The Spike

[MileHigh]

I have a question for you MH, in the spirit of cooperation and good faith.  Also, in line with the topic on this thread. You've been bopping about many forums as the self-proclaimed guru of text book. What are the basic factors we should consider when creating the largest spike possible for the least amount of energy? If you had to nail it down to under 10 main concerns, using a coil, what would they be?

No, you didn't really get under my skin.

I would have to say to you that it's a naive question.  The answer is just basic nuts and bolts and it has already been answered in my previous postings in this thread.  Let's ignore resistive losses to keep it simple.  The energy in the spike will be equal to the amount energy you expend to energize the coil, so the "least amount of energy for the largest spike" is a misnomer.  You pick your inductance and your final current before you stop energizing the coil.  The final current is determined by how much voltage you put across the coil and how long you energize it and the size of the inductance.  The resistance of the load or the size of the capacitance determines how high the voltage spike will be or how high a voltage the capacitor will get charged to.  By playing with all of the parameters you can create any kind of spike that you want.

And here's the thing to think about:  Your buddies on EF in your thread would never say what I said above.  It would be wonderful if they all got to that place so they could have a better understanding and do better experiments.

[minoly]

The answer is just basic nuts and bolts and it has already been answered in my previous postings in this thread.  Let's ignore resistive losses to keep it simple.  The energy in the spike will be equal to the amount energy you expend to energize the coil, so the "least amount of energy for the largest spike" is a misnomer.  You pick your inductance and your final current before you stop energizing the coil.  The final current is determined by how much voltage you put across the coil and how long you energize it and the size of the inductance.  The resistance of the load or the size of the capacitance determines how high the voltage spike will be or how high a voltage the capacitor will get charged to.  By playing with all of the parameters you can create any kind of spike that you want.

And here's the thing to think about:  Your buddies on EF in your thread would never say what I said above.  It would be wonderful if they all got to that place so they could have a better understanding and do better experiments.

E = -L dI/dt
This was a decent post, thank you for adding in a mostly positive direction. We can see and I hope you agree the other stuff is not necessary and only serves to alienate and antagonize which I'm sure is not your goal.


What is the formula for trying to wind an ideal coil ie... number of turns, Awg, coil inner diameter, height, etc? Or is it easier to work the other way around. What is the formula we can use to plug in these parameters to come up with the spike voltage given the supply voltage and time as you say?


No need to repost if there is already a discussion on this can you point me to it...

[MileHigh]

E = -L dI/dt
This was a decent post, thank you for adding in a mostly positive direction. We can see and I hope you agree the other stuff is not necessary and only serves to alienate and antagonize which I'm sure is not your goal.

What is the formula for trying to wind an ideal coil ie... number of turns, Awg, coil inner diameter, height, etc? Or is it easier to work the other way around. What is the formula we can use to plug in these parameters to come up with the spike voltage given the supply voltage and time as you say?

No need to repost if there is already a discussion on this can you point me to it...

There is no such thing as an "ideal coil."  You can look up the formulas for winding coils that will give you the inductance and wire resistance and so on.  For right now the simplest thing to do is start with the basics.

What is the formula we can use to plug in these parameters to come up with the spike voltage given the supply voltage and time as you say?

Just about any coil you have or want to make can produce the same spike voltage.  You don't even need a formula to determine the spike voltage.  The only thing you need to know is the current flowing through the coil and the load resistance.

You need to start at square one.  I am sure that you have a fist-sized or larger coil where the wire is a fairly heavy gauge so the total resistance is less than 10 ohms.  You can use a coil like that to start.

Compliments of Verpies I attached a diagram that shows a charging current waveform for a coil.  The charging time constant is L/R where L is the inductance of the coil under test and R is the the battery resistance plus the coil resistance plus the transistor ON resistance.  In most cases you can ignore the battery resistance and the transistor ON resistance.  The L/R time constant is called "Tau."   Look at the graph and notice that after one Tau the charging current is 63% of the way to the final current.  That means that you can simply look at the charging (or discharging) current waveform for a coil and work the numbers back and determine the inductance of your coil under test.

In other words:   Coil Inductance = R-effective * Tau.   In the discharging case, R-effective is typically the coil resistance plus the R1 resistance.  Measuring the inductance of a coil with your scope is a no-brainer.  The easiest thing to do is measure the Tau by looking at the voltage discharge curve for the coil across the R1 resistance.  Tau is measured at the point where the peak voltage has decreased by 63%.  You do not need an inductance meter if you keep this simple circuit handy.

When a coil discharges you get a current waveform that is simply an upside-down version of the charging waveform.

I made up a schematic for you for investigating the spike.  You can see how the CVR shows you both the charging current waveform for the coil when the transistor is ON, and the discharging current waveform when the transistor switches OFF.  Notice how at the instant when the transistor switches off the current though the CVR does not change.  You should see an exponential increase in the current followed by an exponential decrease in the current with the two Taus determined by your choices for the resistor values.

TP2 will show you the spike.  When you want to try making very high voltage spikes of several thousand volts, then add optional R2 to make a resistor divider network and use TP3.   You don't have to actually see a 3000-volt spike on your scope display, just see a smaller version of it by looking at TP3.

R3 is an optional resistor for changing the L/R time constant for energizing the coil.  Put in a resistor there then L/R, "Tau," becomes a smaller value.  You can observe this on the CVR.   Likewise optional R3 + R1 plus optional R2 will affect the L/R time constant for the discharging of the coil.

So for starters, how do you get a 100 volt spike to display on your scope?  The answer is very easy.  If you adjust the pulse width so that the CVR is telling you that one amp of current is flowing through the coil, then make R1 100 ohms and you will get a 100-volt spike.  Make R1 200 ohms and you will get a 200-volt spike.  It's that easy.  What if you adjust the pulse width so that the CVR is telling you that two amps of current is flowing through the coil?   Then just make R1 50 ohms and you will get a 100-volt spike.

I strongly urge you to make this circuit and then play with different coils and resistor values until you get to the point where everything makes sense to you and you have mastered it.   Then for the next step you can replace R1 with a large capacitor and start investigating that part of it.  You have be careful through because you could easily over-voltage your capacitors.

If you have any questions please feel free to ask.

I also strongly encourage you to share this schematic and the instructions with your peers on the EF thread because they are also starving for the proper information so they too can understand how the spike works.

MileHigh

[TinselKoala]

1.5 V in, over 800 V out.  Circuit is a self triggering JT using principles illustrated by MH's sample circuit:

[TinselKoala]

And just for fun....

24 V in, over 200 kV out: ZVS oscillator driving flyback transformer feeding multielement spark gap to make Spikes to drive the primary of a tuned aircore resonator (aka Tesla coil):

http://www.youtube.com/watch?v=aIZClhoU2Xk