Handbook for Sound Engineers

262 Chapter 10

interference. Y capacitors have high electrical and
mechanical specifications so they are much less likely
to fail.

XY Capacitors. When used together they are called
XY capacitors.

10.2.4.7 Supercapacitors

Supercapacitors, Ultracapacitors, more technically
known as electrochemical double-layer capacitors, are
one more step beyond the electrolytic capacitors. The
charge-separation distance in ultracapacitors has been
reduced to literally the dimensions of the ions within the
electrolyte. In supercapacitors, the charges are not sepa-
rated by millimeters or micrometers (microns) but by a
few nanometers or from electrostatic capacitors to elec-
trolytic capacitors to ultracapacitors. The charge-separa-
tion distance has in each instance dropped by three
orders of magnitude, from 10–3m to 10–6m to 10–9m.

• How a Supercapacitor Works. An supercapacitor
  or ultracapacitor, also known as a double-layer capac-
  itor, polarizes an electrolytic solution to store energy
  electrostatically. Though it is an electrochemical
  device, no chemical reactions are involved in its
  energy storage mechanism. This mechanism is highly
  reversible and allows the ultracapacitor to be charged
  and discharged hundreds of thousands of times.
  An ultracapacitor can be viewed as two nonreac-
  tive porous plates, or collectors, suspended within an
  electrolyte, with a voltage potential applied across the
  collectors. In an individual ultracapacitor cell, the
  applied potential on the positive electrode attracts the
  negative ions in the electrolyte, while the potential on
  the negative electrode attracts the positive ions. A
  dielectric separator between the two electrodes
  prevents the charge from moving between the two
  electrodes.
  Once the ultracapacitor is charged and energy
  stored, a load can use this energy. The amount of
  energy stored is very large compared to a standard
  capacitor because of the enormous surface area
  created by the porous carbon electrodes and the small
  charge separation of 10 angstroms created by the
  dielectric separator. However, it stores a much
  smaller amount of energy than does a battery. Since
  the rates of charge and discharge are determined
  solely by its physical properties, the ultracapacitor
  can release energy much faster (with more power)
  than a battery that relies on slow chemical reactions.
  Many applications can benefit from ultracapaci-
  tors, whether they require short power pulses or

low-power support of critical memory systems.

Using an ultracapacitor in conjunction with a battery

combines the power performance of the former with

the greater energy storage capability of the latter. It

can extend the life of a battery, save on replacement

and maintenance costs, and enable a battery to be

downsized. At the same time, it can increase avail-

able energy by providing high peak power whenever

necessary. The combination of ultracapacitors and

batteries requires additional dc/dc power electronics,

which increases the cost of the circuit.

Supercapacitors merged with batteries (hybrid

battery) will become the new superbattery. Just about

everything that is now powered by batteries will be

improved by this much better energy supply. They

can be made in most any size, from postage stamp to

hybrid car battery pack. Their light weight and low

cost make them attractive for most portable elec-

tronics and phones, as well as for aircraft and auto-

mobiles.

• Advantages of a Supercapacitor
  
  
  1. Virtually unlimited life cycle—cycles millions of
     times—10 to 12 year life.
  
  
  2. Low internal impedance.
  
  
  3. Can be charged in seconds.
  
  
  4. Cannot be overcharged.
  
  
  5. Capable of very high rates of charge and discharge.
  
  
  6. High cycle efficiency (95% or more).
  
  
  
  


• Disadvantages of a Supercapacitor:
  
  
  1. Supercapacitors and ultra capacitors are relatively
     expensive in terms of cost per watt.
  
  
  2. Linear discharge voltage prevents use of the full
     energy spectrum.
  
  
  3. Low energy density—typically holds one-fifth to
     one-tenth the energy of an electrochemical battery.
  
  
  4. Cells have low voltages; therefore, serial connec-
     tions are needed to obtain higher voltages, which
     require voltage balancing if more than three
     capacitors are connected in series.
  
  
  5. High self-discharge—the self-discharge rate is
     considerably higher than that of an electrochem-
     ical battery.
  
  
  6. Requires sophisticated electronic control and
     switching equipment.
  
  
  
  

A supercapacitor by itself cannot totally replace the

battery. But, by merging a supercapacitor and a battery

together—like a hybrid battery, it will be possible for