On 4/5/2014 6:12 AM, jodell wrote:
My kids call me Buzz Killington when I remind them of the safety implications. Still, maybe a gentle reminder that a)any size cell in series at these voltages magnifies the results when any individual cell exhausts the reactants within it. b)the electrolyte in Lithium cells is flammable/explosive c)if you must, personal protective gear and shield your surroundingsI used to work for one of the major battery producers in their R&D facility and because I am rampantly curious, asked many questions and learned a lot about many of the failure modes of consumer electronics and the cells/batteries that power them. If you have cells in series, there will always be one cell that that "runs out" first. When it does, the rest in the series will "charge" it. Very few chemistries or constructions are suitable for this, and generally instead, the water within the electrolyte hydrolyses to hydrogen and oxygen. The gas produced naturally expands until some portion of the case fails. 90V through an old school "heavy duty" Zn-MgO with a weak paper wrapping does no more than ooze, and they were contained in cans surrounded by bitumen to pot them. Failure mode is just leakage and a bit of a mess. In addition, the discharge profile shows gradually decreasing voltage, which allows the consumer time to pick up a replacement battery long before you get to gas production levels. For coin cells, both Ag and Li-type cells have a really nice discharge profile that stays nearly at the rated cell voltage almost all the way to depletion, then it drops off to zero very sharply. Since watches and cameras are very expensive to replace when the cells leak, the seals on the cells are very very good and will hold a much higher gas pressure. (In fact, one test of a watch cell design involved dropping one in a solder pot of molten lead or tin and timing till it explodes. Done in a hood with a big splash shield and the door down.) So when one cell switches to charge mode, pressure within can result in a much more dramatic failure mode. With lithium chemistry, lithium reacts with water, so an organic (flammable) electrolyte is used. On charging, gas production and seal rupture now releases a flammable liquid or gas and fire can result.This is a long-winded explanation that says, if you assemble a 90V cell, use the chemistry they did back then with the type of cells they used back then, or design your experiment to deal with potential explosion and/or fire. Remember that a battery is an oxidation reaction controlled in a can, just like gasoline in a car engine is a controlled oxidation reaction. This is Buzz Killington, signing off :)On Saturday, April 5, 2014 4:06:47 AM UTC-5, petehand wrote: Let's apply some engineering to see what kind of battery would do the job. Assuming a neon strikes at 90V and extinguishes at 60V, the average voltage across the resistor would be 15V. Initially, I arbitrarily choose the series resistor to be 1M and the capacitor to be 2.2nF. The flash rate would be about 1 every 2 seconds. The average current per neon would be 15 microamps. Let's say there are 8, and we want it to run for a year (8000 hours), that means we need 960mA-hrs. Somehow I don't think the old radio battery was anywhere near an amp-hour. So how about 10M resistor and 1nF capacitor. The flash rate would be about 1 every 10 seconds. It wouldn't be very busy or very bright but with 8 lamps, something would be happening often enough to be interesting. The average current would be 1.5uA so for a year we would need about 100mA-hr. That's doable. So take a block of something insulating - wood might do - 3 inches square by an inch deep, drill four 1/2 inch holes right through, each hole takes 15 LR44-size cells. Fashion a couple of end plates out of PCB material, solder on bits of spring out of a ball point pen. Solder a neon christmas tree together like joenixie, attach to base and connect to battery ends. Stick it on top of the TV and enjoy it for a year. Sounds like a perfect wet afternoon project for the (grand)kids! Now excuse me while I submit this as a little project to fill the gap in my favorite magazine. Actually, all kidding aside, this is the kind of thing that might appeal to Make Magazine. --You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected] <mailto:[email protected]>. To post to this group, send email to [email protected] <mailto:[email protected]>. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/215b183a-7540-48ef-b62e-5231de0f432e%40googlegroups.com <https://groups.google.com/d/msgid/neonixie-l/215b183a-7540-48ef-b62e-5231de0f432e%40googlegroups.com?utm_medium=email&utm_source=footer>.For more options, visit https://groups.google.com/d/optout.
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