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.

FYP 2 Week 2 – Research & Simulation of Charging Circuit

The function of charging circuit is to control the amount of current used to charge the super capacitors in super capacitor bank. Over amount of current entering super capacitors will damage it. To avoid any damage, the amount of current entering the super capacitors needs to be reduced when it is reaching its full capacity with the slow, medium and fast charging option provided on the charging circuit.

Simulation of charging circuit.

• For charging circuit, the simulation is as shown in figure above. At the input, input voltage of 12V DC will be step down to 5V using voltage regulator circuits with LM7805 voltage regulator IC as shown in figure below. Output 5V produced will pass through a relay whose function is to connect or disconnect the supply to the charging speed controller which comprises three resistors each in series with a switch and the entire three resistors in parallel to load. The values of all three resistors are much lower (100Ω, 220Ω, and 330Ω) compared to the load. When all three resistors is turned on by closing the switch, slow charging takes place as resistance of resistor in parallel will drop to a value lower than each of the resistor, thus allow more current flow through it rather than flowing into load with higher resistance which satisfies the equation V=IR. Fast charging occurs when all the three resistors are disconnected and medium charging takes place when only one or two resistors are switched on

Figure of LM7805 voltage regulator IC.

FYP 2 Week 1 – Research & Simulation of Voltage Comparator & AC-DC converter

Voltage Comparator circuits:

In this project, the super capacitor bank will be fully charged to 5.4V. To check whether the super capacitor bank are fully charged or not, a voltage comparator circuit are used.

Proteus (ISIS) simulation software was used to do simulation.

Voltage Comparator IC LM293 (not functioning) in simulation shows error stating that no specified model for that particular IC in simulation software.

Since the voltage comparator IC LM293 does not functioning in simulation, it was then replaced with voltage comparator IC CA3140. Following that, the circuits function as required.

Voltage Comparator IC CA3140 (functioning) in simulation will detect input voltage of less than 5.09V:

• Figure showing input voltage detected less than 5.09V and light up Red LED.

Voltage Comparator IC CA3140 (functioning) in simulation will detect input voltage of more than 5.09V:

• Figure showing input voltage detected more than 5.09V and light up Green LED.

AC-DC converter:

The power generate from the dynamo will enter the AC-DC converter that will convert AC power from dynamo into DC power. The AC-DC converter consists of bridge rectifier, capacitor filters, and voltage regulator IC.

• Simulation of AC – DC converter circuit.

Simulation for AC-DC converter circuit was done by connecting its output to an oscilloscope and the output result was verified by analysing the voltage waveform result displayed on the oscilloscope as shown in figure below. The waveform voltage output on channel A is directly taken from the AC supply. While voltage output on channel D is the final DC voltage output from the converter circuits. The reading of the DC voltage output on channel D was read at the smallest scale of the oscilloscope which is 5mV/Division compare to the reading on channel A which read at 5V/Division. This shows that the DC voltage output produced is very stable as the result of using 0.1F capacitor as the filter. When tested with capacitor filter of lower value (10uF-47uF) that commonly used, the DC output was not as stable as of using the 0.1F values. Thus, this proves the circuits met its functionality.

Figure of simulation result of AC – DC converter circuit.