Forward-Reverse Direction Control (Reversing Control)
A control arrangement that changes a motor's direction of rotation via two separate contactors or two relay contacts. This is the basic function of AXI's 2-channel sets: CH1 drives one direction, CH2 the opposite direction. When changing direction it is essential that the two paths are never closed at the same time and that a short dead time is left.
Direction change is achieved on three-phase motors by swapping two phases, and on DC motors by reversing the armature polarity. In both cases there are two separate switching paths, and their overlap is electrically unacceptable.
A correct reversing installation contains all of the following together:
- Electrical interlocking: mutual NC auxiliary contacts.
- Mechanical interlocking: a physical accessory between the contactors.
- Dead time: a short delay before the other direction pulls in after one has been released. Applying the reverse direction while the motor is still turning creates heavy arcing on the contacts and mechanical stress.
- Limit switch: a separate NC limit switch for each direction, in series with the coil path.
Do not break the sequence during commissioning: first verify the direction with no load, then test the interlocking, and lastly trigger the limits. A reversed connection noticed only while working under load is usually noticed too late. When sizing the relay output, also treat the load as inductive and calculate the contact current with derating.
Context in which this term is used: Wireless Crane Remote Control Selection Guide