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  1. #1
    Hi guys,
    Some of you may be interested. I set up the VDF with a potentiometer and the 2.2kw spindle on the bench at 15000rev. The Amp setting on the panel was saying 1.5A

    Then I used my ammeter on the mains power cable and it actually measured 0.8A. I trust this reading to be more accurate than the VFD panel reading.

    Naturally this was without any load, i.e. not cutting anything, so the current will go up under cutting conditions, nevertheless I thought it was interesting to see how little current it draws and also to show the disparity between the panel reading and an ammeter reading.

    I also measured the noise level (again without load) using a digital decibel meter. My room level is 41db. The fan is quite noisy, at around 53db (1 meter distance) and with the spindle on at 15000 revs it read 62db. I was quite surprised that it is so quiet on the bench.


  2. #2
    I also just set up the analog voltage control and ON/OFF of the VFD from my Kflop/Kanalog controller and it all works nicely. I see no fluctuation in the speed as it is, on the bench, nice and sweet. The speed variation between what it says on the VFD panel and my own reading with a tachometer was practically bang on too.

    For the on/off relay I've used a cheap SSR from RS, part number 720-3956. It only costs 6.62 and it operates at 24V. No diode needed.


    Click image for larger version. 

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  3. #3
    The effective voltage to the motor may not be the same as mains and you're driving an inductive load so power factor is also in play ;-)

    If it were a Siemens, Hitachi etc. I would trust the VFD, I don't have and probably never will have experience of tertiary VFD brands, I require good documentation and support in any hardware I use.
    You think that's too expensive? You're not a Model Engineer are you? :D

  4. #4
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 14 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,156. Received thanks 209 times, giving thanks to others 5 times.
    Out of curiosity, are you also able to measure the analogue voltage coming out of the Kanalog? I was looking at my CSMIO+HY VFD combination yesterday. According to Mach3, the demanded speed was 15000; the VFD said 15500. Error of about 3% - not a big deal, and I can't think of many situations where that would matter to me. I would expect the spindle speed to track that pretty closely, given the motor technology and the fact that the motor speed display will be derived from the VFD digital electronics. When I did a similar test while initially configuring the machine, I seem to remember that there was a slight error in the analogue output from the motion controller which probably explains any discrepancy but I'm not sure I would trust my Maplin digital multimeter that well anyway.

    But it's nice to know that it does what you expect! As for current readings - as Nick suggests, you don't know exactly what and how they are deriving these numbers, but it might be interesting to compare off-load and full-load readings.

  5. #5
    Yes, I actually measured the voltage with my multimeter out of the Kanalog before I connected anything. So for example, out of a requested 5V, I got a reading of 5.04V. The analog conversion is not 100 per cent linear, but pretty close. Then with the software you have a multiplier that you can adjust, so when your code says for instance, s12000, you also get the 12000 on the VFD. But then if you want S15000, you may get 15100revs, as I say it's not linear, but in practice it's of zero importance to the cut, I think it's the same with any other boards really, some may have more linear conversion than others throughout the 0-10V scale.

    I think the current reading that's most relevant is the actual current draw at the entry point to the VFD, i.e the mains power. I used a clamp meter, which I think is fairly accurate, though it's not one of the super expensive ones. I am curious too as to how much more current it will draw whilst cutting, as this could give you a good idea of how much you can push your cut settings in order to find when you are close to the limit, and maybe also a give you a glimpse at the current draw at start up and stopping? I guess this could also determine the fuse rating you use.

    Last edited by Edward; 10-09-2017 at 08:01 AM.

  6. #6
    I think the current reading that's most relevant is the actual current draw at the entry point to the VFD
    relevant to what ?

    Regarding current, read this;
    Last edited by EddyCurrent; 10-09-2017 at 07:37 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  7. The Following User Says Thank You to EddyCurrent For This Useful Post:

  8. #7
    Thank you, that kind of throws light on the difference between the panel reading and input current reading.


  9. #8
    Quote Originally Posted by EddyCurrent View Post
    relevant to what ?

    Regarding current, read this;
    Hi Eddy I was waiting for you to chime in, Good read.
    The more you know, The better you know, How little you know

  10. #9
    Relevant to what, you asked?

    Well, for instance, the current at the input is relevant to me as I want to have some idea of how much current the whole system is likely to draw in total when at full blast, including 3 servos, air compressor, water pump and other minor peripherals. I have two mains rings in my workshop, so I may use the second ring for the compressor, which I haven't bought yet, but it will be the largest - silent type- I can safely get away with.


  11. #10
    Quote Originally Posted by Edward View Post
    Well, for instance, the current at the input is relevant to me as I want to have some idea of how much current the whole system is likely to draw in total when at full blast
    Motor Stall Current multiplied by one over the VFD efficiency or the maximum rated current draw for the VFD will give you a far better idea of the maximum current under heavy working conditions than spinning up the motor and sticking a meter on the mains input.
    Maths and manufacturers data are your friends here, not a meter and a finger in the air ;-)

    - Nick
    You think that's too expensive? You're not a Model Engineer are you? :D

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