• Calculating the instantaneous current I (amps) through a supercapacitor
  
  With C (Farads) The capacity of the cell and DV (volts) The variation of the voltage at its terminals for a duration dt (seconds).


• Calculating the energy E (Joules) contained in a supercapacitor
  
  With V (volts) the voltage at its terminals.


• In a more conventional way, energy is expressed in Watt hour

  

• Charge the supercapacitor by applying its nominal voltage Vn (volts) and a constant charge current I (amps).
• Measure the time between T1 and T2 (seconds) during which the supercapacitor is passed from a voltage V1 to a voltage V2 (< Vn)

• Keep the supercapacitor charged for a few minutes at its nominal voltage Vn and then discharge it with a constant current I_DC (amps) up to 0.1 Volt.
• Visualize the potential drop (∆ V in volts) at the start of the discharge.
• This potential fall ∆ V is equal to the discharge current multiplied by the ESR series resistance of the supercapacitor:

• Self-discharge refers to the natural voltage drop of a fully charged supercapacitor at its nominal voltage. Self-discharge evolves in a degressive and nonlinear manner. The self-discharge rate depends on the voltage level of the cell, the temperature, the imperfections of the separator and the impurities present in the electrolyte and on the electrodes. To measure self-discharge simply charge the cell/module to its nominal voltage and maintain the load (≈ 1h). The load circuit is then opened and the voltage is measured at the supercapacitor terminals after 72h.
• The leakage current is largely responsible for self-discharge, it is equal to the charge current required to maintain the supercapacitor at the specified voltage value. The more the supercapacitor is kept in tension, the lower the leakage current is. The measured result is influenced by the temperature, the voltage at which the device is charged and the conditions of ageing. It is sufficient to measure the current to maintain the supercapacitor at its nominal voltage after a period of 72h at room temperature 23 °c ± 2 °c.

• The origins of a voltage imbalance in a module:

The Supercapacitor series cannot be carried out simply because of the different parameters of each cell in the module. These differences are due to capacity values, temperatures, ageing and manufacturing parameters that may be different for each supercapacitor. These three reasons lead to voltage imbalances between each cell.
To overcome this problem, choose the most identical supercapacitors possible and use a voltage balancing system.
In a supercapacitor module, there are three main types of voltage imbalance:

1. imbalance due to different leakage currents
2. imbalance due to different capacities
3. imbalance due to different series resistors (ESR).

• Risk of unbalanced voltages:

If there is no balancing, an overvoltage may appear on one of the supercapacitors in the module. This leads to the gradual and accelerated deterioration of the cell. Indeed, the overvoltage decreases the capacity, increases the series resistance (ESR), and can lead to the destruction of the component (the electrolyte in the cell begins to decompose, producing gaseous products as well as an accumulation of pressure up The destruction of the cell). Moreover, it should be noted that the total life expectancy of a supercapacitor module is equal to the lowest life expectancy of the most critical cell.

The balancing of the voltages within a module is therefore important in each phase of use (load, discharge, rest) in order to maintain its proper functioning and to increase its service life. For this reason, Euracap integrates in its modules an efficient balancing circuit, maintaining the integrity of the cells throughout the cycles of use.