Strange oscilloscope pwm reading

Status
Not open for further replies.
N

Nickedemuz

New Member
Hi
Might be I bought a really cheap (and probably crappy) pwm motorcontroller from China. I hooked it up to my scope and got some very strange reading. There is also a possibility that I’m doing something really stupid with the scope cause I’m pretty green at this
The motor is running ok and the speed control works. I’m just very curious about the strange waveform. I expected it to be a square wave.
appreciate any help or info
 
If you've got the motor connected to the controller, then you won't see the PWM on the motor.
 
motor windings act like inductors, so when a pulse is applied the current ramps. it's the same effect as in a CRT monitor deflection yoke.
 
Oh, thanks! So I guess we’re looking at a noob mistake here At least I learned something new.
Could you please tell me what might be the correct way of hooking up the scope?
 
Nickedemuz said:
Oh, thanks! So I guess we’re looking at a noob mistake here At least I learned something new.
Could you please tell me what might be the correct way of hooking up the scope?
Click to expand...

If you want to view the PWM then you need to use a non-inductive load (not a motor).
 
Thanks a lot for helping me. I really appreciate it! I thought the LED would be the same. I’m learning a lot here And you are correct in the assumption of a car motor. It’s a wiper motor.
 
Nickedemuz said:
Thanks a lot for helping me. I really appreciate it! I thought the LED would be the same. I’m learning a lot here And you are correct in the assumption of a car motor. It’s a wiper motor.
Click to expand...

Over the years I've found car bulbs an invaluable source of 'dummy loads', a combined rear/brake bulb gives you three possible loads, and for higher loads a front fog light bulb or headlamp bulb does the job nicely.
 
that’s a really good idea! Will be getting those to have some options. I had a small 12v rear lamp and...success!
Next thing to watch on YouTube will be how the loads differ from each other
 
Status
Not open for further replies.

Similar threads

Help reduce noise on USB oscilloscope.
Replies
9
Views
1K
Lightium
L
  • Question
Motor Rotation Change, Strange Wiring?! Help!
Replies
2
Views
1K
rjenkinsgb
C
Tektronix T932 oscilloscope problems
Replies
0
Views
899
Cello
C
A
  • Question
low power CPUs that is insertable, strange facts
Replies
1
Views
1K
rjenkinsgb
P
  • Question
Isolating transformer disparity on reading volts out
Replies
5
Views
783
paddy ryan
P
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…