# COTS Battery Charge Equalizer for Small Satellite Applications
## 6 Discussion  
The experimental results presented in the previous section allow a detailed comparison between the balancing topologies developed in this study. The DSSCE topology has reduced power consumption and achieves faster balancing when significant voltage imbalances are present between the cells. However, it should be noted that the efficacy of the device is reduced as the voltage differences decrease. Moreover, due to the greater number of components employed in this architecture, a larger PCB area is required. Conversely, the SFCBE topology consumes a greater amount of power. Nevertheless, it performs more efficiently when voltage mismatches are minimal, ensuring a more consistent balancing rate throughout the process. The compact design and reduced component count facilitate a smaller PCB footprint. However, it should be noted that these advantages are accompanied by a reduction in fault tolerance and an increase in design complexity. Both implementations employ a configuration with four cells in series (4S), which is representative of the most common CubeSat battery packs. As demonstrated in the existing literature [8; 34; 35], 18650-based batteries with 2S to 4S configurations are utilized to supply regulated 8 V to 16 V buses. It is noteworthy that in certain 6U or larger CubeSats, configurations may extend up to 8S. These are compatible with both of the studied topologies, although they require more components and larger PCB area. Therefore, the selected topologies are well suited for typical CubeSat battery configurations. Nevertheless, scaling beyond this range has the potential to present new challenges, such as temperature variations across the entire battery pack. The designs presented were adapted for use with 18650 lithium-ion cells. However, the application of these equalizers to other chemistries employed in CubeSats, such as LiPo or NiMH [36], would require adjustments to the operating voltage and internal impedance values. For example, in the case of NiMH cells, they have a lower voltage per cell (approximately 1.2 V per cell). Additionally, NiMH cells have a higher internal impedance, which contributes to increased losses in the equalizer. Consequently, it may be necessary to re-optimize the capacitor values and switching frequency in order to match the new voltage and impedance levels. Concerning LiPo cells, it should be noted that their minimum voltage is higher than that of Li-ion cells (at precisely 3.2 V) and they exhibit a lower internal impedance. For this reason, it would be necessary to adjust the transformer design in order to support lower nominal voltages. Furthermore, the self-discharge of the cells and the maximum charge current could affect the balancing strategies. Another point to be considered is that, as stated in the 'Experimental Setup' Section, the tests were conducted at 25 \({}^{\circ}\)C in a dry environment. In the context of deep space exploration, significant temperature fluctuations can be experienced by the cells, which can \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & **DSSCE** & & & **SFCBE** & \\ \hline
**Gap** & **100 mV** & **50 mV** & **20 mV** & **100 mV** & **50 mV** & **20 mV** \\ \hline Scenario 1 [V] & 15.420 & 15.394 & 15.386 & 15.312 & 15.279 & 15.268 \\ Scenario 2 [V] & 15.428 & 15.44 & 15.443 & 15.264 & 15.224 & 15.206 \\ Scenario 3 [V] & 15.399 & 15.399 & 15.398 & 15.344 & 15.322 & 15.301 \\ Scenario 4 [V] & 15.405 & 15.414 & 15.412 & 15.291 & 15.267 & 15.253 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Battery voltage after equalization. compromise the performance of the equalizer. As demonstrated in [33; 37], Li-ion batteries exhibit increased internal resistance, diminished lithium diffusion, and reduced capacity at low temperatures. In order to mitigate the effects of temperature fluctuations, the use of heaters is the most common solution in the context of space missions. It is possible to ensure that cells are maintained within an operational temperature range by using this method.