Motor Keeps going after it's turned off.

eddybs23 · Sep 25, 2011

Newman 3 phase induction motor (Bradbury liftmaster MK1) on a four post ramp - . When the ramp is raised it sometimes keeps going - bloke says he can't switch it off by regular switch - has to do it at the main isolator. I haven't been there yet, any ideas?

johnboy6083 · Sep 25, 2011

Contactor sticking?

malcolmsanford · Sep 25, 2011

Poor connection on the contactor which is making it stick might have to change the contactor or strip it down and clean the points of contact with some fine emery paper if it's the old open type.

Check to see if the push button is ok, should be have a contact coil on it, but could still give you problems.

johnboy6083 · Sep 25, 2011

Also could be the raise button sticking? Maybe the contol box needs the buttons and the contacts behind them cleaning and re-assembling

Knobhead · Sep 25, 2011

If it was a sticking raise PB then the raise would cut back in when power was restored.
Does it have a stop PB? Most don’t, you normally have to keep your finger on the PB as a safety precaution.
Will have to think about this one.

vaughant · Sep 25, 2011

It looks to me as though the action of turning the isolator off is dropping out the raise contactor,so I'd guess it's a control issue (which I think we've worked out already!!!).
How does the lift work?motor up and down or does the motor power a hydraulic lift then it just releases the pressure to lower it?

My one was electric power,hold the button in then release wherever up and down.

A lot of them are very crude,literally the push button has a plastic stalk on the back that pushes the contactor in physically to operate it,usually interlocked then to prevent arcing if up and down are operated simultaneously. I'd go for jonboy's idea of a good physical clean up first,something sticking etc.

Engineer54 · Sep 25, 2011

malcolmsanford said:
Poor connection on the contactor which is making it stick might have to change the contactor or strip it down and clean the points of contact with some fine emery paper if it's the old open type.

Check to see if the push button is ok, should be have a contact coil on it, but could still give you problems.

Far better to clean contacts with ''Glass Sticks'' (glass-fibre strands held tightly together by glued fibre tape, or in a purpose made height adjustable pen type construction) The finish is as good as a new contact surface. I haven't used fine emery paper for maybe 25 years now... You can purchase from any good electronic stores, or where i get mine from, RS.

Yes the fault could well be in the push-button, the contacts within the push-button unit could be stuck/wedged in the contact position while the spring release is still sending the button back to it's normal position, making it seem like it's working normally.

eddybs23 · Sep 25, 2011

Thanks all - as stated - contactor sticking - lift installed 1964 and some very crude switching via pulleys and springs etc. all surrounded by hydraulic fluid and, filth!