Power Circuit
Control Circuit
Circuit Operation
The contact on terminals a3-a4 of either the forward or reverse push button energises the required direction contactor, either the forward contactor FC or the reverse contactor RC, the relevant main contacts 1-2, 3-4 and 5-6 close which puts power; with either clockwise or anticlockwise phase rotation; to the motor terminals, normally open auxiliary contacts of the relevant direction contactor on terminals 13-14 close to maintain the power to that direction contactor when the button is released. A normally closed contact on terminals 21-22 of the each direction contactor is in the opposing direction contactor coil circuit to prevent simultaneous operation of both direction contactors. Power is connected from the power supply to the motor terminals and the motor will start and accelerates to full speed in the selected direction.
To stop the motor the stop button is pressed its contacts a1-a2 open which de-energises the energised contactor, thus stopping the motor by removing its power supply and resetting the control circuits.
The auxiliary normally closed contacts on terminals 21-22 of the forward FC and reverse RC contactors are placed into each others coil circuit so that electrically the two contactors cannot be simultaneously energised which would cause a short circuit, this can be seen by examination of the above circuit. It is normal to mechanically interlock the forward and reverse contactors in addition to the electrical interlock. It can also be seen from the above circuit that it is not possible to change the direction of rotation of the motor without first pressing the stop button to de-energise the energised contactor.