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

Re: AC Resistance (formerly Spice Simulation Pictures)



Bert Hickman wrote:

<snip>
> 
> Secondary Parameters:
> Diameter:                10.25 inches
> Coil active Length:      31 inches
> Wire Gauge:              #21 AWG Double Formvar
> Wire (Cu) diameter:      0.0285 inches
> Wire (Cu) diameter:      0.072 cm
> Fo with Toroid:          91 kHz
> DC Resistance:           34.1 Ohms
> Inductance:              73,455 uH
> ZL at Fo                 42,000 Ohms
> Est Turns:               995 (97% close-wound)
> Est Turn:Turn Spacing:   0.0312 inches
> 
> 1. Measured/calculated Value of Rac:
> My estimate for Rac was done by backfiguring from the time constant of
> the decaying exponential secondary voltage captured on a storage scope.
> You could also base-excite the secondary/toroid from a low impedance
> variable-frequency source, measure frequencies at the 0.707 points,
> calculate Q, and then back-figure Rac.
> 
> Conditions: gaps reduced for no corona breakout, gaps quenched at
> end of 1st beat, "single shot" mode, with a pickup plate 7' from
> secondary and connected to a storage scope.
> 
> The time for the output waveform to to go from the peak voltage to 5% of
> peak was about 2 milliseconds. This equates to 3 time-constants (3*Tau)
> for the exponential envelope, so Tau = 670 uSec. But, Tau  = 2L/Rtotal,
> where Rtotal = Rac + Rground. I estimated my RF ground resistance to be
> about 15 ohms based on low-voltage AC (6.3 VAC) current measurements
> from the dedicated RF ground to AC (line) ground. Solving for Rac:
> 
>       Rac =  (2L/Tau) - Rground = 110 - 15 Ohms
>       Rac =  95 Ohms
> 
> 2. Purely calculated method for a close-wound coil (from Frederick
> Terman, Radio Engineers' Handbook, 1943, McGraw-Hill, pp.77-80):
> 
>       Rac/Rdc = aH + (bu1 + eu2)G[(d/c)^2]
> 
> Variables H, a, b, e, u1, u2, and G are all derived from the coil's
> parameters, operating frequency, and a number of look-up tables. Term aH
> is the skin effect  contribution, and the remaining term is from
> proximity effect. Solving for the above conditions yields the following:
> 
>       Rac/Rdc = 1.263  +  1.160 =  2.423 (combined effect)
>                (skin)   (Proximity)
> 
>       Rac = 2.423*34.1 = 82.6 Ohms
> 
> Considering my measurement errors (especially in estimating Tau and
> ground
> resistance), the two values are in reasonably close agreement. BTW, the
> first method is _much_ simpler than several calculations and
> interpolations from multiple tables!
> 
> Given the above parameters, what does your graph predict for Rac?
> 
> Safe computin' to ya, Jack!
> 
> -- Bert --


Nice analysis, Bert!  I am curious as to how the streamers appear on your coil,
do you have any pictures posted of it in operation?  Have you noticed any
peculiarities in how the streamers grow, or move about?  Also, have you by
chance measured the wall-plug power of your coil at a given arc length?

I have been collecting data on all types and sorts of coils, and your region of
parameter space is still sparsely populated (ZL at Fo = 42000 Ohms). 

Quantitative coilin' to ya, Bert!

-GL