# super cap: charging /discharging efficiency and measurement current

According to Annex C(informative) of 62576 ©IEC:2009, the charging and discharging efficiency and measured current of supercapacitors for energy storage can be calculated by the following formula.

C.2 charging efficiency, discharging efficiency, and current

Charge Q after charging or discharging for time t at a constant I, stored energy W, and energy L lost by resistance R are given by Equations (C.1),(C.2)and (C.3), respectively

Q=IT                            (C.1)

W=Q2/2C                        (C.2)

L=I2Rt=RQ2/t                      (C.3)

When a capacitor is charged or discharged to its full capacity at a constant current according to Equation(c.2) or (C.3), respectively, the energy efficiency PC for charging or Pd for discharging is given by Equation(C.4) or (C.5), respectively,  where R is the internal resistance and C is the capacitance of the capacitor.

In this standard, the efficiency for charging or discharging is proposed as 95% after considering exothermal effect and time consumption for the measurement. The time t required for charging at 95% efficiency is given by Equation(C.6) derived from Equation(C.4)

Charge Q stored in a super cap is given as a product of capacity C and charging voltage U, thus leading to Equation(C.7), Current Ic for 95% charging is given by Equation(C.8)  derived from Equations(C.1), (C.6)and(C.7).

Similarly, the time t needed for 95% discharging is given by Equation(C.9) derived from Equation(C.5), and the current Id needed for 95% discharging is given by Equation(C.10)

Equations (C.8) and (C.10) are suggested for determing the value of the current for the charging or discharging test. Once the value of the charging/discharge current is determined, the maximum output at the target efficiency can be calculated.

Supreme Power Solutions Co., Ltd. (SPS) is a leading manufacturer of ultracapacitors, as well as a provider of ultracapacitor energy storage systems and technological solutions. Our products have wide industry applications, such as new energy vehicles, wind turbines pitching control systems, trams and subways, smart grid, micro grid, heavy duty machineries, intelligent instrument, etc. We support more than 200 customers, and our products are exported to 26 countries and territories.

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