Myfords – Brook Crompton Motor Wiring.

[DavidJHolmesParticipant @davidjholmes]

Hi guys, hopefully this is in the right section.

Just bought myself a Myford Super 7 which was fitted with Ann underated motor. I have a Brook Crompton of the correct size but it only has three terminals. The “T” terminal is not there. Only issue is I have a Dewhurst Switch which requires four connections to reverse the motor. Does this mean I can’t reverse this motor?

Thanks in Advance

[DavidJHolmesParticipant @davidjholmes]

[DavidJHolmesParticipant @davidjholmes]

It’s definitely a single phase, not a three phase.

[Neil WyattModerator @neilwyatt]

If you can get a copy of MEW 244 it has an article by Ted Fletcher (who is sometimes spotted in these parts) that describes how to reverse most types of motor.

You do need to be confident working with mains connections.

Neil

[DavidJHolmesParticipant @davidjholmes]

Thanks I will order a copy if all else fails. Was ideally hoping to get it running the weekend.

No problems doing it if I can confirm what needs to be done. I’m guessing a connection can be split for the motor starter windings…

[NJHParticipant @njh]

David

If you click on my photos under my name at the left of this post you will see an album entitled "Myford Reversing" – it contains the "how to do it", I would advise however that unless you are OK with mains working you seek assistance from someone who IS OK. The info. will help them.

Norman

PS I purchased a reversing switch for my S7 some years ago and am yet to find a need to fit it – so I guess you don't need to hurry with this!

Edited By NJH on 25/03/2017 21:13:59

[not done it yetParticipant @notdoneityet]

Any (and every) electric motor can be reversed. Some are easier than others. The typical induction motor, used In many applications, is reversible. It just requires the correct mains connections for the rotation desired. Reversing switches provide this re-organisation of polarity for clockwise or anti clockwise rotation. "T" terminals are, I would suggest, simply a manufacturer or user description. You need to use the basic connections for your motor, not specific instructions for the connections for the factory installed motor.

[DavidJHolmesParticipant @davidjholmes]

Cheers guys. That looks like what I need Norman. Have you done it with a Dewhurst reversing switch?

I’ll have a look first thing in the morning and see if I succeed

[JOHN MANTOVAParticipant @johnmantova72105]

Make sure you have an RCD in the circuit and or suitable fuse just in case you do make a Boob.

[Brian OldfordParticipant @brianoldford70365]

Posted by NJH on 25/03/2017 21:08:21:. . . . .

PS I purchased a reversing switch for my S7 some years ago and am yet to find a need to fit it – so I guess you don't need to hurry with this!

Edited By NJH on 25/03/2017 21:13:59

Try cutting metric threads on an imperial machine.

[DavidJHolmesParticipant @davidjholmes]

Well forwards works ok lol

Reverse… something isn't right as it doesn't spin up to speed. It slowly turns. If I swap the connections the it runs at speed but very noisily and hot which suggests a BANG would be eminent.

I'll leave it in forwards for now and try and figure it out.

[Phil WhitleyParticipant @philwhitley94135]

in order to reverse a single phase motor, you have to reverse the polarity of the start windings, which means you need first to identify them!, can you post up pics of the motor and its connections, and the spec plate. Does it have a start capacitor? does it have a centrifugal switch?

[DavidJHolmesParticipant @davidjholmes]

I’ve added some to my profile. There are three terminals. The stripey cable if you can see it is the capacitor.

To reverse the plate says to swap blue and yellow. Doing this causes the motor to reverse very slowly.

I don’t think this motor can be reversed with a Dewhurst Switch so would need a different one.

I believe the capacitor cables are the stripey ones as these are the same as the ones going to the cap.

[Les Jones 1Participant @lesjones1]

Can you post a picture of the connection box showing it as you have it connected with the blue and yellow wires reversed. This is what I would have guessed was required. I can't think of a way reveresing the wires could be interpreted differently but is worth checking. It sounds like it is trying to start without the start capacitor. Did the motor run properly before reversing the wires. Can you insert the picture into your post so we don't have to keep swapping to view your album.

Les.

[DavidJHolmesParticipant @davidjholmes]

Sorry didn't realise I could insert them to a post. I was on my phone. On the PC now. I have the cables disconnected now for the attempted reverse. I think IIRC I have the black and red connected to L and N which gives forwards. I'll have to get some photos when I'm back in the workshop. Oddly this seems to not use the capacitor if the capacitor is connected directly to those stripey cables. When I was given the motor it had two cables already on the black and red and I just wired it up and it ran fine (forwards). I then decided to try and incorporate the reverse. The motor spins the same way reversing the polarity on those terminals as well, as I did that just thinking reversing the polarity would reverse the motor.

[Les Jones 1Participant @lesjones1]

My understanding is that the black and red wires are the run winding and the yellow and blue wires are the start winding including the centrifugal switch. The Z terminal is just the connection between one end of the start winding and one side of the capacitor. My interpretation of reversing the blue and yellow wires would mean that after swapping the wires Z would have the yellow wire and the striped wire connected to it. The left hand lower terminal would have the red wire and the blue wire connected to it. The right hand lower terminal would be the same as it was. Live and neutral would be connected to the two lower terminals. (It does not matter which way round.)

Les.

[DavidJHolmesParticipant @davidjholmes]

This is what I thought I had. Although I think I see what I might have done. I had the yellow and blue off to make the reverse connection but I'm thinking now that a connection wasn't made back to the capacitor on terminal Z which I don't think can be done on the Dewhurst Switch. This would cause the motor to start without the capacitor hence go slow. I would have to find a different switch.

[Les Jones 1Participant @lesjones1]

If swapping the blue and yellow wires reverses the motor then it can be reversed with a Dewhurst switch. You would need some connector strip (Chock block.) so that you can connect four wires to the motor. Red and black would be the main winding. Connect to these using the chock block. And the remaining wires on the lower two terminals are the start winding in series with the centrifucal swtch and start capacitor. Leaving the yellow and blue wires unchanged and reversing the black and red wires is an alternative way of reversing the motor. ( This is the way the Dewhurst switch will do it.)

Les.

[DavidJHolmesParticipant @davidjholmes]

I will have a go when I'm in the workshop and report back

Thanks for your help!

[DavidJHolmesParticipant @davidjholmes]

I've had a mess. I can't reverse the black and red wires to change the direction it seems. I can reverse it by physically swapping the blue and yellow so I'm guessing a connection was adrift when I did it the first time. I've decided to leave it in forwards and not worry about it though. I'm most likely going to upgrade to a 3 phase motor with inverter to get variable speed.

Examining the chuck it will just come straight off in reverse as there doesn't seem a way to lock it on. Don't fancy having it come off and causing some damage.

Thanks for the help guys

[not done it yetParticipant @notdoneityet]

Examining the chuck it will just come straight off in reverse as there doesn't seem a way to lock it on. Don't fancy having it come off and causing some damage.

Metric threading on an imperial lathe requires the lathe to be driven backwards between cuts You should never operate in such a way that the chuck could unwind. This includes braking the motor, which is an option with a VFD.

[DavidJHolmesParticipant @davidjholmes]

Thanks for the info

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