1
\$\begingroup\$

I have noise on my 60Hz PWM output. The PWM output is going to the ESC to control the motor. Below is the signal with 5V per division. The PWM signal is a 60Hz, 10V signal. The duty cycle can be changed.

enter image description here

What I have noticed is that as i increase the duty cycle, the Brushless Motor suddenly increase and decreases; I believe noise on the PWM signal could be the issue. Below is the signal at 1V per division. What capacitor value should I add to decrease the noise?

enter image description here

Below is the signal when the motor suddenly increases or decrease. This time, it went from 4.1Amps to suddenly 8Amps. I hope someone can explain why this is happening. Some findings: when I increase or decrease the scale on the oscilloscope, it affect the motor. I don't understand why that is happening.

enter image description here

\$\endgroup\$
14
  • 2
    \$\begingroup\$ what are the characteristics of the noise (frequency etc)? \$\endgroup\$
    – BeB00
    Sep 11, 2020 at 23:14
  • \$\begingroup\$ Hmm, I should look into that. Please hold on. I will post the signal soon. Thanks \$\endgroup\$ Sep 11, 2020 at 23:20
  • \$\begingroup\$ I have added the photo of the signal with noise. \$\endgroup\$ Sep 15, 2020 at 3:16
  • 1
    \$\begingroup\$ Doesn't look noisy at all. What's the practical problem? \$\endgroup\$
    – user76844
    Sep 15, 2020 at 3:27
  • 1
    \$\begingroup\$ Everything is behaving very erratically right now, so my suspicion is that there is something else going on that you have not caught yet. It would be good to remove variables from your setup and verify as many things as you can independently. For example, can you use a normal tester to validate that the ESC behaves as expected with the tester? Double check the signal from the tester, too, just for fun. \$\endgroup\$
    – user57037
    Sep 15, 2020 at 5:18

1 Answer 1

0
\$\begingroup\$

I'm not an EE, but from my understanding, no. Twisted pair serves to render the pair "invisible" to electromagnetic interference since any voltage is introduced in both leads in exactly the same amount and phase, cancelling each other out.

An inductive choke, on the other hand, serves to filter AC signals at certain frequencies because those frequencies introduce alternating magnetic fields in the ferrite choke. The twisted pair would not induce a magnetic field in the choke, so you wouldn't filter the frequencies passing through the wire.

Now if you split the twisted pair and wound each leg around a separate choke, then continued with the twisted pair on the other side, you should be able to both get the noise resistance of twisted pair and the high frequency filtering of the choke. (You'd increase the noise in the wire by a small amount since part of the wire wouldn't be twisted pair. Again, I'm talking as a fairly well-informed amateur here, not an EE.)

\$\endgroup\$
3
  • 1
    \$\begingroup\$ This isn't quite correct. Twisted pair does help with reducing differential noise (since noise is theoretically induced in pair at the same time) but it will also help with reducing emissions, since the pair will remain tightly coupled along the whole length. A ferrite choke will also help reduce common mode noise, which again is important for both reducing introduced noise and also emitted noise. see electronics.stackexchange.com/questions/275440/… \$\endgroup\$
    – BeB00
    Sep 12, 2020 at 11:02
  • \$\begingroup\$ Thank you. I will add a choke and then twist the wire. \$\endgroup\$ Sep 15, 2020 at 3:18
  • \$\begingroup\$ Adding a choke and twisting it solved the issue. Thank you \$\endgroup\$ Feb 23, 2021 at 23:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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