Calculation method of farad capacitance capacity

In the application of super capacitor, many users have the same problem, is how to calculate a certain capacity of super capacitor in a certain discharge current, discharge time, or on the basis of the discharge current and discharge time, how to select the super capacitor capacity, below we give a simple calculation, users according to the formula, can simply for capacitor capacity, discharge current, discharge time, very convenient.

Farah capacitance also known as "super capacitor" (supercapacitor, ultracapacitor), "electric double layer capacitors" (Electrical Doule - LayerCapacitor), "gold capacitance", etc.It to store electricity by polarization electrolyte, it is an electrochemical device, but in the process of the energy storage is not produces chemical reaction, the energy storage process is reversible and also because of this, can be repeated charge and discharge hundreds of thousands of times.

How to test farah capacitance

Can use constant current source to determine time constant, the capacitance.Inside some formula design, the following article, on the specific point of my advice is to consult a professional!

1 F = 1 q/V (coulomb/V).

If 5.5 V, 1 f capacitance, the biggest store 5.5 coulomb of charge

1 farad capacitor charged to 5.5 V calculation e = 0.5 * U * c ^ 2 = 0.5 * 1 * 5.5 ^ 2 is approximately equal to 12 j j = 1 w/S, that is to say the 12 w with electrical appliances can be used for a second, general MP3 players and other electrical appliances are zero point zero a few watts, if 10 f capacitance, almost in a few hours.

2: Farah capacitance, high power density, up to 300 w/w/kg to 5000 kg, is equivalent to normal battery dozens of times;Than energy greatly improved, normally only 0.02 kWh/kg, the lead-acid battery and super capacitor battery at present, the research and development has up to 10 kWh/kg, try measure the quality of the capacitance, to calculate how many W, then to judge the feasibility according to the load.

3: on the transverse load as described above, general discharge capacitance is a line segment, but given the inductive load, etc., it is not.

Farah capacitance capacity calculation method

Nominal capacity C (F) : super capacitor;

The nominal resistance R (Ohms) : super capacitor;

The ESR (Ohms) : 1 kz equivalent series resistance;

Vwork (V) : normal working voltage

Vmin (V) : by the working voltage;

T (s) : in the circuit requires continuous working time;

Vdrop (V) : at the end of the discharge or large current pulse, the total voltage drop.

I (A) : load current;

Super approximate calculation formula of capacitance,

Maintaining the needed energy = super capacitor to reduce energy.

The energy required to keep the during = 1/2 (Vwork + Vmin) I t;

Super capacitor energy = 1/2 (Vwork2 - Vmin2) c,

Thus, available capacity (ignore the pressure drop caused by the IR)

C=（Vwork+Vmin）It/（Vwork2-Vmin2）

For example, are as follows:

Such as single chip microcomputer application system, the application of super capacitor as a backup power supply, need to use super capacitor after useing maintain current of 100 ma, the duration of 10 s, single-chip microcomputer system by the working voltage of 4.2 V, you need to how much capacity of the super capacitor can guarantee the normal work of the system?

Known by the above formula:

Work start Vwork = 5 v voltage

Work as Vmin = 4.2 V voltage

Work time t = 10 s

I = 0.1 A working power

Then the capacitance for:

C=（Vwork+Vmin）It/（Vwork2-Vmin2）

= (5) + 4.2 * 0.1 * 10 / (52-4.22)

=1.25F

5.5 V1.5 F capacitance can be selected according to the calculation results, can satisfy the need.

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