Replace crane magnetic contactor to soft starter / VFD

If you are looking to replace the magnetic contactor with a Soft Starter, your main advantage will be energy savings on inrush current at start up. If you replace the contactor with a VFD you will have the increased advantage of energy savings and the ability to vary speed. On a crane this can be helpful to have a high speed for coarse movements and a slow speed for fine adjustments in position.

If you are replacing the contactor control with PLC control you gain the option to add feedback to the system and a display. The major advantage to PLC control is increased adaptability. If in the future you want to be able to view current through the contactor, you merely install a CT, run an analog input into the PLC and add the value to your display.

While both PLC and VFD control add additional costs to the system, I believe the increased control and energy savings of the system pay off in the long run assuming the system is large enough.

Two things you need to check before you go ahead, 1) and the most important, VFD and Soft starts will reduce the power output of the motors, you may need to reduce the working load of the Crane, yes I know manufacturers will say no but I have learnt the hard way, there is a noticeable difference, 2) if you are doing any kind of accurate positioning there will be a slight difference in where the system stops, this is due to the difference between relay logic and the PLC Scan/update time.

If you need it to be accurate get a fast PLC and use the high speed I/O update routines. Also if you tell us what the application is (ie OHC Gantry etc) I think there will be some good detailed advice for you from the other people who have already given you some very good advice. Lastly, get a good software writer, if I had a good budget for every project I have had to sort out because of poorly written/documented/structured/out of date software I would be a rich man. If you don't write software make sure he gives you a proper logic flow chart which you understand. A good design engineer will convey information clearly and accurately. Good luck with the project.