# Application of Infrared Thermography in E-Bike Battery Pack Detail Analysis--Case Study
## 3 Analysis and Diagnostics of the Battery Pack  
### Thermography in the Battery State Assessment and Analysis  
Infrared thermography is a contactless method for determining the temperature distribution on the surface of an observed object by measuring the intensity of radiation in the infrared region of the electromagnetic spectrum. Thermography is often used as a maintenance tool. In the field of electric power engineering, thermography is an unavoidable test method closely associated with the measurement of electrical parameters [30]. Contrary to popular belief that an infrared thermal imager/camera measures temperature, it actually registers electromagnetic radiation in the infrared portion of the spectrum, to which it assigns temperature values depending on the imaging parameters. Figure 4 graphically shows the components of the radiation registered by the infrared thermal imaging camera. Given the distance, the atmosphere may have an effect on the registered radiation. The distance of the camera depends mainly on the optical angle of the camera lens. The closer the camera gets to the object to be analyzed, the weaker the influence of the atmosphere becomes, but the possibility of reflection of the operator's radiation increases. In addition to the fact that the power dissipation inside the battery is higher, its radiation becomes dominant, and the influence of the ambient radiation on the overall balance becomes smaller. The smaller distance to the object has another effect--namely, the radiation captured at different angles relative to the normal on the surface. The acquisition angle is important because of the change in emissivity, which can be seen in detail in Figure 5. Emissivity is the most important parameter and can change depending on the viewing angle or different materials used. The emissivity also depends on the wavelength at which the object is observed [31]. The emissivity of the plastic, used for the housing, is 0.95. It is confirmed by sticking a strip of reference tape on the battery housing, which is not visible on any of the thermograms, thus confirming the choice of the correct emissivity. In Figure 5, in addition to the emission values at each angle shown with a red line, we see (in brown) the temperature value that the camera would associate with the same amount of radiation at different angles for the spot measurement from Figure 6a. A significant error in the choice of emissivity would result in the display of an incorrect temperature value, shown in blue in Figure 5.  
Figure 4: Components of longwave infrared radiation registered by the infrared thermal camera. Figure 3: Kalkhoff Groove 28′′ battery pack model. We can conclude that in the case of plastic enclosures, variations in the angle of capture do not significantly affect the measurement result, especially if we take into account the \(\pm 2\)\({}^{\circ}\)C accuracy of the thermal imaging cameras used in this study, Table 1. Based on the details of the thermograms, it is clear that a camera with a higher resolution was used for the analysis. The higher resolution gives a clearer pattern but not necessarily better measurement results. Thermography easily finds its application in the battery analysis [32]. Unfortunately, the thermographic analysis is challenging in our case due to the closed system, mainly because the measurement of electrical parameters is not possible. The consideration of using the thermographic analysis as a method for evaluating the condition of the battery  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Camera** & **Flir E60 bx** & **Flir E6** \\ \hline IR resolution & \(320\times 240\) pixels & \(160\times 120\) pixels \\ Thermal sensitivity/NETD & \textless{}0.045 \({}^{\circ}\)C @ \(+30\)\({}^{\circ}\)C/\(45\) mK & \textless{}0.06 \({}^{\circ}\)C/\(<\)\(60\) mK \\ Field of view (FOV) & \(25\text{\text{\text  
and diagnosing faults arose from the fact that the available range is constantly decreasing after each full charge cycle.