The microwave tower next door has a lightning arrester attachment. The charge probably goes harmlessly to ground. If it were possible to siphon part of the charge as it went to ground, how would one choose the capacitor (capacitance rating, punch through voltage, etc)?
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It IS possible to store high voltage energy, and probably possible to built a store that would not be destroyed by the first lightning strike. BUT even the biggest cap easily available will store less energy than a 2500 mAh NimH AA cell. Many such capacitors would allow significant energy to be stored "at a strike" but the store cost would be large. It would be possible to construct capacitors capable of say 10's of kV rating which were protected [tm} by spark gaps so that the gap broke down well below capacitor destruction voltage. You would then potentially (pun noted) have a problem with back conduction of the capacitor via the ionisation path, but could very probably build a system that used a spark gap from input to capacitor to initialise charging and then another spark gap from input to ground such that it reduced the available potential of the charging spark gap and extinguished the arc. While this sounds rather "Heath Robinson" it is similar to the sort of things that are really done at extra high potentials. As an example of spark gaps being used as switches, a "Marx Generator" uses arc breakdown to cause spark gaps to act as switches and allow construction of a voltage multiplier witj DC input. Good trick if you can do it. You can ! :-) Capacitors: You can make DIY multi kV capacitors aka "Leyden Jars - with glass jars or bottles - or even plastic "pop" bottles. From here
Here's a 19 nF 10 kV cap made with foil and mylar shopping bags You can buy capacitors in the nF range rated at 10's of kV. Example from above - 40 kV, 10,000 pF disk ceramic. Many very high voltage caps here - very worth looking at 1.3 uF at 100 kV !!!!!!!!!! :-)
Marx Generators - as examples of spark gap switching. This video of a 180 kV output Marx Generator operating is worthwhile just for the sound :-). I am NOT suggesting that a Marx generator is what you need to meet your suggested requirement - but offering it as an example of how switching may be achieved by quite unusual but eminently practical means. The following is far from the most impressive spark-gap-switch unit image available - I chose it because it gives a good view of the spark gap switches working (small arcs along the centre line) plus the resultant overall multiplied voltage arc (you should be able to find that without my guidance :-) ). To make this work you only need a voltage able to break down the small spark gaps.
LOPT in, 200 kV out](http://c4r0.elektroda.eu/_hv/index.php?page=hv/marx) Polish language. Very good project description.
Karl would have been proud!
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None.
In the same article it says that a positive lightning bolt has 100 times more charge, and then you're better not near the capacitor when it gets hit. Russell and Olin mention the Leyden jar, but several sources mention 1 nF as a typical capacitance. Then a 1 µs, 100 kA bolt will charge this to 100 MV, or up to 1 GV if it lasts longer. That will flash through any kind of insulation. If the 100 kV capacitor has an internal resistance of 1 mΩ then a 100 kA bolt will cause a 10 MW dissipation. That looks bad, but if it lasts for 10 µs then it only represents 100 J. (I have 500 Ws light strobes for my photography, which discharge this 500 J in 1/2000 of a second, which is also 1 MW during a jiffy.) |
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Yes, a capacitor can be made to store some of the charge from a lightning strike. Early experimenters with electricity back when both capacitance and lightning were poorly understood used something called a "Leyden jar". It was meant to be a bottle for electric charge. These were glass bottles usually with mercury inside and another conductor outside. Back then they were thinking of storing the charge in a jar, just like you can store other things in a jar. Actually the two electrodes and the glass of the jar formed a capacitor. Look more closely at Ben Franklin's famous lightning experiment and you will see he was actually trying to do exactly what you are proposing. He wasn't just flying a kite in a thunderstorm for no good reason. He had a key attached to the kite string partway up, and a wire going from the key to a Leyden jar. He was trying to prove that lightning was electricity by using it to "fill" the Leyden jar. It worked and he made his case. One problem with capturing lightning energy is that the voltages are extremely high. The final voltage on the capacitor is only going to be a small fraction of the lightning. Think of it this way. How far apart can you keep the two leads of the capacitor? Now consider that the lightning voltage was high enough to arc thru several miles of air. If the capacitor was charged up to that level, you'd need the equivalent of a few miles of air insulation to keep it from arcing and discharging. I vaguely remember that Tesla also did some experiments attempting to capture energy from lightning during his Colorado days. It might be worth a little poking around to see if this is true and find some more information about it if it is. |
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Well like stevenvh's answer. There is probably nothing commercial that you could buy to hold the full power of a lighting strike. Putting high current limiting resistors, in your discharge path. Then trying to siphon a portion of the strike off will most times blow the path as lightning strikes are unpredictable in their duration, max voltage and current. However. In the realm of experimental science and a Bill Gates budget. You could dabble with a Hindenburg dirigible size hanger. Then recreate a cloud inside the hanger. A cloud of moisture can hold a charge under the right conditions. You may be able to recreate those conditions then transfer a strike from an atmosphere cloud to your home corralled cloud. Again. Even if you succeed in transferring the charge. The problem of tapping this energy still remains. And the practically of the project puts it into the Science Fiction arena for now. Perhaps as Chris Stratton's comment suggests. Flux capacitor research should now be a national priority. |
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