Thanks, very interesting. At 00:29 2016-08-10, Sean Breheny wrote: >The voltage needed to jump a gap can be estimated by Paschen's Law > >https://en.wikipedia.org/wiki/Paschen%27s_law > >An arc exhibits a negative slope of resistance. The equation is something >like V=3DK0+K1*I, K0 is a constant term which depends on the geometry of t= he >electrodes. K0 is positive and fairly low compared to the breakdown voltag= e >- tens to hundreds of volts is common. K1 is negative and represents the >fact that higher current flow reduces the voltage drop (although the total >drop will always be the proper sign for the power input to the arc to be >positive, at least in steady-state conditions). This happens because highe= r >current flow raises the arc plasma to a higher temperature, which then >allows a wider plasma channel and more ionization within it. > >A good rule of thumb in air at 1 atm pressure is that 300V is the minimum >DC or peak AC voltage for jumping any air gap, no matter how small (until >you get within nanometers and tunneling can happen) and that 30V DC is the >minimum voltage for sustaining an arc, no matter how small. Note that an >arc may be struck by less than 300V by creating plasma via vaporizing meta= l >by touching the electrodes together momentarily and then pulling them >apart. Arc welders work this way and typically work with about 80V open >circuit voltage for DC welding. > >I have also witnessed accidents where a plasma jet (which cut things quite >effectively!) was created and sustained without high voltage by striking >and then drawing-apart electrodes, as long as the available current was >very high, especially during the striking event. One such accident I saw >was caused by an improperly-spec'd fuse opening with a very large short >circuit current going through it. This was delivered by some large lead >acid batteries along with an array of electrolytic caps. > >Sean > > >On Tue, Aug 9, 2016 at 6:18 PM, Sean Breheny wrote: > >> 50kV is high enough that corona discharge will be an issue. You will >> likely want to pot the diode stack or submerge it in oil to prevent >> excessive loading during the 50kV pulse. >> >> The kind of thing you are suggesting doing is common in starting xenon a= rc >> lamps. I think they usually have a separate starting electrode or they >> float one supply on top of the other (for example, putting an HV pulse >> transformer in series with the high current DC source and then applying = an >> HV pulse to the primary of that transformer). >> >> >> >> On Tue, Aug 9, 2016 at 4:05 PM, David VanHorn wrot= e: >> >>> Yes.. I am half enabled there. Email works but no web or file access. >>> Yahoo >>> is 'working on it'..... Yeah right. >>> >>> On Aug 9, 2016 9:57 AM, wrote: >>> >>> > > Arc resistance will depend on many things. I have seen 60ish ohms = on >>> a >>> > gap >>> > > that 50kv would jump in air. Your mileage will vary but that may w= ork >>> > for a >>> > > rough estimate. >>> > > >>> > > I am looking for spice models that are moderately accurate. >>> > >>> > There have been a number of people on the LTSpice list modelling spar= k >>> > gaps of various sorts. There have been references to papers that have >>> been >>> > found along the way from which models have been generated. >>> > >>> > >>> > >>> > -- >>> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>> > View/change your membership options at >>> > http://mailman.mit.edu/mailman/listinfo/piclist >>> > >>> -- >>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist >>> >> >> >--=20 >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .