# Re: Racing Spark Prediction

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi dest,

Original poster: dest <dest@xxxxxxxxxxxxx>

>>But a beat waveform can also be considered to be a sin wave
>>amplitude modulated by an other sin wave ie sinA+sinB = SinA * sinB

above is incorrect, what Bob wrote before -
sinA* sinB = sin(A-B) + sin(A+B) is incorrect too,
correct formula - sinA + sinB = 2sin[(A+B)/2]cos[(A-B)/2]

I too believe that those equations are wrong. The one you quote is a trig identity and is correct. Im thinking Bob didn't mean them literally but is using them figuratively.

>>> I believe, when the two sin waves "add" there is not the upper and
> lower side bands that occur when the two sin waves multiply.

f1=60khz, f2=66khz, a=sin(w1t)+sin(w2t), fourier analysis of a:

http://himplast.ru/dest/temp/gr1.gif

This I'm having a problem with. If a signal has just sinA + sinB components present and the system is linear, I believe the fourier analysis will show just the two frequencies. After all sinA + sinB are a fourier series of a sort. All the other frequencies in the spectrum can only be generated if the system is nonlinear and the two sin waves interact with each other because of the nonlinearity.

> In the "added" case, there is a beat frequency associated with A-B
> that goes up (and the period goes down) when the coupling is increased.

when coupling is increased the period is going up so beat frequency is
going down.

I think this is backwards. If coupling is increased, the two main frequencies will be forced further apart. The beat frequency (in time domain) is the difference of the two frequencies so the beat frequency will go up and the period of the beat will go down.

you didn`t understand me - i was trying to say, that secondary gets
new resonance frequency Fupper, and that actual working frequency when
two tanks are coupled and resonating is not higher than Fupper, two
maximum in spectrum is not higher than Fupper too, so you can`t get
voltage maximum below the toroid and overvolt the secondary.

and I may still not understand you :-)) I believe both frequencies are present in the secondary at the same time during ring up and ring down. Only when all the energy is in the secondary does it contain one frequency and that being its natural resonance (maybe Paul can confirm this).

> If both frequencies are in the
> secondary and a "full" beat period occurs (and lets say there is no
> decay in this period of time) then the beat envelope could aggrevate
> the voltage gradient to cause a racing arc.  That's the premise this
> discussion is based upon.

sorry, don`t understand - why doesn`t this envelope cause racing in
the first half of the beat?

I didnt say it did. I dont know where in the cycle the worst case stress may occur. I'm just suggesting if quenching occurs before the full beat cycle happens, then there is a possibility that the worst case stress doesnt happen.

Gerry R.