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Strange oscilloscope pwm reading

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:)6556372E-6DD8-487E-861D-01D76AD58A70.jpeg442D1751-284E-4CEC-BCA9-DD2EF19F69F4.jpeg4C7437DB-63B0-4081-9E90-9FD2AA37D2A6.jpeg78E13CFE-3FC9-4B87-88B0-548AA701DE2D.jpeg
 

unclejed613

Well-Known Member
Most Helpful Member
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.
 

Nickedemuz

New Member
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

New Member
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.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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.
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.
 

Nickedemuz

New Member
that’s a really good idea! Will be getting those to have some options. I had a small 12v rear lamp and...success! 1B288C85-E664-4813-BF4A-D2BCE234DEB8.jpeg
Next thing to watch on YouTube will be how the loads differ from each other :)
 

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