Some tests on mono and bifilar coils

[gyulasun]

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When varying the 1 K Ohm pot from "1 K Ohm" to "short circuit" the measurements gradually change between the two extremes noted in the drawing.
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Hi Conrad,

I would like to comment your test results of the series LC circuit magnet spinner. If we assume the 90 Hz was indeed the resonant frequency of the LC circuit, then the AC voltage amplitudes across the coil and across the capacitor should have been the same or at least very nearly the same. But in your upper test setup in your drawing with your 1 kOhm resistor inserted, you measured 13.2 V across the coil and 2V across the 10 uF, unless the 2 V is a simply typo?  When you used the short instead of the 1 kOhm, the AC voltages across the coil and the capacitor were pretty much the same values as they should at resonance.

If the 2 V is not a typo, then something is not okay (it is not only very low but does not change by sweeping below or above the 90 Hz?)  One thing is sure: with the 1 kOhm resistor inserted the circulating AC current in the series tank should be much less than with the short in place, this may indicate that at a certain high enough current via the coil the ferromagnetic core changes its permeability (perhaps it starts saturating), this would also explain the less than 357 mH coil behaviour in your earlier tests as I indicated in my previous post.

In the setup shown in the lower drawing (when your CH2 probe is across the 1 kOhm resistor) the circulating current is 13.2 mA only (13.2 V/1000 Ohm). When the short is used in place of the 1 kOhm the current is about 26.4 V/X_L and now X_L must be about 176.8 Ohm which gives 312.7 mH inductance at 90 Hz with the 10 uF capacitor (X_C should also be 176.8 Ohm at 90 Hz of course).  So the circulating current in this case is about 149.3 mA, more than 11 times higher than with the 1 kOhm in place. This higher current may create a nonlinear core behaviour even if there is no closed magnetic circuit for the core.

Thanks for the capacitor impedance measurements, very good values your meter shows because from normal calculations it also comes that a 10.083 uF capacitor has 157.84 Ohm reactance at 100 Hz, 15.78 Ohm at 1 kHz and 1.58 Ohm at 10 kHz frequency. Please notice that the Z impedance is actually the X_C capacitive reactance of the capacitor (and I assume that for coils the Z impedance is the series combination of the inductance and the coil's DC resistance i.e. the square root of (X^_L2 + R²). Of course when the R value is only a few Ohms with respect to the coil reactance, then the impedance is pretty close to that of the coil's inductive reactance.
The Q is also correctly shown by your meter for the 10 uF capacitor, at least for the lower frequencies but in fact I have no reason to suppose that the Q is not correct at 10 kHz);  Q surely comes from the ESR value of the capacitor and assuming that Z nearly equals X_C (because ESR is much less than X_C at the lower frequencies), so Q=Z/ESR  i.e. say at 100 Hz Q comes out as Q=157.84/0.33=478.3 and the meter showed 480, very close.  Your 10 uF capacitor does not show good Q at 10 kHz, even though its ESR improves a lot from the low frequency values (from 0.33 Ohm to 0.06 Ohm) but the capacitive reactance also reduces as the frequency increases.
If you have questions on this or on my previous post, please ask.

Gyula

[Farmhand]

Conrad I beg to differ only because the motors are designed for 240 volts but will be used well below that and the power draw of this little universal motor is quite low with 30 volts and a small load, better than the motor I used to show a very pronounced speed up under load effect previously.

Anyway I think I changed my mind and want to build a permanent magnet two phase generator/exciter instead. Will be very useful for some experiments. With two phases I can make four ect.

Cheers

[conradelektro]

If the 2 V is not a typo, then something is not okay (it is not only very low but does not change by sweeping below or above the 90 Hz?)  One thing is sure: with the 1 kOhm resistor inserted the circulating AC current in the series tank should be much less than with the short in place, this may indicate that at a certain high enough current via the coil the ferromagnetic core changes its permeability (perhaps it starts saturating), this would also explain the less than 357 mH coil behaviour in your earlier tests as I indicated in my previous post.

@Gyula: as I recall, I looked several times at the 2 V rms Voltage and was puzzled. But I have to redo it next week and some more tests are necessary to solve that strange behaviour.

I might try with an air core and a 20 µF cap (two 10 µF caps in parallel). And I will try the experiments with a 1:1 transformer between the function generator and a band pass filter or notch filter as mentioned by MileHigh http://www.overunity.com/14235/some-tests-on-mono-and-bifilar-coils/msg385592/#msg385592

Thank you for demonstrating the various calculations, that teaches me a lot. I am looking up these formulas and the related theory on the internet and take notes. I hope to eventually learn these very important basic concepts. I also got some books.

Electrical engineering always attracted me, as a kid I built simple radios and amplifiers with valves and I always did the electrical installations in my home. But there were other things in my live which became more important (mathematics, computer science, legislation). But since I have retired I can follow up on this hobby. The astonishing thing for me is that the equipment (oscilloscope, function generator and good meters) has become relatively inexpensive (in comparison to 40 years ago) because it is all little computers now. Of course, if one wants to go into the Giga-Hertz region of the modern computers it would become very expensive again. But nobody repairs electronic equipment nowadays, it is thrown away and replaced. And it is virtually impossible to build something in the Giga-Hertz at home.

Greetings, Conrad

[synchro1]

I proved "The Old Scientist" wrong! Both the single wire coil and SBC of same wire length and gauge have identical Ohmic resistance. The results appear to be too banal to upload a video.

[Farmhand]

I proved "The Old Scientist" wrong! Both the single wire coil and SBC of same wire length and gauge have identical Ohmic resistance. The results appear to be too banal to upload a video.

Two identical pieces of wire under the same conditions having the same Ohmic resistance is a self evident truth or an axiom, it needs no proving.

Cheers