# Concept Design and Development of an Electric Go-Kart
## 5 Design of Electrical System
### Battery System Modeling  
The most important issues in power supply system development are battery cells, and more precisely, the type to be used. To choose the most appropriate station, it was decided  
Figure 14: Energy density comparison of battery cell materials. to use a morphological analysis. The analysis included, among other things, performance, safety, price, service life, power, energy density, operating temperature, and charging times. The most important criterion was the safety of the vehicle users. For this reason, cell types that meet high safety standards have been reduced to two cell types--LTO (Li4 Ti5 O12 --\"lithium titanate\") and LFP (Li Fe Po4--\"lithium iron phosphate\"). These two types do not burn or explode compared to the other cells considered. The number of cycles for both types is large, and the range of operating temperatures of the cells is also very wide and sufficient to operate in the initially assumed conditions. Comparing LTO and LFP cells, the biggest difference, and also the disadvantage of LTO cells, is their high cost. Different batteries have different energy value densities and specific energy. Li-ion cells used in the automotive industry (NMC--\"nickel manganese cobalt\", NCA--\"nickel cobalt aluminum\") have much higher values than LTO and LFP. Table 4 shows the basic parameters of these cells. Nominal vehicle voltage of a 48 VDC for a BDCEM drive can be achieved by a series connection of several Li-ion batteries with a nominal voltage of 3.6 V and a 3000 mAh capacity. The battery type 18650 was selected for this concept. This leads to a simple calculation of the required number of battery units connected in the serial connection: 48 V/3.6 V = 13.333; rounded to an integer, it is a value of 14. Therefore, the expected nominal battery system voltage is \(U_{\text{N}}=14\cdot 3.6\) = 50.4 V. According to the go-kart standard, driving with maximum power can take 10-20 min. For further design of the power supply, the chosen energy capacity is 1.6 kWh (\(E\) = 1600 Wh). Since one battery has an approximate or expected capacity of 3 Ah, this means that one serial \"package\" has the same energy capacity \(E_{1}\):\(E_{1}\) = 50.4 V:3 Ah = 151.2 Wh. Thus, when designed, ten of such packages should be connected in parallel and then the energy capacity would be ten times more, equal to \(E_{10}\) = 1512 Wh. This is close to the planned power consumption and is also within some geometric parameters that are suitable for mounting on chassis tubes. Details of the battery holder box and the design of the battery cell inter-connections are shown in Figure 15.  
Since a Li-ion battery is the most expensive part of the electric go-kart, improving battery performance is one of the most important factors in promoting the electric vehicle market, extending battery life, reducing the cost of purchase, and giving potential customers confidence in the product. Designers of electric battery systems must consider a method to improve battery performance that prolongs battery life and increases grip ability. This can be achieved by finding the best filling profile for the EV battery by identifying that battery time can accept charging and the charging profile, with minimal impact on battery life. The analysis presented in reference [48] shows that including rest periods reduces battery degradation in two parts while charging the battery's ways. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Li-Ion Type**} & **Specific Energy (Wh/kg)** & **Energy Density (Wh/L)** & **Cycle Life** \\ \hline NCA & 220–260 & 600 & 500 \\ \hline NMC & 150–220 & 580 & 1000–2000 \\ \hline Li Fe Po4 & 90–160 & 325 & \textgreater{}2000 \\ \hline Li4 Ti5 O12 & 60–110 & 177 & 3000–7000 \\ \hline \end{tabular}
\end{table} 
Table 4: Specific energy and energy density of Li-ion cells. On the other hand, the reliable battery management system, or BMS, is required for the safe use of Li-ion batteries [47].