Conversion of electrical units (Capacitance) into energy and power units
Symbols used in this notes are:
F – Farad; C – Coulomb; V – Volt; A – Ampere; J –Joules; s – second; W – Watt; g – gram; h – hour
Correlation between electrical (capacitance) and energy and power units
F = C/V
W = A×V
C = A×s
J = W×s (Energy unit)
F =(A×s)/ V
So,
F×(V^2) = A×s×V = W×s = J
Or, F = (W×s) / V^2 = J / V^2
Note:
Faraday's Constant is different from Farad. (Not confused, though both represented by symbol 'F'.)
1 Faraday = 96485 C
1 Faraday = (96485 C /3600 s) = 26.801 A·h
Capacitance is expressed in, F
Energy is expressed in, Wh
Power is expressed in, W
Specific Capacitance is expressed as: F/kg (or) F/g
Specific Energy is expressed as: Wh/kg (or) Wh/g
Specific Power is expressed as: W/kg (or) W/g
Assume a supercapacitor has a Specific Capacitance of 2000 F/g and discharges at a potential difference of 1 V in 900 s, then Specific Energy and Specific Power is related to its Specific Capacitance as:
Formula:
Specific energy = 0.5 × Specific Capacitance × (dV)^2
Here, Specific Capacitance = 2000 F/g and dV = 1 V
= 0.5 × 2000 F/g × (1 V)^2
= 1000 F/g V^2 = 1000 J/g
= 1000 W×s /g
= {1000 W×s /g} / 3600 = 0.2778 Wh/g
= 0.2778 Wh/g × 1000 = 277.8 Wh/kg
So, Specific Energy = 277.8 Wh/kg
Specific Power = Specific Energy / time (in hour)
Discharge time = 900 s/3600 = 0.25 h
So, Specific Power = (277.8 Wh/kg) / (0.25 h) = 1111.2 W/kg
By,
Dr. M Kanagasabapathy
Associate Professor
Department of Chemistry
Rajapalayam Rajus’ College
Madurai Kamaraj University
Rajapalayam (TN) 626117 (IN)
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