Eddy Current to VFD on Stamping Press

[psychosunshine]

I am getting ready to upgrade a press from an Eddy Current to a VFD with a standard motor.


If any of you have previously done this. What kinds of things did you run in to? What things do I need to consider that I may be forgetting?


We are using 40HP Eddy's and I was going to use a 50HP Baldor EM4115T, with the new Yaskawa GA800 VFD(A1000 replacement). The shaft size and motor footprint is nearly identical.



What else do I need to worry about?


I was going to rely on Speed Search to deal with starting into a rotating load.

 

[GaryS]

You don't need to be worry about speed search it will do nothing for you in this application
speed search is for fans and pumps that may be in motion when you start the motor.
typically you start at the top speed and search down until it catches the motor then it accelerates to the setpoint. it limits the current inrush of VFD out out of phase with he motor.
From what you say this may be a very old press you should a safety evaluation you may have to add new guards and light curtains and bring every thig up to todays standards
you may need to look at breaking
there is more to doing a press upgrade then just the motor

 

[psychosunshine]

This press already has light curtains on it. And, we test our brake times frequently. The Eddy motor is rated at 1700 rpm max. The new motor was going to be a 4 pole motor that runs at 1775 or so. So, our brake time should be the same if I do not exceed 1700 rpm. We can move our light curtains back, if we are interested in going faster. But, I think 1700 rpm should be OK.



The reason that I'm interested in upgrading the motor. Is because we are experiencing a lot of downtime replacing the Eddy motors. They don't seem to last long in this environment. We've been using rebuilds and new ones. And, neither seem to last very long.

 

[GaryS]

I am surprised that you didn't replace it a long time ago they have been obsolete for well over 20 years. The biggest problem with them is the center bearing locking up. causing the output to suddenly go to full speed. When the started to come out with VFD's they quit using them.
I was tasked in the mid 80's with building a monitor to shut the power off if the bearing failed. it worked great but I didn't see a future in it as they were already starting to replace them with VFD's
Your 1700, 17575 motor are both 4 pole motors with a base speed of 1800 rpm that was standard for them.
Good luck

 

[widelto]

The last time I replaced and eddy current with and VFD was more than 15 years ago.
I am surprised that eddy drives are still alive and kicking in some places.

 

[jraef]

The last time I replaced and eddy current with and VFD was more than 15 years ago.
I am surprised that eddy drives are still alive and kicking in some places.

Three years ago I was tasked with helping someone evaluate replacing aging eddy current drives with new ones vs new VFDs and motors. I was surprised that anyone was still selling the ECDs, but they put up quite a fight. Their arguments For ECDs and against VFDs were filled with misinformation and because everyone involved was an EE, it didn’t fly very far. But I was still shocked that anyone was still out there doing that. It was obvious that their market must be all the people who don’t know anything about either technology and are inherently resistant to change, so there must be enough of them still out there to keep these guys alive.

One challenge to investigate that came up on a project I did 20+ years ago is that the torque response of the VFD is often much faster than the ECD; it’s virtually instantaneous with a vector control VFD of any sort, whereas the ECD has to “spin up” into a step change in load. In my case it resulted in drive belts slipping and smoking after changing to the VFD. We had to artificially dial it back because the machine was designed around the slower step change response of the ECD. It wasn’t difficult to fix, it was just something I hadn’t anticipated.

 

[widelto]

@Jraef: Good info thanks.

 

[Phil Buchanan]

There are more Eddy Current drives out there than you would think. I upgraded 2 150 ton Blow presses from Eddy Current to ABB VFD's and Motors last year.

 

[Phil Buchanan]

I know several plants that still have several large Eddy Current drives still in production.

 

[Gene Bond]

I have done various Press upgrades to VFD's. There are a ton of them in this area with ECD's or Variable Sheave Drives as well as DC.

JREF is correct, the response of even an open loop VFD is much faster than the ECD or a Variable Sheave Drive with an old Design D (high slip) motor. Tuning can be a challenge!

De-tune the speed regulation, and allow the motor to droop. It will slow down when re-charging the flywheel (lifting the die), and speed up when the press is going down. No biggie as long as the full stroke time is repeatable.
Turn down or off the regen/braking torque/current limit to keep from Over Voltage tripping, or requiring a DB resistor.

It's a fun challenge sometimes, and other times it's a slam-dunk. It just fepends on the particular unit...