We do a lot of calculations behind the benchmarks, filling in values that have not explicitly been declared.
In the latest benchmark we looked at the Ferrari Elettrica battery pack and we thought it would be good to go through the estimations and how we calculated/estimated other values.
What was declared by Ferrari [1, 2]:
- Total energy = 122 kWh
- Capacity = 159 Ah
- Gravimetric energy density
- Pack = 195 Wh/kg
- Cell = 305 Wh/kg
- 15 modules
- 14 cells in each module
- 210 cells in total
This post has been built based on the support of and sponsorship from: Resonate Testing Ltd, Quarto Technical Services, Eatron Technologies and About:Energy
Doesn’t sound like much, but let’s see what we can get from these values:
- Pack mass = 122 kWh x 1000 / 195 Wh/kg = 625.6 kg
- Pack nominal voltage = 122 kWh x 1000 / 159 Ah = 767.3 V
- makes sense as the 880V pack voltage claim is the maximum charge voltage = 210 x 4.2V = 882V
- Cell nominal voltage = 767.3 / 210 = 3.65 V
- Cell mass = 3.65 V x 159 Ah / 305 Wh/kg = 1.905kg
- Total cell mass = 210 x 1.905 kg = 400 kg
- Cell to pack mass ratio = 400 kg / 625.6 kg = 63.9%
Based on the declared peak pack current capability of 1200A and the fact that the cells are configured such that all are in series, the peak cell capability is 1200A.
Assuming this peak capability is at 50% SOC and that this peak current pulls the cell voltage down to a minimum 2.5V we can estimate the internal resistance of the cell (10s DCIR).
- DCIR (10s at 50% SOC) ~ 0.96mΩ
- Converting this into a conductance vs cell capacity (1.79 Siemens / Wh) allows us to scale the cell capability.
As we gather more data we can use these values to piece together more aspects of the pack design.
References
- Ferrari Elettrica, Ferrari product page
- Ferrari Elettrica (pdf), Ferrari News