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What Is a Capacitor Residual?

Capacitors are components of electronic circuitry ranging in size from very small (like those in cellphones) to extremely large (like the ones found in high-voltage electrical power stations). The function of a capacitor is to store a static electrical charge when a current is applied; this function is used to perform a variety of tasks such as directing or filtering alternating and direct currents, regulating voltages, tuning radio frequencies and storing up charge to make flash photography possible with small digital cameras. Capacitor residual is a potentially dangerous -- even lethal -- stored electrical charge that often remains in a capacitor long after the current source has been removed.

Lightning
- The sky acts as a giant capacitor, storing residual charge until lightning discharges it.
  
  Lightning is a natural form of capacitance in which a static charge is stored between two conductors, the cloud and the ground. Until that charge is dissipated in the form of a lightning strike, residual charge remains in the air and the potential for lightning persists.
Old Televisions and CRTs
- Old TV sets use CRT screens which store residual charge in addition to the large tin can-like capacitor components inside.
  
  If you have ever touched or dusted a television CRT (cathode ray tube) screen and felt or heard the tickle of static electricity, you have experienced the residual charge of capacitance which builds up when CRTs are used and remains after they have been turned off. In old-time television sets, this residual charge can build up to levels producing dangerous voltages at the back of the CRT. Old-time TV repairmen always used an insulated wire jumper to discharge this 10,000 to 25,000 volt yoke voltage before servicing television sets.
Digital Cameras
- The electronic flash circuit of digital cameras have capacitors, which hold a residual charge with a potential for 300 volts even when the camera is off.
  
  Digital cameras operate on batteries with a combined voltage of about 3 volts. While you await your electronic flash, electrical charge is being stored in a capacitor, which has a potential to produce 300 volts. This storage process is analogous to water slowly filling a high water tower to produce great water pressure when it is needed. The stored charge is released and produces a very bright flash when you depress the shutter. Stored charge can remain residual in the camera's capacitors even after you have turned off the camera.
Power Line Capacitors and Transformers
- Power substations have banks of capacitors with the residual potential for discharging 100,000 volts or more.
  
  Power line transformers and capacitors regulate high voltage electricity transmission; they can retain residual charges with the dangerous potential for producing many thousands of volts.
Residual Charge: YOU are the Capacitor!
- Under certain conditions, residual charge from static electricity turns you into a capacitor.
  
  Walk around on a carpet in wool slippers during dry, winter weather; touch a doorknob or another person and you will experience a voltage discharge of up to 30,000 volts. This residual charge remains in you and can keep your hair standing on end until it dissipates naturally or is discharged in some shocking way.

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