Phase Voltage Difference and phase angle measurement

[Suresh N]

Hi, I'm new to ES. I'm working on a 3 phase BLDC Axial flux motor (12 Slots 14 Poles), recently used the oscilloscope to measure the voltage difference and the phase angle for the motor.
I used Isolated differential probes for the measurement, connecting the positive and negative terminals in different phase in a circular pattern.
I'm not a electrical engineer so don't have much knowledge on these field, Just learning for experimenting in the Lab. I want to know if the difference in the values are in limit with the industry standards.

The image corresponds to motor rpm of 3825.

Looking for some help in understanding mor on how to design Axial flux motor and testing them.

 

[jetpackjbd]

Hi, I'm new to ES. I'm working on a 3 phase BLDC Axial flux motor (12 Slots 14 Poles), recently used the oscilloscope to measure the voltage difference and the phase angle for the motor.
I used Isolated differential probes for the measurement, connecting the positive and negative terminals in different phase in a circular pattern.
I'm not a electrical engineer so don't have much knowledge on these field, Just learning for experimenting in the Lab. I want to know if the difference in the values are in limit with the industry standards.

The image corresponds to motor rpm of 3825.

Looking for some help in understanding mor on how to design Axial flux motor and testing them.

I’m not an expert at all in standards, but a ~1V difference between phases doesn’t seem concerning. According to at least one standard (no idea what standard this setup is meant to follow), a 1% max voltage imbalance is permitted. You seem to be a very small bit over at a max of ~1.1% imbalance on “mean’” which I assume is fully charged, and a max of ~0.89% imbalance on “mean” which I assume is on a nearly dead battery. Even though you might be slightly out of spec at max voltage I can’t imagine any real issues from it. Other standards claim up to 4% imbalance from the lowest value, so you’re probably alright.

I can’t find any standards about maximum phase degree imbalance other than 120° between phases. I’d imagine your values are nothing to worry about either. If it were maybe 100°, 130°, and 90° or something then you’d definitely have an issue with uneven motion, but at over 400hz with barely a 1° difference you shouldn’t feel it.

Unless this motor is for a precision application like surgical robots or a high-end laser cutter it’ll be fine.

 

[amberwolf]

FWIW, the differences between the voltages will probably be from differences in the coils themselves. Number of turns, Wire lengths from differences in windings, winding neatness, coil-to-coil wire length differences, etc.

 

[Suresh N]

I’m not an expert at all in standards, but a ~1V difference between phases doesn’t seem concerning. According to at least one standard (no idea what standard this setup is meant to follow), a 1% max voltage imbalance is permitted. You seem to be a very small bit over at a max of ~1.1% imbalance on “mean’” which I assume is fully charged, and a max of ~0.89% imbalance on “mean” which I assume is on a nearly dead battery. Even though you might be slightly out of spec at max voltage I can’t imagine any real issues from it. Other standards claim up to 4% imbalance from the lowest value, so you’re probably alright.

I can’t find any standards about maximum phase degree imbalance other than 120° between phases. I’d imagine your values are nothing to worry about either. If it were maybe 100°, 130°, and 90° or something then you’d definitely have an issue with uneven motion, but at over 400hz with barely a 1° difference you shouldn’t feel it.

Unless this motor is for a precision application like surgical robots or a high-end laser cutter it’ll be fine.

Thank you so much for the reference, This is not for precision application mostly I'm going to use it in EV Bikes.

 

[Suresh N]

FWIW, the differences between the voltages will probably be from differences in the coils themselves. Number of turns, Wire lengths from differences in windings, winding neatness, coil-to-coil wire length differences, etc.

I did check for the resistance of the individual coils before soldering the End windings, using a milli ohm meter and all were same values with a maximum change of 0.03 milliohm, But after the soldering the end windings I can see some changes, When measuring phase - phase resistance (Y connection) 0.9 milliohm, which i think is because of the length of wire being used, I for some mechanical constrain not bale to math the wire length for the Neutral connection.

Are these also normal in a motor.

 

[Suresh N]

I’m not an expert at all in standards, but a ~1V difference between phases doesn’t seem concerning. According to at least one standard (no idea what standard this setup is meant to follow), a 1% max voltage imbalance is permitted. You seem to be a very small bit over at a max of ~1.1% imbalance on “mean’” which I assume is fully charged, and a max of ~0.89% imbalance on “mean” which I assume is on a nearly dead battery. Even though you might be slightly out of spec at max voltage I can’t imagine any real issues from it. Other standards claim up to 4% imbalance from the lowest value, so you’re probably alright.

I can’t find any standards about maximum phase degree imbalance other than 120° between phases. I’d imagine your values are nothing to worry about either. If it were maybe 100°, 130°, and 90° or something then you’d definitely have an issue with uneven motion, but at over 400hz with barely a 1° difference you shouldn’t feel it.

Unless this motor is for a precision application like surgical robots or a high-end laser cutter it’ll be fine.

I had a failed attempt in the winding before, although i did not have a oscilloscope then to measure the Backemf I went directly to test the motor in a test bench by loading it, Found our there is difference in the phase current through out the test, which is affecting the performance of the motor and making it to heat up really fast.

When measuring the phase-phase resistance i found a difference of 10 milliohm which for this iteration is around 0.9 milliohm, I also fear i might have done some mistake in the winding.

Now I don't know what actually happened to the winding to have this much changes in the phase current. Is there any testing procedure i can use to check this before going to do the performance testing of the motor.

 

[jetpackjbd]

I had a failed attempt in the winding before, although i did not have a oscilloscope then to measure the Backemf I went directly to test the motor in a test bench by loading it, Found our there is difference in the phase current through out the test, which is affecting the performance of the motor and making it to heat up really fast.

When measuring the phase-phase resistance i found a difference of 10 milliohm which for this iteration is around 0.9 milliohm, I also fear i might have done some mistake in the winding.

Now I don't know what actually happened to the winding to have this much changes in the phase current. Is there any testing procedure i can use to check this before going to do the performance testing of the motor.

Oh, did you wind the coils of the motor yourself? I don’t believe a 10 milliohm difference between coils should cause a problem, and a 0.9 milliohm difference sounds perfectly normal.
I don’t think a small difference in resistance would cause a loss of power or overheating. To me it sounds like the coils aren’t being wound to what the motor wants, for example you might be winding to 10ohms when it should be 20 ohms. Double check the specifications of the motor.

Your English is very good by the way!

 

[Suresh N]

Oh, did you wind the coils of the motor yourself? I don’t believe a 10 milliohm difference between coils should cause a problem, and a 0.9 milliohm difference sounds perfectly normal.
I don’t think a small difference in resistance would cause a loss of power or overheating. To me it sounds like the coils aren’t being wound to what the motor wants, for example you might be winding to 10ohms when it should be 20 ohms. Double check the specifications of the motor.

Your English is very good by the way!

Thanks For the complement,

No I didn't wind myself, I ordered the coil from china, it was much cheeper and since I used rectangular coil, the availability here in my location is quite low and, endge-wise winding machines are also not available, Making a 3D print jig to do the job turned out to be a failure

What I feel is could be because of inter phase short in the winding, although there is not short between the body and the coils, interphase winding can change the voltage of the phases and make and increase the parallel paths. what do you thinks on this matter?

 

[jetpackjbd]

Thanks For the complement,

No I didn't wind myself, I ordered the coil from china, it was much cheeper and since I used rectangular coil, the availability here in my location is quite low and, endge-wise winding machines are also not available, Making a 3D print jig to do the job turned out to be a failure

What I feel is could be because of inter phase short in the winding, although there is not short between the body and the coils, interphase winding can change the voltage of the phases and make and increase the parallel paths. what do you thinks on this matter?

I think it could be a short somewhere too, I’m not familiar with the term “inter phase short” though. On brushed motors I’ve seen issues where the motor overheats and is low on power as the insulation is melted on a coil causing a partial short.

 

[Suresh N]

I think it could be a short somewhere too, I’m not familiar with the term “inter phase short” though. On brushed motors I’ve seen issues where the motor overheats and is low on power as the insulation is melted on a coil causing a partial short.

What I ment was short between two phases, The motor is a two layer winding so the coils of two phases are adjusent to one another, and may clause the short if the enamel is damaged

 

[jetpackjbd]

What I ment was short between two phases, The motor is a two layer winding so the coils of two phases are adjusent to one another, and may clause the short if the enamel is damaged

Could be possible, definitely check for that.