You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

Reply
 
Thread Tools Display Modes
Old February 2nd, 2006, 08:03 PM   #1
mjkoc518
Member
United States

mjkoc518 is offline
 
Join Date: Dec 2004
Posts: 46
VFD Speed Question

I currently hooked up a Power Flex 4 to one of our machines. In order for us to get the feet per minute with our drive we have to run the motor at 100Hz........Now I can changed the FPM of the belt by changing the drive sprocket, but is this needed? Does running a drive faster do any harm to an AC Motor? Would are some opinions? Changed the drive sprocket or run motor at higher HZ through VFD? Thanks
  Reply With Quote
Old February 2nd, 2006, 08:06 PM   #2
CroCop
Member
United States

CroCop is offline
 
Join Date: Aug 2005
Location: Utah
Posts: 1,050
As long as:

A. You don't need high amounts of torque
B. The motot bearings will handle it

You will be aok.
If it were me, and it weren't too much trouble, I'd change the drive sprocket anyhow.
  Reply With Quote
Old February 2nd, 2006, 08:25 PM   #3
Terry Woods
Member
United States

Terry Woods is offline
 
Join Date: Apr 2002
Posts: 3,170
In general, you can run a suited motor (any decent motor) at 200% of rated speed. You are in the US, so that would be at 120 Hz.

While it is always best to run the motor as close to rated speed as possible, there generally isn't much of a problem running at 200%.

However, judgements are best made if you understand the particular loading and torque requirements.
  Reply With Quote
Old February 4th, 2006, 10:04 AM   #4
DickDV
Member
United States

DickDV is offline
 
Join Date: May 2002
Location: Kalamazoo MI
Posts: 2,324
As long as the motor is nameplated 1800rpm or less, going to 100Hz is probably a good idea. Being a PLC4, the hp is low so, if I were designing a new system like yours, I'd probably choose a sprocket so the motor went to 90Hz.

Bottom line: leave it the way it is. You are getting better speed regulation, higher starting torque, and better motor cooling as a result. And, don't worry about the bearings--they use the same bearings in a 2-pole motor to run at 3600rpm.
  Reply With Quote
Old February 4th, 2006, 03:53 PM   #5
Sliver
Member
Canada

Sliver is offline
 
Sliver's Avatar
 
Join Date: Feb 2004
Location: Kingston, Ontario
Posts: 488
I have a 'Team Leader' who argues any motor driven over nameplate frequency (60 hz) is bad practice, harmful to the motor, blah, blah, blah..
I have seen many cases where mechanical changes were made to pulleys and gearboxes where an increase to even 70 hz was required.
Can anyone give me an authoritative source to help prove to this neanderthal that overspeeding a motor, especially an inverter rated motor is OK. If I tell him DickDV says its OK he'll go off his rocker again!

Thanks,

Brian.
  Reply With Quote
Old February 4th, 2006, 04:08 PM   #6
CroCop
Member
United States

CroCop is offline
 
Join Date: Aug 2005
Location: Utah
Posts: 1,050
Easy. If the motor is inverter rated to 3600 RPMs, the drive is rated to 400 Hz r whatever, and you drive the motor at 2000 RPMs and the drive at 75 Hz, you're well under manufacturer's ratings for the systems.
  Reply With Quote
Old February 4th, 2006, 05:16 PM   #7
DickDV
Member
United States

DickDV is offline
 
Join Date: May 2002
Location: Kalamazoo MI
Posts: 2,324
Yah! Sliver! Just the mention of my name often makes people go off their rocker. I've noticed that with some chagrin!! Haven't been able to stop it however! Frustrating!

Seriously, tho, simply obtain a hard copy or download a standard Reliance Electric Motor catalog. It doesn't have to be an Inverter Motor catalog, just a commodity motor catalog will do.

Take a look at the torque-speed curves in the front of the book (at least they used to be when I was working for one of their distributors). You will see that even the commodity TEFC motors are shown to have acceptable operating ranges often to 90Hz, a bit less as the hp goes up over 50 or so.

If the mfgr says its ok, that's good enough for me and should be good enough for most neanderthals too.

And, the best part is that my name doesn't show up anywhere!!!

Good luck!
  Reply With Quote
Old February 4th, 2006, 06:18 PM   #8
drewcrew6
Member
United States

drewcrew6 is offline
 
Join Date: Apr 2002
Location: allentown, Pa
Posts: 418
We had an issue where a machine would trip the drive off after the drive was about a year old. Change the drive and good for another year.

We finally really looked at the system after 2 drives and found that when the machine was set to its fastest speed the drive was running at about 160 hz.

The operators normally run at the fastest speed. I believe it was about a 2.5 - 3hp motor with a 1336 drive I believe.

We ordered a new pulley for the motor to bring full speed of the drive down to 70 -80 hz and its been running solid for well over 3 years now.

In short the system will not have an issue running there but longevity might be sacrificed. I have seen other types of machines with no issues running at the same hz.

Drewcrew6
__________________
      We're all here
Cause were not all there!

  Reply With Quote
Old February 4th, 2006, 07:56 PM   #9
Terry Woods
Member
United States

Terry Woods is offline
 
Join Date: Apr 2002
Posts: 3,170
Dick,

In your opinion, assuming a motor is controlled by a ramping 4-20 mA signal, if a motor is lightly, or at least reasonably, loaded, under all conditions, would running at 200% (120 Hz) be acceptable?

Why, or why not?
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
VFD and Well Pump Question Drake Lindsay LIVE PLC Questions And Answers 7 August 24th, 2005 05:38 PM
Vfd Speed Following JOHN ARMSTRONG LIVE PLC Questions And Answers 5 July 6th, 2005 07:53 AM
a vfd INDUStrial ELECTRIC AC motor SPEED CONTROLLER(inverter) crying_baby LIVE PLC Questions And Answers 19 May 12th, 2005 09:48 AM
GE Fanuc VersaMax PID control problem Shawn Cassidy LIVE PLC Questions And Answers 6 May 16th, 2004 09:10 AM
VFD open loop speed control Steve D LIVE PLC Questions And Answers 5 October 26th, 2003 08:39 PM


All times are GMT -5. The time now is 05:23 PM.


.