Lathe wiring problem

[Morrisman]

I pulled the motor and loads of other parts off of my ancient pre war lathe, when I moved houses six months ago, and today I got it moved into the new shed and started to assemble it.

However, dickwad here didn’t appear to take notes of which wires went where on the motor.

There is an old mechanical type switch, and four wires go from that to the motor.

But I have no idea what connects to what.
Help.

Two reds, two blacks on the motor. The two reds at the end appear to just be joined together.



The wire to the motor.



The control switch.

 

[Pete.]

Nothing on the back of the cover?

 

[skotl]

Definitely single phase?

It might be a reversible motor (mine is) so you have L + N plus a set of crossover cables?

 

[Morrisman]

Nothing on the back of the cover?

No, just plain metal.

It’s a simple 13 amp plug supply.

 

[Morrisman]

Definitely single phase?

It might be a reversible motor (mine is) so you have L + N plus a set of crossover cables?

Definitly, forward - off - reverse, the switch is.

 

[Morrisman]

 

[Agroshield]

You have probably seen this already, but the green-yellow is not being used as earth. It is on the third terminal down on the switch.

With it unplugged from the mains, put an ohm meter on the input to the switch and see what happens to the four output wires. One pair will be live and neutral in both forwards and reverse. The other pair will be live and neutral in forward and then swap to neutral and live in reverse.

Once the pairs are identified, one pair goes to one red-black in the motor and the other pair to the other red-black.

This is how you reverse a split-phase motor: swap the live and neutral to either the start or the run winding (if you swap both, it does not reverse).

 

[Morrisman]

You have probably seen this already, but the green-yellow is not being used as earth. It is on the third terminal down on the switch.

With it unplugged from the mains, put an ohm meter on the input to the switch and see what happens to the four output wires. One pair will be live and neutral in both forwards and reverse. The other pair will be live and neutral in forward and then swap to neutral and live in reverse.

Once the pairs are identified, one pair goes to one red-black in the motor and the other pair to the other red-black.

This is how you reverse a split-phase motor: swap the live and neutral to either the start or the run winding (if you swap both, it does not reverse).

I was thinking That might be the case, so I’d have to hard test it, to see what comes out of the switch. I’m assuming the first red and first black on the motor will be one pair, and the others the opposite rotation?

If I got them wrong it will simply do nothing.... I hope, rather than release the magic smoke?

 

[Pete.]

The motor has been re-wired so logically you would expect one winding to be black wires and one to be red wires. Easy to check with a multimeter.

 

[Seadog]

I’m assuming the first red and first black on the motor will be one pair, and the others the opposite rotation?

Not if it's a capacitor start motor. One pair will show a resistance reading on a meter, the other pair will/might show a quick flick of the needle/digital display, and then nothing. That pair is the start winding. To reverse the motor you reverse the polarity of either pair of windings but they will both be connected in parallel.

 

[Morrisman]

The motor has been re-wired so logically you would expect one winding to be black wires and one to be red wires. Easy to check with a multimeter.

That makes more sense.
What about the spare pair of reds tied together at the end of the connector block? The other side of the block has the screw down tight, so nothing was in there when disconnected, it’s just the two reds being connected.

Not if it's a capacitor start motor. One pair will show a resistance reading on a meter, the other pair will/might show a quick flick of the needle/digital display, and then nothing. That pair is the start winding. To reverse the motor you reverse the polarity of either pair of windings but they will both be connected in parallel.

There doesn’t appear to be any sort of capacitor on the outside, that I can see.,

 

[Seadog]

It could be a split-phase motor in that case. Not had any experience of those but essentially the same as a capacitor start motor, without the capacitor You will get a resistance reading from both pairs. but the start winding will be in series with the centrifugal switch.
The number of wires is a little confusing, I have to admit. Anyone else any bright ideas?

 

[Pete.]

The two joined together might be bypassing a thermal cutout.

 

[RichardM]

I was going to see if I still had my old Dewhurst diagram but this should give you something to go on:
https://wiringall.com/dewhurst-switch-wiring-diagram.html

 

[Morrisman]

I was going to see if I still had my old Dewhurst diagram but this should give you something to go on:
https://wiringall.com/dewhurst-switch-wiring-diagram.html

The text seems a little disjointed..and the wiring diagrams fry my brain, I’m an electrical ignoramus.

 

[Seadog]

I'd be scratching my head looking at that diagram. The first thing is to identify the motor type and what each wire does.

 

[Morrisman]

I spent an hour trying to work out exactly what the switch does, as it appears to make exactly the same connections either direction.

Then I decided to take a chance and just connected the wires up in what appears to be the way they were bent, two were crossed over when I started yesterday.
It worked, starts and runs, in both directions. No smoke or flames....yet.

The whole machine is a bit cobbled up, but it’s older than me.
Challenger Precision Lathe British Made.

 

[RichardM]

I was just about to say yes it was carp, this one will give you better insight:
https://autocardesign.org/dewhurst-reversing-switch-wiring-diagram/
but you've sorted it so all is good

Now just have to try and get the dog to go out as he said "no it's raining earlier"

 

[Morrisman]

I was just about to say yes it was carp, this one will give you better insight:
https://autocardesign.org/dewhurst-reversing-switch-wiring-diagram/
but you've sorted it so all is good

Now just have to try and get the dog to go out as he said "no it's raining earlier"

My switch seems to work the same either direction, it just connects 3 sets of terminals, I can’t see how it wouldn’t be, but it obviously is.

I don’t know if it is just coincidence, luck, or some latent skill, but I was expecting sparks and flames when I switched it on.

 

[RichardM]

does the reversing switch not reverse motor direction?