How can you interlock 2 electric motors so that one will stop if the other stops.?

Question

I need to syncronise two hoists raising a single load, so that - for safety sake - if one should quit for any reason, the other hoist will stop also.

Answer 1

There are VFD's that have this ability. Some are vector and will monitor the load.
But to stop on all situations you would need some kind of feed back. An encoder, resolver or something if you are going to a PLC or other controller.

If it is wired to a contactor, you can make one run with the other, but it will not guarantee they are running.

Please do not wire them in series. You just might end up with FLA on 1 motor.

Answer 2

Do not attempt to wire the motors in series.

If the motors are not already controlled by contactors, they should be. Take an auxiliary contact from the contactor of the hoist that can run on its own and wire it in series with the coil of the contactor for the other hoist.

If you need either to stop in the event the other does you can interlock both but will need some way of getting them going from the start and you may want to consider having an electrician, at least, draw the circuit for you. It pretty simple to anyone that works on this kind of thing

Answer 3

I dont suggest what troy said this not good
the best way is by using simple PLC
( programable logic control)
by taking output from the motors let say a small generator which works as a sensor which give a low voltage output that indicates the motor s are workings
inter these outputs into the PLC and take one output from the PLC to the contactors which are in serious with the motors
let the contactor normally closed
and let the PLC output signal open the contactor so the motors are off when the signal is giving
in the PLC give a very easy command of an OR gate
( in a ladder diagram that means in parallel)
when any of the motor is turned off for any reason the PLC will give a signal to open the contactors and open the circuits so the motors are off
note when programing the PLC remember to let the inputs from the motor in the Inverse input so a signal is giving when one of them is off
I think this is the easiest and safeist way and I use quite often in my work

Answer 4

A brute force way would be to use an op-amp circuit to monitor voltage across or current through the motor of the first hoist, and have it trigger the power circuit of the second hoist. I'd have to see the application to get into specifics, but it should be very easy to do.

Answer 5

You will need a control system if you want to do it right. Wiring them in series is not a good idea. If one freezes up, the other will have full voltage across it. If this is a one time job, rent an appropriate hoist. The control system would take months to design