Myford ML7 motor wiring

[SeadogParticipant @seadog54734]

[SeadogParticipant @seadog54734]

I've just had to get a new 240v single phase motor for my ML7 and can't work out how to physically wire it up to the Dewhurst switch in order to get it to change direction, the connection diagram shows 'simply' changing the red and black wires over will change the motor rotation, but how can I do that using the Dewhurst switch? As the switch only changes one pair of wires between live and neutral is it actually possible? Attached a pic of the motor wiring diagram and a schematic of the motor terminals and wiring.

[Howard LewisParticipant @howardlewis46836]

Here we are talking about a single phase AC induction motor, which does not behave in the same wway as a DC motor.

If you check, you may find that the blue wire goes to the start windings.

Rversing the connections to the start windings will cause the motor to start in nthe opposite direction, (because of the phase shift caused by the start capacitor )

They will be disconnected when the motor runs up to speed. (You will hear the cemtrifugal seitxg "click" as the motor slows, when powere is seitched off.

Those with greater knowledge of electrics will correct me, if any of the above is incorrecrt in any way.

Howard  Misplaced plural!

Edited By Howard Lewis on 13/05/2023 21:42:54

[SeadogParticipant @seadog54734]

We thought that the red (and black) wires might be for the start windings, as they are the ones that you are changing over to reverse rotation. Might be easier if we knew which wire went where……

[DiogenesIIParticipant @diogenesii]

There are a number of earlier threads about Dewhurst Switches.

The switch connections are explained at the bottom of this one.

Model-Engineer.co.uk – Wiring Dewhurst Switch

(Supply = Neu to '3', Line to '1', Earth to case)

Edited By DiogenesII on 14/05/2023 09:06:12

[SeadogParticipant @seadog54734]

Yes, I know all about which switch connections do what, BUT if you look at my motor wiring, if we assume red is supply to start windings (T1 and T5 are linked) then black is the return, simply connecting the black and red to the Dewhurst switch would reverse the windings, however, that would mean there would be no return to T3 – we had thought about this as a solution…

[noel shelleyParticipant @noelshelley55608]

One needs to know how 1,2,3,5, and A fit in the scheme of things. Presuming a cap start then there are 2 wires for the cap, 2 for the centrifugal switch, 2 for star and 2 for run. Live feeds the cap, the switch, the start, in series, then back to neutral, with the run windings across line and neutral. The dewhurst is a simple device and the link gives the wiring, I also described it in a similar thread last week. To wire in the dewhurst you need to bring out the start circuit, which is not always that simple..I hope you are NOT using the dewhurst to stop and start the motor ? It is not made to do this and will badly burn the contacts ! You should (in an ideal world) have a stop/start switch,preferably a DOL (direct on line) starter, with overload or NO VOLT, then the dewhurst to select direction, feeding the motor. As with ANY mains equipment a GOOD earth connection to ALL metal parts ! Good luck. Noel.

[Author]

Posts