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  1. #1
    Join Date
    May 2011
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    Murray Bridge S Aust.
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    72
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    6,205

    Default VFD size enquiry

    Sorry if this question had been here before, but, I can't seem to find an answer.
    How does someone work out what size VFD is required for a machine, is it the Amperage required, horse power or its newfangled kw, or something else?
    I'm looking at getting several to do the jobs, one per machine, so I need to make sure I get what's required.
    Thanks in Advance.
    Kryn
    To grow old is mandatory, growing up is optional.

  2. #2
    Join Date
    Oct 2019
    Location
    Adelaide, SA
    Posts
    1,625

    Default

    The short answer is to size the VFD based on motor horsepower/kW.

    Suggestions are whatever your motor hp to buy the next size up.

  3. #3
    Join Date
    May 2020
    Location
    Willowbank QLD
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    679

    Default

    All VFD's I have seen are rated in Kw. There are also two different outputs available depending on if the motor is Star or Delta. As I understand it, there is no issue with having a VFD with a larger rating than the motor, XXXXample 2Kw VFD on 1.5Kw motor.

    If this is all new to you a photo of the motor data plate will help.
    I purchased my first VFD from Connon motor. They are Australian based and it was a bit dearer than online sellers. I rang a couple of times and both times he could explain in detail which setting I had wrong and how to solve. If I look at the price I paid I certainly got value for money with after sales service.

    They have many setting available, but the average home user will only use a few.

    Steve

  4. #4
    Join Date
    Oct 2019
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    Adelaide, SA
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    Default VFD size enquiry

    Agree but these days I prefer not even talk about the delta or star configuration aspects. Or 220v 3ph vs 380v 3ph.

    It confuses people a lot and a simple job appears over complicated.

    Out of most industrial setups the machines are set at 415v star. So better to leave them at that.

    Obviously my suggestion is a 220v 1ph to 380v 3ph stepup VFD.

    No more mucking around with rewiring motors or replacing motors.

    Some people get too carried away by marketing points such as sensorless vector and V/Hz. I am not saying its not real, I am questioning does it really matter to the average person.

    There are a few important considerations regarding setting up the controls to work directly with a VFD such as existing e-stops, fwd/reverse, motor braking etc.

    Or making it even more simpler by connecting the motor directly to the VFD and doing everything via the VFD interface.

    One other important consideration is also regarding machinery with multiple 3 phase motors, the main motor, the powerfeed, and the coolant pump. We can run multiple motors on the same VFD but there are other aspects to this and I think at this stage let us park it here VFD size enquiry

    My requirements are so simple:

    - I want it to behave as it I plugged it into a 415v 3 phase outlet
    - Use the machine as it was designed at 50Hz (variable speed perhaps +/-10 Hz for quick adjustments only)
    - I want soft start and e-stop

  5. #5
    Join Date
    Nov 2017
    Location
    Geelong, Australia
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    58
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    2,830

    Default

    Definitely no issue with running a higher power rated VFD than what the motor rating is eg if you have a 1hp (0.75kw) it will run perfectly on a 2.2kW VFD.

    I think that having a little bit of extra capacity on the Chinese VFDs is a good thing and makes me feel warm and fuzzy that I’m not pushing it to the limit, but I’ve also run 2.2kw motors on 2.2kw VFDs with no issues (as you would expect).
    Basically if there’s minimal price difference then it doesn’t hurt to go up a size, but don’t feel that you HAVE to.

    If you’re dealing with older machines then just go for the 220 1ph to 380v 3ph Ecogoo/Nflixin units.
    If you have something with a nice modern motor that has ratings for both ~400/415v and 220v 3ph listed on the nameplate then you can definitely save a couple of dollars by using the 220v 1ph - 220v 3ph ones, but if it’s not 100% obvious on the nameplate just stick with the 220-380v ones.

    Steve

  6. #6
    BobL is offline Member: Blue and white apron brigade
    Join Date
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    Perth
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    Default

    Regarding running a higher power rated VFD than what the motor rating.

    This is fine
    BUT
    what everyone seems to be forgetting is that a VFDs maximum current parameter must be adjusted to suit the motor otherwise the motor and VFD can be damaged beyond repair.

    A 240V 750W motor will usually have a nominal maximum current parameter of 3A with something a 150% overshoot for a short time.
    A 2.5 kW motor might have a nominal maximum current parameter of 10A with some a 150% overshoot for a short time.

    If a 750W motor is is used with a 750W VFD then no current max parameter is usually needed.
    If a 2.5kW VFD is used and the motor is overworked it may draw more than 3A for an an extended period before it reaches 10A. This will quickly overheat and burn out the motor

  7. #7
    Join Date
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    Default

    Good point Bob. Something I do but hadn’t stated.
    As a bare minimum I always go through the basic motor parameter settings on the VFD on initial setup - such as voltage, current etc and do an auto tune. I also do a quick check of the running frequency settings to make sure they they have the correct values.
    Typically the only other settings that I always change are the Accel and decel times. Defaults are usually 10sec which is very safe (I always leave them alone for an initial test run then change after I’m happy everything is OK) but usually run 1-5sec values depending on the particular machine.

    Steve

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    Default

    Quote Originally Posted by OxxAndBert View Post
    Good point Bob. Something I do but hadn’t stated.
    As a bare minimum I always go through the basic motor parameter settings on the VFD on initial setup - such as voltage, current etc and do an auto tune. I also do a quick check of the running frequency settings to make sure they they have the correct values.
    Yep good points. I think it was the 3rd Huanyang VFD I bought where I automatically assumed the frequency was set to 50Hz, turned it on and the motor spun up to over 200Hz before the VFD turned itself off. Turned out someone had l set the F to 400Hz!

  9. #9
    Join Date
    Oct 2019
    Location
    Adelaide, SA
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    Default

    My Huanyang VFD had 400Hz set by default when I received it and those days they were very commonly used on CNC router spindles which go from 0 to 400Hz. I bought mine from a CNC supply store on AliExpress.

  10. #10
    Join Date
    Dec 2013
    Age
    57
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    Default

    I must have missed this post originally and thought you were coming through again, lol

    More than welcome to call in at any time again.

    I'm running a couple of vfds if you need help, but the other members have got it covered.

    Sent from my SM-A235F using Tapatalk
    Using Tapatalk

  11. #11
    Join Date
    Oct 2019
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    Adelaide, SA
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    Default

    I believe Dave said an important thing: “If you need help”.

    Kryn, If you want, i can easily spend a morning or an afternoon with you and show you how to setup one.

    We have that 1.5kw 415v star motor to play with in your shed. It’s the perfect test bed for learning.

    We can set it up on the bench and go through a few settings and play with some parameters so you can feel comfortable changing them yourself.

    Setup frequency range, set up current limits, soft start, forward/reverse, auto tune etc. You can literally count what needs to be done on your finger tips.

    Let me know once you have ordered and received your VFD and I will come across.

  12. #12
    Join Date
    Oct 2018
    Location
    Australia
    Posts
    5

    Default

    That is easy enough to setup VFD - I put couple of them into my old lathe and grinder removing old contactors and transformers.
    Just go through list of parameters thoroughly - not all of them are obvious. I spent some time on first one trying to start motor on button.

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