## 4 Electrical System
### Energy Supply  
Due to the duration of the Microtransat Challenge, an energy budget must be estimated such that the vessel can cross the ocean autonomously. Ideally, the drone's lifetime is infinite, which can be assured using rechargeable batteries. However, the effectiveness and \begin{table}
\begin{tabular}{c c} \hline \hline
**Task** & **Period (Seconds)** \\ \hline Data logging & 5 \\ GPS read & 10 \\ Wind read & 5 \\ Compass read & 0.5 \\ Rudder control & 1 \\ Course update & 60 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Time periods for different tasks. likelihood of failure of the energy supply system must also be considered. In this section, the choice of a non-rechargeable energy source for the SeaLeon is justified. Note that several attempts were made to cross the Atlantic. The energy supply for some of the most competitive designs is summarized in Table 3, along with the number of days lasted at sea. It should be noted that the mission duration seems to have been very short for sailboats relying on rechargeable batteries. In the design of the SeaLeon, the expected mission duration was approximately 90 days, with a fairly wide margin (plus or minus 30 days) depending on the sea conditions. In order to establish the energy supply requirements, Table 4 shows a calculated power budget for the SeaLeon. The power budget was made using estimates from data sheets and actual measurements when possible. Note that in the design of the SeaLeon, the Iridium communication system was a standalone radio, with an independent battery. The SeaLeon's power system was designed to give as many amp hours as possible given the constraint of the size of the sailboat. This idea led to a power system consisting of 128 Lithium Thionyl Chloride (LiSOC\({}_{2}\)) D-Cell batteries, distributed by Eagle-Picher. The batteries were placed in series giving a supply voltage of 14.8 volts, and thirty-two sets of four were placed in parallel in order to increase the amp-hour capacity. Altogether, the batteries provided a total of 680 Ah capacity. Figure 3: Navigation algorithm. Rechargeable methods for supplying power to the sailboat were also considered. Solar panels have been a popular choice for other Microtransat participants. For example, solar panels were used by the the Breizh Spirit, designed by Ensta-Bretagne. The Breizh Spirit had an energy supply that could last 3 days minimum, and used lead acid batteries that could be recharged up to 500 mA by solar panels. In addition to non-rechargeable cells, rechargeable cells, such as lithium iron phosphate (LiFePO4) cells, are considered as an option to increase the lifetime of the drone. Table 5 shows a comparison of metrics for four LiSOC2 versus four LiFePO4 cells placed in series. An arrangement of eight 280 Ah prismatic (LiFePO4) cells with two sets of four placed in parallel can provide 560 Ah of capacity and the ability to increase the amp-hours further by recharging the cells. However, from the table, it is apparent that LiSOC2 PT-2300 batteries weigh less and occupy less volume per amp-hour in comparison to the LiFePO4 LF280 cells. The LiSOC2 PT-2300 cells were chosen for the SeaLeon energy supply based on its comparison to the rechargeable cells. In addition, a rechargeable method such as solar panels would take up a significant amount of space on the sailboat. It was decided that a larger density of cells would be the best approach to a long-lasting energy supply. Rechargeable lithium cells do provide an interesting alternative solution, particularly for sustainability considerations. Specifically, rechargeable batteries are more convenient for testing purposes, since they can be recharged rather than removed and replaced after trials. Rechargeable lithium cells also create the potential for a higher effective capacity when paired with renewable energy such as solar panels. In addition, the use of renewable energy can lead to research into software power conservation techniques.