How many channels does a two-speed (two-step) crane consume?
On a two-speed motor, low speed and high speed mean separate windings/contactors. If you want to drive the forward-reverse motion in two steps you need 4 relay outputs: forward-slow, forward-fast, reverse-slow, reverse-fast. So two speeds on a single axis turn a 2-channel job into a 4-channel one.
On relay-output remote controls the speed information is carried not by an analogue signal but by the number of contacts. There is no magic shortcut: on a two-step Dahlander or dual-winding motor each step demands its own contactor.
The channel budget works out like this:
- Single axis, single speed: 2 channels (forward, reverse).
- Single axis, two speeds: 4 channels.
- Two axes, two speeds: 8 channels — at this point a PLC, or an auxiliary relay circuit that generates the speed-step logic inside the panel, is more economical than relay logic.
The common and cheaper solution is to automate the speed step on the panel side: the single direction command coming from the remote control first pulls in the slow step, and a time relay switches to the fast step a few hundred milliseconds later. This keeps the channel budget at 2 and also softens the starting surge. It is essential to leave interlocking and a short dead time in the transition between steps; if both steps pull in at the same time a short circuit occurs between the windings.
Alternatively you can drive the motor from an inverter and fix the speed reference inside the panel; in that case the remote control only carries the direction and run command.
The full topic: Wireless Crane Remote Control Selection Guide