VFD Control of Hoist Motor and Break

This 40 Tons overhead crane has a standard general purpose VFD with break chopper and also controls the mechanical break. The problem is it does not use DC breaking to hold the weight before applying or releasing the mechanical break. This results in very high wear of break leathers. A few times weight fell and drive or break could not hold. Fortunately no one was hurt.

I need suggestions for a suitable VFD and guidelines regarding wiring and commissioning of this VFD.
I haven't done anything with cranes for years, before VFDs for that matter when all cranes were based on slipring motors.

I would imagine that a VFD should be able to raise and lower the load without using brakes at all and just use the brakes for emergency and parking. It should be possible to fully release the brakes before slowly accelerating away.

Of course on power fail the brakes have to be capable of arresting the load under brakes alone.

I will be interested to see what sort of comments you get.

James Ingraham

I don't want to sound too much like I'm shilling for Allen-Bradley here. They're a major supplier for us, just in the way of full disclosure. With that being said, I think the PowerFlex 755 drive is a good fit. I've never dealt with that big of a vertical load, but I do know that A-B makes drives plenty big enough for that, and recommends that drive for vertical loads. They even have specific documentation for vertical load applications.

Many times I've said that technical issues shouldn't be the driving force for picking a supplier. Given my company's relationship with A-B, they would be my first call for a project like that. However, some other vendor may be a better fit for you. Location is part of this; Rockwell / A-B is the preferred supplier for a lot of people in the United States. In Europe, Siemens is the top dog. Similarly, if you've got a plant full of Logix PLCs, then A-B is the obvious choice, whereas if everything in on Profibus, then Siemens make more sense. (Although every major drive these days plays nicely with just about everything, with a few corner cases.)

I think any of the major drives suppliers would be happy to help with an application like that. If I were doing it, I'd get bids from Rockwell / Allen-Bradley, Siemens, Yaskawa, ABB, Danfoss, Mitsubishi Electric, Toshiba, and Schneider Electric (not necessarily in that order.) If you already have a relationship with one of those, that's who I'd lean towards.

-James Ingraham
Sage Automation, Inc.
I have done lots of Hoist / Crane applications with VFDs, specially Siemens MM4 & Sinamics G120 & S120. There are some features that allow "Overlap" between VFD holding the motor using DC injection brake and enabling the mechanical brake.

if you need more info, feel free to contact me: [email protected]
MoSawy a few questions for the curious.

On a common VFD application the Voltage sort of follows the frequency in a somewhat linear fashion. I imagine this wouldn't be ideal for a crane, if you did that it would accelerate away as the field stopped rotating. Do they increase the Voltage to provide more braking? Would they run field backwards to overcome slip under a heavy load.
What is the ideal Voltage/frequency relationship.

What type of motor is used, regular squirrel cage or something else?
How is the brake operated, some sort of electro hydraulic?

It would be interesting to get a simple explanation of how a typical modern crane works. A long way from slip-ring motors and drum controllers I'm sure.