You do NOT want to switch to vector control. Andew was suggesting that you switch FROM vector TO V/Hz control. I agree with him.
If you are going to run two motors on one VFD you must use straight V/Hz control. True vector control needs encoder feedback from the motor so that it can control the magnetic field "vectors" inside the motor. If you have two motors on the same drive, the drive can't possibly know what is going on inside each motor. One might be spinning fine and the other might be stalled, etc. Vector control can offer very good performance, but it MUST know the motor speed to do that. With two motors it will be confused. Many drives offer "sensorless vector" that doesn't need an encoder. The exact meaning of "sensorless vector" varies from manufacturer to manufacturer. Those words are defined by the marketing department, there is no real standard definition of a "sensorless vector" control algorithm. But most sensorless drives still assume that there is only a single motor on the other end of the wires, and will try to figure out what that motor is doing in order to control it. Again, two motors will likely confuse the drive. Straight V/Hz control simply makes AC power of a specified frequency, and lets the motor do what it will. It isn't much different from running the motor directly from the line, except that you can change the frequency. Because V/Hz is very similar to running the motor straight from the line, you can run more than one motor. However, there are still some things to watch out for. When you are running a single motor from a VFD, you tell the VFD the rated current of the motor. If the load on the motor increases and it starts to draw too much current, the VFD will shut things down before the motor overheats. Suppose you have two motors, each rated at 7A. You connect them to a single VFD and tell the VFD that the rating is 14A. Now suppose the load on one spindle is very light, but the other one is taking a heavy cut. So heavy that the motor is overloaded, drawing 11 amps. But the other one is only drawing 2A, the total is 13A, and the VFD is perfectly happy. Until the smoke comes out of the overloaded motor. In industry, if you run two motors from one VFD, you MUST supply individual overload protection for each motor - typically an overload relay as used with conventional motor starters. The relay contacts are used as interlocks to shut things down if either motor exceeds its rated current. By the way, the "motor gets hot but doesn't develop much torque or speed" problem you described is something that can happen even with a single motor on a vector VFD if the motor data isn't accurately entered into the drive. A V/Hz drive (or straight line voltage) is simple and forgiving - you apply voltage to the motor and it draws whatever current it needs. Vector is much more complex - the drive adjusts the voltage, current, and phase of the power it sends to the motor, trying to run the motor as precisely as possible. But it relies on knowing the motor characteristics to do that. It needs to accurately know the nominal voltage, no-load frequency, no-load current, full-load speed, and full-load current. Your no-load current of 0.2 amps seems way too low for an 8.7A motor, and in a vector drive would result in a lack of magnetic flux and a major loss of torque. To summarize: 1) for more than one motor on a single drive, use V/Hz, not vector. 2) for a single motor, if you want to use vector, you must enter all the motor nameplate data accurately into the drive. (Some drives have a self-tuning process or other start-up procedure to determine the no-load current, since that often is missing from the motor nameplate.) Hope this helps, John Kasunich On Tue, Nov 25, 2014, at 04:09 PM, Viesturs Lācis wrote: > Thank you! Yes, there is such a setting. > Could you, please, explain in more detail, if there are any > addditional settings I should pay attention to, when switching over to > vector control? Or should I just start with this one change and check > for any improvements? > > Viesturs > > > 2014-11-25 23:00 GMT+02:00 Andrew <stormbringe...@mail.ru>: > > > > Hi Viesturs! > > If your VFD has a vector control, maybe you should switch it over to V/F > > control with constant torque. I had the same trouble with my Hyundai VFD. > > Regards,Andrew > > ... > > > > > > > > > > > > > > > > 23:43 +0300 от Viesturs Lācis <viesturs.la...@gmail.com>: > > Hello! > > > > I need to drive 2 high-speed spindle motors, 3,7 kW each. For that I > > have 11 kW VFD. > > The problem is that I attached motors to the drive, tried to run them, > > but VFD does not increase frequency above 8-9 hertz (all the default > > frequency values are 50 hertz, I checked them and set to 100 to make > > sure that it not a problem). And in addition to that motors get really > > hot in a minute or so. I set "no load current" to 0,2 A, max current > > currently is set to 17 A (max current for each motor is 8,7A). > > > > This VFD worked fine few weeks ago with 7 kW motor. I checked the > > motors today with 2kW VFD - worked just fine. > > > > Ok, I can decrease max current to 2-3 amps, while testing, probably > > that should fix the overheating, but why does it not allow to increase > > frequency? > > > > I would appreciate also any additional advices on how to run 2 motors > > with 1 VFD. > > > > Viesturs > > > > ------------------------------------------------------------------------------ > > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > > with Interactivity, Sharing, Native Excel Exports, App Integration & more > > Get technology previously reserved for billion-dollar corporations, FREE > > http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ > > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > > with Interactivity, Sharing, Native Excel Exports, App Integration & more > > Get technology previously reserved for billion-dollar corporations, FREE > > http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > with Interactivity, Sharing, Native Excel Exports, App Integration & more > Get technology previously reserved for billion-dollar corporations, FREE > http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
