Running older induction motors on VFDs

[Guineafowl]

First find the A_L value for the core.
Wind a test coil of say 10 or 20 turns, then measure the inductance.
A_L = uH / turns².
uH = A_L * turns².
While measuring A_L, use a test frequency closest to the intended operating frequency of the inductor.
Solve for the number of turns needed to get the required inductance.
Select a wire size with sufficient ampacity. I use 5A / mm².
Check that you can pass the required number of turns through the toroid.

Avoid thick plastic wire, it gets hot and melts. Use magnet wire. Find an old transformer and salvage what you need.

Experiment while measuring A_L. Place two cores flat against each other, then wind the test coil through both. That doubles the magnetic section available, so may reduce the chances of saturation. Let us know what A_L values you get.


If possible, switch the probes to x10, then neutralise them to show a square wave while the probe is connected to the probe adjust terminal on the front panel.

Thanks - I’ll get on with building the inductors when I get a chance.

I have adjusted the probes using the CAL terminal, and they were on x10 for that picture.

 

[Guineafowl]

I found some 1 mm$^2$ magnet wire. My LCR meter (actually an ESR meter with L as a side function) is quite limited, so I ended up with 5 turns around the Mn-Zn toroid giving 196 $\mu$H and so $A_L = 7.84$

28 turns was all I could fit, and certainly highlighted my carpal tunnel syndrome, but should give around 6 mH. I’ll report back after scoping.

 

[Baluncore]

28 turns was all I could fit, and certainly highlighted my carpal tunnel syndrome, ...

How to wind a coil faster, and more safely, with less pain. Get a nerve conduction study to confirm CT. If CT get the surgery. If RSI is not CT, notice if it is less during the day after NCS. If so, you can test it by holding an electric fence in that hand, a traditional farmer's remedy for RSI, treated every morning, before the milking. If that relieves the pain for a day, you have a chemical neurological problem, maybe a small part of long covid, or similar. Then, if you still need to wind coils, evaluate a low-dose SSRI, which has the same effect on neurotransmitters as does the electric fence, but is less shocking. Invest in your neurological and coil winding future by getting your B12 checked, as neuropathy is a longer term co-symptom. This is coil winding advice, if you need medical advice, consult a doctor (of medicine). That way you can wind more turns, through smaller cores, to get square-law higher inductance, all without the pain.