[Prev][Next][Index][Thread]

Tesla Coil Q Factors


----------
From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Monday, August 24, 1998 11:57 AM
To:  Tesla List
Subject:  Tesla Coil Q Factors


  To All -

Like most of the other Tesla coil parameters the Q Factor has been
discussed many times in the past on the Tesla List. However, these Q
Factors are the Q Factors of unloaded single coils so this information
cannot be used with operating Tesla coils. To determine the Q Factor of an
operating TC a loaded Q Factor is required plus several equations must be
coordinated such as

  Q = 6.283 x F x L    Q = Vs/Vp       Q = 3.1416/ Log Dec

  Vs = Vp sqrt(Cp/Cs)   Vs = Vp sqrt(Ls/Lp) 

  Vs = sqrt(2 W/(Cs x BKS))    Vs = Ls di/dt

  Note that in the above equations all of the variables can be determined
by proper tests except Q, R, and Vs. The Log Dec can be found using an
oscilloscope as I show in my Tesla Coil Notebook. This would give the Q
Factor which would then give the R variable which then would give the
secondary voltage Vs. All of these critical TC parameters would then be
found giving a complete picture of the TC in question. In the past coilers
have given some of these parameters but they were not coordinated.

 Note that the half power test for Q Factor is of no value here because the
coil is unloaded. Note also that R cannot be determined without first
finding the value of the Q Factor.

  With real coils the secondary voltage Vs increases when the input wattage
is increased. This means that in the equation Q = Vs/Vp the Q Factor would
increase with an increase in wattage. However, with real coils just the
opposite happens. The Q Factor decreases as the wattage increases. I show a
graph in one of my books of this relationship where the Q Factor decreases
with an increase in the wattage. To my knowledge there is nothing in the
present literature that shows why there is this apparent discrepancy with
the equations.

  I have been able to coordinate most of the variables with the JHCTES
computer program but not all of them. Has anyone ever been able to
coordinate all of these variables for their coils or for a proposed coil
design?

  Did someone say we know how a Tesla coil operates?

  Comments welcomed.

  John Couture

--------------------------------------