harnessing lightning, or not
in [Design]
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From: StickThatInYourPipeAndSmokeIt on 12 Jun 2010 18:42 On Sat, 12 Jun 2010 15:18:37 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 12 Jun 2010 15:29:53 -0500, Bert Hickman ><bert-hickman(a)comcast.net> wrote: > >>Greegor wrote: >>> What were these Maxwell capacitors originally built for? >> >>All sorts of high-energy pulsed-power applications. Typically, banks of >>HV metal-cased energy-discharge capacitors are used to supply 10's to >>1000's of kilojoules at 100's of kA - MA levels. Common examples include >>pulsed magnetizers to charge rare-earth magnets, industrial >>electromagnetic metal forming (and coin shrinking), > >What sort of switch would be used there? When I was a kid, I used to >make banks of electrolytics (from old TV sets), charge them up, and >dump them into coils using, pretty much, just wire contacts. They >welded shut every shot. I could magnetize most anything. > >John http://205.243.100.155/frames/Newgap2a.jpg I'll bet that he gets more than one cycle on his MTBF 'numbers'.
From: Bert Hickman on 12 Jun 2010 18:56 Winfield Hill wrote: > Bert Hickman wrote... >> >> Winfield Hill wrote: >>> John Larkin wrote... >>>> Winfield Hill wrote: >>>> >>>>> My Maxwell capacitors hard at work energy from harnessing lightning, >>>>> see my post with photo, at the CR4 forum. >>>>> http://cr4.globalspec.com/thread/55751/Lightning-Arrestor#comment579837 >>> >>>> Why not use the lightning to heat water? The impedance match is >>>> potentially better, and it's easy to store hot water. We could >>>> throw a neighborhood hot-tub party after every strike, every >>>> 40 years or so. >>> >>> Aren't there serious problems with developing a high electric >>> field in water? I mean, above about 1V it wants to break apart >>> into H2 and O. And what about the electrode double layers? >> >> Win, >> >> For short (a few usec or shorter) pulses, water is actually a very good >> dielectric. Because of its high permittivity (~80), water is often used >> as the dielectric material in high voltage, low impedance transmission >> lines and interim capacitive storage units used in high-energy pulsed >> power systems, such as Sandia's ZR machine. The shorter the pulse width, >> the greater the peak voltage that can be supported across a water gap. >> An empirical relationship was developed by J. C. Martin under a uniform >> E-field over a range of voltages, pulse times, and electrode area based >> upon his work at Sandia: >> >> F = k*(t^(-1/3))*(A^(-1/10)) >> >> where: >> F = the peak breakdown field (in MV/cm) >> t = duration of applied voltage (in microseconds) >> A = area (in square cm) >> k = 0.3 for water (positive streamers– the normal case) >> k = 0.6 for water (a special case where field enhancement is purposely >> adjusted to cause streamers to form preferentially from the negative >> electrode instead of the positive electrode) >> >> For example, positive streamer breakdown field (F) for a pair of 100 >> square-cm electrodes in water, stressed by a 1 microsecond pulse should >> withstand a field of ~189 kV/cm. If we used a 100 nsec pulse, this >> increases to ~408 kV/cm, and to ~879 kV/cm for a 10 nsec pulse. YMMV - >> media degassing (or outright pressurization) is essential to prevent >> premature breakdown. >> >> Considerably more detail can be found in "High Power Switching" by >> Ihor M. Vitkovitsky, ISBN-10 0442290675,“Introduction to High Power >> Pulse Technology” by S. T. Pai and Qi Zhang, ISBN-10 9810217145, and >> "High-Voltage Electrical Breakdown of Water" by M. Kristiansen and >> L Hatfield, ISBN-10 1934939005. >> >> Breakdown behavior changes with longer (>10 microsecond) pulses, since >> ionic conduction begins to alter the E-field distribution within the >> gap. Metallic salts are often intentionally added to water to create >> high power/high voltage aqueous dummy load and divider resistors for >> pulsed power work. The electrolyte and end terminal materials must be >> compatible for long-term stability. Some excellent on-line information >> sources include a 5 page report from R. E. Beverly III& Associates and >> a large (147 page) report from Sandia. >> >> http://www.reb3.com/pdf/r_appl.pdf >> http://www.ece.unm.edu/summa/notes/ESDN/ESDN%205.pdf > > Thanks, Bert, awesome and inspiring information. And I enjoyed > those reports. Hey, do you have copies of those books for sale? > >> Let me know when you want to begin using that cap to do some >> serious EM metal-forming/con shrinking... :^) >> >> Bert > > It's high on my list as soon as H&H AoE III is finished. > > BTW, do you know about the water bridges? > Yeah - these are really curious. Under the right conditions, a cylindrical 2-4mm diameter liquid bridge of distilled water can stretch between two Pyrex beakers separated by up to 25mm. Just one more in a LONG list of amazing properties of water. Although this phenomenon was first discovered 117 years ago (by Sir William Armstrong), it has recently been rediscovered, and studied in much greater detail. There's an excellent YouTube clip by physicists Elmar C. Fuchs, Karl Gatterer, Gert Holler and Jakob Woisetschlager (J. Phys. D: Appl. Phys. 41 (2008) showing a water bridge being extended using an adjustable HVDC supply voltage of up to 25 kV. Also included are thermal and density profiles: http://www.youtube.com/watch?v=FhBn1ozht-E http://www.youtube.com/watch?v=PXJcSt8VYpo&feature=related http://www.youtube.com/watch?v=GLb5HmfiPpU&NR=1 In the above experiments, a current-limited HVDC supply was connected between the two beakers, and a 42 nF capacitor was connected in parallel with the beakers. The current was found to be about 0.5 mA. Instead of using a string to start the process (ala Armstrong), the experimenters increased the voltage between beakers while they were placed side by side, until "Taylor Cones" (jets of electrostatically-repelled water) were ejected from the surface, and bridging the gap. The researchers also found that there was mass flow (usually from anode to cathode beaker) accompanied by rotational flow near the outer surface of the bridge. Interesting stuff! Although I have all of the above books in my personal library, I don't have any extra copies at this time. However, they're all currently available via Amazon. BTW, have you seen HV "air threads"? These were first reported by amateur researcher Charles Yost and subsequently studied by Bill Beaty? These tight filaments of air are probably related to ion wind... but the real mystery is how they can maintain such a tight stream? I'm not aware of any good explanations for these as yet. :^) http://www.youtube.com/watch?v=iLG8gKb-lyk Physics is fun! Bert -- ******************************************************************** We specialize in UNIQUE items: coins shrunk by ultra-strong magnetic fields, Captured Lightning Lichtenberg figure sculptures, and scarce technical Books. Please visit us at http://www.capturedlightning.com ********************************************************************
From: John Larkin on 12 Jun 2010 19:06 On Sat, 12 Jun 2010 15:40:30 -0700, StickThatInYourPipeAndSmokeIt <Zarathustra(a)thusspoke.org> wrote: >On Sat, 12 Jun 2010 15:18:37 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Sat, 12 Jun 2010 15:29:53 -0500, Bert Hickman >><bert-hickman(a)comcast.net> wrote: >> >>>Greegor wrote: >>>> What were these Maxwell capacitors originally built for? >>> >>>All sorts of high-energy pulsed-power applications. Typically, banks of >>>HV metal-cased energy-discharge capacitors are used to supply 10's to >>>1000's of kilojoules at 100's of kA - MA levels. Common examples include >>>pulsed magnetizers to charge rare-earth magnets, industrial >>>electromagnetic metal forming (and coin shrinking), >> >>What sort of switch would be used there? When I was a kid, I used to >>make banks of electrolytics (from old TV sets), charge them up, and >>dump them into coils using, pretty much, just wire contacts. They >>welded shut every shot. I could magnetize most anything. >> >>John > >http://205.243.100.155/frames/gallery/newgap5a.jpg Oh. Brute force. I could have done something like that, operated by a hammer maybe. John
From: StickThatInYourPipeAndSmokeIt on 12 Jun 2010 19:07 On Sat, 12 Jun 2010 16:06:06 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 12 Jun 2010 15:40:30 -0700, StickThatInYourPipeAndSmokeIt ><Zarathustra(a)thusspoke.org> wrote: > >>On Sat, 12 Jun 2010 15:18:37 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sat, 12 Jun 2010 15:29:53 -0500, Bert Hickman >>><bert-hickman(a)comcast.net> wrote: >>> >>>>Greegor wrote: >>>>> What were these Maxwell capacitors originally built for? >>>> >>>>All sorts of high-energy pulsed-power applications. Typically, banks of >>>>HV metal-cased energy-discharge capacitors are used to supply 10's to >>>>1000's of kilojoules at 100's of kA - MA levels. Common examples include >>>>pulsed magnetizers to charge rare-earth magnets, industrial >>>>electromagnetic metal forming (and coin shrinking), >>> >>>What sort of switch would be used there? When I was a kid, I used to >>>make banks of electrolytics (from old TV sets), charge them up, and >>>dump them into coils using, pretty much, just wire contacts. They >>>welded shut every shot. I could magnetize most anything. >>> >>>John >> >>http://205.243.100.155/frames/gallery/newgap5a.jpg > >Oh. Brute force. I could have done something like that, operated by a >hammer maybe. > >John Mecury contactors ain't cheap, or small.
From: Bert Hickman on 12 Jun 2010 20:42
John Larkin wrote: > On Sat, 12 Jun 2010 15:29:53 -0500, Bert Hickman > <bert-hickman(a)comcast.net> wrote: > >> Greegor wrote: >>> What were these Maxwell capacitors originally built for? >> >> All sorts of high-energy pulsed-power applications. Typically, banks of >> HV metal-cased energy-discharge capacitors are used to supply 10's to >> 1000's of kilojoules at 100's of kA - MA levels. Common examples include >> pulsed magnetizers to charge rare-earth magnets, industrial >> electromagnetic metal forming (and coin shrinking), > > What sort of switch would be used there? When I was a kid, I used to > make banks of electrolytics (from old TV sets), charge them up, and > dump them into coils using, pretty much, just wire contacts. They > welded shut every shot. I could magnetize most anything. > > John > High power switches ("power modulators") can be very simple or fairly esoteric. Lower power applications can use stacked IGBT's or SCR's. However, silicon cost rapidly escalates for higher voltage and current applications. Series stacks becomes necessary at voltages over 5 kV, dynamic voltage sharing and simultaneous triggering adds significant design complication, and current/voltage reversals may require anti-parallel high current free-wheeling rectifiers. Thyratrons can handle moderately high-current pulses at higher standoff voltages, but they begin to run out of gas above 100 kA, and most thyratrons don't handle oscillatory discharges gracefully. Other low pressure switches, such as pseudospark and triggered vacuum gaps have also been developed, and these can handle maximum currents to about 500 kA. Current densities for gas volume gaps (thyratrons, ignitrons, and various vacuum triggered gaps) are limited to about 10+6 amperes/square meter. Higher power switching is commonly done via pulse-rated ignitrons (which use refractory metal anodes to safely handle oscillatory current reversals), triggered spark gaps, or electromechanical switches. For hobbyists, a simple solenoid-driven switch, with massive brass (or tungsten-copper or tungsten-silver) contacts are very robust, relatively inexpensive, and very reliable. Very low-inductance "nail switches" are used for at even higher power levels. These use a conductive "nail" to puncture a polyethylene or Mylar dielectric sheet, creating a short circuit between bus bars that are configured as a low-Z transmission line. The result is a constrained, high pressure, low inductance, low resistance arc. Electrically- or laser-triggered spark gaps are used in applications where tighter timing accuracy is needed or where multiple switches need to be triggered simultaneously. These use air or another dielectric gas under normal pressure, or higher pressures to increase standoff voltage. Insulating liquids are used (such as mineral oil) to further increase power density and hold-off voltage. Triggering can be via a high voltage triggering electrode or a high-energy laser pulse. In comparison to lower pressure gas volume switches above, current densities for gas, liquid, or solid spark gaps are of the order of 10+12 Amperes/square meter. Bert -- ******************************************************************** We specialize in UNIQUE items: coins shrunk by ultra-strong magnetic fields, Captured Lightning Lichtenberg figure sculptures, and scarce technical Books. Please visit us at http://www.capturedlightning.com ******************************************************************** |