1940s watch cleaning machine motor wiring

[daffyduxxxParticipant @daffyduxxx]

Hi everyone,

I’m me here and I do watch repair as a hobby in my retirement.After over 40 years as a maintenance fitter in a large Naval base. Repairing and maintaining anything from a 1930s 80ft long lathe for propellor shafts to a 5 axis CNC machine.

I am restoring a 1940s National watch cleaning machine MKVI,  but I am struggling with the wiring.

The 240 v single phase 0.006 HP motor has 5 cables coming from it.

These were cloth covered and very frayed,  so I sent the motor to a local company for repair.

It came back with only 3 cables,  so I returned it and asked them to restore the 5 cable configuration.

That have called today to say they are struggling to find where the wires go.

I have attached a circuit diagram of how it was wired up when I received it.  The 2.6k rheostat is used to control the speed of the motor. But I’m struggling to see how this would work.

Would anyone be able to correct the diagram,  or explain how this works?

Is it possible this is a Universal motor? If so,  does that need dc input as well?

Sorry for so many questions,  but I really am struggling.

Many many thanks for any help you can give

Paul

[SillyOldDufferModerator @sillyoldduffer]

Wait for others to comment, but:

• I see no sign of the commutator found on a Universal Motor.
• I think you have an AC slip-ring motor where speed is varied by dropping the voltage with a rheostat.  If so, try this circuit:

 

Note the motor only has 3 connections in my circuit.  If I’m right the missing 2 of 5 go to the rheostat, not the motor, which is why the repairer was baffled.

SAFETY!   I’ve deliberately not labelled the 3 connections on the motor because I can’t tell from the photos which is earth (well done for providing pictures)   I think earth is 2, but find out for certain.   Test resistance from each terminal to the exposed metal with a multimeter.  Earth is the terminal connected to the outside metalwork.  Exterior metalwork must be earthed, and definitely not accidentally connected to Live! Take care.

If I’m right, the operator simply turns on the motor and adjusts the rheostat until the stirrer rotates at a sensible speed.

A picture of the rheostat would be good.   0.006HP is 5 or 6W input, so the rheostat will be rated that, or a bit more.  It will get hot, so be careful not to touch or cover it.

A modern controller would be cool-running electronic rather than a rheostat, and they’re readily available.

Dave

 

[daffyduxxxParticipant @daffyduxxx]

Dave,

Thank you so much for your prompt and thorough reply.

I shall pass the info on to the motor company. Your diagram certainly makes more sense to me.

The rheostat is the photo below the diagram.

Your help is very much appreciated

Best wishes

Paul

[daffyduxxx]

On daffyduxxx Said:

…The rheostat is the photo below the diagram.

…

Of course it is, doh!  I see it now.   My excuse. this stuff is easier when you can touch and see everything.

Which dockyard?   Impressive places, even now the Navy is much smaller.  Read recently that Portsmouth dockyard was the largest industrial complex in the world until about 1910.  More trivia,  the railway wagons in “Force 10 from Navarone”, set in the Balkans, are marked PSTO(N).   Which is odd because Principal Supply and Transport Officer (Naval) was the guy in charge of logistics in a British Royal Navy Dockyard…

Dave

[john fletcher 1Participant @johnfletcher1]

What are those circular spring looking things, with I think, wires attached doing, secured with grub screws, are they brush box holders ? The diagram Dave posted is much the same a sewing machine, so look out for a com. I’ll vote with Dave

[MacolmParticipant @macolm]

Surely a brush motor judging by the circular spring connectors. We need a picture of the rotor.

Likely a parallel field commutator motor with the reostat feeding the commutator so as to vary the speed over a wide range.

[noel shelleyParticipant @noelshelley55608]

I believe it is a universal motor though we have no photo of the rotor or com. If the repair company did not have the rheostat then they would simply fit it up with L,N,E, and it would run at constant speed. put the rheostat in circuit as shown by Dave and you then have varispeed.

Continuing the marine context I keep a pair of ex US LARC XVs  running. Good luck Noel.

[daffyduxxxParticipant @daffyduxxx]

Dave,

I was at Devonport Naval base in Plymouth. Very old place, it still has the prisoner block and gallows used in Napoleonic prisoners of war. Great apprenticeship and great characters and banter. I joined at 16 and left 42 years later.

Many fond memories.

Paul.

[Robert Atkinson 2Participant @robertatkinson2]

It can’t be a slip ring ACmotor because the brush holders are in the same plane.
I wounder if the field winding has a tap  like an autotransformer with the ends of the Pot across this low voltage and the wiper feeding the armature.

Circuit to follow, got to feed the dog.

[daffyduxxxParticipant @daffyduxxx]

John,
<p style=”text-align: center;”>Yes they’re the brush holders.  Not great photos because I didn’t think it would become such a problem.</p>
Thanks for the help, much appreciated.

 

Paul

 

[daffyduxxxParticipant @daffyduxxx]

Noel,

Thank you for your help,  very much appreciated. I’ll forward all the help i get here to the motor company.

Very interesting job you have keeping those LARC XVs going.

Best wishes

Paul

[daffyduxxxParticipant @daffyduxxx]

Malcolm ,

For some silly reason, I didn’t take a photo of the rotor.

Apologies for that. Of course it’s all surg the motor company now.

I very much appreciate your help

Paul

[daffyduxxxParticipant @daffyduxxx]

Robert,

Thank you for your help it is much appreciated. Being a mechanical fitter, this is all above me.

Thank you for taking the time to do a circuit diagram.

Give your dog a pat from me.

Best wishes

 

Paul

[Robert Atkinson 2Participant @robertatkinson2]

On second thoughts just in series with the field

Need some resitance values toget a better idea

[daffyduxxxParticipant @daffyduxxx]

Robert,

Thank you very much. I’ll report back on what the motor company say.

Best wishes

Paul

[noel shelleyParticipant @noelshelley55608]

If the motor is sound and the rheostat/pot fails in the great world of re purposing the speed controller from a vacuum cleaner can be used but be VERY CAREFUL as the heat sink may be live so how it is mounted needs to be thought about – the cleaner will be all plastic so it is not an issue. The pot in this type of unit can be linear or rotary knowing the value one can change if need be. Just a thought.

Using the fan/blower motor from a washer/drier on my furnace. Same type of motor and controller as above gave me variable blast without needing a shutter in the airway.  Noel.

[daffyduxxxParticipant @daffyduxxx]

Noel

Those are great tips and certainly something to bear in mind if they can’t fix the motor.

Many thanks for taking the time to answer and help me out.

 

Paul

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