I have a BLDC motor with these info (please don't pay attention to the striped column):
How from these info, how can I get the Back-emf constant ? Is it just 36V/4krpm = 9 V/krpm ?
Thank you a lot.
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1\$\begingroup\$ Welcome! Likely less than 36 V at 4000 rpm, but there is not enough data to know. The inverter will also obfuscate it to a high degree. What do you need the back-EMF constant for? \$\endgroup\$– winnyCommented Aug 22, 2023 at 8:14
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\$\begingroup\$ @winny Thank you. I'm using ST Motor Control Workbench for a project and I need to set some parameters such as the ones you can see on the picture. The last parameter to set is the back-EMF constant and I don't know what to put in. The default parameter is 4.0 Vrms/kprm \$\endgroup\$– Classy FiedCommented Aug 22, 2023 at 9:57
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\$\begingroup\$ The inverter inside it will again obfuscate it for you. If the motor has a PWM or speed control input, you don't need any motor driver for it since it already contains a motor driver. \$\endgroup\$– winnyCommented Aug 22, 2023 at 10:12
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\$\begingroup\$ For brushless DC motors Kemf = Kt. \$\endgroup\$– John DCommented Aug 22, 2023 at 17:31
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1 Answer
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For an ideal synchronous AC motor (including so-called "brushless DC motors"), the voltage constant is equal to the torque constant. Real motors, of course, are not ideal, but this is still a good enough approximation for most uses.
So for this one, the voltage constant is 0.063 N·m/A = 0.063 V·s = 6.6 V/krpm.
