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

[mike smith 5Participant @mikesmith5]

[RobboParticipant @robbo]

Mike,

Will have a look at this later, but meantime, off the cuff, A and AZ are the running windings, Z and T are the start windings, you can check with a meter to see if they are connected correctly. If you use on ohmmeter then one winding will give a higher reading than the other. Or just check continuity between the terminals mentioned.

The "classic" Dewhurst wiring would connect A to terminal 5 and AZ to terminal 7, yours is the other way around but it shouldn't make a difference, but maybe worth a try.

The colours of the internal wiring don't mean a lot, as the B*****s used to change them at will. Will check them out though.

Ted will come along and give the definitive answer in due course!

[Hairy PeteParticipant @hairypete39644]

In the photograph it looks like there is a capacitor between A and Z. If this is the case, you will need to break-out the capacitor and/or its winding to a separate terminal. Similarly, there appear to be two windings connected to the AZ terminal – as if the motor has been configured for only one directional running.

[mike smith 5Participant @mikesmith5]

I have metered all the wires and I have 4 pairs running winding, start winding , century fugal switch and capacitor. which wires go to which posts to make it run correctly for the reversing switch, this is now where I am lost. ive searched the net for a diagram for which wires go to which posts but I cant find one.

[john fletcher 1Participant @johnfletcher1]

Your diagram is correct. Test using a multimeter, the start winding which is short time rated will have a higher resistance than the run winding. The capacitor together with the cetrifugal switch are both connected in series with the start winding and should be connected to 2&6. I can't remember which terminal on the terminal strip which wires goes to the switch but they are usually solder to the copper or brass strip of metal.So if you connect your terminal Z to one lead of the capacitor, the other capacitor lead to one side of the centrifugal switch then the second terminal of the switcg to your terminal T you have it. Whilst its best if you use the correct terminals it doesn't really matter providing the two destictive separate are connected in effect in parallel across the mains. Choclate block connectors are OK. DONT forget the most important wire the EARTH, good clean contact is needed.Now those dewhirst switches are not really rated for ON/OFF the contact easily burn, some times there are unused terminal at the bottom of the switch which if necessay you can with care change. Its best if you get a proper motor starter fitted with green and red buttons, have it wired so that you use it for ON/OFF and the dewhirst for direction only. So select direction then press the green button. Also a proper starter give No volt protection,if the mains goes off the lathe stops and won't come on again until you press the green button, you might be making some adjustment when the mains comes on again very Doggy. One other thing the manufactures didn't always use the same or should we say correct colour cable,so that can cause a bit of confusion when sorting the windings. Best use a multi meter then you can't go wrong. Ted

[EmgeeParticipant @emgee]

Trying to paste a sketch into the reply, no success.

Need to find a Cmd key on the keyboard !!!

Emgee

 

 

 

Edited By Emgee on 24/10/2013 19:47:46

[RobboParticipant @robbo]

Mike,

Again I find I can't insert images from my album into a post. If only management would help with the problem!.

If you look in my album "Motor connections" there are two diagrams from Tubal Cain's "Model Engineers Workshop Manual" which may help. Plus one of various different naming of motor terminals.

I find Ted has posted while I am writing this – hoped he would.

Phil

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