08-16-2017, 10:19 PM
electric double layer capacitor full report
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Electric Double Layer Capacitors (EDLC)
INTRODUCTION
Electric Double Layer Capacitors (EDLC) are also called super capacitors or ultra capacitors. They store energy in the form of static charges. EDLC resembles the ordinary capacitors but having high energy density. EDLC have very low working voltage ,and are used in hybrid vehicles. EDLC s are rated from Farads to Kilo Farad ranges
HISTORY & PRESENT
Electric double layer effect was first noticed by General Electric engineers in 1957. But this effect is rediscovered and researches are done by Standard oil of Ohio in 1966. But it is NEC,who finally marketted the result as SUPER CAPACTORS.
Due to the development of Material Science in 90 s,this technology improves rapidly. Today , electronic devices, Locomotives uses this technology.
CONSTRUCTION
EDLC s construction is similar to that of ordinary capacitors. EDLC s doesn't have any conventional dielectric rather than ,two plates separated by an inverting substance. The Super Caps uses plates of same material having same electrical properties and are called electric double layer.
Main materials used for the construction are
Activated Charcoal
CarbonNano Tubes
Aerogels
EDLC use Activated Charcoal as plates.
It is because
It s a powder made of very small & rough particle
It s having a low density particles with holes
Over all surface area is very much larger than other materials like Al , Ti etc.
But Activated Charcoal is not a perfect material for EDLC. It's because
The charge carriers are quite larger than the pores in the Charcoal .
Some times too large pore size in charcoal.
Carbon Nano Tubes are used today.
They have same charge storage capability as that of Charcoal
Having much more mechanically arranged rigid pattern.
Having much more surface area.
PRINCIPLE & WORKING
EDLC store electrical charges similar to that of ordinary capacitors. But charges doesn't accumulate on electrode, instead it is stored in the interface between surface of the conductor and electrolytic solution.
Capacitance of EDLC is given by the equ:
C= A e / 4 p d
A- Area of the contact plates
d- distance between the plates
e dielectric constant of the medium between the plates
ADVANTAGES
Eco friendly
High Efficiency
Rapid charging & Discharging
Low internal Resistance
High power density
Reliable in harsh environment
Virtually unlimited cycle life
Simple charge methods
DISADVANTAGES
Unable to use full energy spectrum
Low energy density
High self discharge
Low working voltage
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