Tesla's "COIL FOR ELECTRO-MAGNETS".

[Farmhand]

Mags did you do a test for a short using the continuity function ? Distractions and fatigue can get the better of anyone, temporarily. If something doesn't seem right it probably isn't.

Cheers

[gyulasun]

The coils capacitance is 6.7nf with one meter and 7nf with another. Not sure why.
...

Hi Mags,

You may wish to check the two C meters with a 5.6 nF (or 10 nF) normal capacitor and compare the two values, of course you may have done so?
Also, if you check the measuring frequencies of the C meters with a scope when you measure say an 5.6 nF capacitor with them: perhaps the differing measuring frequencies could also explain the difference.

Gyula

[conradelektro]

I managed to do the first "speed up under load" test, please see the video at

http://www.youtube.com/watch?v=vAXQBpuLu68&feature=youtu.be (Please read the video info.)

The more the rotor speed goes away from the resonance frequency of about 52 Hz (lower or higher) the more the "speed up under load" diminishes.

25 Hz , no load, motor consumption 2.0 V and 0.82 A
            load, motor consumption 2.0 V and 0.91 A, speed drops to 23 Hz

52 Hz, no load, motor consumption 4.4 V and 1.7 A
           load, motor consumption 4.4. V and 1.09 A, speed rises to 68 Hz (the magic happens)

110 Hz, no load, motor consumption 6.4 V and 1.06 A
             load, motor consumption 6.4 V and 1.06 A, speed stays at 110 Hz

Please comment and make suggestion for further tests and scope shots. (I will test air core and monofilar, but would like some discussion before I go on, I might do something wrong.)

@MileHigh: thank you again for the help, finally I managed an interesting test. The 12 V DC motor was a great idea. The motor made it simple to build a versatile and stable magnet spinner. I have nor problem with posters who do not do experiments as long as the posts are helpful and state important principles and facts. Posters with relevant knowledge are very rare.

Greetings, Conrad

[gyulasun]

Hi Conrad,

Thanks for your efforts and kind words, very good work! 

As I mentioned in the first few lines of my earlier post ( http://www.overunity.com/13460/teslas-coil-for-electro-magnets/msg383401/#msg383401 ) I suspect the bolt as a core may "trick" the LC circuit by changing its magnetic properties as the AC current inside the tank changes: first when the magnet gets near to the bolt and then starts spinning and second when the 100 Ohm load is attached.  (Perhaps it would be good to check the coil inductance when the magnet is stationary in front of the bolt and the 10 uF cap is disconnected, with both magnet polarity.)

This is why a normal ferrite core would be ALSO good to use, and when you have such (I gave a link to obtain it in my earlier post), then you would  insert it into the coil to have the same resonance what the bolt gave in the unloaded case.
I mention this because the bolt core may "trick the circuit because when you attached the 100 Ohm load, the phase relationship between the current and the voltage in the tank changed from the nearly 90° to almost  180° out of phase.  I suspect this phase shift happens due to the permeability change in the bolt due to the much less current amplitude in the tank: in the unloaded case the tank current is 108 mA and in the loaded case it is 56 mA.

I believe the effect of this change in the excitation current would not influence a ferrite core's permeability as much. I mainly consider here the eddy current losses in the bolt: it increases when excitation is increased and vice versa.

You may have noticed that the voltage amplitude across the tank decreased to a too low value (from 31.2 V rms to 4.8 V rms) when you attached the 100 Ohm load: if the load is matched to the generator, then the loaded output voltage may have half the value of the unloaded output, in this case it should be around 15.5 V instead of the measured 4.8 V. This may indicate that the inductive reactance of the coil changes as per the excitation i.e. by the AC current magnitude in the tank, hence influencing the Quality factor of the coil, hence influencing the generator output impedance. 

Perhaps you happen to have a 470 or 1000 or even a 2200 Ohm variable resistor, either a trimmer or a normal potmeter and you may wish to use it instead of the fix 100 Ohm to adjust the 15.5 V AC rms across the tank and also slightly adjust the motor speed to reastablish the best resonance (because the changing load affects the core magnetic properties).

So it is very good you show the tests with the bolt core. 

Greetings,  Gyula

[conradelektro]

I did some more tests with one wire only (still the steel bolt as core).

wires in parallel, mild steel core  (DC resistance 20 Ohm)

110 Hz, no load, motor consumption 7.3 V and 1.79 A
              load, motor consumption 7.3 V and 1.06 A, speed rises to 130 Hz


only thicker wire, mild steel core (other wire open, DC resistance 27 Ohm)

110 Hz, no load, motor consumption 7.1 V and 1.64 A
              load, motor consumption 7.1 V and 1.01 A, speed rises to 126 Hz


only thinner wire, mild steel core (other wire open, DC resistance 70 Ohm)

100 Hz, no load, motor consumption 6.5 V and 1.44 A
              load, motor consumption 6.5 V and 1.1 A, speed rises to 113 Hz


It look s like the DC resistance of the wire has an influence?

I will proceed to tests with air core. I have a Ferrite rod which just does not fit into the hole of the coil. I will try to widen the hole a little bit. But I do not want to do that till I have enough measurements with air core and steel bolt core (the coil might be damaged when manhandling it).

Greetings, Conrad