Are VFD's bad for motors? - Page 3
Close
Login to Your Account
Page 3 of 3 FirstFirst 123
Results 41 to 46 of 46
  1. #41
    Join Date
    Feb 2018
    Country
    UNITED STATES
    State/Province
    Texas
    Posts
    170
    Post Thanks / Like
    Likes (Given)
    31
    Likes (Received)
    29

    Default

    Quote Originally Posted by Briney Eye View Post
    I know from experience designing small motor drivers that switching too fast can blow the H-bridges (I warned the engineer and he did it anyway - made a nice little light show), so I'm pretty much with you on this one. If you switch them too fast the transistors never have time to switch fully on or off, look like resistors, and cook. But I would assume that VFD carrier frequencies are limited to a "safe" value (mine are 15kHz) to keep that from happening. I have mine maxed out so I don't have to listen to them whistle, and haven't had any issues. All this new inverter tech is based on IGBT's, and they've gotten pretty good in the last ten years or so. Seems like they're typically rated for 30khz or higher switching frequencies. Earlier ones were slower.
    I run mine at 15kHz as well, because the whine annoys the hell out if me. I have poor hearing but somehow I hear even 15kHz, which should be impossible for me. Maybe I'm hearing a lower harmonic.

  2. #42
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    27,334
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8523

    Default

    Quote Originally Posted by ptsmith View Post
    I run mine at 15kHz as well, because the whine annoys the hell out if me. I have poor hearing but somehow I hear even 15kHz, which should be impossible for me. Maybe I'm hearing a lower harmonic.
    VFD's haven't bothered my hearing in the least, near two years already.

    Far as I know, they are 20 feet down in a cut and cover landfill about 15 miles away from the shop.

    Annoying Phase-Perfect is going to have to go share a blanket in the back garden shed with the RPC, Delta => Wye transformer, and the Diesel though.

    Five each of 100' spools of #4 THNW Copper wire and some conduit and Square-D goods made that possible.

    Bog-standard electrical goods. Gotta LOVE the stuff!


  3. #43
    Join Date
    Mar 2009
    Country
    UNITED STATES
    State/Province
    California
    Posts
    5,052
    Post Thanks / Like
    Likes (Given)
    91
    Likes (Received)
    924

    Default

    Quote Originally Posted by DennisCA View Post
    What do you guys think?
    Here are some more guys.

    Mill Motor Runs on Line Power 3P/240VAC But Not on VFD - Why???

  4. Likes everettengr liked this post
  5. #44
    Join Date
    Jan 2006
    Location
    Radcliffe Iowa
    Posts
    631
    Post Thanks / Like
    Likes (Given)
    22
    Likes (Received)
    73

    Default

    Quote Originally Posted by whidbey View Post
    If you talk to motor companies, they will tell you not to use a vdf with old motors. I have also asked this question online before and have yet to find anyone actually experience a failure due to VFD use. So basically for low volume use (home workshop) it doesn't matter and for full time use you are going to need more modern equipment or at least more power than you can get out of a single 20amp outlet anyway so it won't be a problem.

    I have run the same machines on vfd and 3phase out of the wall and while I have no proof but they seem to run better with the real thing. If you can get 3ph it is the way to go and really I don't think you should be using a vfd with a fp2 as you have multiple motors and many switches in that machine. (The vfd needs to be wired directly to the motor with nothing in-between. This is also a problem with two speed motors for obvious reasons.

    Luke
    I have seen a motor that ran across the line for 15 plus years fail within 2 weeks of being on a VFD.

  6. #45
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    7,806
    Post Thanks / Like
    Likes (Given)
    392
    Likes (Received)
    6489

    Default

    Quote Originally Posted by BMyers View Post
    I have seen a motor that ran across the line for 15 plus years fail within 2 weeks of being on a VFD.
    Of course you can do this, depends on how you setup the VFD and there are all sorts of things to tweak. It takes time and effort to get through all the options.
    Some engineers who commission such were obviously sleeping in class. I've seen that, this is not plug and play.
    You drag out the test equipment and check what is going on so that you know it will go another 15-30 years.
    Bob

  7. #46
    Join Date
    Jun 2001
    Location
    St Louis
    Posts
    17,936
    Post Thanks / Like
    Likes (Given)
    1847
    Likes (Received)
    3011

    Default

    Quote Originally Posted by Briney Eye View Post
    I know from experience designing small motor drivers that switching too fast can blow the H-bridges (I warned the engineer and he did it anyway - made a nice little light show), so I'm pretty much with you on this one. If you switch them too fast the transistors never have time to switch fully on or off, look like resistors, and cook. But I would assume that VFD carrier frequencies are limited to a "safe" value (mine are 15kHz) to keep that from happening. I have mine maxed out so I don't have to listen to them whistle, and haven't had any issues. All this new inverter tech is based on IGBT's, and they've gotten pretty good in the last ten years or so. Seems like they're typically rated for 30khz or higher switching frequencies. Earlier ones were slower.
    There is the direct "too fast" where the "on" time is too short as you describe.

    The "speed" of switching can mean the actual speed of the switching event, or it can mean the number of times per second that the device is switched. Carrier frequency is the latter. Each turn-on or turn-off event has a "loss" which appears as power dissipated in the device, since the device is essentially operating in a "linear" or "resistive" manner during the time of switching on or off. If switched too many times per second with insufficient heatsinking, the switching devices (usually IGBTs these days) simply overheat and fail, because the total energy dissipated per second is too high.

    IGBTs in particular have issues common to all "bipolar" transistors, that do not exist in a power MOSFET. These include a tendency to "stay on" after they are "turned off", due to what is called "tail current". MOSFETs , however, trade low losses during switching for higher losses when conducting current. IGBTs have lower losses when fully turned "on". Newer devices, both MOSFETs and IGBTs are getting much better, tending to mix the best features of IGBTs with the best features of MOSFETs in one device.

    The losses associated with turn-on and turn-off are also affected by the design of the gate drive. A weak gate drive leads to slow switching times, and more losses. A fast switching time has less loss, but takes more gate drive power (another form of "loss"), and also generates more EMI (radio interference). And the best devices tend to be the most expensive, which often dictates the use of a device type that is not the best possible, limiting the choices the designer has.

    It's all a trade-off, and engineers are expected to find the best trade-off for a given application.

  8. Likes Yan Wo, Jraef liked this post

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •