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How do the capacitors affect the tesla coil? Answered

So when I look at how capacitors are wired into a tesla coil they are outputting dc.  How does this help performance if the actual cause of electrical discharge is when a change or stop occurs in the primary magnetic feild. 

8 Replies

LargeMouthBassBest Answer (author)2011-05-24

I don't know exac tly what you mean when you say that the capacitor is outputting DC.

I assume you are refering to the capacitors in the primary circuit. The capacitor charges up from the 60 Hz source, until the voltage is great enough for the air between the terminals of the spark gap to ionize and conduct. This action is like a switch closing. At this point, the energy stored in the capacitor is able to flow through the primary coil. The energy that was stored in the capacitor flows back and forth between the capacitor and the inductance of the primary coil, dissipating through losses until it is gone. This is what creates the oscillation in the primary that generates a magnetic field that then couples to the secondary.

If you have a scope, you can observe this action with other capacitors and inductors. Just charge the capacitor to some voltage, remove the charging source, then switch the inductor across the capacitor If you measure the voltage across the cap it will be a decaying sinusoid, the frequency of which is dependant on the values of the inductor and capacitor.

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jj.inc (author)LargeMouthBass2011-05-24

I guess I basically wanted to know why it needs the capacitors because the output is ac and that doesn't work with dc capacitors, but now I think I get it.
I still wonder if they are needed. Can a tesla coil run with ac applied to the primary at high voltage without capacitors or a spark gap. Just a continuous run.

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LargeMouthBass (author)jj.inc2011-05-25

The primary capacitance, inductance, and the spark gap form the high frequency drive source, so they are indeed essential.

For test and tuning of your coil, you can drive the primary with a signal generator. A signal generator output is only capable of several volts, not 10,000 or more more volts, so its drive is not sufficient to generate any sparks on the secondary. But it can be useful for determining the resonant frequency of the secondary by measuring the secondary output and seeing the drive frequency where the peak output occurs.

If you had some kind of signal generator that could produce a continous high voltage AC output at the high frequency necessary to resonate with the secondary, then it could drive the primary.

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jj.inc (author)LargeMouthBass2011-05-25

Well, I just thought that because I will be using a high voltage flyback transformer which is either AC or pulsed output DC it would resonate.

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iceng (author)jj.inc2011-05-25

I have to get into your skin... affect.
The main effect.... The big Thrill of a Tesla coil is the shooting electricity
and it  Will Not Kill YOU !!!            How is this possible ??

The lightning, The Sparks, The amazing lamp affects are all RF frequency.
There is a property of HIGH Voltage RF electricity that makes it travel over
the surface of your skin. Instead of burning your muscles and cooking
your brain and internal organs on the spot.

Tesla was a genius at working RF without the benefit of pumped cavity
resonating tubes.   A simple spark is an RF generator when ( Pumped )
fed by 60 cycles into a spark gap in parallel with a capacitor in series
with the inductance of the low voltage primary coil.

Sparks have long been used as radio dots and dashes because they
are RF EM fields ( radio waves ).

If you did ( You Must Not ) make a high voltage without the spark gap
and capacitor.  The arcs emananating from your secondary coil would be
only 60 cycle and Lethal to our lives !!!.


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Extreme Intellect (author)2012-03-26

The capacitor will charge the first few moments after you turn the tesla coil on. When it is completely charged, the electricity going to the capacitor will go to the spark gap. But a spark will not fire across the spark gap without the help of the capacitor discharging into the main current.

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The MadScientist (author)2011-05-25

When the capacitor charges to a certain point the spark gap will fire causing a surge in the primary coil at the resonant frequency of the tank circuit. This will cause the secondary to resonate and create the voltage spike that is seen as the lightning. I think the capacitors main purpose is to create the resonant frequency.

Capacitors can't output AC they will charge on one polarity, discharge then charge again. Capacitors basically store charge in the form of static therefore it is not possible for them to discharge AC.

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iceng (author)2011-05-24

Capacitors store electrical charge.
Depending on what circuit you see ?
I am supposing the capacitor is part of the high Fq LC oscillator.

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