[Prev][Next][Index][Thread]
Re: 2 questions on resonance
Hi Harvey,
> Original Poster: "Harvey Norris" <tesla4-at-excite-dot-com>
>
> On Sun, 04 Apr 1999 21:10:06 -0600, Tesla List wrote:
>
> > Original Poster: FutureT-at-aol-dot-com
> >
> > In a message dated 99-04-03 21:09:00 EST, you write:
> >
> > << Number One:
> > > What is resonant charging?
> >
> > Chris,
> >
> > Resonant charging occurs when the inductance of the TC power
> > supply equals the capacitance of the TC tank cap. Under this
> > condition, with L and C equal, only the resistances in the system
> > limit the current input. In an NST system, the cap should be
> > matched to the NST to give resonant charging. The cap capacitance
> > will then neutralize the leakage inducance of the NST. For instance for
> > a 15kV, 30ma NST, the resonant sized cap is 11nF, but up to
> > 15nF will work well. It is important to realize that using resonant
> > charging, an NST can draw double or more its rated current input.
> > This is good from the standpoint that you can get more spark output
> > than otherwise, but bad from the standpoint that it stresses the
> > transformer a little more than normal. There's a formula for selecting
> > the resonant cap size, which I don't have handy,
> > but I'm sure someone else will post it. Using resonant charging,
> > in non-shunted xfrmer system, the ballast inductance can be
> > adjusted to give resonant charging.
> > > I am somewhat confused here, is not this cap value determined by the
> acting impedance of the secondary at open condition? If this is true than
> how can it be that the inductance of the power supply (secondary of
> transformer expressed as inductive reactance X(L)?) is matched to the
> capacitance of the TC tank cap {X(C)? as in resonance where X(L)=X(C) ?}
> Many different values of C could be used in different coil setups as
> determined by L of TC primary. How then are these matched in any way? HDN
The impedance of the secondary is largely ( >90% ) inductive. I too
have measured a Q >7 in a charging circuit with a cap impedance
matching the V/I rating of the transformer. There is no reason why
you can't use different values of cap with the transformer. Some rise
will be experienced if the cap value approaches Xl (or V/I).
> > > Number Two:
> > > What is the cause of a resonant rise in voltage?
> >
> > This is what occurs in a child's swing when you push at the
> > correct times to build up the swinging height. Each push, pushes
> > the swing higher and higher. Likewise in the TC circuit, each AC
> > cycle pushes the voltage higher and higher. This is why it is
> > important to have the spark gaps, and safety gaps in place when
> > testing resonant charging TC systems, otherwise, the voltage will
> > build higher and higher (limited by system Q) until the cap or
> > transformer is destroyed by overvolting.
> >> I the case of no high frequency effects and just simply resonating a
> large inductor at 60 hz, where X(L)=X(C) in series,a resonant rise of
> voltage can also be measured ( about 15/1 in my model) Does this voltage
> buildup instantly in 1/4 cycle or does it take several cycles as in the TC
> high frequency model. I was wondering about this in light of the fact that
> since no frequency conversion takes place in the simple LC circuit does the
> voltage instantly built up? HDN
In my opinion based on experiment, no. The most telling piece of
evidence is the reduced firing rate as the variac setting is reduced.
I posted another note on this.
Malcolm