FYP 2 Week 3 – Research & Simulation of Voltage Balancer Circuit

In serial connection, the strings of capacitors require voltage balancing to prevent any cell from going into over-voltage. A proper cell balancing scheme as shown in figure below, needs to be placed within series connected super capacitor to ensure no super capacitor sees higher than rated voltage. In this project, two super capacitor that rated at 2.7V each are used as the charge storage and are connected in series to become super capacitor bank that of rating 5.4V. Three diode, with each rated at 0.7V are placed in parallel to each super capacitor because the total of the three diode yield a total voltage of 2.1V which almost near to the value of the single super capacitor used. While series of four diodes cannot be placed in parallel to each particular super capacitor is because the total of the four diodes yield a total voltage of 2.8V which is more than the rating value of the single super capacitor used.

Figure of voltage balancing circuit.

Simulation of voltage balancer circuit.

Voltage balancer circuit are used as a safety circuit in this project to protect the super capacitor from being charged over its rated voltage. The voltage balancer used here is series of three diodes in parallel to each super capacitor used as shown in figure above.

As discussed above, two super capacitor that rated at 2.7V each are used as the charge storage and are connected in series to become super capacitor bank that of rating 5.4V in this project. Each of the diode use is rated at 0.7V and series of the three diodes yield a total voltage of 2.1V. When charging the super capacitor, each series of diodes will make sure each super capacitor does not be charged more than 2.1V although it can be charged up to 2.7V.

Series of four diodes cannot be placed in parallel to each particular super capacitor is because it will yield a total voltage of 2.8V which is more than the rating value of the single super capacitor used. If series of four diodes are placed in parallel to each super capacitor, then the super capacitor will get damaged.

The function of diode D10 and D11 as shown below is to allow current flow from battery into super capacitor and not to flow back. Thus, when this super capacitor bank is used to charge a load, the current will flow into the load (D13) only.