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Old induction motor - direction reversal

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Rupert_Bear

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Hi all,

Motor gurus advice needed, please!

I have an old Coronet Major lathe, with an original type 2850rpm motor. Even with the belt set to lowest speed, it seems too fast for any turning over about 4 inch dia.

IMG_20210421_212422709.jpg


IMG_20210421_212435566.jpg


So I bought a newer motor, made by AEI, same size, single phase, 1425rpm, B56 frame, 5/8" output shaft, spins lovely. See photos. I fitted it to the lathe, to find it turns the wrong way! Aaargh.

s-l1600 (1).jpg


s-l1600 (2).jpg


s-l1600 (3).jpg


s-l1600.jpg


Youtube has lots of advice for reversing the direction of start-capacitor motors (no, you don't just swap live and neutral!). But this one does not have an obvious capacitor, and when you take the wiring access plate off there are only two terminals, and no instruction for reversing. There is a spare terminal visible, but a multimeter shows it's not connected to any of the others.

Can I (should I?) take it to bits and see whether there in an internal connection to a starter coils that can be reversed, or take it as a learning experience? :)

Any advice appreciated!
Rupert
 

guineafowl21

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Single phase motors like that all need something to kick them into motion, usually done by a start or auxiliary winding. This winding is set ‘out of time’ with the main winding, sometimes with a capacitor, sometimes by other means such as resistance.

To reverse, you must swap line and neutral for the start winding relative to the supply connections. As you correctly point out, simply swapping the incoming supply will have no effect.

EDIT - I can only see the last of your pictures. Can you (or did you) provide one of the connection box so we can see the terminals and wires clearly?

Either that or twist the belt into a figure-of-eight :D
 
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Rupert_Bear

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Single phase motors like that all need something to kick them into motion, usually done by a start or auxiliary winding. This winding is set ‘out of time’ with the main winding, sometimes with a capacitor, sometimes by other means such as resistance.

To reverse, you must swap line and neutral for the start winding relative to the supply connections. As you correctly point out, simply swapping the incoming supply will have no effect.

EDIT - I can only see the last of your pictures. Can you (or did you) provide one of the connection box so we can see the terminals and wires clearly?

Either that or twist the belt into a figure-of-eight :D
Thanks for that! Attached photos of the connection box.

A is not connected to anything, by ohmmeter.
B is neutral power supply
D is live power supply, current then goes out through thermal switch and back to C
C is a red wire into the motor
E is a yellow wire that comes out of the guts of the motor, and is soldered into a rivet-like terminal.

Resistance C to B is 6ohm
Resistance E to B is 3.5ohm
Resistance E to C is 1.1ohm.

I think it must have a resistor on the starter winding, not a capacitor.

The answer, if there is one, must be with the yellow wire... But I think it may be a take-it-to-bits investigation...

Thanks
RIMG_20210421_212442008.jpgLabelled connections 2.JPGIMG_20210421_212442008.jpg
 

Rupert_Bear

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James Ley

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Thanks for that - but the detail of that post is for a version with capacitor... not sure what to do with this one, except follow his advice to carefully take it to bits...
Hi Rupert all single phase motors have a capacitor. Typical way to reverse one is to swap the position of the red and the black wire.
 

MikeK

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Hi Rupert all single phase motors have a capacitor. Typical way to reverse one is to swap the position of the red and the black wire.
Some single-phase induction motors do not use capacitors, but instead have a main and starter winding, as @guineafowl21 stated. These are called split phase motors. To change the rotation in a split phase motor, the two internal wires for the starter winding are reversed.
 

Robbo3

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The standard Major had a capacity of 8" over the bed & a low speed of 1000 RPM, medium 2850 & high of 6000 (flippin' eck).
For a well secured & balanced work piece 1000 RPM shouldn't be a problem.
My original Brook Gryphon motor was reversible by moving one wire to a different terminal post (if I remember correctly). This was presumably to accommodate work mounted on the face plate with the head swung 90 degrees.
 

Rupert_Bear

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The standard Major had a capacity of 8" over the bed & a low speed of 1000 RPM, medium 2850 & high of 6000 (flippin' eck).
For a well secured & balanced work piece 1000 RPM shouldn't be a problem.
My original Brook Gryphon motor was reversible by moving one wire to a different terminal post (if I remember correctly). This was presumably to accommodate work mounted on the face plate with the head swung 90 degrees.
Yes the pulleys ratios are right for that. Hmm but I have a little 3-jaw chuck, too tight to buy a bigger one, and I have big chunks of the cherry tree that fell over! :) Remembering when I did my workshop training, way back, and bounced a 12" x 12" aluminium workpiece off the roof girders! It was fine, no-one died! :) :)
 

guineafowl21

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I can’t quite identify what ‘E’ is from those resistance values. There’s also a blue wire behind the panel which may be significant.

A careful stripdown is needed, I think. It’s a four pole motor, so the stator (outside) windings should be in two groups of four. One group is the main winding, the other, the auxiliary.

If it’s the the type of motor I think it is, the auxiliary winding wire will be thinner, giving a lower reactance/resistance ratio, and so providing the phase shift needed for starting torque.

If you find a centrifugal switch, one wire will go to the aux winding, the other to the connection panel.
 

samhay

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This might be useful reading - I refurbed a drill with a single phase capacitor-less induction motor.

You can identify the starter/auxiliary winding as it has a higher resistance than the main winding. I found it helpful to draw out the wiring diagram to make sense of it.
 

minilathe22

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Also might be useful as part of your diagnosis - if you manage to disconnect the start winding, you should find that the motor no longer self starts, and has to be started by flicking it by hand in whatever direction you want it to go in. Not a permanent solution but once you get to this stage it may help you work out the wiring of the starter winding and reverse the terminals.
 
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