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Re: Energy storage in primary?
Original poster: "Jolyon Vater Cox by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
It is strange but it it seems the requirements of the quenching switch
(which I shall term SW2) -that it should turn off below an extinction
voltage, or after a set period of time are exactly the same as those
respectively for a static and a rotary spark gap;both of which I presume
would be unsuitable in this instance due to the relatively low voltage of
the current-driven primary.
Other than saturating reactors what if any are the other possible options
for quenching in a current-driven TC?
Would the best position for the quench switch to be connected be between the
lower lead of C1 and the ground rail?
For the voltage-controlled quench, would DIACs, neon bulbs, or
thyristors/TRIACs triggered by zeners or neon bulbs be of any use?
Or, for a time-controlled quench would it be possible to used a monostable
(another 555?) to gate SW2, which would close the moment the first switch,
SW1, opened.
The quench switch would turn on for a period of time less than the "off"
period of SW1, terminating the flow of current in the primary-capacitor loop
after the timed period elapsed. The monostable would be triggered by the
falling edge of the squarewave from the astable.
Would any of these ideas work?
Jolyon.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, January 30, 2003 7:23 AM
Subject: Re: Energy storage in primary?
> Original poster: "Bert Hickman by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>
>
> Hi Jolyon,
>
> My response is interspersed below...
>
> Tesla list wrote:
> >Original poster: "Jolyon Vater Cox by way of Terry Fritz
> ><teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> >So the primary oscillation will not be quenched when the switch turns on
> >again -short-circuiting the primary capacitor?
>
> The goal of quenching is to strand energy in the secondary side at the
> appropriate time by opening the primary LC current loop. If we short
> circuited the primary capacitor instead, this has the effect of short
> circuiting the primary inductor, but it still leaves the primary as an
> "active" element in the primary-secondary magnetic circuit. The primary
> would behave as a short circuited transformer winding, robbing energy from
> the secondary resonator. To achieve a proper quench, the primary current
> loop must be broken.
>
>
> >Could quenching be accomplished by means of saturating ferrite core in
> >series with the TC primary- these have a high impedance to current
changes
> >at low voltage but low impedance to current changes at higher
voltage -when
> >the core saturates.
>
> Interesting question... this might work. However, Including a nonlinear
> off-axis inductive element in the LC loop may also create additional
> voltage standoff problems for the main switch when the inductor goes in
and
> out of saturation, and interesting tuning characteristics... :^)
>
> >Jolyon
>
> Best regards,
>
> -- Bert --
> --
> Bert Hickman
> "Electromagically" (TM) Shrunken Coins
> Stoneridge Engineering's Teslamania
> http://www.teslamania-dot-com
>
> >----- Original Message -----
> >From: "Tesla list" <tesla-at-pupman-dot-com>
> >To: <tesla-at-pupman-dot-com>
> >Sent: Tuesday, January 28, 2003 7:20 PM
> >Subject: Re: Energy storage in primary?
> >
> > > Original poster: "Bert Hickman by way of Terry Fritz
> ><teslalist-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>
> > >
> > > Jolyon,
> > >
> > > In theory, yes. However, in practice, it's difficult to find an
"opening
> > > switch" that can handle high current and then quickly be able to
withstand
> > > the subsequent high voltage developed across the inductor. Some
pulsed
> > > power systems have been successfully designed to use energy initially
> > > stored in inductors (quite desirable, since inductors can store
> > > significantly more energy in a smaller volume than HV capacitors).
> >However,
> > > opening switches for these systems tend to be "single shot" devices
> > > (exploding wire, exploding foil, or using high explosives to destroy
the
> > > conductor). Closing switches (spark gaps, thyratrons, SCR's,
ignitrons)
> >are
> > > much easier to find and use, especially for repetitive operation,
hence
> > > their greater popularity.
> > >
> > > Pulsed inductive energy storage can easily be scaled down to make it
> > > repetitively usable. For example, older "point and condenser"
ignition
> > > systems stored energy in the ignition coil primary, releasing it by
> > > suddenly disrupting the current supply when the points opened, and
then
> > > "ringing" it with the condenser that was across the points. Magnetos
on
> > > small engines operate in similar fashion.
> > >
> > > So, in principle, a small classical air core TC using inductive
energy
> > > storage should also be feasible by using the primary of your TC as
the
> > > energy storage inductor and connecting your tank cap directly across
it or
> > > across your opening switch. A high current low voltage source would
be
> > > briefly connected through the TC primary through a semiconductor
switch,
> > > charging the primary inductor. Assuming the switch can then be
quickly
> > > turned off, most of the inductor's stored energy (bang size =
0.5*Lp*Ip^2)
> > > would oscillate in the primary tank circuit to be transferred to the
> >secondary.
> > >
> > > No to your question: To obtain a 6" spark, we could figure that we'd
need
> > > at least 50 watts of input power at 120 BPS (predicted via John
Freau's
> > > spark length estimator for a 12" spark in an efficient system). This
> > > implies a bang size of about 0.42 Joules. The semiconductor switch we
use
> > > must be able to withstand the initial current and also the peak
voltage
> > > developed across the inductor. It must also be able to switch off
rapidly
> > > enough (this may be tough if the device is heavily saturated).
Assuming a
> > > tank inductance L and primary capacitor C, the peak voltage developed
once
> > > the switch opens will be V = Io(sqrt(L/C). Let's plug in some numbers
for
> >a
> > > small system:
> > >
> > > Let:
> > > L = 50 uH
> > > C = 0.2 uF
> > > Then Fo = 50.3 kHz
> > > Desired Bang size = 0.42 Joules
> > > Required Ip ~ 130 Amps
> > > Vmax = 2055 volts... a bit on the high side
> > >
> > > Increasing C decreases Vmax, but this also decreases Fo. Going to a
0.5 uF
> > > tank cap reduces Vmax to about 1300 volts and drops Fo to about 1300
volts
> > > - not an unreasonable value. Either an IGBT or MOSFET switch could
work,
> > > but the challenge will be turning it off quickly enough so that most
of
> >the
> > > energy remains in the LC circuit.
> > >
> > > BTW, one other problem with this configuration is that, once
oscillating,
> > > there is no simple way to "quench" the primary circuit, and energy
will
> > > cycle back and forth between the TC primary and secondary. A more
> > > sophisticated switching arrangement, using another switch, would be
> > > necessary to "break" the primary LC circuit for proper quenching.
> > >
> > > Building a coil that operated in this mode would be a good
demonstration
> > > vehicle, but its unlikely that it would be nearly as efficient as a
more
> > > conventional disruptive coil.
> > >
> > > Best regards,
> > >
> > > -- Bert --
> > > --
> > > Bert Hickman
> > > "Electromagically" (TM) Shrunken Coins
> > > Stoneridge Engineering's Teslamania
> > > http://www.teslamania-dot-com
> > >
> > > Tesla list wrote:
> > > >Original poster: "Jolyon Vater Cox by way of Terry Fritz
> > > ><teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> > > >Is it possible to build a TC where energy is stored initially as
high
> > > >current in an inductor (the primary) rather than high voltage in a
> >capacitor?
> > > >I am thinking of a setup where current ramps up slowly through the
> > > >inductor before being abruptly switched off (by semiconductor switch
or
> > > >similar) after a predetermined current or period of time has been
> > > >exceeded; the current in the primary rising and falling as
"saw-tooth"
> > > >waveform.
> > > >As primary input power for this would be largely determined be
current
> > > >rather than the voltage of the PSU
> > > >how high would the current have to be/ how low could the voltage be
for
> > > >decent spark output say, a minimum of 6 inches or more?
> > > >For the control logic would this likely need an exotic switch-mode
power
> > > >supply IC with PWM and dead-time control or could a simple astable
like a
> > > >555 do the job?
> > > >For the high-current, high-speed switch would bipolar transistors
(e.g..
> > > >TV line-output power devices) or MOSFETS be suitable or would IGBTs
be
> > > >necessary?
> > > >Would it not be necessary to connect a capacitor across the switch
to
> > > >absorb/slow down the high-voltage transient produced when the switch
> > > >opens/ would necessary voltage rating of switch and capacitor be
> > > >comparable to that of the primary capacitor in a conventional
spark-gap
> >TC?
>
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