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  1. #16
    Join Date
    May 2008
    Location
    BELL POST HILL, 3215
    Age
    87
    Posts
    93

    Default I think you are right.

    Hi Ueee,
    I still have the sheet somewhere, as my unit had a specific name.
    Yes, I believe that is what it is, but had to look up vfd.
    Look, I could not be happier with this Unit. It sits on 3000 RPM. most times I use The Lathe, It also has a Fan, & on a warmish day it will cut in, & just keeps going.
    Had some initial probs after the Leccie had wired it up, as it made all kinds of noises.
    I rang SEW in Tullamarine, spent about ˝Hr. pushing Buttons, & then all of sudden away it went.
    So I get 3006 RPM from it,& stops in approx. 3 Secs.
    What more could one want, besides a bit more power, but one gets used to what one has.
    Regards,
    issatree.
    Have Lathe, Wood Travel.

  2. #17
    Join Date
    Oct 2008
    Location
    N.W.Tasmania
    Posts
    1,407

    Default

    Quote Originally Posted by cba_melbourne View Post
    Hi Rob. As a rule, you CAN run several motors simultaneously from a VFD, but:

    - the VFD must at least be rated for the sum of all motors to be run simultaneously.
    - if fitted, the "sensorless vector" feature must be turned off. Hence you can buy the cheapest VFD there is (it is the sensorless vector feature that makes VFD expensive). Even an older obsolete or used VFD will do perfectly well. You must use the simple V/Hz characteristic that all VFD's offer.
    - you can not use the VFD features related to "motor protection" - you must instead use separate motor protection for each motor.
    - you cannot use variable speed, unless it is ok that all motors run simultaneously at the same higher or lower speed. If you are the only user in a workshop, that may be perfectly fine. But if there are multiple user, it is not practical if the spindle of the mill changes speed with the lathe spindle.
    - you cannot use ramp up / ramp down or braking, unless all motors connected are started and stopped simultaneously.


    Example 1: you have a 3ph lathe, and this lathe a 3ph spindle motor and a 3ph coolant pump. No problem run them all together from one VFD. It will not matter if they start/stop together, and it will not matter if they change speed together.

    Example 2: you have a mill and a lathe and a grinder and a bandsaw (all 3-phase), and you want to turn them on or off at random, and you want to use them sometimes simultaneaosly. In this case you must use the VFD exactly as if it was a phase converter, eg no variable speed no ramps etc etc.


    By the way, some VFD manuals explain in detail how to attach several motors. The better VFD brands have quite thick manuals, and you can additionally download application notes etc. Whereas the cheap Chinese VFD's found on eBay are just a few condensed pages, and there is no application notes or the like that you could download, and if there was then maybe only in Chinese. But these too can by default be used toi drive several motors at the same time.


    Hi Chris, thanks for setting me straight here, although I was reasonably confident that a small motor like that of a coolant pump would probably cause no problem for a VFD running a much larger motor driving a lathe spindle for example, I did not realise that it was possible to run machines such as lathes, grinders and bandsaws from the one VFD with random switching of the various machines. Everything that I have read on the subject gave me the opposite impression. It just seemed that a random switching on or off of another significant load on the VFD would trigger a fault indicator, which would shut the whole lot down. If I understand you correctly, it would probably still detect the event, but you can program out its ability to use that input to shut down. That certainly makes the argument for the VFD pretty compelling. One remaining advantage the RPC would have is that machines like lathes and mills with their own inbuilt electrical controls, could be left as is, and would not need rewiring to make the switching on the machines work as inputs to the VFD.
    How does the separate motor protection system work? I am familiar with the old technology contactors with heaters, which if they got hot because of excess current draw from the load, would activate a bimetal mounted contact to cut the power, but now we need a control input to the VFD, and not simply opening the circuit between the VFD and the load. I presume that there are adjustable current sensors to do this but I have not come across them at all, or is there some other clever method to give motor protection? Thanks again for the knowledge update,
    Rob.

  3. #18
    Join Date
    Aug 2007
    Location
    Melbourne
    Age
    68
    Posts
    1,410

    Default

    Rob

    Here an introductory article from a VFD maker about running multiple motors from one VFD:
    VFDs Can Control Multiple Motors
    You will find many more documents if you do a Google search for "VFD multiple motors".



    > .... I did not realise that it was possible to run machines such as lathes, grinders and bandsaws from the one VFD with random switching of the various machines......

    If random switching is required, you must oversize the VFD by at least a factor of 1.1, better a little more. Example: if you had two 1HP motor and one 2HP motor, the tolat being 4HP, you would choose the next size up VFD of 5HP. Thius is so, because there will be quite an inrush current when adding a 2HP motor to two already running 1HP motors, and the VFD cannot slowly ramp up the added 2HP motor.


    > ...... One remaining advantage the RPC would have is that machines like lathes and mills with their own inbuilt electrical controls, could be left as is, and would not need rewiring to make the switching on the machines work as inputs to the VFD.......

    That is correct. Because in this case you are NOT controlling the VFD, you are just adding or removing loads from the running VFD.


    >........ How does the separate motor protection system work? I am familiar with the old technology contactors with heaters, which if they got hot because of excess current draw from the load......

    Individual motor protection is exactly as is used to be in the times before VFD. Just the same as if using a phase converter.



    Rob, it is not that I think running several machine tools from one VFD that it is a particularly smart thing to do. I jst wanted to point out that it is perfectly feasible. And it is done in industry. Probably not to run machine tools, more like to run fans and pumps. For machine tools, I strongly recommend individual VFD's, if only for the invaluable advantages of induvidual variable speed, ramp up/down, braking.

    But if someone really wants to go the old fashioned way, it is good to know that there are not only phase converters or rotary converters - a single VFD can perfectly serve as well for this purpose. And may nowdays be even cheaper. Chris

  4. #19
    Join Date
    Oct 2006
    Location
    Armidale NSW
    Age
    52
    Posts
    915

    Default

    I may be mistaken, but it looks like a simple static phase converter. I run all my 3 phase machinery off a similar system (and at 480V at that) and I can assure you that the dire consequences have not eventuated. The only rider I would put on it is that all of the motors are decent brands, and not cheap chinese ones.

    I run a 5+1HP panel saw, 3HP dust extractor (together) and a 3HP metal lathe.
    Cheers.

    Vernon.
    __________________________________________________
    Bite off more than you can chew and then chew like crazy.

  5. #20
    Join Date
    Aug 2008
    Location
    near Rockhampton
    Posts
    6,216

    Default

    Quote Originally Posted by cba_melbourne View Post
    Rob

    Here an introductory article from a VFD maker about running multiple motors from one VFD:
    VFDs Can Control Multiple Motors
    You will find many more documents if you do a Google search for "VFD multiple motors".

    That is quite informative... Good for machine with multiple motors, like grinders..... My cylindrical grinder for instance has six electric motors..

    My J&S 540 surface grinder has three electric motors...
    Gold, the colour of choice for the discerning person.

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