VFD Can they run a motor at 1.5 Hz - Page 3
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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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    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
    Any update? Dig you get it to work?

    For giggles I went to see how slow I can run my modified (POS, needless to mention) bench drill on VFD:
    19 February 218 - YouTube

    ACS800 on sensorless setup running at 0,5hz. Speed will drop down noticeably for a tenth of a a second if I suddenly apply full load to motor.

    lowest speed setting is unpractically slow for almost any use on bench drill, except maybe tightening/loosening the chuck with pliers

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    Change of plan. I got hold on a original motor So I get it back to original
    Some day

    Peter

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    Couple of points - not sure that all discussed was totally accurate:

    - AC induction motor with a VFD has not problem in your application at 1.5 hz - as mentioned, it is in constant torque range up to base speed so it has full torque capabilitry at 1.5 hz.
    - with tach feedback it would run the best - does not need to be a fancy tach but the drive needs to have tach feedback capability.
    - it will not work in scalar mode (volts/hertz) - I don't believe you mentioned if you tried to run it in scalar mode or not
    - you should have the drive in sensorless vector mode and potentially do a speed tune - but I can't guarantee that it would work in sensorless vector mode but it should if the drive is properly set up.
    - ABB ACS800 or ACS880 I believe claim to be able to get all the way down to zero speed with full torque with good speed regulation. However, don't get up in DTC being better than other PWM schemes. Many other drives do well in this low speed range.

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    Quote Originally Posted by MattiJ View Post
    Any update? Dig you get it to work?

    For giggles I went to see how slow I can run my modified (POS, needless to mention) bench drill on VFD:
    19 February 218 - YouTube

    ACS800 on sensorless setup running at 0,5hz. Speed will drop down noticeably for a tenth of a a second if I suddenly apply full load to motor.

    lowest speed setting is unpractically slow for almost any use on bench drill, except maybe tightening/loosening the chuck with pliers
    That is SUCH a bad joke, I may make the time - perhaps a year or two out, I should even live that long - to put one of the stashed 180 VDC RPM III Dinosaur-Current Type T and a modest KB-Penta onto my Walker-Turner and SHOW you just HOW bad!

    Pliers? Tear your arm off. Slowly and painfully. No "tenth of a second" warning, either.


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    Quote Originally Posted by markz528 View Post
    Couple of points - not sure that all discussed was totally accurate:
    Just got a lot worse as well.

    VFD are good enough at what they do. Some things. Not everything. No more than that. "Faith" in bullshit specs won't change that.

    Peter has SEEN it. "Real world", not world of specs on paper. He is not alone.

    DC does what it is good at in turn. Some things. Not everything.

    At the opposite edges of an envelope or a Venn Diagram that overlaps only in the middle?

    Each is king of its own realm.

    No fear.

    Day and night are much the same opposites, only dusk and dawn overlap.

    We JF deal with that. We can deal with this "in the real world", too.

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    Quote Originally Posted by thermite View Post
    Just got a lot worse as well.

    VFD are good enough at what they do. Some things. Not everything. No more than that. "Faith" in bullshit specs won't change that.

    Peter has SEEN it. "Real world", not world of specs on paper. He is not alone.

    DC does what it is good at in turn. Some things. Not everything.

    At the opposite edges of an envelope or a Venn Diagram that overlaps only in the middle?

    Each is king of its own realm.

    No fear.

    Day and night are much the same opposites, only dusk and dawn overlap.

    We JF deal with that. We can deal with this "in the real world", too.
    I don't know why I try to help with these types of issues on this board. I tried some years ago and got the same type of attitude.

    All I have to say is that I make a darn good living solving motor, VFD application and VFD installation issues all over the world. I don't know everything, but I have very strong contacts at most of the large Automation vendors that have taught me well and give me guidance when needed.

    This response is quite unfortunate.

    There is no reason the VFD would not work in this application properly set up.

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    Quote Originally Posted by markz528 View Post
    I don't know why I try to help with these types of issues on this board. I tried some years ago and got the same type of attitude.

    All I have to say is that I make a darn good living solving motor, VFD application and VFD installation issues all over the world. I don't know everything, but I have very strong contacts at most of the large Automation vendors that have taught me well and give me guidance when needed.

    This response is quite unfortunate.

    There is no reason the VFD would not work in this application properly set up.
    Yes, there are several reasons. Start with basic physics. For starters, what you need to do THIS task with 50/60 Hz AC motors simply will not FIT! Motor OR VFD.

    Call that an "attitude" if that makes you feel better, but it ain't going to respond to politics, religion, nor "social engineering" from the inexperienced.

    It is what it is.

    And It beggars belief you WOULD "try to help" with a religious faith and fervor contrary to the easily demonstrated fact of it if even you could read well. And simply made the choice to not do so. This is not new information. It is history.

    "When the only tool you have is a ham... "VFD"..."

    If you had the same amount of DC experience as you claim to have VFD experience, you would KNOW the difference, what each type does, and does NOT, do best.

    Then you make the choice appropriate to the need.

    It isn't ABOUT "superiority". It is about fitness to a purpose. Neither are "universal".

    Also least cost compromises. Just ask Peter to remind us what the cost difference was right HERE at new prices.

    Or go and price a 5 HP Reliance RPM III Type T DC motor. Just ever-so slightly above your budget at over $11,000 USD? Surely above my budget as well!



    And the reason I have stashed so many good NOS, used & professionally rebuilt ones.

    When you need DC, you need DC. ELSE NOT.

    Your motorcar engine is started with a VFD?

    And then there are servos and steppers, and, and, and....
    Last edited by thermite; 03-05-2018 at 07:37 AM.

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    Quote Originally Posted by markz528 View Post
    I don't know why I try to help with these types of issues on this board. I tried some years ago and got the same type of attitude.

    All I have to say is that I make a darn good living solving motor, VFD application and VFD installation issues all over the world. I don't know everything, but I have very strong contacts at most of the large Automation vendors that have taught me well and give me guidance when needed.

    This response is quite unfortunate.

    There is no reason the VFD would not work in this application properly set up.
    Best thing to do with Thermite Always laugh at his writing
    He is a language junk No more no less

    I appriciate any information regarding these issues
    The reasson I went with the DC drive is because it is original a DC drive
    And original sells beter
    I am a dealer so this machine is not for the keeps
    I got the motor cheap too That helped
    Thanks again for posting

    Peter

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    Quote Originally Posted by SeaMoss View Post
    I was just kidding ... but you know, with some a-to-d converters ....

    More seriously, resolvers were pretty damned robust - coolant didn't phase them, they lasted a looong time. Is it just that they are analog that people don't like ? Seems like for some things they'd still be better ?
    Quote Originally Posted by motion guru View Post
    We use resolvers all the time in new systems where heat is an issue - they are robust as you say and hard to kill.
    Revolvers are still a very effective and robust technology.


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