Help with mains electric motor

[Greybeard]

I'm sure there are members of the forum that can help me with this please.
I've bought myself a table saw from Facebook Marketplace. The saw was sold as a 'spares or repair'. When I plugged the saw in and pressed the green switch button there was a click which I believe was inside the switch. The motor doesn't run. I've taken the motor out of the frame and have it on my bench. I would like to check the motor only. I've made a sketch of the connections. Would you have a look and explain to me what is going on with the connections and how should I connect power to the motor to test it?

PS. I know what the yellow/green wire is for 😁

[limeyrob]

I can't help with the motor, but does it have a safety switch - the red button type that trip if the power supply is cut?  These have a fine solenoid coil that burns out.  Without that there's no power to the motor.

[Swarfcut]

 With a  big capacitor illustrated, my guess is that the motor is an induction motor, not a conventional carbon brush type.  With a failed condenser the motor will not work, as it needs this "start capacitor" to give the field windings generated magnetic field a little kick to align them with the AC current. Simple explanation for something quite clever.

 The switch may also be faulty, well said Rob, so by-pass this for the time being. Plenty on the net about wiring an induction motor and test procedure.  On the motor, two wires are the capacitor connection, yellow and black. The remaining black and blue pair are live and neutral. Trace back to the switch to see which is which.

 When our central heating failed (Oil Fired, with induction motor on the burner), I substituted the start capacitor off a Belle Cement mixer, and that got the heating working. There's probably one in the washing machine.......and maybe one on your pressure washer or compressor.

 Cheap as chips these days, all made in China.

  May be something as simple as a loose connection or failed fools' repair. Duff fuse or mains lead also to be expected.

 Swarfy.

 PS Reckon a new shed is on the cards....

 

[Bsareg]

The simple way to check the capacitor is to spin the motor as you switch on. If it keeps turning, the the problem is the capacitor or centrifugal switch if it has one.

[Rex]

There's two types of these induction motors, capacitor start, and capacitor start and run. The second type isn't so common now but on the capacitor start type the internal centrifugal switch can stick open meaning the cap isn't in-circuit on starting, hence no start. Could also be a duff cap, but if you get a replacement make sure it's rated for electric motor starting otherwise things can get 'king dangerous very quickly.

[Greybeard]

Thanks for the posts guys. I would like to know how I should connect power to the motor on the bench. The brown from the switch connects to two blue wires; one goes into the motor, the other goes back into the switch 🤔

[Swarfcut]

 Reckon the brown wire going back to the switch powers the solenoid, so this can be left where it is. Just power the motor live and neutral feeds. If it works, switch is the problem. Starts only with push? Capacitor failure. Nodoubt as a survivor of numerous electrical escapade, I don't need to labour the safety aspects required to be observed when  jury rigging motors. Also clamp it down, some will dance about with the starting torque.

 Swarfy.

[limeyrob]

Yes clamp it down, the starting torque can flip them and tangle the wires and then you grab it and its live, game over. 
I would not test the motor on the bench, there's no need.  All you need to do its confirm live supply to the motor with it installed. Then check whether it starts with a spin.
Testing the capacitor can be done with a meter and a battery (very carefully!).  Its very unlikely the motor windings are burned out, but if they are you should be testing this with a meter not 240v on the bench.  Don't put 240v if you think the motor is duff as the windings burn out to earth and it will be live, not a sensible fault finding plan.

[Greybeard]

Thanks again. There is no evidence or smell of burning. Good advice about clamping the motor and about the possibility of the casing being live. I'll be careful. My plan is to see if it's the switch or the motor that's the problem.

Swarfy, which wire is Neutral do you reckon? Must be that black wire from the switch?

[Swarfcut]

 Reckon that blue wire is the neutral, terminal block connection means this wire to the motor is the neutral, also connected back to the switch via that brown wire....a bad choice of colour as UK wiring signifies brown as live feed. Black wire from switch will be the live.

 With AC motors is does not matter which way the mains feed goes in, they still turn as designed. Field coil should show continuity, small single phase motors have no electrical connection to the armature.

 Swarfy.

[chaterlea25]

Hi GB,
If you connect a 3 core lead with a mains plug at one end to the Brown and black connections where the wires from the switch go into the motor terminals. brown to brown, blue to black and gr/yllo to gr/ yllo
Then plug into mains.  The motor should "humm" and probably run if you spin the shaft.
Only connect to the mains for as short a time as possible to do this test 
Let us know if this works

John

[Greybeard]

So...if I've understood this...Power comes from the switch via the black wire. The motor is energised and power returns to the switch via the brown wire. The pale blue wire that is teed into the return circuit feeds a solenoid/relay inside the switch who's purpose is to prevent the motor automatically starting following a resumption of supply after an unplanned power cut.
Does that all sound correct?

John, your post got in moments before this one. This is exactly what I intend to do. 👍 I was fooled by the cable colours thinking brown must be live.

[Swarfcut]

 I would remove the switch from the terminal block entirely for now. You know which are the capacitor connections, so just needs blue motor wire to direct mains neutral feed, remaining black motor wire to live. 3 core cable as suggested and choc block will be fine. This will test the motor in isolation.

 Those solenoid switches have a hard life, the idea being that once ON is pressed the internal solenoid is energised, holding the electrical connection. Pressing red OFF deactivates the solenoid, cutting the power, and in a panic situation, banging a  big red button is quicker than struggling to find a small toggle switch.

 A  possible internal circuit for the switch is that blue wire  feeds neutral back to the mains, but also neutral back to the non live side of the switch solenoid, via the brown wire. When the switch is pressed ON, the solenoid is energised and holds the internal contacts closed and maintains the mains feed to the motor  as long as the switch is ON.

 Goes without saying to keep live and neutral apart, otherwise you will be in the papers. That brown wire is a recipe for disaster waiting to happen.

 Swarfy.

[RDfella]

Please don't take this as being rude, but following the post makes me believe the questioner is not familiar with mains wiring. Your life depends on knowing what you're doing, and asking these questions suggests otherwise. Please ask someone else to look at it.

[BagONails]

All I know is it's vitally important to keep the magic smoke inside the machine. Once the smoke comes out that's it, game over!