AC capacitor question
in [Basics]
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From: default on 25 Mar 2010 11:07 On Wed, 24 Mar 2010 15:28:38 -0700 (PDT), lerameur <lerameur(a)yahoo.com> wrote: >Hi, > >I believe it is possible but I would just like a confirmation. >I would like to know if I can use an AC capacitor and make it behave >like a DC cap, I would like to do a rail gun. Are DC capacitor better >suited, do they perform better for a quick discharge.?? > > >K You are getting into something where the internal construction of the cap may matter more than type. For a rail gun, you want all the energy out of the cap in one fast discharge - so the cap has to have low "external series resistance" and a low inductance type of construction - interleaved sheets of dielectric/plate work better than a cap with the dielectric and sheets wound up. Large heavy braided copper connections - or copper pipe with large surface area, and short connections to minimize losses. Caps designed for "commutation" use are a good bet - non polar and designed for relatively high voltage, high discharge rates. RF caps another good choice - very low ESR/inductance, very high voltages. AND very expensive as a rule Check out what Tesla coilers use - they have the same requirements, high voltage high discharge etc.. Do it yourself glass plate caps are fun - maybe too low in capacity for your aps, but they are inexpensive, big bulky, and can be made nearly indestructible. (a paper cutter will cut thin sheets of aluminum flashing material - to make some dynamite stacked foil caps) Photoflash caps are a good choice - DC electrolytic designed for fast discharge at moderately high voltages. Lastly, an ordinary electrolytic or HV cap will sometimes fail open when the lead connecting to the internal foil vaporizes at the connection (usually a spot-weld between copper and aluminum) commutating caps, photoflash, RF caps are usually designed with that in mind. Rail gun or coil gun? Same type of cap requirements though. These days AC caps can be made quite small - so a lot of the "motor run" caps are now non polar, non electrolytic, with good "dissipation factor." --
From: Michael A. Terrell on 25 Mar 2010 13:59 Don Klipstein wrote: > > And these huge capacitors can probably electrocute an elephant. Once again proving that Elephants have no business playing with high voltage! ;-) -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: Michael Robinson on 26 Mar 2010 10:06
"lerameur" <lerameur(a)yahoo.com> wrote in message news:a115bc51-cf30-408f-b3e6-1a339c006d3d(a)15g2000yqi.googlegroups.com... > Hi, > > I believe it is possible but I would just like a confirmation. > I would like to know if I can use an AC capacitor and make it behave > like a DC cap, I would like to do a rail gun. Are DC capacitor better > suited, do they perform better for a quick discharge.?? > > > K Check out http://4hv.org |