Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Interpret VFD spec for motors

Interpret VFD spec for motors

Interpret VFD spec for motors

Hi, there. I'm trying to use a VFD for my motor. I was reading VFD spec and it says
maximum current/power with 115% overload for 60 seconds; every 10 minutes

Does this mean I can operate VFD at 115% for 1 minute and 100% for 9 minutes or 115% for 1 minute and 0%/no load for 9 minutes?

RE: Interpret VFD spec for motors

Hello Cheetos

A very good question and is not very clear anywhere.
I always interpret this as continuous run at 100% with an overload up to 115% for 60 seconds every ten minutes. i.e. no cool down period specified.
Interested to see what others say!

Mark Empson
Advanced Motor Control Ltd

RE: Interpret VFD spec for motors

0% load for 90% of time means VFD (and hence the motor) would be shut off for 90% of time, which does not make any sense.


RE: Interpret VFD spec for motors

Hi Cheetos,
That simply means you can overload the VFD to 115% for a maximum of one minute. But it does not mean you run it at 100% for 9 minutes and every 10th minute you run at 115%. Why it is like that? Because when overloaded you heat up the power electronic components to it limit. Now you need to cool it down. If you continue to run at 100% load, you are not allowing them to cool down.
I am sure if you look into the manual they would explain that once you have run the VFD at 115% for 1 min, in order to allow the power semiconductors you have to run it at less than 100% (most of the time 90% or less load) for another 9 minutes to be able to regain the overload capability.

RE: Interpret VFD spec for motors

Hello Tanweer

That is certainly one interpretation, but equipment that I have designed has thermally been on the basis of 100% rated load plus 120% for 60 seconds every 10 minutes. i.e. the average thermal loading is higher than at 100% rating continuous, so that is also valid.
If the assumption was that you would run at 90% when not overloading to 115%, why would you rate at 100%? Why not rate at 90% with a higher overload limit?

Mark Empson
Advanced Motor Control Ltd

RE: Interpret VFD spec for motors

Hello Marke,
You are right. It depends what is your 100%. My statement is based on standard practice adopted by most of the major brands. Exceptions are always there, as you said.

RE: Interpret VFD spec for motors

I think overload to 115% is to address dynamic of rotational load during acceleration or deceleration, when in addition to static load there is load from inertia which needs to be overcome.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close