(05-09-2023, 05:47 AM)tihomir Wrote: Nice setup.

The coil I'm using is from an old (30 years) power cable that has two wires which are not twisted. A spool of speaker cable would be a similar thing. It has mass which is important, because Tesla said that his experiments had better results when there was more mass (in terms of wire size). I still think that coils like yours and mine can provide much more than we are currently seeing.

As for the skin effect: Tesla said that this happens mostly at high frequencies which we are not employing in those setups. What is interesting to me is that I can't produce back-EMF from such coils at higher frequencies. I've managed to get some at a few kilocycles, but not faster. There are spikes at higher frequencies, but they are much smaller and I don't know if they produce any gain.

(05-10-2023, 09:57 AM)tihomir Wrote: That's gotta be the right interpretation. I measured the inductance of my coil and if the meter is correct (a multimeter with an inductance measuring option), it's 2.15 mH which is about the same ballpark — 730 Hz. Smaller capacitors will give me lower current. Smaller coils will give me lower voltage spikes, but at higher frequency. Not sure which outweights the other yet. I have to measure with the same capacitor but a different coil and vice versa.

I still haven't been able to run something more significant. I tried with a capacitor bank, but it's too small to loop the power back. I'll try with a battery.

(05-14-2023, 08:10 AM)tihomir Wrote: I think the duty cycle is a very important feature. Let me share my experiment. I'm just cap dumping into a primary coil of a Tesla transformer.

My coil is 31 uH, the capacitor is a 400 V 22 uF. That gives me a resonant frequency of 1.9 kHz. My SCR cap dump is using a neon lamp (100 V) for the trigger.

I set my function generator to 50% and at a high frequency (11 KHz) and the capacitor did not charge, because the spikes were not very high voltage. I lowered the frequency and the capacitor quickly charged, but once the dump was initiated I was not able to get the SCR to turn off, because current was always flowing in. I had to short the capacitor out so the SCR gets closed. If I did not, current was alwaysing flowing in from my DC power supply (that was set to 6 V, 20 mA limit and at that moment it was drawing 20 mA at 1.5 V, almost like a short circuit case). I don't know if it's the SCR (some 800 V one) or the frequency or the capacitor, but at 50% duty cycle I was not able to get it working at any frequency (tried up to 1 MHz).

I changed the capacitor with a 200 nF non-eelctrolytic one and I was able to make it work at 23 KHz at 50% duty cycle, but the cap dump was very slow - 11 Hz and a lot of power has been drawn - 1.3 V at 20 mA (26 mW). I changed the duty cycle to 8%, the cap dumps' frequency was the same (11 times a second), but the power consumption was 6 V at 2 mA (12 mW). Mostly voltage, as it should. The power consumption is just from the DC power supply. I'm not including the frequency generator in the calculation.

With that I just wanted to note the importance of the duty cycle. I guess that a 50% duty cycle would work fine with smaller caps, but not smaller coils because they won't give you enough voltage spikes to charge a capacitor up to 100 V. This means you'll probably need to trigger it with a Zenner diode. I tried to connect it to the base of the SCR (just like the neon lamp) and it did not seem to work as expected though (I only have a 5 V one). I don't have much time to experiment right now in order to find out the reason.

(05-14-2023, 09:47 PM)tihomir Wrote: I have managed to find the problem. It was a wrong connection on the breadboard. Now it oscillates with a backward-connected transistor (without the base, which in my case is a 15 V threshold) or with a Zenner diode (5 V) at 50% duty cycle at the 5 MHz range. The DC power supply shows 5 V at 20 mA which means it eats all the current I'm giving it.

BTW: Is it possible to create an oscillator with a short duty cycle without using a 555 timer or any other IC component? Just basic components. I don't think the flyback oscillator circuits use a short duty cycle, because they oscillate, they don't create pulses.
(end of BTW)

(05-14-2023, 10:27 PM)JoeLag Wrote: Maybe you can use a transistor astable multivibrator circuit. This circuit uses two transistors (Q1 and Q2) to create an oscillation.
To achieve a short duty cycle, you can increase  and decrease the value of Rs. You can also increase and decrease the values of Cs. These changes will result in a shorter on-time and a longer off-time, which will give you a shorter duty cycle. Maybe look online for a basic circuit diagram and play with the values.