brandnewb
Going for serious. starting as newb
so the science has finally begun. and again I am not doing it all alone. This time I stand on the shoulders of..
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yes you have guessed it
ChatGPT....
The latest and greatest of their models.
Context is now we have a bit of a larger PMA pulley so that the motor does not overheat so quickly and the VFD does not trip out my breaker cabinet so eagerly
please let me know if I and/or this parrot which still has no name yet is blundering big time.
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User: I have a PMA in an axial configuration with 96 magnets. The PMA spins at 60 rpm. At what frequency does the magnetic field reverse polarity?
Assistant:
To find the frequency at which the magnetic field reverses polarity, you need to determine the number of pole pairs and apply the formula relating mechanical speed (in RPM) to electrical frequency (in Hz).
User: Great formula. Can you please turn it around so that we start with 48 Hz and find the RPM?
Assistant:
Starting from the formula:
f=Number of pole pairs×RPM60f = \frac{\text{Number of pole pairs} \times \text{RPM}}{60}f=60Number of pole pairs×RPM
Solve for RPM:
RPM=f×60Number of pole pairs\text{RPM} = \frac{f \times 60}{\text{Number of pole pairs}}RPM=Number of pole pairsf×60
If you know f=48 Hzf = 48 \, \text{Hz}f=48Hz and have 48 pole pairs:
RPM=48×6048=60 RPM\text{RPM} = \frac{48 \times 60}{48} = 60 \, \text{RPM}RPM=4848×60=60RPM
User: I have taken measurements of my PMA and a 3-phase delta wired coil configuration in an open-circuit setting. I forgot to also measure the VDC after full rectification initially, which is why not all rows have the VDC column populated. Can you find any anomalies in this data?
Assistant:
You’ve provided a set of measurements for various frequencies, RPMs, line-to-line VAC, and in some cases VDC after full-bridge rectification. The data appears as follows (using an example table structure):
Analysis:
wait for it

yes you have guessed it

ChatGPT....
The latest and greatest of their models.
Context is now we have a bit of a larger PMA pulley so that the motor does not overheat so quickly and the VFD does not trip out my breaker cabinet so eagerly

please let me know if I and/or this parrot which still has no name yet is blundering big time.
-------
User: I have a PMA in an axial configuration with 96 magnets. The PMA spins at 60 rpm. At what frequency does the magnetic field reverse polarity?
Assistant:
To find the frequency at which the magnetic field reverses polarity, you need to determine the number of pole pairs and apply the formula relating mechanical speed (in RPM) to electrical frequency (in Hz).
- Number of pole pairs:
With 96 magnets arranged in alternating polarity around the rotor, the number of pole pairs is half the number of magnets:
Pole pairs=962=48\text{Pole pairs} = \frac{96}{2} = 48Pole pairs=296=48 - Frequency calculation:
The frequency fff (in Hz) is given by:
f=(Number of pole pairs)×(RPM)60f = \frac{\text{(Number of pole pairs)} \times \text{(RPM)}}{60}f=60(Number of pole pairs)×(RPM)
Substituting:
f=48×6060=48 Hzf = \frac{48 \times 60}{60} = 48 \, \text{Hz}f=6048×60=48Hz
User: Great formula. Can you please turn it around so that we start with 48 Hz and find the RPM?
Assistant:
Starting from the formula:
f=Number of pole pairs×RPM60f = \frac{\text{Number of pole pairs} \times \text{RPM}}{60}f=60Number of pole pairs×RPM
Solve for RPM:
RPM=f×60Number of pole pairs\text{RPM} = \frac{f \times 60}{\text{Number of pole pairs}}RPM=Number of pole pairsf×60
If you know f=48 Hzf = 48 \, \text{Hz}f=48Hz and have 48 pole pairs:
RPM=48×6048=60 RPM\text{RPM} = \frac{48 \times 60}{48} = 60 \, \text{RPM}RPM=4848×60=60RPM
User: I have taken measurements of my PMA and a 3-phase delta wired coil configuration in an open-circuit setting. I forgot to also measure the VDC after full rectification initially, which is why not all rows have the VDC column populated. Can you find any anomalies in this data?
Assistant:
You’ve provided a set of measurements for various frequencies, RPMs, line-to-line VAC, and in some cases VDC after full-bridge rectification. The data appears as follows (using an example table structure):
Frequency (Hz) | RPM | VAC (line-to-line) | VDC (after full rect) |
---|---|---|---|
9.646 | 12.0575 | 9.688 | (not measured) |
12.08 | 15.1 | 11.78 | 14.5 |
20.03 | 25.0375 | 20.02 | (not measured) |
39.3 | 49.125 | 39.73 | (not measured) |
42.58 | 53.225 | 43.03 | 55.2 |
- Frequency and RPM relationship:
With a fixed number of pole pairs, the frequency is directly proportional to RPM. The given frequencies and RPM values match perfectly with the earlier formula. For example:- At ~9.646 Hz and assuming 48 pole pairs: RPM≈9.646×6048≈12.06 RPM\text{RPM} \approx \frac{9.646 \times 60}{48} \approx 12.06 \text{ RPM}RPM≈489.646×60≈12.06 RPM The measured RPM is 12.0575, which is spot-on.
- Checking another point (e.g., 42.58 Hz):
Matches exactly with the measured value.
So, no anomalies here. The frequency-to-RPM data is perfectly consistent. - Line-to-line VAC scaling with speed (and frequency):
The line-to-line VAC should scale roughly linearly with rotational speed under no-load conditions. Checking a progression:- At 12.08 Hz (15.1 RPM): 11.78 VAC
- At 20.03 Hz (25.0375 RPM): 20.02 VAC
The ratio of frequencies (20.03/12.08 ≈ 1.66) matches the ratio of voltages (20.02/11.78 ≈ 1.70), which is close enough to show a near-linear relationship. - Similarly, doubling from ~20 Hz to ~40 Hz nearly doubles the VAC from ~20 V to ~40 V. This is again consistent and expected.
- VDC after full-bridge rectification:
The DC voltage after a three-phase full-bridge rectifier at no load can be approximated by:
VDC≈VL−L,RMS×2−diode dropsV_{DC} \approx V_{L-L,\text{RMS}} \times \sqrt{2} - \text{diode drops}VDC≈VL−L,RMS×2