Page 2 of 3 FirstFirst 123 LastLast
Results 13 to 24 of 25

Thread: Will a VFD output single phase?

  1. #13
    Registered handlewanker's Avatar
    Join Date
    Sep 2006
    Location
    Australia
    Posts
    3671
    Downloads
    0
    Uploads
    0

    Default

    By the way, a single phase motor is tied to the incoming mains frequency of 50, or over the pond, 60 cycles per second.
    As soon as you load the motor to the point when the synchronisation causes it to go out of synch, you get a condition that is like hiccups but electrically orientated.
    When you use a VFD on ANY motor, single or three phase you are injecting a frequency that is synthetic, almost sine wave, but good enough to power the motor in the manner that it is designed to work at, and that is in pulses at a certain frequency, any frequency, the frequency rate and the number of poles will determine the RPM of the motor.
    The subject of motor drive is vast and too technical for me to delve into except at the level I have learned over the years.
    One thing is for sure you cannot use a 1 ph motor with speed control if you have start winding present, also if you have capacitors to effect phase shift for running.
    It would be interesting to know, if it is possible, what a VFD will do for a 1 ph motor, providing the start winding was disconnected.
    3 ph motors have an inbuilt phase shift in the power supply, by nature of the 3 input waveforms, but 1 ph on the run cycle won't run below a certain speed.
    With this in mind, I would try using a motor rated at 2,800 rpm, and pushing the speed UP not DOWN to effect speed control.
    The armature of a 1 ph motor is solid metal, a composite of metal stampings that rotate in the stator core, and provided the balance is good, shouldn't disintergrate at the raised rev range.
    Motors with wound armatures and consisting of copper wire in insulated slots run at 10,000 rpm, as in angle grinder motors, do not have a problem in this respect.
    This way you would get a rev range above the motor speed and to a certain extent below it, but to all intents and purposes a rev range.
    This would suit a machine with a belt drive as the pulley sizes can be changed to allow for the new high RPM range, but if the motor is built in with no access to the gear train or drive mechanism, then the drive train will have to be worked out.
    Whether or not it can be got from a VFD, designed to output 3 phases, but only using one output I couldn't say.
    That's why I prefer 3 ph for speed control, so much simpler and cheaper.
    Ian.



  2. #14
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    20577
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by handlewanker View Post
    By the way, a single phase motor is tied to the incoming mains frequency of 50, or over the pond, 60 cycles per second.
    As soon as you load the motor to the point when the synchronisation causes it to go out of synch, you get a condition that is like hiccups but electrically orientated.
    .
    Actually a standard 1ph or 3 phase squirrel cage induction motor can never run at synchronism, if the rotor catches up to the rotating field, there is nothing induced into the rotor & hence no rotor field.
    They will always run somewhat lower frequency due to this 'slip' otherwise they would run at exactly 3600rpm (2 pole 60hz) or 1800rpm (4 pole 60hz).
    There is a way to create synchronism, a circuit detects when the slip frequency is approaching and injects a DC field into the rotor, hence locking the rotor to the rotating field, but not in your average motor.
    A 1 ph motor will never start without a phase-shifted start winding, due to no rotating field at switch on.
    Also a Standard motor rotors appear to be a solid chunk of metal, but actually has windings, these are conductive bars embeded in the rotor and connected with shorted turns at the end of the rotor, they used to comprise of copper many years ago, but now are generally aluminum composition.
    Hence 'Squirrel Cage' motor
    This is also why the high current is caused by a stalled motor, there is full current reflected back from the shorted turns on the rotor to the stator.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


  3. #15
    Registered
    Join Date
    Feb 2007
    Location
    USA
    Posts
    424
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by handlewanker View Post
    It would be interesting to know, if it is possible, what a VFD will do for a 1 ph motor, providing the start winding was disconnected.
    With this in mind, I would try using a motor rated at 2,800 rpm, and pushing the speed UP not DOWN to effect speed control.

    The armature of a 1 ph motor is solid metal, a composite of metal stampings that rotate in the stator core, and provided the balance is good, shouldn't disintergrate at the raised rev range.

    This way you would get a rev range above the motor speed and to a certain extent below it, but to all intents and purposes a rev range.

    Whether or not it can be got from a VFD, designed to output 3 phases, but only using one output I couldn't say.
    That's why I prefer 3 ph for speed control, so much simpler and cheaper.
    Ian.
    Ian,
    If you connect a single phase motor to a VFD and disconnected the start winding it would just sit there and hum, like I said most motors won't work, in the case of PSC motors the the windings are typicaly the same size of wire and number of windings, so if the flux is strong enough a VFD outputing on single phase may make a PSC motor spin, it also depends upon how much phase shift the motor was designed to run with(the cap strength if you will). This is one of the reasons that a PSC motor can quick reverse if the manufactor allowed for it on the wiring end, some cannot however I have seen caps blow when this is tryed(these seemed to be bigger caps) .

    If you speed up any induction motor, be it 3 phase , 2 phase(4 wire) or single phase it will not work as well above its rated speed, the torque flat lines, and eventually you will stall, its been my exeperince that around %150 or greater output for your average run of the mill 3 phase motor. The best place for most polyphase motors to run is at there nameplate speed.
    In motor lingo when you say armature you are referering to a motor who has brushes or slip rings. If you refer to a induction motor then they have a rotor, no conections to the outside power. Asyncrounous motors have a shorted rotor core, they are made of laminations held together with alum. cores, only seen one come apart and that was a prototype, they act as one sold piece of metal but if it were the eddy currents would fry the stator in matter of minutes. Stators also have lams, and again the idea is to fool the eddy currrets from frying the motor just like a transformer.
    Syncrounous motors have an armature, which can be shorted or run through ressitance grids to provide varying levels of slip, or connected to another motors stator core to provide a cascade connection.
    Some VFDs are now able to produce a single phase signal with causeing an error, there are also specialty single phase drives, they all can only run motors with no start winding or more correctly motors with the same size windings, or PSC motors. Agreed that 3phase motors are best run for a vfd, you are other wasting 73% of your capacity for work.

    chris



  4. #16
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    20577
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by in2steam View Post
    Syncrounous motors have an armature, which can be shorted or run through ressitance grids to provide varying levels of slip, or connected to another motors stator core to provide a cascade connection.
    I think you are referring to Wound rotor motor for non-synchronous speed control, as is often used in Crane applications etc.
    A synchronous motor does not, or should not run with any slip, as the idea is to run in perfect synchronism with the supply frequency.
    The AC induction motor with DC injection to the rotor type were a very popular synchronous motor, 50hp and up for many years, these would run at exactly 3600/1800 or 3000/1500 rpm, depending on the supply Freq. .
    With modern magnetic materials used for motor rotors & electronic control methods, synchronous motors are now seen in AC servo's, Where the rotor can faithfully follow the rotating field.
    Al.

    Last edited by Al_The_Man; 05-09-2007 at 02:49 PM.
    CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


  5. #17
    Registered
    Join Date
    Feb 2007
    Location
    USA
    Posts
    424
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by Al_The_Man View Post
    I think you are referring to Wound rotor motor for non-synchronous speed control, as is often used in Crane applications etc.
    A synchronous motor does not, or should not run with any slip, as the idea is to run in perfect synchronism with the supply frequency.
    The AC induction motor with DC injection to the rotor type were a very popular synchronous motor, 50hp and up for many years, these would run at exactly 3600/1800 or 3000/1500 rpm, depending on the supply Freq. .
    With modern magnetic materials used for motor rotors & electronic control methods, synchronous motors are now seen in AC servo's, Where the rotor can faithfully follow the rotating field.
    Al.
    Yeah you are right I was bluring some facts there, sync motors do have an armature though. I was called to a press in the midest of my message, so I lost track of my thoughts. I actual have a wound rotor motor on one of my die cutters at work its around a 5HP I think, I cannot read Italinan so I am not positive the press dates from around 1955 its got brushes and slip rings. Casacading is done on wound rotor motors, wound motor rotors are seeing a resurge in the hybrid car market of all places.

    chris



  6. #18
    Registered
    Join Date
    Mar 2007
    Location
    Australia
    Posts
    85
    Downloads
    0
    Uploads
    0

    Default

    If you have a 5Hp three phase motor available, that will work fine on your lathe if it will physically fit onto the motor mounting bracket.

    Just because it is 5Hp does not mean it is going to draw more power than a 3Hp motor, if it is only loaded up to 3Hp. Just set the current limit on the VFD at some safe value, and the VFD will limit the motor to 3HP output.

    As others have already said, single phase motors are just completely unsuitable for any reasonable speed reduction.



  7. #19
    Registered
    Join Date
    Feb 2007
    Location
    USA
    Posts
    424
    Downloads
    0
    Uploads
    0

    Default

    ???



  8. #20
    Registered vladdy's Avatar
    Join Date
    Feb 2004
    Location
    Perogie Flats, Canada
    Posts
    350
    Downloads
    0
    Uploads
    0

    Default

    my origional interest was to allow about a +15/-35 % in speed using the vfd, from what I have read some places, a vfd will apparantly work with a single phase input, and I was hoping to get it to output single phase as well, but the baldor motor that I have on the old Gisholt has start windings, and looks like it won't work, not even a 'kinda close' speed range capability..
    I wasn't able to get any 3 phase motors [as of yet, anyways] so I guess it goes into the 'good, just can't use it right now' corner....
    guess i'm stuck with a six speed lathe...

    thanks all..



  9. #21
    Registered
    Join Date
    Nov 2009
    Location
    USA
    Posts
    2
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by in2steam View Post
    Ian,
    If you connect a single phase motor to a VFD and disconnected the start winding it would just sit there and hum
    In a sales brochure for Optidrive E2 (available here) is the following language:

    The Optidrive E2 Single Phase is the world’s first fully digital, fully
    packaged variable speed drive for controlling low power single phase
    motors.
    Designed to be cost effective and easy to use, the Optidrive E2 Single
    Phase is for use with PSC (Permanent Split Capacitor) or Shaded-
    Pole Single-Phase induction motors.

    Seems to me the price is reasonable, and it looks to be able to allow speed control on a standard lather motor...

    Is there something I'm not understanding?

    Regards,

    CNC_Hacker



  10. #22
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    20577
    Downloads
    0
    Uploads
    0

    Default

    If you notice they mention Permanent split phase induction motor, this applies to to types that have the phase shift capacitor connected in both start and run, as opposed to the type that just used the cap for start only.
    The permanent split phase are often low power or fan usage etc. Shaded pole the same.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


  11. #23
    Registered handlewanker's Avatar
    Join Date
    Sep 2006
    Location
    Australia
    Posts
    3671
    Downloads
    0
    Uploads
    0

    Default

    When all else fails and you just gotta have speed control, using one of those variable pulley drives takes a lot of beating.

    Some years ago the firm I used to work for in UK was engaged in the rebuilding of cigarette making machines, (yaaaa boooo hisssss, enviro idiot.....etc) oh well it was their bread and butter, and at the same time I was able to scavange a whole load of bits and pieces that otherwise got thrown in the scrap bin.

    One of the "bits and pieces" was a pulley about 75mm diam that had a spring loaded flange to vary the diam of the belt groove, and used an A section belt, (about 15mm wide at the top of the V).

    The belt rode in the pulley groove at the 75mm diam and by applying tension to the belt made the flange under spring pressure move sideways so causing the belt to ride deeper to the 45mm diam, thus effecting a variable pulley diam.

    This method is also used on the Bridgeport mill and possibly others too, to effect an infinately variable speed change whilst the machine is running.

    The Bridgeport type has large diam pulleys about 300mm, or thereabouts, and a special wide belt, but works very smoothly.

    The beauty of the variable belt drive is you get an increase in torque as you slow the output speed, without slowing the motor, whereas the motor speed control, if used to slow the motor down, does so at the expense of increasing the power to the motor to get the torque, often leading to overheating.

    The main interest in three phase motors is they are so cheap in scrap metal yards due to only being used in industry, and have very little value to the DIY person who only has a single phase supply.

    The other thing about 3 phase motors is you can load them up to the hilt and only blow a fuse whereas a single phase motor would probably burn the start windings out when approaching heavy loading.

    Just for the record, I dumped all my single phase 1/4 HP, 1/2HP motors in favour of 3 phase for the above reasons, but mainly after I invested in a 1HP VFD unit for about A$200.

    If you can get 3 PH motors at a cheap price then the VFD is the way to go without a doubt, also depending on the size of the motors and your mains, but in the range up to 1HP is a very handy set-up price wise, but as the HP rises so does the cost of the VFD.
    Ian.



  12. #24
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    20577
    Downloads
    0
    Uploads
    0

    Default

    I happened to be picking up a 25hp VFD from my WEG supplier last week, he showed me the latest VFD's they have which if used with a WEG motor guarantees 100% rated torque down to 1 rpm without the use of fan cooling.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum from DIY CNC Machines to the Cad/Cam software to run them. The site is 100% free to join and use, so join today!

Follow us on

Facebook Dribbble RSS Feed