In addition to permanently installed speed cameras with a permanent power supply and purely mobile measuring devices that are only in use for a short time, there are also semi-stationary speed measurement systems. These are set up temporarily at a specific location and remain there for a longer period of time. Such speed cameras are powered by batteries and therefore work independently of the mains for up to a week.

Speed measurement systems must be protected against vandalism and the effects of the weather. They are therefore housed in a hermetically sealed steel housing, which also contains the batteries. In summer, it can get very hot in this housing, which can be problematic for the batteries. At temperatures above 35 °C, every 10 °C rise in temperature halves the service life of the battery.

With this in mind, the Electric Battery Storage research group at the Institute of Energy Systems and Fluid Engineering (IEFE) at the ZHAW School of Engineering, together with CES complete electronic systems Ltd from Wallisellen, a company specialising in traffic measurements, investigated whether the service life of batteries in speed cameras can be extended by cooling. As part of a preliminary study funded by Innosuisse (innovation check), battery and temperature measurements were carried out under real conditions.

The researchers measured the battery temperatures on a sunny August day with an outside temperature of up to 36.2 °C during normal operation of the speed measurement system and during charging outdoors. In addition, the temperature in the batteries was analysed during the charging process (150 A) in the garage. The results show that the maximum battery temperature in normal operation is 39.1 °C, which is well below the 65 °C specified as the operating limit by the battery supplier. During the short outdoor charging phase, the temperature rises to 45.8 °C and to 43.7 °C in the garage. This means that even on hot summer days, the additional heating of speed camera batteries due to the high outside temperature is negligible. The load is somewhat greater when charging. However, the charging times are short and therefore have no major influence on ageing.

All eight cooling systems analysed cause additional costs and require space. As the temperatures in the speed cameras are lower than originally expected, the service life of the batteries can be extended by cooling to a lesser extent than assumed. In this respect, the installation of additional cooling makes little sense from an economic point of view.

Project name
Cooling system for battery module

Participants 
Project team: Andreas Jehle, Andreas Heinzelmann, Andreas Müller, Peter Schmidt
Project partner: ces complete electronic systems ag, Wallisellen
Funding: Innosuisse

Project duration
June 2023 to June 2024