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## Regarding Back EMF measurement.

Level 5
Level 5

Hello.

I captured the part I measured. Please check the picture.

When measuring the Back EMF, I told you to turn the motor by hand, but the measurement value is different every time I turn it hard or weak by hand, so what should I do about this part?

Calculation and measurement are too difficult for Back EMF measurement. Help me, please.

I don't know how to handle the scope and it's hard to calculate even.

No matter how much I read the data, it's difficult for me.

This is the value I measured. Please look at the picture and make sure it is correct.

1. LS : 21.941mH
2. Resistance : 3.8ohm
3. Back EMF : ?....

1 Solution

## Re: Regarding Back EMF measurement.

Moderator
Moderator

Hello @JasonLEE

I hope you have gone through our document https://www.infineon.com/dgdl/Infineon-How-to-Measure-Motor-Parameters-ApplicationPresentation-v01_0... to know more about the back emf calculation method.

1. It is not possible for us to check which test points you are probing. The images only show that readings on the multimeter and the LCR meter. If you have confusion, please refer to the motor datasheet to know of the resistance and inductance values (provided the motor is of standard make). You may measure these parameters in a multimeter and LCR meter and verify it from the values mentioned in the motor datasheet.

2. In the image of the scope measurement you have shared, you may see that your peak to peak voltage is 35.2V (Vpp) and Frequency is 10.30Hz (fmeasured). Put these values in the equation mentioned in slide 9 of the document mentioned above. Npolepairs is the number of pole pairs for your motor.

However, I am curious to know if you rotating the motor by hand (as you have mentioned) or using a dynamo to rotate the motor? If you rotate the motor by hand, based on practical experience it is unlikely that you will achieve such a clean sinusoidal waveform. Please explain where your probes are connected.

Regards

RupakC
5 Replies

## Re: Regarding Back EMF measurement.

Moderator
Moderator

Hello @JasonLEE

I hope you have gone through our document https://www.infineon.com/dgdl/Infineon-How-to-Measure-Motor-Parameters-ApplicationPresentation-v01_0... to know more about the back emf calculation method.

1. It is not possible for us to check which test points you are probing. The images only show that readings on the multimeter and the LCR meter. If you have confusion, please refer to the motor datasheet to know of the resistance and inductance values (provided the motor is of standard make). You may measure these parameters in a multimeter and LCR meter and verify it from the values mentioned in the motor datasheet.

2. In the image of the scope measurement you have shared, you may see that your peak to peak voltage is 35.2V (Vpp) and Frequency is 10.30Hz (fmeasured). Put these values in the equation mentioned in slide 9 of the document mentioned above. Npolepairs is the number of pole pairs for your motor.

However, I am curious to know if you rotating the motor by hand (as you have mentioned) or using a dynamo to rotate the motor? If you rotate the motor by hand, based on practical experience it is unlikely that you will achieve such a clean sinusoidal waveform. Please explain where your probes are connected.

Regards

RupakC

## Re: Regarding Back EMF measurement.

Level 5
Level 5

Hi, @RupakC

1. This motor was rotated by hand.

2. Probe is U.V. connected

3. The motor is 10 poles.

4. I have a question.
The measurement varies depending on whether the motor is turned sharp or weak.
How do I control my strength?
I think this is the most important part.

5. Can you calculate the Back EMF for me? I can't calculate even if I look at the formula.

Thanks

## Re: Regarding Back EMF measurement.

Moderator
Moderator

Hello @JasonLEE

As is reflected in your image, subsequent periods of the sinusoidal back emf will see varying magnitude. However, the time periods will also change. For every new set of peak to peak voltage magnitude and Frequency (time period), you may check the back emf using the equation mentioned in the previous document. The back emfs thus calculated may vary slightly for subsequent time periods. You can take multiple readings and then consider averaging the value of back emfs calculated.

Regards

RupakC

## Re: Regarding Back EMF measurement.

Level 5
Level 5

Hello @RupakC

I can't calculate even if I look at the equation.
Could you calculate the Back EMF by referring to the picture I sent you?

This part is very difficult for me.

## Re: Regarding Back EMF measurement.

Moderator
Moderator

Can you let us know what is the exact difficulty you are facing?

The figure that you have attached does not indicate the peak to peak voltage and the time period. Hence it is not possible for me to tell you the back emf value from this figure. Please attach the peak to peak measurement of the voltage and the time period for the respective cycle.

The equation is fairly simple. You just need to enter the value of the peak to peak voltage for one cycle and measure the time period for that cycle. Your motor has 10 poles. So, the Npolepair will be 5. Enter those values in the equation in the document mentioned in my previous reply.

If you still face problems, let me know exactly what kind of help you need.

Regards

RupakC