how to properly connect an oscilloscope to diagnose stepper motor? - Electronic Circuits Projects Diagrams Free

james56 · 31st October 2009, 01:24 AM

I have a bipolar (4 wire) stepper motor that isn't working right.

It runs on 24VDC. How do I analyze the voltage waveforms going into the stepper motor? I know it has 2 coils. The possibilities should be:
coil 1: wire 1=+24V, wire 2=GND
coil 1: wire 1=GND, wire 2=+24V
coil 2: wire 3=+24V, wire 4=GND
coil 2: wire 3=GND, wire 4=+24V

I want to see which coil has current flowing through it at different times.

My scope has 2 probes, ChA and ChB. Each probe has a spring loaded tip and an alligator clip.

Do I hook up the the GND black alligator clips to the negative terminal of the battery (battery ground) then hookup the spring loaded tip to the base of one of the coils (wire 1). Then for the second probe, should I hook up the black alligator clip to battery ground and the probe to (wire 3)? Does this mean I need 2 scopes (4 total channels) to see what's going on in the stepper motor?

Or can I hookup the black end of the probe to one end of the coil (wire 1) and the springy tip to the other end (wire 2)? Then hookup the second probe to (wire 3) and (wire 4) ?

I tried the second one and a big spark took place so I took it off. Am I doing the write thing?

Help out a newbie please

Boncuk · 31st October 2009, 01:31 AM

Are you sure it's a stepper motor?

A stepper motor requires a certain order of polarity change in both coils in order to run.

Sceadwian · 31st October 2009, 01:36 AM

If you want to measure current through a coil you use a series resistor low enough to not drain too much power, but high enough to cause a voltage drop to measure..

Please read the 'current measuring' section of.
Shunt (electrical) - Wikipedia, the free encyclopedia

james56 · 31st October 2009, 01:37 AM

Yes I'm sure it's a stepper. I know the polarity changes in the coil.

That's why I want to figure out how to look at the voltages with the scope to figure out the voltages at each of the coils and the direction.

I just need to figure how to hook it up...

Thanks!

james56 · 31st October 2009, 01:42 AM

Do I need to measure the current through the coil? I really just want to verify the circuit is firing properly.

Can't I just measure the voltages going into the motor coils somehow?

james56 · 31st October 2009, 01:46 AM

Hmm I've been thinking about it and the motor coil itself has a resistance of 15ohms or so.

Can I just hook up my scope across the coil (wire 1=black alligator) and (wire 2=scope clip) and read out the voltage?

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31st October 2009, 01:24 AM	#1
james56	how to properly connect an oscilloscope to diagnose stepper motor? I have a bipolar (4 wire) stepper motor that isn't working right. It runs on 24VDC. How do I analyze the voltage waveforms going into the stepper motor? I know it has 2 coils. The possibilities should be: coil 1: wire 1=+24V, wire 2=GND coil 1: wire 1=GND, wire 2=+24V coil 2: wire 3=+24V, wire 4=GND coil 2: wire 3=GND, wire 4=+24V I want to see which coil has current flowing through it at different times. My scope has 2 probes, ChA and ChB. Each probe has a spring loaded tip and an alligator clip. Do I hook up the the GND black alligator clips to the negative terminal of the battery (battery ground) then hookup the spring loaded tip to the base of one of the coils (wire 1). Then for the second probe, should I hook up the black alligator clip to battery ground and the probe to (wire 3)? Does this mean I need 2 scopes (4 total channels) to see what's going on in the stepper motor? Or can I hookup the black end of the probe to one end of the coil (wire 1) and the springy tip to the other end (wire 2)? Then hookup the second probe to (wire 3) and (wire 4) ? I tried the second one and a big spark took place so I took it off. Am I doing the write thing? Help out a newbie please

31st October 2009, 01:31 AM	#2
Boncuk	Are you sure it's a stepper motor? A stepper motor requires a certain order of polarity change in both coils in order to run. __________________ Proper Planning Prevents Piss Poor Performance

31st October 2009, 01:36 AM	#3
Sceadwian	If you want to measure current through a coil you use a series resistor low enough to not drain too much power, but high enough to cause a voltage drop to measure.. Please read the 'current measuring' section of. Shunt (electrical) - Wikipedia, the free encyclopedia __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

31st October 2009, 01:37 AM	#4
james56	Yes I'm sure it's a stepper. I know the polarity changes in the coil. That's why I want to figure out how to look at the voltages with the scope to figure out the voltages at each of the coils and the direction. I just need to figure how to hook it up... Thanks!

31st October 2009, 01:42 AM	#5
james56	Do I need to measure the current through the coil? I really just want to verify the circuit is firing properly. Can't I just measure the voltages going into the motor coils somehow?

31st October 2009, 01:46 AM	#6
james56	Hmm I've been thinking about it and the motor coil itself has a resistance of 15ohms or so. Can I just hook up my scope across the coil (wire 1=black alligator) and (wire 2=scope clip) and read out the voltage?