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i'm driving BLDC using sensorless method. The driving algorithm is woking fine, but on the bemf oscilogram i can see, that the power-on stage length is little bit different for each of the 3 phases. I'm just curious why. I think that it could be caused by the motor assymetry or imperfect magnets positioning, but i'm not sure. Could it be caused also by something else? Lets assume the motor is perfectly symetrical. Will i see this effect too? Why? Thank you for any ideas.

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    \$\begingroup\$ Show picture or link to same. 3 phase magnetic are never perfectly symmetrical. What you need is a defined tolerance and correction factor with temperature or deadband. \$\endgroup\$ – Sunnyskyguy EE75 Jun 11 '18 at 20:12
  • \$\begingroup\$ Here is the picture: img. It is not mine as i have not acces to osciloscope now, but i tried to show what i mean. The X1 and X2 in the picture in my case are not equal. \$\endgroup\$ – Carl L. Jun 11 '18 at 20:51
  • \$\begingroup\$ How constant is the rotor speed? \$\endgroup\$ – JonRB Jun 11 '18 at 21:15
  • \$\begingroup\$ Speed is pretty constant. Potentiometer was set on fixed value and I did not observe any strange movements or speed drops. \$\endgroup\$ – Carl L. Jun 11 '18 at 21:33
  • \$\begingroup\$ Thanks Cark, I see 12 cycles in each X1,X2 so depending on asymmetry and quantization errors, detection errors etc, you should expect the wiring to be within 1% symmetry but the magnet strength can vary +/-25% for different reasons or suppliers , mixed batches and loses strength with rising temp differently depending on sources and quality control. This is most likely the reason for asymmetry but just a SWAG so far. But then I haven't seen your design yet. \$\endgroup\$ – Sunnyskyguy EE75 Jun 11 '18 at 22:05

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