Boxford CUD loud buzzing from motor when rotary switch in off position

[TobyOne]

Hi,

I hope someone may be able to shed some light on this issue. As the title suggests I have a Boxford CUD with a single phase motor that has started buzzing when the rotary switch is in the off position, also sometimes the motor spins slowly when in the off position too! The motor is a Brooks Compton KP7575 and the switch is a apparently a Sanson 16a 380v, it's the one that has a square box with two off positions with forward and reverse. Looks like the way that the switch is wired the main winding is on even if the switch is in the off position which surprised me. The start windings go off between direction changes. Anyone got any ideas as to what is causing this?

 

[RichardM]

Some rotary switches you shouldn't use to stop the motor for exactly this reason.
Do you have a separate on / off switch?

 

[Agroshield]

...a Sanson 16a 380v

More likely Santon.

Disconnect the motor from the switch, work out what each wire does (i.e. how it should be connected for forward and reverse), connect up temporarily with chocolate blocks or Wagos and verify that the motor is healthy. If it is, then the switch is faulty.

 

[TobyOne]

Some rotary switches you shouldn't use to stop the motor for exactly this reason.
Do you have a separate on / off switch?

This how it's always been wired, it does have a contactor and NC/NO on off switches, that side works ok. As far as I know this is a standard Boxford FWD/REV/OFF switches and was fitted to many Boxford lathes. However Wiring and motor could have been changed over the years. Always used to be ok when using the OFF position.

 

[TobyOne]

More likely Santon.

Disconnect the motor from the switch, work out what each wire does (i.e. how it should be connected for forward and reverse), connect up temporarily with chocolate blocks or Wagos and verify that the motor is healthy. If it is, then the switch is faulty.

Yes quite probably. So I know what each wire does I'm just amazed that the switch is wired so the run windings are permanently on, is that normal? The more I think about it the more it doesn't make any sense. I would assume that to stop the motor you would need to disconnect the LN from the run coil? I've attached a picture of the switch, the connections are 7 and 1, the blue and brown wires from the right are from the contactor, the blue and brown wires to the left go to the run windings on the motor. The Blue and Brown wires go to the U2 and U2 terminals(run), the black wires to the R and S terminals(Start).?

 

[TobyOne]

Just noticed something else, there is an orange wire on the last segment and I think that used to go to the contactor, could it be that this wire trips the contactor when in switch is in the OFF position? it is currently not connected.

 

[Agroshield]

Yes, that is a Santon switch. Somewhere on it will be the model number. You can look up the logic diagram for it. You can also confirm that logic with a multimeter set for continuity.

The motor should have four wires (cores) + earth going to it. Live and neutral for the start winding and live and neutral for the run winding. Input to the switch should be live and neutral from the power station.

In the off position, there should be no continuity between any input and any output.

In 'forward', live and neutral of the supply should connect to the two live and neutral outputs.

In 'reverse', live and neutral of the input should connect to live and neutral of one output and neutral and live of the other output.

In other words, to reverse the motor, you reverse the connection to _either_ the start or the run winding but not to both.

An outside chance if something is still connected even when off, is that the switch has been replaced with an incorrect one (Santon swithes are modular so ones that look the same may have differnt logic).

There is a Boxford group at groups.io where you might find a manual. Have you looked online for a factory wiring diagram?

 

[jimbo84]

I'm a member of a couple of Boxford groups and have checked the files but have been unable to find any diagrams. In one group there are multiple people saying they've had various issues with Santon switches mainly stating damaged/burnt out contacts. Maybe a similar issue with yours. From anecdotal evidence they're easy to strip to check contacts but fiddly to rebuild.

 

[RichardM]

Just noticed something else, there is an orange wire on the last segment and I think that used to go to the contactor, could it be that this wire trips the contactor when in switch is in the OFF position? it is currently not connected.

Most likely, I think orange was used for the low voltage system control, but it's a long time since I had an early boxford.

 

[TobyOne]

Thanks for all the replies chaps, most grateful. I suspect that this lathe has been "modified" over the years. It has a Danfoss CI9 contactor which only operates at 240 volts so there is no low voltage system, again something that surprised me. I have had a look at the switch and taken some of it apart, not particular complicated but already found sooty contacts so will need a complete overhaul. I would like to keep the switch and see if I reconfigure it so that it does completely disconnect the motor in the off position something that I think was probably performed by the orange wires tripping the CI9. The motor seems to run ok when the switch is in either position FWD or REV so I am hopping that's ok and that this issue is down to dodgy wiring and an old switch.