Motor won’t start

[Rowan Sylvester-BradleyParticipant @rowansylvester-bradley37244]

My lathe (which is about 70 years old) is powered by a Brooks Gryphon 1/3 hp motor. The motor won’t start by itself. It will run perfectly well in either direction if you just give it a shove in the required direction, but this isn’t very safe, and certainly not for my teenage grandchildren who want to learn to use it. Will it have a separate starter winding which is switched off by a centrifugal switch? If so how do I most easily test that the winding is OK, and that the switch is working properly? Should it have a capacitor? I can’t see anything that looks like a capacitor, assuming that this would be a cylindrical thing several inches long with wires coming out of it. The motor seems to have 4 terminals plus earth.
Any hints on how to get this fully working would be most helpful.
Thank you – Rowan
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[Grizzly bearParticipant @grizzlybear]

Hi,

Does the motor have a Start or Run Capacitor?

Please ignore, you have mentioned capacitors.    Edit.

Good luck………..

[Les Jones 1Participant @lesjones1]

When the motor is stopped the resistance between the centrifugal switch  contacts should be close to zero ohms. The resistance between the ends of the start winding should be between a few ohms an a few tens of ohms. (This will only test for an open circuit winding. It will not show up shorted turns.) The start capacitor is not quite as easy to test. A rough test would be to connect it to the mains in series with an incandescent lamp (Between 40 and 100 watts.). The lamp should light but not quite as bright as when it is connected diretly to the mains.  I would think that it should have a start capacitor. Has it ever started without assistance ?.

Les.

[MacolmParticipant @macolm]

It looks like the cable has four wires, in which case there may be a control box at the other end with a capacitor and/or a reversing switch. If there is a centrifugal switch it will be inside the motor and wired in series with the start winding. Assuming both are present, suspect capacitor first, closely followed by broken or burnt centrifugal switch.

[Paul KempParticipant @paulkemp46892]

Looks very similar to the motor on our old ML7.  The centrifugal switch on that has an audible click and it became sticky, closing a few seconds after the motor came to rest, very occasionally it failed to close at all unless you gave the motor a clump!  After machining a lot of cast iron castings it eventually started tripping the earth trip.  Took it off and stripped it down and there was a lot of cast iron dust that had got inside it and through the windings.  Washed with electrical cleaner several times to get rid of it, dried and meggered and reassembled at the some time cleaning and lubricating the start switch and it was fine for a few more years.  Switch is relatively easy to access by taking off the end housing at the terminal box end.  If you can’t hear a click at all then it’s possible you have the same problem and the switch is stuck open.  I can’t remember if ours has a capacitor in circuit, I think not but I may be wrong, will try to remember to look next time I am close to it.

Paul.

[noel shelleyParticipant @noelshelley55608]

You say there is NO capacitor ? Then it is split phase starting and either there is a fault in the start winding or more likely the centrifugal switch has failed ! It is in the non drive end of the motor. It may simply have become worn or sticky. The motor will have to be removed from the machine and stripped to check the switch. There are through bolts that secure the 2 ends, these must be removed then the ends will come off. The insulation is old and may be brittle so treat with great care. The switch contacts may be burnt, careful cleaning with GLASS paper may bring them back to life. There is no point in checking continuity as the windings and switch are in series, so if either is US there will be an open circuit. Where abouts are you ? Noel.

PS looking at the pic, Does it have a reversing switch ? Is it a Dewhurst ? If so then it is possible that the contacts in this switch have failed on the start circuit, again using glass paper it may be possible to clean them and get it to work again. This switch should NOT be used to start and stop the motor, that’s why the contacts fail. It should have a separate switch to start it. N.

[Macolm]

On Macolm Said:

It looks like the cable has four wires, in which case there may be a control box at the other end with a capacitor and/or a reversing switch. If there is a centrifugal switch it will be inside the motor and wired in series with the start winding. Assuming both are present, suspect capacitor first, closely followed by broken or burnt centrifugal switch.

+1, except I see 5 wires.   Brown live, Blue neutral, and Green/Yellow earth are clear enough.   But what’s on the end of the black and grey wires?  At the moment the type of motor is unidentified.   Chief suspects are faulty centrifugal switch and/or a faulty capacitor, but not all motors gave switches, and not all motors have capacitors.   Is there a capacitor inside the control box?  Or do the wires go to a reversing switch?

Also, the photo hides most of the terminal markings:  A, Z, AZ, T, S, K or whatever.   Helps to know what wires connect to which terminal.

Dave

[BazyleParticipant @bazyle]

If you take off the belts and run the motor alone as you have done, then turn off, as it slows down you will hear sometimes a click and a change in tone, often a sort of ‘swish’ as the mechanical part of the centrifugal switch operates. When closed the switch has a rubbing contact against the bronze spring contacts which accounts for the noise. This is where it can wear and after 70 years maybe break or fail to move enough to make electrical contact. If it failed the worst case is that it remained closed and burned out the start winding.
Be careful as you take off the motor end housing as the switch is bolted to the housing and the wires are often too short to stretch far.

[larry phelan 1Participant @larryphelan1]

Most likely to be nothing more than dirt around the switch or pitted contacts.

It takes very little to cause that switch to act up, but it,s easy to fix.

Take the end cap off the motor and all will be revealed.

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