I would to know if make sense to obtain the current of the BLDC motor, using the BLDC motor torque measurement. In particular, i'm able to measure the torque of a BLDC motor but not the current that flow in a single phase of the BLDC. My idea is to manipulating this equation:

T(t) = Kt*i(t) --> i(t) = 1/Kt * T(t)

So I think that I'm able to obtain the total current that flow of all three phase of the BLDC.

The problem is that i'm able too to measure the current between the battery and the ESC, and this current have the maximum value of about 7 [A], but the current that i calculate using the equation above give me a value of about 50[A], using the value of Kt as the inverse of the Kv value of the BLDC. This is the current for all the three phases, for one phase i obtain a value of about 16[A] (50/3 = ~16)

I have read this question: question

and the first answer tell me that the current that flow in the BLDC motor can be higher than the input current.

So, the values that i obtain from my experiment are correct or are they wrong?


I'm sorry, i have done a stupid error in the acquisition system firmware. In practice i have used the windows calculator to translate the arm of the torque sensor from cm to m, but digiting the value i have used the "dot" to separe value after the comma and the windows calculator doens't recognize the dot, but recognize only the comma.. so 3.5 cm became 0.35 m and this is the error. Now i have correct this error and the result are what are expected as you can see in next image. enter image description here The yellow signal is the current calculated with the formula above and the purple signal are the current measured.

I think that the mismacth are due to the other factors that i not considered in the formula above like friction and so on.. Moreover the Kt value is from the motor datasheet and I not measured it directly..

the problem now is with the question in the link above...

  • \$\begingroup\$ Too many flaws in statements without conditions. Torque = kt* I and Rpm=kv *V with no load then load increases current and decreases RPM \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 3 '19 at 22:44
  • \$\begingroup\$ " the values that i obtain from my experiment are correct or are they wrong?" - what results did you get from your experiment? \$\endgroup\$ – Bruce Abbott Feb 3 '19 at 23:20
  • \$\begingroup\$ The motor coils resistance , DCR determines the start current I=V/DCR \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 4 '19 at 3:28
  • \$\begingroup\$ @SunnyskyguyEE75, you are right i have missed the conditions. However all my reasoning are referring to the load condition. Using the coils resistance I obtain a value of current near a 14[A]. \$\endgroup\$ – Luca80 Feb 4 '19 at 9:34
  • \$\begingroup\$ @BruceAbbott I have obtained a current signal of about 50[A] for all the three phases, for one phase the current flow have a value of about 16[A]. I have obtained this value measuring the Torque T(t) and using the formula above where Kt is the inverse of Kv of the BLDC. \$\endgroup\$ – Luca80 Feb 4 '19 at 9:40

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