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Thread: VFD for 3 phase table saw

  1. 03-14-2018, 9:24 PM #31
    David Kumm
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    Just for information, take a look at the electrical section of the practicalmachinist forum. They have some really good electrical guys and refuse to even discuss that brand of VFD. Not saying good or bad, but read about VFD before spending. A mistake is costly. Dave
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  2. 03-14-2018, 9:30 PM #32
    Chris Parks
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    Just for further information purposes Powtran VFD's have the ability to have different profiles for different machines programmed into them so the same VFD is easily used for multiple machines, I think it can have 10 different profiles put into it from memory.
    Chris

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  3. 03-15-2018, 9:54 AM #33
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    Tom Bender
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    My table saw has variable speed. It is great, easily worth the extra cost and effort. I normally run it at a tip speed around 2000 fpm.
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  4. 03-29-2018, 1:57 PM #34
    James White
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    Can anyone tell me what this board is for? It powers the third leg of the main motor. It gets it's power from the third leg off the relay output and is labeled R3 in the photo. However the board also gets feeds from legs two and three up stream of the relay. What is labeled M3 goes to the motor.

    My hair brained plan was to take single phase 220 from legs one and two post relay and feed that to the VFD. Then the VFD would be wired direct to the motor. However this board complicates things since it gets power both post and pre relay.

    It would have been an ideal solution since it powers the scoring motor with the house fed 220v single phase and also powers the VFD post relay. This would allows use of emergency stop buttons on the saw.

    Could I power this board entirely off of the VFD?

    Now tell me why I am dreaming and I overlooked....


    James
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    Last edited by James White; 03-29-2018 at 2:02 PM.
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  5. 03-29-2018, 2:34 PM #35
    James White
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    The wiring diagram can be seen in the manual on page 59.

    http://cdn2.grizzly.com/manuals/g0674_m.pdf
    Last edited by James White; 03-29-2018 at 2:37 PM.
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  6. 03-29-2018, 2:58 PM #36
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    Rod Sheridan
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    It looks to me like a DC braking injection board for the main motor. In the EU, blade braking is required to meet a time parameter to stop the arbour in under a given length of time.

    If that's what it is you won't need it with a VFD, you'll program the VFD for the correct braking. In that case the board and main motor contactor can be removed.

    You'll have to connect any limit switches on the machine (such as door open) to the VFD as well as the stop and start buttons, including and E-stop buttons in other locations......Rod.
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  7. 03-30-2018, 2:17 PM #37
    James White
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    Rod,
    Thank you very much! I was able to remove the board for the most part. There is a fuse on there that is being used to supply the relay of the scoring motor. I wanted to leave the board in position anyway. Then I will not to loose it.
    The saw is working great with the 7.5kw VFD from Amazon. I can slow the blade down to loose the burning I was getting in maple. The saw has a general purpose/sheet goods blade in it and it turns out 8/4" maple burns. Not anymore!
    James
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  8. 03-30-2018, 6:20 PM #38
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    Dan Friedrichs
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    Yay! I'm excited you got it running!

    If the VFD didn't come with one, you can add a braking resistor so the blade can be brought to a stop very quickly. A nice safety feature (that the saw originally had), but that you can create with the VFD, too.
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  9. 03-30-2018, 7:59 PM #39
    James White
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    It has a built in braking resistor. What is a good stopping time in second? The saw does not have the two post to prevent the blade from spinning. The washer is keyed to a flat on the shaft. So there is no issue with loosening the nut. But I don't want the blade slipping either. I was unsure what to make the stop time.

    James
    Last edited by James White; 03-30-2018 at 8:01 PM.
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  10. 03-30-2018, 10:09 PM #40
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    Dan Friedrichs
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    My SWAG is that my Hammer stops a 12" full-kerf blade in about 2 seconds (it would vary based on the inertia of the blade). That's probably fast enough that even the most impatient person wouldn't be tempted to reach to grab an offcut (or whatever) too quickly. I probably wouldn't set it to stop too fast, though, as you'd be putting some unnecessary torque (and wear) on belts, etc.
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  11. 03-30-2018, 11:58 PM #41
    Bill Dufour
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    I have seen 3 seconds recommended but with no gears to strip you can safely stop faster. I would not go below 1 second. On some cheap VFDs the acceleration is the same as the deceleration time. I would not accelerate less then 3 seconds.
    If the decelerate is set too fast it can overload and switch to coast down mode. But you have a resistor to dump the braking energy into so that should not be a problem.

    For a lathe with a heavy log you would have to take more time to change the rpm.
    Bill D.
    Last edited by Bill Dufour; 03-31-2018 at 12:01 AM.
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  12. 03-30-2018, 11:59 PM #42
    Bill Dufour
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    Quote Originally Posted by Dan Friedrichs View Post
    My SWAG is that my Hammer stops a 12" full-kerf blade in about 2 seconds (it would vary based on the inertia of the blade). That's probably fast enough that even the most impatient person wouldn't be tempted to reach to grab an offcut (or whatever) too quickly. I probably wouldn't set it to stop too fast, though, as you'd be putting some unnecessary torque (and wear) on belts, etc.
    Is that coast down time or a controlled braked stop time?
    I
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  13. 03-31-2018, 8:30 AM #43
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    Dan Friedrichs
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    Quote Originally Posted by Bill Dufour View Post
    Is that coast down time or a controlled braked stop time?
    It's braked via DC injection (not a VFD), so it's not coasting down, but it's also not controlled
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