Re: Energy storage in primary?

["Tesla list" <tesla-at-pupman-dot-com>]

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?