So I have set up a little experiment which involves a HDD BLDC Motor, a scope and a multimeter. Pretty simple, I know. Is it possible to determine the inductance of a phase by the voltage the phase produces? I would like to set up a model of the circuit in MATLAB or PSpice, but cannot do so until I find the inductance of one of the phases.

Unfortunately, all of the formulas I have come across involve the diameter of the wire and number of turns, however this is one electronic pressure fit case I would rather not destroy. I was hoping to figure this one out mathematically or even better scientifically. Maybe something that involves the rotation of the spindle vs. the voltage produces. Am I on drugs? Thanks for your help.


If you can get at the winding ends without electronic switches etc in the way then there are a number of possible methods.

Direct measurement (some (few) multimeters).

Time constant response to an applied square wave.
Tc = L/R.
R of coil can be measured and additional R can be added, then apply a square wave and note current ramp rate of rise.

Add second known inductor in series. Apply AC to series string and note relative voltage drops which are proportional to inductance for pure inductors.

  • \$\begingroup\$ Somehow I knew you would come to the rescue! Thanks for your help. \$\endgroup\$ – atomSmasher Aug 15 '12 at 15:38
  • \$\begingroup\$ It's always a good idea to NOT accept an answer for a day or few. It doesn't bother me either way BUT some people get put off answering questions that have been accepted. \$\endgroup\$ – Russell McMahon Aug 15 '12 at 16:10

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