Tesla's "COIL FOR ELECTRO-MAGNETS".

[conradelektro]

I just did something for training:

The "1/2 Voltage, impedance comparison to a known resistor" to determine inductance of a coil, according to http://daycounter.com/Articles/How-To-Measure-Inductance.phtml.

And, the impedance of the pan cake coils comes out as 34 µH (as it should).

See the attached drawings and scope shots.

I used Voltage "peak to peak" instead of RMS because it is easier to see on the scope. Is that good?

Greetings, Conrad

[synchro1]

"In this study, we combined an array of giant magnetoresistive (GMR) sensors with an array of Hall sensors to measure all three components of magnetic vectors with a high spatial resolution and visualize the magnetic field distribution on a 2-D plane. The sensors were arrayed in a matrix arrangement such that the limitation to the number of sensors could be overcome. To test the device, "we generated a magnetic field using a pancake-type magnetizer" and a cracked magnetized ferromagnetic specimen and imaged the vectors. We obtained a spatial resolution of 0.78 mm in the z-direction with 1024 Hall sensors and 2.34 mm in the x-direction with 100 GMR sensors. Moreover, the x and z components could be imaged at 6 fps. The proposed device is promising for application in magnetic flux leakage detection".

Additional fact about the Pancake Magnetizer coil:

"It is well known that the inductance of a pancake type coil put on the metallic specimen changes according to the electromagnetic properties of the metallic specimen"


It's possible to run DC current through Leedskalnin's PMH and get zero magnetic effect!

[gyulasun]

Hi Conrad,

Okay on your probes, then you have choices on their input capacitance 'selection' but then the 1:10 or 1:100 choices influence the amplitude sensitivity of the measurements of course what you should compensate either by increasing the generator output or choosing the most sensitive scope input range and both of these have limits.

Regarding your observation on the low indication sensitivity of the series LC measuring setup, it happens because the two 50 Ohm resistances in the circuit reduces very much the natural quality factor, Q of the LC circuit (50 Ohm from the generator and another 50 Ohm from the R resistance (where you also used 1 kOhm), alltogether a 100 Ohm shunts the series LC tank, ok?

Because in this measuring setup, the output resistance (impedance) of the generator adds in series with the series LC circuit, effectively increasing the loss resistance of the series LC tank,  ideally a generator resistance (impedance) of much less than 50 Ohm would be needed, preferably near to 1 Ohm or leven less but such a low generator output impedance can be had for instance from amplifiers designed for low output impedance.
OF course, alternative solutions do exist, see this link http://www.circuitstoday.com/q-meter where a 0.02 Ohm is connected in series with the coil to measure its natural Q and in that circuit a function generator can substitute the oscillator, no need for the thermocouple voltmeter either and at the output your probe with a series 1 pF would serve as the resonance voltage indicator and the C resonating capacitor would be your 10 nF or any other even some 10 pF capacitor value. You would terminate the gen output with a 50 Ohm resistor and connect say a 0.1 Ohm  non-wire-wound resistor in series with it to drive the coil, that is all. You may wonder whether this is a series or a parallel LC? from the generator output point of view it is a series LC where you check voltage maximum across the tank capacitor.


By your choosing a tank capacitor of 10 nF i.e. in the some nanoFarad range, this simply masks any detuning effect of
any probe capacitance or coil self capacitance they would otherwise manifest, as you found such manifestation earlier in the lack of the 1 pF coupling capacitor.

...
I used Voltage "peak to peak" instead of RMS because it is easier to see on the scope. Is that good?
...

In this case it is good because their ratio is the same as it comes out from their rms value ratio, ok?

Greetings,  Gyula

[Farmhand]

Conrad, can you please give us a break down of the results of the series  test as compared to the parallel test, what is the difference if any ? Is the series resonant frequency of the bifilar coil lower than the series resonant frequency of the monofilar coil ? Is it the same as the parallel resonant frequency ?

I must say Conrad with the very good assistance you are getting you have gained some impressive results, I'm not sure I need to continue with such small coils.

Here is a thought Conrad, to test my theory that the applied voltage can vary the extra capacitance secured by the bifilar coil or any coil I guess, I intend to make a bifilar coil with the turns spaced so that with only a few volts or the meter used shows the capacitance secured between the two open windings is less than when they are wound closer together, thicker insulation more plate gap in the capacitor.

That will allow me to attempt to get a resonant frequency with only the few volts with the increased "plate gap", then also to get a resonant frequency with a higher voltage that should secure a higher capacitance between turns and therefore a lower resonant frequency of the coil for a higher applied voltage, within limits. If the gap that makes the capacitor is too wide for the applied voltage the capacitance secured should be less, just like if the plates of a capacitor are brought closer the capacitance reading increases. A parallel plate capacitor with a plate gap of 10 mm will give less capacitance secured in practice when only charged with 1 volt than when charged with 1000 volts, is what I am imagining to describe an extreme. If I'm right or wrong is another matter.

It might help if I learn how the meter works.

Cheers

[Magluvin]

Decided to go a different route with winding the 2in bifi.  I have a few bobbins of the same wire 42awg that the wire broke before finishing the wind on my Lasersaber ez spin motor . Sooo, I can use those to wind a bifi ez spin coil. This way Im already set up to test comparable coils with the motor also. Been wanting to do this anyways. For some reason I feel a bit inspired. And it wont take as long to wind and should work as a good comparison test of normal vs bifi.

The coils are just over 3000 turns, 650ohm, 81mh single strand.  About 450 ft of wire, of which should give me decent capacitance. Compared to some other coils I have made, I guestimate near 50nf.  Which is around 2500hz. My ez motor running near 400rpm can feed a bifi with just over 4kz with all coils in series using the least amount of current. 24 NSNS mags on the rotor, 12 full cycles per rotation. The motor is a torque'y lil monster with all coils in parallel at 27ohms. I have to remake the rotor to run it like that so the magnets dont become projectiles. Havnt let it go to full speed. Was scared.

For me, it pays to think before I do. To test the 2in coil with a motor, I would have to make a rotor that has mag spacing according to the coil width. But the ez is set up so that a N mag is approaching the coil while the S mag is departing. So output is a nice sinewave where the coils are always being induced by the mags while the rotor turns. Perfect to operate the bifi, I can get the rotor to go much faster running just one of the drive coils. More current, as compared to 24 coils in series, 15kohm vs 1 coil 650ohm. So no doubts the motor will be able to hit the bifi resonance even if my capacitance doesnt reach my estimate. And other comparison tests can be done.

Mags