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Thread: 3ph to 3ph VFD

  1. #1
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    Default 3ph to 3ph VFD

    G/day all,
    The splines on the spindle shaft and variable pulley sheeve on the mill are a bit sad so I would like to fix that spindle pulley in one position if practical, option 2 would be to put 2 or 3 step pulleys on it.
    I searched for parts a while ago to no avail, it's a Anayak FV1

    I have bought a 3 phase to 3 phase VFD and don't have clue about these things, I always avoided those
    VFD threads because smoke would come out my ears and I never thought I should need to subject my tiny brain to such torturous abuse with something that I will never need to know
    Anyway now I did a little reading, but just enough to make me dangerous.

    I'm trying to work out what belt ratio might be suitable, the speed indicator plate says high range is
    450-3600 RPM and low range through a 9:1 reduction is 50-405 RPM.

    I really don't care so much about getting 3600 RPM out of it, I am more concerned that I might not get enough grunt down low.

    The motor spec's are - 3ph, 3hp, 1430rpm @ 50hz, Y - 400-440v, brand is Reivaj (Spanish?)

    I don't have a clue what the frequency limitations of the motor are so I don't know if I might be conservative or not here.

    My amateur calc's are for a 1:1.5 belt ratio for the motor/spindle, I don't know if my slip calc is correct but I worked it out to
    - 4.5% ? 120 x 50 / 4 = 1500 - 4.5% = 1432.5rpm (maaaybe???)

    High speed, 120(phase angle) x 75hz / 4(poles) = 2250rpm - 4.5% (slip) = 2148 x 1.5 (ratio)= 3223rpm spindle speed.

    Low speed, 120 x 10hz / 4 = 300 - 4.5% = 286.5 x 1.5 = 429.75 / 9 (g/box) =47.75rpm

    So if'n my calcs are anywhere close? Will that motor have enough grunt at that low rpm/hz to push maybe a 1 1/2" drill bit ? or am I dreaming and need a two pulley setup to get the motor rpm up a bit?

    thanks, shed

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    Quote Originally Posted by shedhappens View Post
    So if'n my calcs are anywhere close? Will that motor have enough grunt at that low rpm/hz to push maybe a 1 1/2" drill bit ? or am I dreaming and need a two pulley setup to get the motor rpm up a bit?

    thanks, shed
    I'd say you're dreaming. Low frequency and big torque demand is the worst possible combination. Years ago I tried this with my B/port mill and I could easily stall out the motor. I swapped to a J head to get the benefit of back gearing and torque multiplication.

    PDW

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    Quote Originally Posted by PDW View Post
    I'd say you're dreaming.
    Agreed

    As I understand it, at best you're going to have 0.6hp at 10hz(really you wont even have that).

    Stuart

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    Quote Originally Posted by Stustoys View Post
    Agreed

    As I understand it, at best you're going to have 0.6hp at 10hz(really you wont even have that).

    Stuart
    g/day Stu, I assume your 0.6 is at the motor ?

    286.5 / 47.75 = 6

    so if I have a reduction of 6:1 and we call it 0.4hp ?

    0.4 x 6 = 2.4hp ?

    what am I missing, torque?

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    Agreed on the lack of power. I would at least add a pair of drive speeds, maybe even 3. Unless of course you go to a much bigger motor.
    As i found out with the C10, you also want a VFD at least a size bigger than the motor. My 2hp VFD just could not supply as much power as the motor wanted.

    May be better to think about fixing the splines or add a reeves drive.

    Cheers
    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    Quote Originally Posted by shedhappens View Post
    g/day Stu, I assume your 0.6 is at the motor ?
    Yes,

    286.5 / 47.75 = 6 ???

    A hp is a hp is a hp. Changing the ratio changes the torque but the hp stays the same. Halve the speed double the torque......... hp still the same.

    Stuart

    p.s. nvm worked it out 286.5 / 47.75 = 6 ???...... No 50hz 10hz=20% now at best torque stays the same so at 20% rpm with the same torque gives you 20% of the hp.

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    Hi there,

    In the beginning I went through a similar thought process as you. I wanted to VFD my gear head mill and wanted to "rip out" the noisy gears in the gear head and leave just one selection. However, as mentioned above, it's a big ask of a motor/VFD system to deliver speed ranges that we want and still have the required torque at the lower speed ranges. I replaced the 2HP motor with a 3 HP (and a 3 HP VFD) and I mainly toggle between 2 speeds. In fact I do 80% of my work in one gear selection but use a slower gear for the slower work to maintain the torque. With my motor in my situation, I cannot stop the motor at 10Hz in a 1:1 ratio but I have noticed motor slip if machining at such a low frequency. My useable range is about 30Hz - 120Hz.

    There was a thread a while back (maybe a year or so ago) where people here were looking at the pros/cons of VFD and DC motor conversions. DC motors can be speed controlled AND they have high torque from the get go. This is why people like Ueee and a few others have chosen the DC motor option. Treadmill motors are a common source of these DC motors in the 1.5 - 2HP range.

    Personally I have been very happy (so far) with the VFD mill conversion. Just need to realise the system limitations.

    Cheers,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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    Shed,

    assuming your old motor had 3HP too, then you will not be happy with power at 10Hz. If you want to do away with the gear steps that you have now, you would need something like a +10HP VFD and motor. That is going to be big and expensive.
    What most home users do, is to keep the gear steps (gearbox or step pulleys) as is, and add a VFD/motor of same power that was installed previously. That is biggest bang for the dollar. What some home users do, is to halve the number of gears and/or maybe go one size up with the motor/VFD. But that is often a lot more work.

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    PDW, I should have mentioned that the VFD that I have purchased is the type that has sensorless vector control, they are presumably far more efficient through the entire rev range, supposedly this thing will
    self learn the motor parameters and give the motor bulls balls at low Hz, no doubt that could be BS or I just have it wrong?

    http://www.ebay.com.au/itm/2-2KW-3HP...item3f2e0a61f1

    There is a bit about SVC here http://en.wikipedia.org/wiki/Vector_control_%28motor%29

    Simon, Stu, Ueee & CBA thank you for your replies, I already have the VFD and no more cash, I have been outta action for a while and will have to make do. It would pretty hard to make new shaft without the mill. You know if I wanted to drive this mill with a hydraulic motor and a swash plate pump I could find just about everything I needed to know, charts graphs and all the technical data to match components to the job.
    NOT SO with these ef'n VFD's, I can't even find a graph that will give me an approximation of what performance to expect from the motor.

    Reflecting on the comments/advice and the small amount of info I have gleaned from googlen I think I will set the belt ratio to give the spindle 50rpm at 20hz in low range and just see how it does/doesn't perform chewing through metal, and do the same in high range with some cutters.
    At least that will give me a starting point to know what pulley ratios would be most suited.

    I dunno about this? The spring loaded variable pulley on the motor is still in pretty good nick, if I was to cut a suitable hole in the side of the casting I could mount a flat idler pulley to push on the back of the belt, I might get enough usable variation with that and the VFD?
    Dunno how that belt would like being bent backwards?
    I spoze I could use the Hercus camelback if I need to drill big holes, could be a pain sometimes though.

    Can someone tell me how to work out what the high freq should be limited to? The manual that came with the VFD would probably tell me but to be quite honest I think I could read ancient Babylonian easier.

    shed

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    Quote Originally Posted by shedhappens View Post
    Can someone tell me how to work out what the high freq should be limited to? The manual that came with the VFD would probably tell me but to be quite honest I think I could read ancient Babylonian easier.
    It's probably more about what the motor can handle. Most motors seem to do 30* to 100rpm without any issues. A good motor can probably be pushed more but how much...?

    *rule of thumb - below around 30rpm, motor cooling becomes an issue. If you plan to go there for any period of time you will need an independent cooling fan.

    Michael

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    Hi Shed,

    If you've got it, give it a go. It depends what you have in mind for the low speeds. With a HSS flycutter you might be happy enough, a 20 tip carbide face mill maybe not so much.

    I'm not so sure you have a sensorless vector control VSD there..I'm sure others will be able to tell you.

    You can set the freq as high as you're game. Though depending on the motor you're not likely to get more than about 100hz and even then its not likely to have much power. Its said that the rotors and bearings are the same for 1400 and 2800 rpm motors so it should be OK to run up to 100Hz on a 1400rpm motor....

    Stuart

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    Just don't set the max frequency for you first test and see at frequency your motor stops accelerating. You will find that it will very likely go to 125 or 130Hz. Then set the limit a little below that. I found all of the older heavier motors run very well at 120Hz but the only really recent motor I have (3Hp) doesn't want to go above 115Hz.
    There is another experience I can share: A larger motor than the VFD rating will produce bigger torque at lower revs - as you would expect, because it can 'use' the bigger current the VFD can provide at lower frequency, wheras a smaller can't. The VFD will limit its maximum output to the VFD limit at higher frequencies. If you load it more than that, the VFD simply shuts down and shows you an overload error. Just as when you overload a smaller motor. Nothing nasty is goint happen. The bigger motor doen't care wheresas a smalkler motor woul get hot if fed by a larger VFD.
    The other observation I made is that a 6-pole and 8-pole motor has a lot more torque than a 4-pole motor. It follows that they have a lot more torque at lower frequiency. So you can keep your eyes open for a slower motor if you machine feels marginal at the lowest revs yuo want to run it at.
    The last thing I would advise is 'suck it and see'. I can't stop my 3Hp lathe motor at 10Hz!

    BTW, Stuart is right, this is NOT a sensorless vector control VFD. The advertising is misleading.... the 'space vector' is the 'space' in the Voltage/ frequency graph and has nothing to do with vector control... sorry. You need to double the price to get vector control...
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

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    I just found a really cheap vector control 2.2kW VFD - but only for single phase....
    http://www.ebay.com.au/itm/111378577196
    380/415V is more expensive.... e.g, this 1,5kW one... http://www.ebay.com.au/itm/200955092480
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

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    If it is not a sensorless flux vector VFD it will not deliver much power below about 20Hz - still good enough for low power jobs such as reaming/countersinking etc, but not for serious cutting. And will run far too rough below about 12 Hz to be of any use at all, even for low power tasks.

    By all means, give it a try and get a feel for it. But my prediction is, you will come back and restore a two or three speed gearbox or belt drive to it.

    You can also try to go for a motor with more poles, if there is space for it that is. Because motor of a given HP get bigger and heavier the more poles they have. If your current motor was say a 4pole, and you can find an 8 pole of same power, it will be two frame sizes larger. But it turn at half the speed. Cutting your top speed in half, but doubling available power at any low speed compared to the 4pole motor.

    To help you getting a better idea what to expect:
    - as a rule, VFD drives are constant torque up to base speed, and constant power above base speed
    - base speed is usually 60Hz, sometimes 50Hz for some older motor model.
    - a common (not VFD rated) motor is constant power from base speed up to about 70 or 80Hz, then its shaft power drops to zero at about 120 to 130Hz
    - non vector VFD's are only constant torque from about 20Hz up to base speed, torque drops off rapidly below 20Hz. In a machine tool they have a useful speed range of about little more than 4:1
    - sensorless flux vector VFD's are constant torque from about 3Hz to base speed, torque remains useful from almost standstill. In a machine tool they have a useful speed range of about 6:1 and up to 8:1 with a perfectly matched VFD rated matched motor
    - power is torque*speed, or HP=torque*rpm.

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    Quote Originally Posted by Michael G View Post
    It's probably more about what the motor can handle. Most motors seem to do 30* to 100rpm without any issues. A good motor can probably be pushed more but how much...?

    *rule of thumb - below around 30rpm, motor cooling becomes an issue. If you plan to go there for any period of time you will need an independent cooling fan.

    Michael
    Hi Michael,

    I had thought about cooling at low speeds, I thought that I would cut out the fins on the existing fan cover and mount a 240v fan.
    I'd like to put a temp switch on the motor somewhere to switch it on.
    Where ? The between the fins at the top I suppose, it would have to be insulated from the fan air ?

    shed

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