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Name: Jon
Status: Other
Grade: Other
Location: AE
Country: United States
Date: April 2008


Question:
I wish to make a 'lightning detector' as described by Robert Penfold the famous scientist in Everyday Electrics about 30 years ago. To make it you would need: 1 neon 1 collector (a 12 inch square piece of aluminium) 1 capacitor ( value not known) an earth. He said a neon fires at 110 volts and dies at 90 volts so you connect the neon and the capacitor to the earth. The collector would collect the static in the air and so charge the capacitor until it reached 110 volts. The neon would then fire and discharge to earth until the current fell to 90 volts at which point it would turn off and repeat the cycle.

The amount of static in the atmosphere would regulate how often the neon fired. I know that it works as I built one years ago but I am afraid that with the passage of time I have forgotten the value of the capacitor (I seem to recall that it was '20' something but I have tried so many values but nine seem to work. I would dearly love to remake this as it is simplicity itself -- no batteries
--just make, fit and enjoy.



Replies:
Hi John,

The capacitor value is not at all critical. A larger capacitor will take longer to charge each time, but will discharge more energy into the neon lamp, resulting in brighter flashes. A value of 10 or 20 microfarads would take a long time to charge, but produce a bright flash in the neon lamp. The problem here is that this type of capacitor is a so-called electrolytic type, and is polarized (there is a positive and negative terminal). Unfortunately, there are lightning discharges, and static buildup, of either polarity.

To avoid the polarity problem, I suggest you use a 0.1 to 1.0 uF (or microfarad) mylar or ceramic capacitor. These types work with either polarity. The neon lamp flash will not be as bright as with a larger capacitor, but at least it will charge faster.

By the way, a typical neon lamp for this project would an "NE-2" lamp. also note that the voltage rating of the capacitor must be at least 200 volts.

The connections are as follows: Connect the capacitor in parallel with the neon lamp. Then one terminal of the lamp/capacitor pair is grounded and the other terminal connects to the plate.

Good luck but be careful.

Regards,

Bob Wilson



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