# Back Emf Waveforms

#### electronicsLearner77

Jul 2, 2015
306
This is the back emf waveform from motor data sheet

I can understand the back emf as A, B and C. But what does C+ A-, A+ B-, B+ C- mean?

#### Delta Prime

Jul 29, 2020
2,191
What are you doing? I'm talking to you here. Then explain to me what is the back EMF as a b and c for that matter what is EMF or commutation? I'm asking this for those who are first reading this post because of your prior posts.
I'm sincerely trying to help you and I think you're joking around. Believe me I know!

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#### electronicsLearner77

Jul 2, 2015
306
When a motor rotates, each winding generates a voltage known as Back emf. Back emf equation is

this voltage back emf opposes the main voltage applied on the windings.

#### Delta Prime

Jul 29, 2020
2,191
Show me the entire data sheet that way we can both be on the same page

#### electronicsLearner77

Jul 2, 2015
306
Ok, i am attaching the motor data sheet.

#### Attachments

• Hurst DMA0204024B101 BLDC Motor DataSheet.pdf
628.1 KB · Views: 1

#### Delta Prime

Jul 29, 2020
2,191
Hold on I'm working on it I'm going to give you a visual representation of what it's doing. As you know a magnetic field is created when current is applied in a coil think of the magnetic field as a bubble. There's no current in the coil the bubble collapses. "But what does C+ A-, A+ B-, B+ C- mean?" It is showing you the relationship of the three phases with respect to one another when face c is positive and phase a is negative that 120° separation between phase is the point where the controller applies current which is zero crossing of the waveform my freaking phone he's not cooperating.

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Jul 29, 2020
2,191

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#### Delta Prime

Jul 29, 2020
2,191
Sorry buddy I got to get to my house get on the computer I'm going to destroy this phone

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#### Delta Prime

Jul 29, 2020
2,191
Also look closely at the hall waveform. S1 S2 S3 the colors used in particular.
compare those two BEMF waveforms the colors b+ c-on the bottom corresponds to the waveform S1 for the hall waveform is on top.
They are inversely proportional to each other. My arrows are incorrect it's just showing you the zero crossing or at what point the current is applied by the controller is applied. is applied. Horrible explanation good tonight kiddo

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#### electronicsLearner77

Jul 2, 2015
306
Ok, is it correct to think that C+ A-, A+ B-, B+ C- are the line - line voltages? and the below waveform from other document

are the phase voltages A, B, C (with respect to Neutral point)?

#### Delta Prime

Jul 29, 2020
2,191
No! I believe I pointed you in the right direction in your other thread. Good luck to you.

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