I picked up a Wye-wound brushless DC motor with three leads, three wires coming out of it via a flex PCB. Unfortunately, this flex PCB has no color indication. How can I figure out which lead is phase A, phase B, and phase C without moving the motor?

The motor is in an enclosure that heavily limits its range of motion.

  • \$\begingroup\$ read the data sheet or ask the manufacturer? \$\endgroup\$ Commented Nov 20, 2018 at 23:06
  • 1
    \$\begingroup\$ also, if there's three phases coming out, it's not a DC motor... (you might be referring to the actual motor within what is called a brushless DC motor, which is a 3-phase motor + DC - to - three-phase converter/controller) \$\endgroup\$ Commented Nov 20, 2018 at 23:07
  • \$\begingroup\$ This motor could be 3 phase delta, or it needs a 3 phase VFD to drive it. \$\endgroup\$
    – user105652
    Commented Nov 21, 2018 at 2:16

1 Answer 1


If this is a brushless motor with only three wires, there is no hall effect or encoder feedback, so the assignment of phase labels is arbitrary. To run sensorless, choose any wire you like to be phase A, B and C. If you want to reverse direction, swap any two of the phases.


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