Self running coil?

[skywatcher]

Now i have 2 different coils (one with 315 mH (1 layer), the other with 2480 mH (3 layers) combined inductance).

But i'm not able to replicate any of the interesting effects.   

There is no clearly visible resonant frequency. I tried it with frequencies from 100 Hz up to more than 100 kHz. I looked at the voltage measured across one half of the coil. It changes it's shape (sometimes it's more rectangular, sometimes it looks more than one half of a sine wave) and it changes also its magnitude but only slightly.

The voltage measured across the 1 ohm resistor is generally very low. With 5 mV/div resolution of my scope i can barely see any differences.

Also the magnet has no visible effects. It reduces the inductance only slightly (about half the value measured without magnet) although it's a very strong neo magnet (N48, 10 mm diameter x 10 mm).

Maybe the ferrite core is not suitable to see the effects. I don't know. But i'm not motivated to make dozens of new coils with other cores to try this out.   

[LightRider]

Now i have 2 different coils (one with 315 mH (1 layer), the other with 2480 mH (3 layers) combined inductance).

But i'm not able to replicate any of the interesting effects.   

There is no clearly visible resonant frequency. I tried it with frequencies from 100 Hz up to more than 100 kHz. I looked at the voltage measured across one half of the coil. It changes it's shape (sometimes it's more rectangular, sometimes it looks more than one half of a sine wave) and it changes also its magnitude but only slightly.

The voltage measured across the 1 ohm resistor is generally very low. With 5 mV/div resolution of my scope i can barely see any differences.

Also the magnet has no visible effects. It reduces the inductance only slightly (about half the value measured without magnet) although it's a very strong neo magnet (N48, 10 mm diameter x 10 mm).

Maybe the ferrite core is not suitable to see the effects. I don't know. But i'm not motivated to make dozens of new coils with other cores to try this out.   

Similar result on my side 
LightRider

[gyulasun]

Hi Skywatcher,

Here is what I would do:

use the 315mH coil

Try to use 25V DC supply or so (because your BUZ11 has an output capacitance of 750pF at Vds=25V

Give 10.5kHz input pulse frequency to the gate source from your freq source because the 315mH resonates with the 750pF about that frequency, see: http://www.whatcircuits.com/lc-resonance-frequency-calculator/
and data sheet for your FET: http://skory.gylcomp.hu/alkatresz/buz11.pdf

Of course you wish to sweep the frequency up and down near the 10kHZ frequency because there is no garantie for your FET to have just 750pF at 25V.

You may repeat this procedure with the other coil, just use the near correct values. If you do not have a variable power supply, use one or two batteries in series and estimate the output capacitance from the data sheet, (C_oss in Fig. 10).

EDIT: With the magnets on, you have to measure the mH value of the coil to bring the circuit readily into resonance. Otherwise, much trial and error as Luc found.

rgds, Gyula

EDIT: if you measure with the scope between the drain source, you have to see amplitude increase at or near resonance, together with the waveform becoming nearly sinusoidal (input is square wave).

[skywatcher]

My cap (120000 uF) is only rated 15 V. So i can not go up to 25 V with this one.

I have found a 33 uF film cap (250 V). Maybe i can try this one.

[NextGen67]

@Gyula,

Send you a PM again.. you should see it :-)

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NextGen67