0
\$\begingroup\$

For analysis [oscilloscope wave form] purpose I am running a BLDC motor at 9Vdc. Power Sorce is giving the constant DC voltage to BLDC Motor. But whenever I am disconnecting the voltage there is a spike seen in voltage (Approx 15.4 v).

  • What is this spike?
  • If its Back EMF why its not showing in reverse direction?

Refer the Picture (I am Disconnecting the input by disconnecting the Ground Manually)

enter image description here

\$\endgroup\$
  • \$\begingroup\$ Flyback? Don't kill your scope.. \$\endgroup\$ – Gregory Kornblum Apr 18 '17 at 17:26
1
\$\begingroup\$

If you were experimenting with a brushed DC motor, then the spike should be negative, as you expected.

But you wrote you are using a brushless DC motor. Then there must be a controller somewhere. The controller drives each of the motor’s 3 phases with a half-bridge, which certainly has flyback diodes. And thanks to those diodes, if you’re looking and the power input of the controller, you will see positive back-EMF spike.

Note that that back-EMF may damage the controller, so you should better not do that. (You might also kill your scope…)

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.