Presentation of tests in extreme use and fast charging of WATTALPS batteries
This TechLetter will present the real tests of a WATTALPS battery fitted to a circuit car. Not only is the power delivered 2 times higher than what a Porsche Taycan can deliver, but this power can be delivered throughout the discharge of the battery, even with an outside temperature of 30°C and this with a simple air exchanger to cool the battery No need for an air conditioning system. The vehicle does a series of laps at full power, alternating with fast charges!
Background
The main objective is to be able to use the vehicle on the track at its maximum power until the battery is completely discharged, then to perform a quick recharge and continue to do laps of the circuit, while maintaining the temperature of the battery in its maximum performance range.
The 55 kWh battery is discharged in 8 laps of the circuit at an average speed of more than 140 km/h, with regular acceleration to 375 kW followed by regenerative braking at 100 kW, as illustrated in the following figures.
Sportscar speed with WATTALPS batteries
Sportscar power with WATTALPS batteries
The different steps of the project
The first phase of the project began in May 2023 with a pre-feasibility study, which compared the thermal simulations of the preliminary design with electrothermal tests on a single battery module. Tests carried out in July showed excellent thermal behaviour, allowing the maximum battery power to be increased from 350 kW to 375 kW.
The second phase of the project was launched in September 2023 with specific developments to ensure the proper functioning and safety of the battery at these very high power levels. The junction box in particular has been completely revised and adapted for this project. Further developments were carried out in collaboration with our customer in order to lighten some battery components. A specific battery heating system has also been developed to be able to respond to environments requiring operation in extreme cold, down to -20°C.
The complete battery with its thermalization system was delivered for first integration into the vehicle in February 2024. Tests on full-power benches were carried out at the beginning of April and corroborated the theoretical approaches. The circuit tests took place during the month of May.
Comparison with an existing automotive battery
The WATTALPS battery pack used for this application consists of 42 modules, a dielectric fluid circulation pump, a heating system and a fluid-air heat exchanger. The energy embedded in the WATTALPS battery is 55 kWh, for a power delivery of 375 kW. We have not found electric vehicles with the same characteristics on the market. We therefore propose to compare with a vehicle from the emblematic Porsche brand, which has a larger battery capacity. For a fair comparison and to compensate for the differences in the energy carried by the batteries, we will use the energy/power ratio, which is representative of the electrothermal stresses exerted on the battery.
Comparison Table
| Battery | Energy | Power | Energy/Power |
| Porsche Taycan | 89 kWh | 300 kW | 3.37 |
| WATTALPS | 55 kWh | 375 kW | 6.82 |
| Gap | -38% | +25% | +102% |
Note: WATTALPS did not have the opportunity to test a Porsche Taycan on the track to study the stability of performance over the laps. A cooling system that is less efficient than WATTALPS would automatically lead to a decrease in battery performance as the battery heats up.
Results
The tests carried out on the test bench showed the ability of the battery to provide the energy and power necessary to complete 8 laps of the circuit, as initially planned.
Sportscar SOC variation
The limitations of the test bench did not allow for the simulation of sufficient air velocity through the cooling radiator (lower than the average vehicle speed of 140km/h). Despite this, the temperature increase is in line with expectations, as can be seen in the figure here below, with a good ability to cool the battery during charging (a phase during which the air speed is regulated by a fan, embedded on the heat exchanger).
Sportscar battery temperature variation
Circuit tests show much better cooling performance as shown in the figure below, which illustrates a complete discharge at very high power. There is an average difference of 2°C over the entire battery and a maximum of 4°C when very strong discharge peaks are achieved. The average temperature increase over the entire discharge is 2°C, confirming the better cooling efficiency when the radiator sees the actual air speeds (up to 240 km/h).
Race car battery temperature monitoring
Note: vertical lines correspond to transmission breaks in the measurement system
Conclusion
Despite a high ambient temperature (>30°C) and extreme stresses, the patented WATTALPS cooling system made it possible to maintain performance throughout the battery discharge, while allowing rapid charges, directly after use. Even when charging quickly, our innovative cooling system cools down the battery, thanks to its extreme efficiency.
Once again, WATTALPS proves that its patented technology of immersion cooling directly at the cell level allows the use of the full battery power, even under extreme conditions. WATTALPS batteries are particularly well suited to the most demanding conditions in motorsport or off-road vehicles. For any information on WATTALPS products, you can fill out the form on our website https://www.wattalps.com/, tab “CONTACT”.