# Calculation method of EDLC’s Power Density

Power-type EDLC refers to the application range where discharge currents span from milliampere to ampere levels. These kind of capacitors exhibit high capacitance and low internal resistance characteristics, making them suitable for Category 3 as specified in measurement classification under IEC 62391-1. The definition and calculation steps for power density can be found in Appendix A of IEC 62391-2, as detailed in the following text.

#### 1. Definition of Power Density:

Power Indicates the electrical power value of the capacitor, in watts (W). Power density indicates the electrical power of a capacitor per unit quality (or volume). The higher the power density, the higher the current efficiency.

#### 2. The calculation of power density involves several steps:

2.1 Calculation method of power density per unit mass

a) Calculate the Internal Resistance of the Capacitor as per Method Described in IEC 62391-1 Section 6.2

b) Calculate the Discharge Current Value using the Formula below. is 20% of the Charging Voltage

I=U6/Rd

refers to the internal resistance obtained through the DC internal resistance measurement method.

c) The Power Density per Unit Mass is calculated using the following formula:

• is the power density per unit mass (W/kg).
• is the charging voltage (V).
• is the voltage drop value (V), which is 20% of the charging voltage.
• is 40% of the charging voltage.
• is the discharge current calculated through A.3.1 b)(A).
• is the internal resistance value obtained through the DC internal resistance method.
• is the weight of the capacitor (kg).

#### A.3.2 Calculation Method for Power Density per Unit Volume

The power density per unit volume is obtained by replacing the capacitance quality in Formula A.3.1 C) with the capacitor volume, calculated using standard dimensions in liters (L).

Note: The capacitance mentioned here is calculated using the standard dimensions of the capacitor, measured in liters (L).

1. The voltage drop is not the voltage value right after the start of discharge; rather, it’s the intersection of the backward extension of the linear part of the discharge curve with the moment of discharge initiation .
2. The discharge current mentioned here is determined by specific specifications, and doesn’t necessarily have to be 0.2U.

Note: According to this standard, the discharge current for a single unit of Zhifengwei Technology’s 3000F capacitor can reach up to 1800A, although this level might not be achieved in typical usage scenarios.