lull / Il HARDWARE HACKER ÏII 1111111111 = Using Double - Layer Capacitors ; Computer Power Interface , Underground Radio Technology

How Big is a one -Farad capacitor? Would you believe less than a cubic inch? Conventional wisdom and poorly done cartoons notwithstanding, a new capacitor technology is now available that crams incredible capacitance values into very small volumes. As Fig. 1 shows, these are called double -layer capacitors. They are both reasonably priced and available from distributor stock. For instance, a 1.0Farad, 5 -volt NEC # FZOH 105Z is available from Mouser Electronics for $4.59 each (part 5511.0Z05). Being a brand new and "hacker friendly" part, there's lots of exciting new possibilities here. But there are also some definite use limits and restrictions. One major use for double -layer capacitors is as power backup for CMOS memory chips. The capacitor can fake memory nonvolatility during a short power outage. Unlike most batteries, these devices can be cycled indefinitely, have at least a 10 -year life, can easily be soldered in place, are not polarized, usually cannot leak or explode, and readily indicate their charge. Back to the basics. A traditional capacitor consists of two conductors separated by an insulator. When a current is routed through a capacitor, a charge will build up and will be stored. The amount of the charge depends on the current and how long the current is applied. The charge also depends on the surface area of the conductors, the spacing between conductors, and a property of the insulator material known as the dielectric constant. Capacitors have many electronic uses, ranging from storing dc in power supplies; coupling /bypassing ac signals; resonating coils for frequency selection; and for integrating precision waveforms. The storage size of a capacitor is measured in Farads. A 1 -Farad charge will supply a current of 1 ampere for 1 second. Most capacitors have traditionally been much smaller than this, and are measured in microfarads (μF) or picofarads (pF) instead of Farads. SuPERCAP