The only kind of operation where I think the BLDC motor would work completely fine with a typical VFD (no commutation sensor feedback) is if the maximum load on the motor was only a small fraction of its capability. In this case, the motor rotor will tend to self-align with the phase of the driving current. Some VFDs may be able to accept position feedback input so that they can work with BLDC motors (which are also called PMSM or Permanent Magnet Synchronous Machines and aren't really DC motors at all). Induction motors have no permanent magnetic poles on the rotor - the field from the rotor comes from current induced in it by slip - which is the difference in the driving electrical frequency and the rotor rotational frequency (times pole count divided by 2). This means that not only is there no special alignment information to know about the rotor at startup, but in fact the motor needs to be operated in a slightly asynchronous operation in order to function. If you were using a BLDC motor and it got out of sync, there would be 0 torque averaged over a full rotation but there would be torque ripple and yes, if that were slow enough (by limiting the maximum driving frequency), it might be able to rock the motor free from a stall condition, but that would still be pretty suboptimal operation. A third option is PM brushless motor sensorless operation. Maybe some VFDs can do this, too, I don't know. I designed one that can but it was specifically designed for use with PM motors in a specific application. There are several variations of sensorless operation. One of them starts up assuming no heavy load but once it is running it can maintain synchronization with varying and heavy loads by watching the phase of the back-EMF voltage. Another variant uses knowledge of the way the motor inductance varies with rotor angle to obtain an initial rotor angle estimate at startup. Obviously that needs to be matched well to the motor it is using. Sean On Tue, Aug 7, 2018 at 6:33 AM, Justin Richards wrote: > Outside of the OP requirements but I am curious to know if it would perfo= rm > favorable if the BLDC was only ever driven at relatively slow speeds by a > VFD turning a heavy load. > Justin > > > On Mon, 6 Aug 2018 03:22 Jason White > wrote: > > > Okay, thanks Sean and Alan. I figured that probably was the case. > > > > On Sun, Aug 5, 2018 at 2:37 PM, Sean Breheny wrote: > > > > > Most likely it would work most of the time. However, I would be > somewhat > > > concerned about what might happen if the load on the motor changed > > > suddenly. In such a case the motor might stall with the VFD continuin= g > to > > > drive an AC sequence at high frequency since it has no feedback about > the > > > motor movement. > > > > > > With an induction motor, there would still be torque in such a > situation > > > and if the load on the motor became slightly lighter the motor would > > begin > > > to spin again. With a permanent magnet motor, there woudn't be much > > torque > > > at all when the slip is so extreme so it would require resetting the > VFD > > or > > > manually slowing it down until there was sufficient torque again to g= et > > the > > > motor spinning. During this time when the slip was extreme the motor > > could > > > be getting quite hot. > > > > > > > > > Sean > > > > > > > > > On Sun, Aug 5, 2018 at 12:17 PM, Jason White < > > > whitewaterssoftwareinfo@gmail.com> wrote: > > > > > > > Hello, > > > > > > > > I am working on rewiring a small CNC mill. For the spindle the > existing > > > > unit has the following brushless DC motor with hall effect sensors > (see > > > > attached drawing). It is rated at 160V, 7A. > > > > > > > > Could this motor be driven by a VFD intended for conventional 3-pha= se > > AC > > > > induction motors? As I understand it most 3-phase AC motors are > 220Vac > > > > which would suggest that the answer is no. > > > > > > > > For this application I do no care about slippage or precise speed. > > > > > > > > Thanks, > > > > Jason White > > > > > > > > -- > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > > View/change your membership options at > > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > > > > > -- > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > > > > > -- > > Jason White > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .