motor and switch wiring Myford ML7

[1957jmhParticipant @1957jmh]

This has all taken a little while……I bought an ML7 with a few known issues….motor ran ok but selecting reverse on the dewhurst switch produced a buzz and the beginnings of smoke so Ive stripped the motor out to assess….motor is a split phase single phase with a centrifugal switch but no capacitors

previous owner had made several bodges – one was leaving one of the switch wires disconnected and floating free inside near the motor connection board so i need to check everything is correct before continuing. Because i cant assume the dewhurst switch is good I want to go back to a simple mains connection first and if the motor appears good introduce the dewhurst in later.

Ive checked the 2 windings and they seem ok – 4 ohms on the run winding and 12 on the start. this is a view of the motor connection board before dismantling….

Not easy to see in that shot but the terminals from top down are T2 A1 A2 T3. Motor leads for start winding are soldered to back of the board as here:

and the switching for the centrifugal switch is from A2, the front of the board is here

so red and black are the run windings.

For a simple mains connection to test I’m thinking 1) move the black wire to A1

2) put 220v line to A2, and Neutral to A1……..on startup A2 energises the start and run windings simultanously, but then centrifugal switch operates breaking the current to the start winding.

Please confirm if you think that is correct. I’ll test the motor out and if ok I’ll post again for the dewhurst switch wiring (while adding a proper mains switch upstream of the dewhurst)

Many thanks in advance

Joe

 

 

 

 

 

 

 

 

 

[noel shelleyParticipant @noelshelley55608]

One convention was red and black were the run windings and blue and yellow were the start windings. Your motor seems to be to this convention. So wire up accordingly and see what happens, start windings through the centrifugal switch. If smoke has already been seen then if you can perform an insulation test preferably with a 500Volt or greater tester. Good luck. Noel.

[SillyOldDufferModerator @sillyoldduffer]

Just a suggestion, but this is a glorious opportunity to replace the single-phase motor and Dewhurst with a 3-phase motor and VFD.   A 3-phase motor is smoother, more reliable, and has more torque and power than a single phase motor of the same size.  The VFD povides speed control and gets rid of the Dewhurst.

It’s the easiest way to make a Myford even better!

Dave

[1957jmhParticipant @1957jmh]

Thanks guys. The motor was so full of swarf and congealed grease it was surprising it ran at at all. Good point about the megger …and the 3 phase motor too (that had crossed my mind if this doesn’t work out well).

[noel shelleyParticipant @noelshelley55608]

Hi Joe The Dewhurst reverser ! With the cover off, left hand terminals numbered 1 top to 4 bottom and right hand 5 top to 8 bottom. Live to No 1, neutral No3   Start (yellow ) to No2, Start ( blue ) to No6, Run (black ) to No 5 and run (red ) to No7. Good Luck. Noel.

[Howard LewisParticipant @howardlewis46836]

Hope that this is of some help.

For safety, it always worth having a NVR switch between the Mains supply and the Dewhurst. (In any case the contacts din’t benefit from making or breaking the current to the motor. Better to let the NVR do that.

Somewhere below this, there should be a diagram showing the connections

Howard

 

[1957jmhParticipant @1957jmh]

Thanks for all the tips – I successfully rewired all the connections for a reversible motor to the dewhurst (nvr still to be added) ……..ran well…..BUT under load there is a lot of wobble from the motor pulley….must be the motor bearings or shaft even though no slop is detectable by hand. I have another motor though so I’ll try that one out to see what happens. Its an AEI motor with a capacitor but the wiring is different to the GEC above. I’m confused. Here’s the pics

as with the GEC motor the terminals from top are T2 A1 A2 and T3. The capacitor (55uF) is wired between T2 and A1 on the Neutral side (Neutral is connected to A1). Line goes to A2.

But on this motor the blue and yellow start windings go a different way…blue goes to T2 as the next pic shows….

and the front of the board:

I found a useful looking chart on a previous forum post ….

….and T2 is designated as a run winding – I’m therefore thinking of moving the blue motor lead from T2 to A1 – and connecting the run windings to T2 and T3 with other connections via the dewhurst switch. BUT where would the capacitor connect to then? is the capacitor really necessary?

A1 – Neutral, Blue start winding, DS 2

A2 – Line, DS 6

T2 – Red main winding, DS 5

T3 – Black motor winding, DS 7

[Howard LewisParticipant @howardlewis46836]

Not an electronics expert, but the capacitor is needed. It is there to provide a phase shift between the start and run windings so that the rotor is pulled round .

Once the motor is up to speed, the centrifugal switch disconnects the start windings and the capacitor.

(You will hear a click when you switch off and the motor slows down, and the centrifugal switch remakes contact).

This is for a capacitor start motor.

There are different sorts of single phase motor!, so check which type.

Some single phase motors have the capacitor permanently connected

If you are not sure, get in someone who is expert. You do not want bangs, smoke or an electric shock, (A capacitor discharging through you could prove lethal)

Howard

[Charles LamontParticipant @charleslamont71117]

Not common now, but older motors may be split-phase start without a capacitor.

[cogdobblerParticipant @cogdobbler]

It might be easier to sort out the “wobbly pulley” on the other motor you already have running. Bearings must be OK as you say there is no slop. So possibly a simple fix to tidy up the pulley if you inspect it and determine the cause.

[1957jmhParticipant @1957jmh]

Yes. Thanks! The capacitor does indeed seem to have been wired wrong. It should be in series on the hot side of the start winding and not the neutral side. I’ll check this out further with a suitable source and report back

[Les Jones 1Participant @lesjones1]

It does not matter which side of start winding is connected to the capacitor. As long as the centrifugal swtch, the start winding and the capacitor are in series the sequence does not matter.

Les.

[1957jmhParticipant @1957jmh]

@lesjones1 yes, thanks for clarifying…I realised after I’d posted that this was the case. I’m gonna go ahead and use a new capacitor and run the motor in one direction to see if it cures the problem….

@cogdobbler maybe right…..I could also feel something glitchy when I turned the motor over by hand, so if the new motor cures the symptom I’ll just use it for now and maybe reassess the old motor later….

@howardlewis46836 yes you’re right, safety first is essential….always discharge a capacitor before fiddling ….

Fingers crossed now. I’ll report back!

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