Recently, I was using the Myford and everything was fine. I'd turned the lathe off to change something and when I went to turn it back on, the lathe spun up but died as soon as I removed my finger from the green 'On' button. So I removed the NVR switch and wired the lathe direcly to a 13A plug and switched it on. The lathe started normally as far as I could tell and ran OK.

Assuming the 'on' coil might be damaged (in the NVR switch) I found another switch on Ebay and ordered a replacement. It arrived yesterday and I fitted it this morning. No change, the fault remains the same. Had a think about this and decided that the emergency stop button hadn't been eliminated, so went down later and removed that from the circuit by shorting it's wires together. Nothing changed.

So I'm back to wondering about the motor. It's a centrifugal switch (not capacitor start) kind and I can hear it click out as the power is removed but the 'on' coil must be unhappy about something.

Any thoughts or suggestions for further tests? I've had this NVR switch fitted for some years now, so something has clearly changed. Think I probably got it from Axminster but it was a while ago now but the NVR (KJD17) switch itself is pretty generic…

Regards,

IanT

Sorry for delay, been off-line for a few days busy with trips away etc.

I did manage to fugure this out. The original NVR switch had four connections, two inputs and two outputs. The coil was simply across the output connections (live & neutral) so that when the green button was pressed, the coil latched. In my set-up there is also an emergency botton, which was originally wired in series with the live input.

The new NVR switch has five connections, apparently the same as the original four connector version but with the addittion of an 'A1' pin. I was somewhat misled by an older thread (on another forum) suggesting this pin was an "optional" connection for some types of motors. That is certainly not true of my switch.

I metered (tested resistance) across all connections on both switches. I could still 'see' the coil across the ouput connections on the old switch (so it had not gone open circuit) but it was clearly no longer functional.

When I looked at the new switch, it became obvious that the coil was just wired across the 'A1' and one O/P connector. I connected the mains (live & neutral) to the two I/P connectors and the motor to the matching O/P connectors. A connection was then made from 'A1' ( via the emergency switch) to the coil side of the O/P. This is probably an improvement on the original set-up, as the emergency switch is now in series with the coil, rather than the full motor current. I haven't named the connectors, as my switch numbering appears to be different to others mentioned elsewhere. The key is to establish where the coil is connected and wire up accordingly.

The new set-up now works exactly as before and the old NVR switch has been consigned to the bin.

Regards,

IanT

Edited By IanT on 31/07/2023 13:02:15