While the circuit proved to be functional in theory, choosing the correct components would be vital in making sure the circuit is operating at maximum efficiency. The preliminary circuit design was completed towards the end of Phase 3. Virtual simulation showed that with an input of 20 VAC, the PFMEC which corresponds to 15 Vrms. The capacitor would smooth out the waveforms and reduce the ripples while the voltage regulator would stabilize the voltage at a steady 5 VDC. Electrical simulations of the circuit show that the the peak output voltage out of the capacitor would be 13.38V. This represents 89% efficiency from the conversion of AC to DC. The electrical schematic used for constructing the circuit is shown in Figure 9. The results of the simulations and  transient analysis are displayed below in Figure 10. These simulations show that the output voltage of the voltage regulator is 5.79V. Though this is more than the battery can intake, the group is anticipating additional resistance losses to occur internally within the circuit, lowering the voltage. This should begin the voltage down to an acceptable limit. An alternative solution would be to simply add a resistor in parallel to the capacitor to manually decrease the voltage. 

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Figure 9: Electrical Schematic

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Figure 10: Transient Analysis

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The team decided to work backwards, choosing a battery unit first. The battery unit needed to be lithium ion to allow for recharging. Furthermore, the battery needed to be capable of storing 5V of charge. Ultimately, the group chose Energizer AA Rechargeable Batteries NiMH with 2300 mAh and 1.2V. A typical phone charger can tolerate voltages from 4.5V to 5.0V. By putting 4 of these batteries in series, the stored voltage would be 4.8V, well within the acceptable range. The batteries have a internal capacitance 0.2C. This value corresponds to the discharge rate of the battery. Depending on the amount of current applied at a given time, the battery can hold charge for anywhere between 5 to 10 hours, depending on charging current. 

Next, the team deliberated on the type of capacitor to use. The purpose of the capacitor is to smooth out the ripples between each cycle. It does this by storing energy in an electric field and releasing it to stabilize its output. In this circuit, the capacitor will act as a filter, creating a smooth curve for the output DC voltage. There are many factors that went into choosing an appropriate capacitor. Because the PFMEC will rely on VIV to power the induction system, the frequency of the system will change as the speed of the current changes. Using data obtained from Davidson Laboratory, the group understood that the surface current varies between 0 knots/ sec to 2 knots/ sec. 2 knots/ sec corresponds to approximately 1 m/ sec. The group used this value in all future electrical calculations. A sample of the data is shown in Figure 11.

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Figure 11: Urban Ocean Observatory Data for Hoboken Provided by Davidson Laboratory 

 

 

 

Based on the technical analysis, the group determined that the period of the input AC voltage, the time required to complete one cycle, was .245 sec. The frequency was then calculated to be 4.08 Hz. This value was approximated at 4 Hz. Capacitors with varying rating values were compiled and the reactance of each was calculated. Based on this value, the output current corresponding to each capacitor was calculated. Based on the amount of current each capacitor allowed to pass, an appropriate capacitor was chosen. 

The group ultimately chose a 250 uF capacitor that allowed an output current flow of 9.6 mA. Knowing the amount of current traveling from the capacitor is necessary because the linear voltage regulator can only handle a certain range of input currents. The minimum input current allowed for a L7805A 5V linear voltage regulator is 5mA. This capacitor is within the range of acceptable currents, validating its usage. Below is a schematic of the preliminary circuit setup. Seen below is the four diodes in a diamond setup, representing the full wave rectifier, connected to the 250 uF capacitor as well as the L7805A voltage regulator.

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Figure 12: Circuit Setup

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Further development for the electrical beta prototype will include ordering an insulated enclosure to protect the electrical equipment when submerged in water bodies. This enclosure will then be mounted unto the body of the device. Necessary testing of the circuit will also be conducted in Phase 5, utilizing an AC power source to mimic real life conditions. Moreover, the batteries will be connected to evaluate the charging capabilities before the circuit is hooked up to any electrical devices.