Batteries will be an essential feature of zero-emission mobility and electrified construction, but will only be successful if they provide sufficient power, are operated safely, and are permanently available.
Heavy vehicles in particular, such as buses, trucks, excavators, cranes, and fire and rescue vehicles, need large batteries with high capacities that operating personnel and also passengers can rely on at all times. However, battery capacity and service life depend on the outside temperature and the battery cell temperature. Extreme fluctuating temperature ranges reduce battery life. Very high or very low outside temperatures affect the battery's performance.
Heat and cold impact the battery in various ways
The greater the load on the batteries, the hotter they become, not only when driving but also when charging. Additional high outside temperatures can lead to irreparable battery damage or total vehicle failure.
Cold outside temperatures also influence the batteries in vehicles. The colder it gets, the faster the available capacity of the battery decreases. Skiers are familiar with this effect when they sit at the top of the mountain in front of a hut and are surprised that the fully charged battery of their smartphone suddenly only shows half.
That may not be a bad thing on a small scale. But when a bus can no longer make it to the depot because it has suddenly become colder, or the ambulance won't start on a freezing cold day because the battery is too sluggish, then it's not just the performance of electric vehicles that's at stake but their reliability – and this is precisely where there can be no compromises. This is where the development team of Webasto came in.
So simple and yet complex: Intelligent active cooling and heating of batteries
As is so often the case, development started with a simple what-if question: What if we could condition the batteries so that they are at optimum temperature at all times? A collaboration between the Webasto battery department and Webasto air conditioning experts resulted in the development of a concept for an efficient battery pack cooling solution. Webasto Customized Solutions was able to successfully incorporate its many years of experience into the new project.
Right from the start, the team focused on actively cooling and heating the batteries. Instead of merely sending the heat through a heat exchanger, as in passive air cooling, gas or water is cooled down via a compressor. This allows a significantly higher cooling capacity to be achieved compared to passive air cooling. "The eBTM has an exceptionally high power-to-volume ratio. This is also reflected in the eBTM's high heating capacity, which enables 10kW at 800 volts," explains Tobias Maier, Product Manager at Webasto.
Electric Battery Thermal Management ready for series production
The Webasto batteries are integrated with the eBTM via standardized water connections and matched high-voltage connectors. The Webasto system elements communicate to determine the delta between battery cell temperature and the corresponding setpoint in real time. Maier says: "To be able to guarantee the optimum battery cell temperature, our eBTM decides independently whether heat or cold has to be provided. In this way, the Webasto system ensures a stable battery cell temperature, regardless of the outside temperature and the electrical load.
As simple as this sounds, the technical implementation turned out to be difficult. In the end, the team developed a system that already included all necessary components, such as pumps, heat exchangers, and power electronics. "The advantage of the 'plug-and-play' system is that it can be used immediately with no further development work," says Maier.
Keeping batteries reliably at an optimum operating temperature: What reads like a vision of the future is now ready for series production at Webasto. The eBTM is already working reliably in various prototypes from vehicle and construction machinery manufacturers. Soon, thermal management for batteries could be standard in large electric vehicles and machines on the world's roads and construction sites.