Selection of Inverter for Hoist

[dip04051978]

What will be the parameter affect on selection of Inverver for Crane Hoist Mechanism??

[jraef]

You will want an inverter that is designed for that application. It will need to be Closed Loop Vector, meaning that you will put an encoder on the shaft to feed back to the inverter for true motor shaft position in the vector calulatiions. Open Loop Vector is good for most any application EXCEPT hoists. I have heard that those who offer DTC (Direct Torque Control) claim to be capable of hoist control without an encoder, but I would NOT stand underneath one!

 

The next thing to insist on is commonly referred to as a "Torque Proving" feature, although the name may be different among manufacturers. This provides for testing that the motor is at 100% torque at zero speed BEFORE the mechanical holding brake is released. It seems like a given, but not all inverters, even Closed Loop Vector, are capable of this. Without it the load may begin to drop slightly before the inverter can calculate the proper output vector, then the motor may become incapable of stopping a moving load on the fly!

 

You must also carefully consider the input signal requirements. If you are retrofitting an existing hoist control, the voltage levels of the inputs must be capable of matching the existing control system. this seems like a minor issue but it is one that can cause lots of problems right at the very end of the project cycle (I have learned this the hard way!)

[Carl]

I done a application for a hoist in Cape Town, the one thing that I do remember about it..I'm talking a few good year now, Is that there was a *beep* of a lot of regen. We had to fit a bank of resitors in a seperate panel I remeber the resitors glowing red hot!! Infact it would have made a good food cooking unit

[bob]

I agere perfectly that the drive should be ble to provide full torque at zero speed before releasing the mechanical brake. I also suggest that the drive should also be able to old the load in case of breakdown of the mechanical brake. Some drives do give an output known as zero speed control and this can be used to hold the load and gradually lowering the load at reduced speed.

Bob

[Guest]

In reply to jraef, I have used DTC drives on hoists, and the manufacturer strongly recomends that encoder feedback is installed. However, I have failed the encoder feedback and there is no noticable difference in performance with out it.

 

The drive spec does state that the speed accuracy is slightly worse with out the encoder, but we're only talking a fraction of a % of the motor slip frequency.

 

In general, when putting a drive onto a hoist do your self a favour and use one with an active front end. The drive may cost a bit more but it is worth it for the peice of mind, you don't have to worry about sizing brake choppers and resistors or install extra fuses and cables. You just commission the drive and let it do its thing.