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IndustryArena Forum > CNC Electronics > Spindles / VFD > VFD Setting Help not much torque at low speeds.
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  1. #1
    Join Date
    Dec 2006
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    947

    VFD Setting Help not much torque at low speeds.

    I've got a Mori Seiki SL-1 Lathe that I've completely rebuilt with all new electronics. Works very well, but I was drilling at low RPMs today, 500 RPMs with a 3/8" Drill and the chuck definitely bogged down. I work with VFDs all the time, but don't know much about power and torque settings. I'm more used to dealing with settings for control and the like.I'm using a 7 1/2 HP 3PH Motor with a Huanyang 7.5kw VFD. I bought one for 10HP motor by accident and figured that a little bigger shouldn't be a problem.I went through the motor tuning section.I was wondering if anyone had any ideas of what I need to make the VFD work better at lower RPMs. I certainly have enough HP.

  2. #2
    Join Date
    Apr 2003
    Posts
    540

    Re: VFD Setting Help not much torque at low speeds.

    Most lathes obviously use either pulley or gear reduction so the RPMs remain in the best torque range while reducing the final drive rpm to the desired speeds. There are motor VFD combinations that will maintain torque throughout a wider RPM range but as expected price increases with performance. Size the VFD to the motor based on the maximum current requirements under peak torque demands. Do not size the VFD based on horsepower ratings. I don't know your specific motor and VFD specs but 500 RPM for a motor that is capable of much higher is pretty slow depending on your reduction system and torque and HP can be hugely affected as you already know. It's also more likely to overheat and burn out the motor if you run below spec operating RPM for any period of time. Torque vs HP vs VFDs can get a bit confusing. Here's fairly good explanation of the basics that may help. Good luck!

    https://www.pumpsandsystems.com/topi...-vfd-frequency

  3. #3
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    My lathe is a professional lathe that I changed to modern electronics. It uses a little more horsepower than the original machine. The motor's RPMs are 3600 and with the pulley arrangement stock on the lathe it has a maximum of 4100 RPM. This maintains the original RPMs the machine came from the factory with. The factory machine could do as slow as 130 RPM.So I'm wondering what they did to maintain torque at low speeds. I'm figuring it must be a VFD setting to maintain torque at slow speeds.Thanks. I'll read this over.

  4. #4
    Join Date
    Dec 2013
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    5717

    Re: VFD Setting Help not much torque at low speeds.

    Does your Huanyang VFD have sensorless vector capability? If so, you may need to turn on that function in the parameters. That should give you nearly a flat torque curve from 0 to 3600 RPM. If your VFD is V/Hz only then you will not get full torque at lower RPMs.

    EDIT: If you replaced the motor, you chose the wrong one. The 3600 RPM motor is a 2 pole, an 1800 RPM motor is a 4 pole. The difference in the two motors is 11 Ft/lb of torque vs. 22 Ft/lb of torque. Most 1800 RPM motors in that HP range will run just fine at 3600 RPM, and are normally rated higher than that.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    Yes it has sensorless vector. I'll try that. Do you think it's worth getting a new motor or will that function help solve the problem?

  6. #6
    Join Date
    Dec 2013
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    5717

    Re: VFD Setting Help not much torque at low speeds.

    I would make sure the sensorless vector function is turned on first before going out and buying an expensive motor. Then if it doesn't work the way you want, you can always change out the motor later.
    Jim Dawson
    Sandy, Oregon, USA

  7. #7
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    ok thanks

  8. #8
    ericks Guest

    Re: VFD Setting Help not much torque at low speeds.

    Can you possibly post an image of the motor "nameplate"?I mostly found torque issues re VFD's to be improper voltage selection or improper motor connection.So to start it would help if you could either show me your motor "nameplate" or give me the motor spec's

  9. #9
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    Re: VFD Setting Help not much torque at low speeds.


  10. #10
    Join Date
    Dec 2013
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    5717

    Re: VFD Setting Help not much torque at low speeds.

    If I were going to repower that lathe, I would seriously look at a Marathon Black Max motor. They are designed for that type of service. Look at the lower part of the data plate in the example below, gives the torque/rpm values. 230V values are the same as the 460V values.

    https://www.ebay.com/sch/i.html?_fro...Motor&_sacat=0

    These are also available with an installed encoder if needed.
    Jim Dawson
    Sandy, Oregon, USA

  11. #11
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    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    Cool Thanks for the suggestion. I would want a 7 1/2 or 10 HP motor though.

  12. #12
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    Dec 2013
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    5717

    Re: VFD Setting Help not much torque at low speeds.

    Hmmmm, the link above is for a 7.5 HP
    Jim Dawson
    Sandy, Oregon, USA

  13. #13
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    LOL missed that. Those are pricey.

  14. #14
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    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    Ok so I turned on the Sensorless Vector and then turned on the spindle and it only goes 140 RPM when I set it to 1200 or 3000. So manual says when setting SV to retune the motor. So I went into motor paramenters and made sure all settings were correct and that didn't solve anything. Still runs at around 140 RPM.Now the weird thing is on all my other VFDs when you run the auto tune parameters it will turn on the motor for a while and then turn off and say that auto tuning was complete. IN this VFD manual it didn't do that, it looks like you just set the parameters and it fills in the gaps for the other settings, it doesn't run the motor. I'll look closely at the manual later and see if I can figure out if that's normal.

  15. #15
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    Ok the motor tuning section was at the front of the manual not at the section where it tells you what the parameters are. I have to unhook the load and do it.

  16. #16
    ericks Guest

    Re: VFD Setting Help not much torque at low speeds.

    Thanks for the image. Next step is to know what your supply voltage to the VFD is?Then i need to know how you connected your motor? (that is inside the motor terminal box)

  17. #17
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    240VAC, wired it according to the wiring name plate for low voltage, which is 230VAC.

  18. #18
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    So i ran the Auto tune and everything seems to work fine. No way to test the torque though.

  19. #19
    Join Date
    Dec 2013
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    5717

    Re: VFD Setting Help not much torque at low speeds.

    Quote Originally Posted by Cartierusm View Post
    So i ran the Auto tune and everything seems to work fine. No way to test the torque though.
    Maybe try the same drill routine you did before and see if the changes made any difference?
    Jim Dawson
    Sandy, Oregon, USA

  20. #20
    Join Date
    Dec 2006
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    947

    Re: VFD Setting Help not much torque at low speeds.

    LOL that would be nice, but during that the drill broke, so I'd like to not repeat that. I'll figure out some way. Thanks.

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