VFD on a 25HP Rolling Mill even practical?

[mfgbydesign]

I'm proposing converting a cold-rolling mill to CNC control. The process involves controlling the 25HP AC motor to very slow speed, stopping at a programmed position within an 1/8" (based on linear scale feedback of the product), downfeeding the top roll with servo motors, and reversing. Taking multiple passes.
I'm a CNC guy, so perhaps I'm guilty of having a hammer and everything looks like a nail.
ANY insight on how to do this would be greatly appreciated!

 

[rk9268vc]

you can get VFD's over 300 HP, i see quite a few on Automation Direct for around 1 to 1.5K$ for your 25HP
just make sure you get a good one obviously

There is a big push to convert as many large motors over to VFD's as possible, it is a lot easier on the grid. Some power companies, for example Xcel Energy, actually give credits/ rebates for switching big motors over to VFDs

 

[GENERALDISARRAY]

To me, a lot of Automation Direct's pricing is fairly high. Are their VFD prices more reasonable?

compared to what? Alibaba? Wish.com?

 

[rk9268vc]

To me, a lot of Automation Direct's pricing is fairly high. Are their VFD prices more reasonable?

If something is much cheaper than automation direct, it is probably a scam or Chinese junk.

In my experience, their prices are either industry standard, or better

 

[Garwood]

Automation direct VFD pricing has always been high for me. I have bought many other things from them, but never, ever have they had a decent price on any VFD's I have needed.

 

[garyhlucas]

And then there is AD tech support. Best in the business and FREE! The typical VFD has about 300 parameters that can set and ussually only 20 or so get set. For your application, very slow speed, encoder feedback etc. you might need that to set a whole lot more, and all of a sudden that drive will look cheap.

 

[Archer120x]

You aren't going to have hardly any torque to restart the motor once it stops under load.

 

[johansen]

You aren't going to have hardly any torque to restart the motor once it stops under load.

Not true. the correct voltage and frequency delivered by a properly configured vfd will produce more torque at startup than direct online starting at 60hz.

Typical starting torque is 1.5 to 2x rated torque, peaking at 3 to 4 times rated torque typically at say, 1500 rpm for a 1750rpm motor, when simply plugged into mains supply.

A vfd could probably be configured to get 5 times nameplate torque briefly before the motor burns up.

Here is an example, I wired a 2hp 240\480v motor for 138volts delta, and to check that my wiring was good I plugged it into 208v mains. It started up substantially faster than it did when wired for 240. But it pulled 17 amps at no load! 240v nominal amps is 5.4.

I then configured a vfd for 138v 60hz and it ran properly at 4 amps no load. (full load for 138v delta is 9.4). The intent is to get 2hp at 5400 rpm from a 208v supply for a friend's harry home shop milling machine.

Anyhow depending on the motor, peak torque at startup for a given current will be something on the order of 6 to 20hz and 20 to 50% nameplate volts.

Induction Motors have a skin effect problem that is intentional, the different torque curves are a result of different rotor bar designs. the 60hz line frequency at startup does not penetrate deep into the rotor and this is intentional, otherwise the starting current would be too high. The vfd can keep the delivered frequency to be 3 to 20hz higher than the rotor is turning, and the field will penetrate deep into the rotor.

 

[Archer120x]

Not true. the correct voltage and frequency delivered by a properly configured vfd will produce more torque at startup than direct online starting at 60hz.

Typical starting torque is 1.5 to 2x rated torque, peaking at 3 to 4 times rated torque typically at say, 1500 rpm for a 1750rpm motor, when simply plugged into mains supply.

A vfd could probably be configured to get 5 times nameplate torque briefly before the motor burns up.

Here is an example, I wired a 2hp 240\480v motor for 138volts delta, and to check that my wiring was good I plugged it into 208v mains. It started up substantially faster than it did when wired for 240. But it pulled 17 amps at no load! 240v nominal amps is 5.4.

I then configured a vfd for 138v 60hz and it ran properly at 4 amps no load. (full load for 138v delta is 9.4). The intent is to get 2hp at 5400 rpm from a 208v supply for a friend's harry home shop milling machine.

Anyhow depending on the motor, peak torque at startup for a given current will be something on the order of 6 to 20hz and 20 to 50% nameplate volts.

Induction Motors have a skin effect problem that is intentional, the different torque curves are a result of different rotor bar designs. the 60hz line frequency at startup does not penetrate deep into the rotor and this is intentional, otherwise the starting current would be too high. The vfd can keep the delivered frequency to be 3 to 20hz higher than the rotor is turning, and the field will penetrate deep into the rotor.

I'll put my money on any reasonably sized VFD tripping on overcurrent protection in this application.

 

[johansen]

I'll put my money on any reasonably sized VFD tripping on overcurrent protection in this application.

If you want 3x nameplate torque it will require 3x nameplate current.

 

[sfriedberg]

Yes, TEFC cooling will not work at pokey motor speeds, and the motor will be generating significant heat regardless of speed. Cooling fan spinning at constant speed, independent of motor speed, will be important.

 

[MwTech Inc]

We have used Automation VFD's for 15 years, never had one failure. Have 5 here right now going into a project. Are there cheaper, sure.

False economy, one failure will cost us considerable more than a few bucks up front.

The layout, programming and reliability are unmatched .......we will not change..

Personal use, you can buy cheap if downtime means nothing, for our customers, not.

 

[mfgbydesign]

WOW Thanks for all the great info provided on my thread!
Sorry I haven't been on here all weekend, I had trouble getting on at home. Account issues, email, password.

 

[Mike RzMachine]

Look into Lenze. They make good quality VFD's, support feedback/advanced motion functions and have good application engineer support. Pretty reasonable pricing as well.
I also had good service with the VFD I got from automation direct.

 

[mfgbydesign]

Update: I purchased the machine so now the fun begins!

 

[rbent]

I've been having good luck with ABB ACS880 drives for closed loop control using encoder feedback for 1000:1 speed reduction, or more, and full torque. I use Marathon Black Max motors with the encoder, typically a Dynapar HS35. There are other good VFD's for closed loop control off motor encoders, but I haven't seen any of the cheap ones do it.