Formula Page

On this page are listed Tesla coil formulas for a reference to those who prefer to make calculations on paper. Below is a table of formulas on this page.

Ohm's Law Transformer Input and Output Capacitive Reactance
Inductive Reactance Resonant Circuit Formula Spiral Coil
Helical Coil Inverse Conical Coil Secondary Coil Dimensions
Medhurst Toroid Capacitance Sphere Capacitance
Plate Capacitors Leyden Jar Capacitors AC RMS/Peak Voltage
Rotary Gap Firing Rotary Gap Electrode Speed Energy for L and C


Ohm's Law

E = IZ P = IE


E = volts
I = current in amps
Z = impedance or resistance in ohms
P = power in watts


Transformer Input and Output

EPIP = ESIS

EP = primary voltage
IP = primary current in amps
ES = secondary voltage
IS = secondary current in amps


Capacitive Reactance



XC = capacitive reactance in ohms
F = frequency in hertz
C = capacitance in farads


Inductive Reactance



XL = inductive reactance in ohms
F = frequency in hertz
L = inductance in henrys


Resonant Circuit Formula





F = frequency in hertz
L = inductance in henrys
C = capacitance in farads


Spiral Coil Inductance



L = inductance of coil in microhenrys (µH)
R = average radius of the coil in inches
N = number of turns
W = width of the coil in inches
  


Helical Coil Inductance



L = inductance of coil in microhenrys (µH)
N = number of turns
R = radius of coil in inches (Measure from the center of the coil to the middle of the wire.)
H = height of coil in inches
  


Inverse Conical Coil Inductance



L = inductance of coil in microhenrys (µH)
L1 = helix factor
L2 = spiral factor
N = number of turns
R = average radius of coil in inches
H = effective height of the coil in inches
W = effective width of the coil in inches
X = rise angle of the coil in degrees
  


Secondary Coil Dimensions

T = AH


L = length of wire in feet
D = outer diameter of coil form in inches
H = height of windings in inches
A = number of turns per inch
T = total number of turns
B = thickness of wire in inches


Medhurst



C = self capacitance in picofarads
R = radius of secondary coil in inches
L = length of secondary coil in inches

 

Toroid Capacitance

C = capacitance in picofarads
D1 = outside diameter of toroid in inches
D2 = diameter of cross section of toroid in inches
This equation courtesy Bert Pool.

 

Sphere Capacitance


C = capacitance in picofarads
R = radius in inches


Plate Capacitors



C = capacitance in microfarads
K = dielectric constant
A = area of each plate in square inches
N = number of plates
D = distance between plates in inches (thickness of dielectric)


Leyden Jar Capacitors



C = capacitance in microfarads
K = dielectric constant
D = diameter of jar in inches
H = height of jar in inches
T = thickness of jar in inches


AC RMS and Peak Voltage

ERMS = 0.7071·E P

ERMS = RMS voltage
EP = peak voltage


Rotary Spark Gap Firings per Second



F = firings per second (hertz)
R = motor RPM rating
E = number of rotary electrodes


Rotary Spark Gap Electrode Speed



S = electrode speed (MPH)
R = motor RPM rating
D = diameter of electrode placement circle (inches)


Energy for L and C

Capacitance Inductance
J = 0.5 V2 C J = 0.5 I2 L

J = joules of energy stored
V = peak charge voltage
I = peak current
C = capacitance in farads
L = inductance in henries

Peak values of V and I are stated in order to emphasize not to use RMS values. The energy stored at any given time is of course: J(t) = 0.5 [V(t)]2 C and J(t) = 0.5 [I(t)]2 L.