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Super capacitor is an electrochemical capacitor with the ability to store more energy than conventional capacitors. Super capacitors can charge and provide energy faster than batteries. The increasing application of instantaneous standby power supply promotes the demand for super capacitor.
The remarkable advantage of super capacitor is that it can cycle thousands of times before aging, while the battery can only cycle hundreds of times.
The latest development of super capacitor has introduced lithium-ion hybrid capacitors which can be charged to high voltage (up to 4V), which has less self-discharge and high energy density. The disadvantage of these super capacitors is that they cannot discharge to less than 2.2V, otherwise they will be damaged.
The composition of super capacitors makes their self-discharge rate significantly higher than that of battery. The higher the working temperature of super capacitor, the higher the charging voltage, the faster the aging; The capacitance of super capacitor will decrease and the equivalent series resistance (ESR) will increase. This means that the super capacitor can provide less energy for the application. ESR of capacitor increases power loss of the system.
The temperature is only 10% higher, the life of the super capacitor can be reduced by half. In addition, it is usually used to charge the super capacitor to a voltage below the nominal voltage to increase its life.
Since the maximum voltage of the super capacitor charging is between 2.7V and 3V, it is necessary to connect several super capacitors in series for most applications. Therefore, the super capacitor must be balanced; Otherwise, one unit may charge more than another, leading to the aging of unequal capacitors, reducing the capacity of capacitor banks to provide the energy required for application.
The methods used to balance the super capacitor include: passive balance of resistor string, switch resistor, zener diode and active balance. The first three methods can cause power loss in resistors, and the fourth is the most effective but also the most expensive.
When super capacitors are used for standby power applications, their capacitors and ESRs must be monitored to ensure that the minimum energy required for the application can be provided.
Super Capacitor applications: RAM; Detonator; car recorder; smart meter; Vacuum switch; digital camera; motor drive; clock circuit; UPS; toy; program-controlled switch; etc.
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