Body
Hi Mick,
The resonant frequency is given by the circuit parameters. If the iron core saturates most of the inductance vanishes which increases the resonant frequency. How fast the coil is demagnetized determines the peak voltage of the flyback pulse at a given current and inductance. The product of the voltage and time is the same for the input and output pulses when the circuit parameters aren't changed. Thus an output pulse of one tenth the length of the input pulse gives ten times as high peak voltage of the flyback pulse. The secondary then transforms that voltage by the ratio of the number of turns between the primary and secondary coils. For a tesla coil this ratio has to be calculated like for a transmission line transformer. I don't think transmission line theory is strictly necessary for calculating the output voltage of an iron cored induction coil. Use the formulas for normal transformers. A capacitor is placed across the switch to limit the flyback voltage peak to a safe value for the switch. If using a power MOSFETs as switch the MOSFET probably goes into avalanche mode without this snubber capacitor. A mechanical switch will just arc across the contact points without the capacitor. What is seen as ferro resonance could be an avalanche (breakdown) through the MOSFET. This happens very fast just like ferro resonance. It may degrade the MOSFET to give it a shorter life.
How fast the coil can be demagnetized depends on its parasitic capacitance and the load of the coil. A totally open circuited coil without any capacitance will demagnetize immediately and thus induce an infinitely high voltage. Such ideal coils doesn't exist as even vacuum has a dielectric constant. Thus parasitic capacitance is formed between neighboring turns which dampens the voltage. I.e. the energy is converted from magnetic field energy to electric field energy.
The induced high voltage of the secondary coil creates an electric field between the output terminals. If close to the earth or any metal parts the field will charge those parts even through a vacuum. If the distance isn't great enough the field will punch through and discharge the field. Else the energy is stored as an electric field around the coil and in the dielectric material between the windings. When the windings share a common connection between the primary and secondary coils the electric field has to be stored on the outside of the induction coil. Metal parts close by may get charged and discharge to the air by ionization or to persons touching them. Thus be careful when experimenting with high voltages. Everything is coupled by the capacitance between them.
Regards
Ole
---In [email protected], <mkjekyll@...> wrote :
Warren,
The earth spike seems to work weather or not there is a ferroresonance signature on the coil waveforme, just a whole lot better when there is.
Therefore the frequency become speculative as to what resonance one is working with, be in the spark gap or the modulation or the beat frequencies.
I think a wideband approach of filling some caps from a spark gap or plasma tube as fast as they can be discharged is the ticket. This is where the experiment becomes costly as the high voltage multi mF caps are not cheap.
In the Colorado notes Tesla has an extra coil in his Magnifying transmitter that no one seems to understand what he was doing with it. I propose this is the ferroresonant modulator.
A less costly way to harves is by PF correcting the energy to work in a transformer so the field requires much research and moving slow in order not to burn up parts