VFD Can they run a motor at 1.5 Hz - Page 3
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  1. #41
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    I just tried to see if the rapids motor ( 1.5Kw, 4poles ) on my Maho700 can be used for feeds - it already had a VFD. Schneider, I think. It ran "fine" at 2Hz. There was noticeable cogging but... it worked. I think an 8 pole motor would be perfectly acceptable. Two Chinese made VFD's did not cut the mustard and I haven't tried a Hitachi - but that one should work.

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    Quote Originally Posted by AlexO View Post
    I just tried to see if the rapids motor ( 1.5Kw, 4poles ) on my Maho700 can be used for feeds - it already had a VFD. Schneider, I think. It ran "fine" at 2Hz. There was noticeable cogging but... it worked. I think an 8 pole motor would be perfectly acceptable. Two Chinese made VFD's did not cut the mustard and I haven't tried a Hitachi - but that one should work.
    But there yah go.."cogging".

    I suppose a ceiling fan on low RPM is TRYING to cog as well. It just has way more poles, plus the inertia of the blades aiding - instead of resisting, as the inertia is in Peter's application. Also lower aerodynamic loading that is inherent with lower RPM. And, of course, no 'stiction'.

    DC motors don't much mind putting more torque into a load from dead-rest. They just pretend they are a solenoid for the moment.

    CAN'T "slip". Brush is sitting right atop the relevant coils, going nowhere until the load is moved. Load. Not the "Hertz".

    Only when it actually moves do they get to take a new grip for the next step.

    As if the entire approach to "life" were exact opposites at the extremes of their respective performance ranges, overlapped only in the "middle", AC & DC motors.

    Odd, isn't it? Given that they are the same rotating electromagnetic critters at the end of the day. Greyhounds chasing an artificial rabbit 'round a dog race track.

    DC motor holds its OWN damned rabbit on a selfie-stick. Or closer. Even stopped, teeth sunk into the rabbit in a literal "death grip", commutator-bar "wedging" a certainty coming, it chases harder yet. Move the load or die trying!

    AC motor's "rabbit" is managed externally. Line or VFD, it can never entirely stop. Just slow waaaay down...and "slip" right out of the Greyhound's grasp, over and over again.

    No suicidal "hero" here. Wasn't its own hand grenade anyway. VFD tossed that critter, not the motor.

    There you have it. Siblings in Iron and Copper, shafts and bearings.

    With different personalities, if you will.


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    Interesting thread.
    Peter - Let us know how it works out, please.

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    Quote Originally Posted by Monarchist View Post
    But there yah go.."cogging".



    I did not complain. Just mentioned it was noticeable. I wouldn't like people suffering from coggophobia to be exposed.

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    Quote Originally Posted by AlexO View Post
    I did not complain. Just mentioned it was noticeable. I wouldn't like people suffering from coggophobia to be exposed.
    Most WOULD complain. Seriously.

    The USUAL goal, when running low and slow, is SMOOTH. We NEED fine incremental motion more than ever when operating in that zone, not bumps, jumps, overshoots, and surprises.

    So we get that "Catch 22" situation. Greatest need at weakest resource time.

    And we have to throw money at that beast, whether it be fine planetary mechanicals with sensitive clutches, or expensive electronics that cheat by BALANCING opposing forces and letting one ever-so-slightly "win the battle", but only briefly.

    Our own fine muscle motion works the same way, if you've forgotten.

    The balance between large flexor and extensor muscles up in the forearm conveyed by tendons to thumb and fingers of the hand.

    Those muscles won't fit right IN the hand. Everything done down there is about guiding the tendons and sensing strains.

    The "power source" has to be placed remotely - where there is space to house it.

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    Quote Originally Posted by motion guru View Post
    Just for reference.. gearbox, feedback, ratios, feedback, gearmotor, feedback, belting, feedback, chains, feedback..

    Direct drive, NO ratios or gearing, NO, ELSE inadequate feedback?

    Well.. you did have enough experience to know in advance that was harder.

    Others are still pioneering 'til they gather their OWN pincushion of arrows in the backside...

    "Those who do not learn from the history of others repeating it become doomed .. "

    ...or something like that.


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    Quote Originally Posted by Peter from Holland View Post
    Yes we need that 3000rpm to meet the technical data for this machine
    Thats for the rapids


    Peter
    Exactly...

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    This is a VERY fascinating set of lectures on motors ...

    Teaching Old Motors New Tricks - Part 1 - YouTube

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    I have the new VFD in house now
    Its huge
    4 times as big as the old one It will not fit the original cabinet
    Peter

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    Quote Originally Posted by Peter from Holland View Post
    I have the new VFD in house now
    Its huge
    4 times as big as the old one It will not fit the original cabinet
    Peter
    Long-wire it. See what the practical limits are, anyway. Money was spent, time as well. Could save-back the resources thrice over, next challenge.

    Ours, if not yours.

    Greedy minds - lazy as well - want to know.

    PM at work.. etc.



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