crompton motor and dewhurst switch problems

[mike smith 5Participant @mikesmith5]

I've got the wiring diagram for the Dewhurst switch to the Crompton motor , I have followed the diagram and this is how it is wired.This is where the problems start ; in forward the motor runs rough and not up to speed,in reverse it trips the power.I had the motor off a friend, he had never bothered with reverse and it was wired up diect to a NVR switch and runs sweet in forward and up to speed. That was connected to AZ and A.I think the problem is that the wires in the motor connection block have been moved about because there are no jumpers to make it run direct from a plug, here is a photo of the motor connection block

wires coming out of the motor housing to the connection block are as follows; 2 red to AZ

red and black to T

black to A

black to Z

capacitor to A and Z

hope you can help as i'm pulling my hair out

many thanks, mike

 

Edited By JasonB on 23/10/2013 18:29:15

[mike smith 5Participant @mikesmith5]

[petejchadwick@gmail.comParticipant @petejchadwickgmail-com]

Hi folks, I digitised a similar design for my own use today with my Myford Super 7 and thought others might benefit from having a copy themselves. Feel free to print out.

NOTE – A safety switch is highly advised between the AC supply and the Dewhurst switch. And depending on how you are mounting the switch and to what surface, it may well be worth adding an additional ground point as illustrated, too many grounds can never really hurt.

 

 

[Howard LewisParticipant @howardlewis46836]

Sounds as if the wiring ton the Start windings and Run windings might have been reversed

The Start windings are fed through a centrifugal switch on the end of the motor. As the motor speeds up, the Start windings are disconnected. (You may hear a clock a click as the motor slows down after being switched off.

Dewhurst switches do mot like being used as ON/OFF switches, and the arcing will burn the contacts. Better to have an ON/OFF switch, or an NVR switch between the mains supply and the Dewhurst.

On petejchadwick@gmail.com Said:

Hi folks, I digitised a similar design for my own use today with my Myford Super 7 and thought others might benefit from having a copy themselves. […]

Very tidily done, Peter

Thank You

MichaelG.

[not done it yetParticipant @notdoneityet]

Mike, as a beginner a few points which may improve your chances of a successful outcome.

The most common Dewhurst switch is only sufficiently robust for relatively low powered motors.

Only change the motor direction with the motor power turned off.  Otherwise it will likely fail in a short time scale.

Is this fresh motor of an appropriate size -both power-wise and speed?

[noel shelleyParticipant @noelshelley55608]

Petes drawing is excellent but ONLY if no one has messed with the wires to the terminal block. From the terminal block it seems it MAY have a thermal cutout. A single cap indicates that it is cap start, induction run. A copy of Tubal Cains book The Model Engineers Hand book has a good section on motors including wiring diagrams that will answer your questions. Old convention was red and black = run windings and yellow and blue = start windings. Good luck, Noel

[Author]

Posts