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Capacitors |
R. W. Stuart A capacitor is an electrical device which can store electrical energy in a form that resembles static electricity. The first laboratory capacitors were made by putting one glass cylinder inside a slightly larger cylinder after plating the inside of both cylinders with silver. Terminals were soldered to the two silver platings and the resulting capacitor could then be charged; and, with glass and air as the separators, the charge would hold for many months. These were more than gallon sized cylinders and after being charged could blow the end off a screw driver which was used to short (discharge) the capacitor. The laboratory capacitors made this way were called Lyden jars. The Lyden jars, carefully taken apart so no discharge occurred, could then be separately handled, passed around a class, washed, and stored as long as they were not reassembled. When assembled again, they were right up to full charge and ready to go. This is counter-intuitive. The unit of capacity is the Farad, but the microfarad is the basic useable size and many are designated as picofarads. Since capacity is a function of surface area; older production of capacitors depended on rolling up two metal strips with an oiled paper insulator between- still static electricity and although the electricity is polar the device is non-polar. Subsequent technology to increase capacity and decrease both cost and size resulted in chemical capacitors (nothing more than short term batteries) which stored energy as chemical change and are polar- the device has a plus terminal and a minus terminal and must be connected accordingly. This is pretty much the state of the art. Batteries (Nicads, et al) are great for storing energy-- its the charging and discharging that causes problems. Charge too fast and they crash; draining them quickly is either damaging or impossible. An emerging technology depends on capacitors made by rolling a sandwich of plastic and porous solid carbon soaked with electrolyte. Called super-capacity capacitors, these units absorb and return as much as 4500 times the electricity as conventional capacitors. Since no chemical reaction is involved they can be charged and discharged without wear. In devices that require large pulses of power, super-capacitors can make the batteries lives smoother and longer- for only a buck or two. This stuff may show up in a year or so. Very large capacitors could be used in power plant operations to store energy during demand lows and then return power to the system during demand peaks. This would allow the generators to be operated at their most efficient setting and thus reduce the cost of electrical power. Super- capacitors might allow this technology to develop. Beware of capacitors that may be lying around because they may be charged. You will not see, hear, smell, or feel anything until the capacitor discharges-- then you will see, hear, smell, and feel- all in one big bang. |
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