Mags that will get the frequency down no doubt, I'm considering winding some spirals, I've never wound a spiral for a particular reason, I'm thinking I will make them physically as large as is practical for me, and able to take fairly high voltages. Looking forward to all results, it is interesting stuff.

If it wasn't for the high frequencies of the Tesla coil setups and the large inductive field around the coils I would try to measure the voltages and currents in the setup at different states of tune.

I have no choice but to keep my experiments to bench sized arrangements for a while yet.

..

The description of the operation of the series LC circut.

So the setup is: function generator  -> capacitor -> coil  -> load resistor -> ground.  The function generator is outputting a sine wave at the resonance frequency.

We will just look a few "pieces" or datum points of the circuit, enough information so that if you wanted you could connect the dots and draw out a timing diagram.  If you draw out the timing diagram you will see all the pieces fit together and it should all make sense.  All that you need to know are a few basic facts about circuit analysis and how coils and capacitors work.

The first point to consider is deceptively simple:  If there is no resistance then the voltage output by the function generator must also be seen by the load resistor.  It simply has to be the case.

You can reword that like this:   The voltage output by the function generator plus the voltage across the capacitor plus the voltage across the coil is also the voltage that is seen at the load resistor.  It's almost like the voltage across the capacitor plus the voltage across the coil is always equal to zero.  Like those two components almost disappear.

Likewise, the current through the circuit is directly proportional to the function generator voltage.  It has to be the case, there is no other choice.

I am assuming that people understand how the voltages and currents work for capacitors and coils.

Now for some datum points:

What's happening when the function generator voltage is at it's peak?  We know that current must be the maximum.  Just as importantly we know that at the voltage peak the current is unchanging.  There is "micro spot" at the top of the sine wave peak where the voltage is constant and unchanging, therefore the current has to be unchanging.

Continued in part 2....

Part 2:

For coils we know that if the current is unchanging, then the voltage has to be zero, there is no other choice.
For capacitors we know that if the current flow is at maximum, the the voltage must be zero, there is no other choice.

So you can see that we have generated two datum points:

1 and 2:  At the top (and bottom) of the function generator sine wave, the voltage on the coil is zero, and the voltage on the capacitor is zero, there is no other choice.  (Note that this all works out, no voltage drops so the function generator voltage is seen at the load resistor, no other choice.)

Now let's consider when the output of the function generator is zero and rising.  We also know that the voltage is rising at the fastest rate of change here.  That means the current is also changing at it's fastest rate of change.

One more datum point:

With the fastest rate of change of increasing current, we know that the voltage across the inductor has to be at a maximum.  No choice, the coil puts a constraint on the voltage and fixes it at the maximum.

So look at this unique situation:  The voltage output from the function generator is zero.  But there is a maximum voltage across the coil, but we know that the voltage at the load resistor must also be zero.  There is only one solution to resolve this:  The voltage on the capacitor must be at an equal and opposite voltage as compared to the coil.  So there is the other datum point.

Then of course we know that if the capacitor is at a maximum voltage, that means it's fully charged to its maximum charge.

So what you end up with is this:  As the function generator outputs a sine wave at the resonant frequency, the coil and capacitor are in a kind of "voltage tug of war" that is a pair of pure and opposite sine waves, because when coils resonate with capacitors by definition you get sine waves for the current and voltage.  Note that the function generator output is also a perfect sine wave.   So you have a double resonating sine wave interaction with a sine wave from the function generator.  It's like the resonant part of the circuit and the function generator are two people that are perfect dance partners that dance together very closely in harmony but they never touch or disturb each other.  The male makes a move and the female moves perfectly in tandem and they never actually touch.

Sorry that was too long.  But there is enough information there to construct a full timing diagram:

Function generator voltage and current  (identical waveforms for the load resistor)
Coil voltage
Inductor voltage
Coil Energy
Inductor Energy
Coil + Inductor energy

Now if you are crazy enough to take the plunge, and you build a timing diagram starting from the few data points given, you should find that the waveform for the (Coil + inductor energy) is a flat line.  The flat line is telling you that the coil and capacitor are acting like an LC resonator with a fixed amount of stored energy.

So what that means is that when you first power up your series LC resonator circuit, the LC resonator portion of the circuit quickly fills up with energy drawn from the function generator.  Once the LC resonator is full, it becomes a kind of "pumping station" that is synchronous with the function generator waveform such that it effectively disappears.

MileHigh

Quote from: Farmhand on January 14, 2014, 09:16:33 PM
Mags that will get the frequency down no doubt, I'm considering winding some spirals, I've never wound a spiral for a particular reason, I'm thinking I will make them physically as large as is practical for me, and able to take fairly high voltages. Looking forward to all results, it is interesting stuff.

If it wasn't for the high frequencies of the Tesla coil setups and the large inductive field around the coils I would try to measure the voltages and currents in the setup at different states of tune.

I have no choice but to keep my experiments to bench sized arrangements for a while yet.

..

Hey farmhand

Yes. Bench size for me too. I try to maintain things to desktop sizes.

This 3000 turn bifi is about the dimensions of 2 nickles. Wire only. Got 55000 ft for 35 bucks a while back. I cracked open a RS reed relay, 1000 some ohm, and the coil popped out like a can of snakes. Scared me. lol  But that wire must be like in the 50awg compared to the 42. My hair is just a bit thicker than the 42 under a microscope. But man you can produce some strong mag fields with all that resistance and very low currents. Neat to work with.

Mags

About lowering the resonating frequency:

That's a good strategy because if you work on the bench your "comfort zone" might be between say DC and less than one megahertz.  With those frequencies stray capacitive effects and the low-pass filtering inherent in everything doesn't come into play.  By low "low-pass filtering" I mean your square waves start to get all rounded and mushy.  Likewise at lower frequencies even touching a component with your fingertip will only marginally disturb the circuit so you won't really notice it.  Perhaps for a finger tip touch having no significant effects lower the upper frequency limit to 100 KHz.  You can experiment and check those things for yourselves.

Also, try to sick to capacitor values of one microfarard or larger.  Picofarad caps store pico amounts of energy.  Note a picofarad is one millionth of a microfarad.

You can see when Conrad just brought his hand near the bifilar coil things started changing on his scope display.  That's akin to doing circuit investigations in a kind of mushy and spongy environment.  Most or all of the effects you might be interested in investigating will still take place at lower, more manageable frequencies.

Where of course you do make a change is you use a real capacitor that is always there as opposed to the inter-filar capacitance.  However, just in looking at self-resonance of a coil, there is the voltage sine wave.  So the current sine wave has to be there also.  For a monofilar coil you could envision each end of the floating coil at the voltage peak.  There will be an electric field outside the coil that goes from the top to the bottom almost looking like magnetic field lines.  The monofilar will reach higher absolute voltages at each end relative to the bifilar because the measured capacitance is lower.  For the the bifilar you assume that much more electric field energy is stored in the spaces between adjacent windings.

The extra energy storage capacity in the bifilar and the high voltage capability sound interesting at first glance.  However, you have to remember for both cases, regular and bifilar, the source of the energy to charge the capacitance comes from the inductive energy.  Both the regular and bifilar coil store the same amount of inductive energy.  The source for putting energy into the monofilar or bifilar capacitance is identical.  So what's the high voltage between windings getting you if the source of the energy is the same?

In that sense, the regular and the bifilar self-capacitance act as the "catcher's mitt" to receive the energy thrown at it from the inductance, or inductive energy to be more precise.

In both cases, the capacitive "catcher's mitt" is so tiny that the energy is caught, and the "pressure" in the mitt goes super high for a tiny tiny fraction of a second before the energy is spat back at the inductor.

To mix analogies, you have a humongous elephant hurling a ton of energy.  On receiving end to catch the energy you have too tiny tiny catcher's mitts.   If one mitt is eight picofarads and the other mitt is 37 picofarads, they really look pretty much the same from the perspective of the elephant.  The two capacitances are of the same order of magnitude and the inductive elephant might be five to seven orders of magnitude larger.  So that just about puts the differences in capacitance values in the "don't care" file.   If you are a millionaire, you don't care if you are worth $1,000,008 or $1,000,037.

Beyond that, here is a way to look at the whole situation:  You experiment with real series and parallel LC circuits on your bench using real capacitors at lower frequencies.  Then you know that as the capacitance gets smaller and smaller the LC resonator resonates at a higher and higher frequency.  At the extreme limit you actually remove the capacitor completely and the coil self-resonates.  You intuitively can picture in your mind roughly what would be happening in the coil.  You also know that the frequencies are so high that you are in that mushy and spongy territory where the scope probe capacitance affects the circuit and just waving your hand affects the circuit.  It's kind of the "Twilight Zone" unused region for the operation of the coil.  Sometimes just visualizing it in your head is good enough.

MileHigh