GENWiki

                          TESLA  COIL THEORY

     LINE  VOLTAGE  IS STEPPED UP BY THE HIGH-VOLTAGE  TRANSFORMER  TO  A
  MAGNITUDE SUFFICIENT TO CHARGE THE CAPACITOR AND FORCE THE SPARK GAP TO
  BREAK  DOWN.  THIS ACTION IS REPEATED AT THE 60 HERTZ  LINE  FREQUENCY.
  EFFICIENT  ENERGY  TRANSFER IS ENHANCED BY CHOOSING A  CAPACITOR  WHOSE
  IMPEDANCE IS EQUAL TO THAT OF THE SECONDARY WINDING.
   ESSENTIALLY,  THE  CAPACITOR AND TESLA COIL PRIMARY FORM ONE  PAIR  OF
  TANK  CIRCUTS:  WHEN  THE SPARK GAP ARCS, THE  MOMENTARY  SHORT  CIRCUT
  CREATED  DUMPS  THE  CAPACITOR'S CHARGE INTO THE  COIL'S  PRIMARY.  THE
  RESULTING  L-C  CIRCUT RINGS AS THE CHARGE OSCILLATES  BACK  AND  FORTH
  BETWEEN  THE  CAPACITOR  AND THE COIL.  THE  OSCILLATIONS  DECREASE  IN
  AMPLITUDE  AS  THE  CHARGE IS DISSIPATED  BY  RESISTANCE.  THE  RINGING
  GENERATES WHAT IS REFFERRED TO AS A "DAMPED WAVE". THE NEXT  HALF-CYCLE
  OF 60-HZ RECHARGES THE CAPACITOR, STARTING THE PROCESS ANEW. A TRAIN OF
  HI-FREQUENCY WAVES, SPACED AT 60-HZ INTERVALS, IS THE PRODUCT.
   RESONANCE  MUST  BE  ACHIEVED  TO EFFECT  RINGING:  THIS  DEMANDS  THE
  CAPACITOR AND PRIMARY HAVE THE SAME REACTANCE:
    X(L) = X(C)  THE CIRCUT RESISTANCE (CAPACITOR, COIL AND  INTERMEDIATE
  WIRING) LIMITS THE OVERALL EFFICIENCY OF THE TANK CIRCUT. EFFICIENCY IS
  RATED IN TERMS OF "QUALITY FACTOR", REPRESENTED AS 'Q':
                         Q  =  W(L)/R  =  X(C)/R

    INCREASING  RESISTANCE  REDUCES Q, THEREBY REDUCING  EFFICIENCY.  THE
  EFFECT  IS MINIMIZED BY WINDING THE PRIMARY WITH A FEW TURNS  OF  HEAVY
  CONDUCTOR,  WELL-SPACED,  OVER  A LARGE RADIUS FORM -  THE  LARGER  THE
  BETTER.  THE  CAPACITOR  SIZE AND CONSTRUCTION ALSO BEAR  UPON  Q:  THE
  PHYSICAL  SIZE  AND  AREA SHOULD BE  MINIMIZED.  THIS,  HOWEVER,  WORKS
  AGAINST  LARGE CAPACITANCE VALUES AND DICTATES THE COIL BE  WOUND  WITH
  MORE TURNS. THE GOAL, THEN, IS TO ACHIEVE A WORKABLE RANGE OF COMPONENT
  SPECIFICATIONS RATHER THAN TO STRIVE FOR OVERLY CLOSE TOLERANCES. COILS
  OFTEN ARE WOUND WITH TAPPED PRIMARIES TO FACILITATE FINE TUNING.
   THE SECONDARY COIL IS SITUATED BOTH ELECTRICALLY AND PHYSICALLY WITHIN
  THE  PRIMARY.  THE SECONDARY AND ITS DISCHARGE ELECTRODE,  GENERALLY  A
  SPHERE OR TOROID, MAKE UP THE SECOND TUNED CIRCUT. THE WINDING SUPPLIES
  INDUCTANCE;  THE CAPACITOR IS CREATED BY THE ELECTRODE AND THE  (EARTH)
  GROUND-PLANE.   AIR  IS  THE  DIELECTRIC.  MOST  TESLA   COILS   EMPLOY
  SECONDARIES  OF  1/4-WAVELENGTH AT THEIR  OPERATING  FREQUENCIES.  THIS
  ESTABLISHES  A CONFIGURATION WITH MAXIMUM CURRENT AT ZERO VOLTAGE  WITH
  MINIMUM  CURRENT  AT  THE  ELECTRODE.  THIS  SITUATION  PROVES  TO   BE
  BENEFICIAL, IN THAT IT ENHANCES COUPLING WITH THE HIGH CURRENT PRIMARY,
  AVOIDS  ARCHING  BETWEEN THE PRIMARY AND SECONDARY  AND  GENERATES  THE
  DESIRED HIGH VOLTAGE AT THE TOP END.
   THE  "OUDIN  COIL  IS  A 1/2-WAVE VARIATION  ON  THE  TESLA  COIL.  IT
  POSSESSES THE ESSENTIAL TESLA COIL OPERATIONAL CHARACTERISTICS, BUT  IT
  EMPLOYS  A HORIZONTALLY PLACED SECONDARY WITH DISCHARGE  ELECTRODES  AT
  BOTH  ENDS AND A PRIMARY AT THE CENTER. THE OUDIN PRIMARY SOMETIMES  IS
  MERELY  A PAIR OF TAPS ON THE SECONDARY (AN AUTOTRANSFORMER). THE  1/2-
  WAVE ARRANGEMENT AFFORDS A COIL WITH MAXIMUM DISCHARGE AT EACH END  AND
  A VIRTUAL GROUND AT THE MIDPOINT OF THE WINDING(S).