad'd be my guess.

 

[Marvo]

Follow Tony's link for some good info. My guess would be it's a centrifugal start switch on the bottom of the motor that's stuck, could also be a faulty start cap or winding.

 

[Knobhead]

There’d a quick way to find out if it’s the start winding / capacitor or run winding that’s knackered.
It needs a real Hi-Tech bit of equipment, a bit of string! Wrap the string around the shaft, do not knot it on! Turn the motor on and just like your lawnmower pull. If the motor runs the run winding is OK. For god’s sake, please keep your fingers safe!
The start windings and capacitor need testing in the usual way. The centrifugal switch can be a bit of a sod. But a bit of prodding and poking usually frees them off. Clean the contacts and test for continuity at zero speed.
Please do all testing at zero voltage where possible! (I near said “dead” testing, but thought better of it).

I’ve got to do a drawing of a centrifugal switch, but it will take me a couple of days. Sorry miracles I can perform, the impossible takes a bit longer.
Yes I do know that’s someone’s signature, and I apologise!