| Scenario | Power (kW) | Efficiency (%) | Coolant ΔT (°C) | Aux (W) | Safety (×) | Design heat (W) | Flow (L/min) |
|---|---|---|---|---|---|---|---|
| A | 60 | 96 | 8 | 30 | 1.15 | 2,910 | 6.1 |
| B | 120 | 95 | 8 | 50 | 1.20 | 7,639 | 16.0 |
| C | 180 | 93 | 10 | 80 | 1.25 | 17,035 | 28.6 |
- Efficiency method: Q̇ = P × (1/η − 1)
- Resistance method: I ≈ P/V, then Q̇ = I²R
- Total heat: Q̇_total = Q̇ + Q̇_aux
- Design heat: Q̇_design = Q̇_total × SF
- Coolant heat pickup: Q̇_design = ṁ × cp × ΔT
- Mass flow: ṁ = Q̇_design / (cp × ΔT)
- Volumetric flow: V̇ = ṁ / ρ
- Convert: L/min = V̇ × 1000 × 60
- Choose a method: use efficiency if you know η, or resistance if you know DCIR.
- Enter operating power, plus auxiliary heat from pumps, fans, or electronics.
- Set temperatures: ambient, max cell, and coolant inlet/outlet targets.
- Select a coolant preset, or enter custom cp and density values.
- Apply a safety factor for aging, fouling, and real-world variability.
- Press Submit to see results above the form.
- Use Download CSV or Download PDF to share results.
Why battery heat rises with power demand
Heat in a traction or storage pack primarily comes from electrical losses and auxiliary components. For an efficiency-based estimate, losses scale with output power using P × (1/η − 1). For a resistance-based estimate, losses scale with current squared using I²R, so high C‑rates and low voltage can sharply increase thermal load.
Interpreting design heat removal and safety factor
The calculator reports a design heat removal rate that includes your safety factor. This multiplier is useful when pack aging increases resistance, coolant channels foul, or airflow varies across operating conditions. Typical early-stage sizing uses 1.10–1.30, then reduces uncertainty after dyno testing and thermal mapping.
Selecting coolant temperature targets and ΔT
Coolant inlet and outlet targets determine the allowable temperature rise across the cold plate or module. A larger ΔT lowers the required flow rate, but may raise maximum cell temperature if thermal resistance is high. Many liquid loops start with ΔT of 6–10 °C and then validate hotspot margin during peak transients.
Flow rate, pump sizing, and pressure drop
The flow result is based on energy balance: ṁ = Q̇/(cpΔT). Use it as an input to hydraulic design, where pressure drop depends on channel geometry, viscosity, fittings, and radiator core selection. After you estimate pressure drop, select a pump that meets both the required flow and head at the intended operating point.
Using margins to support thermal limits and reliability
The temperature margins highlight how close your coolant outlet is to the maximum cell limit. If margin is small, consider lowering coolant outlet temperature, increasing flow, improving contact resistance, or reducing peak power duration. For safety-critical systems, confirm results with a validated thermal model and instrumented testing across state of charge and ambient extremes.
For air-cooled packs, you can treat the reported design heat as a target for ducting and fan selection, then estimate airflow using Q̇ = ṁ_air cp ΔT with an appropriate air temperature rise. Compare multiple scenarios to understand sensitivity to efficiency, resistance, and temperature setpoints. Keep assumptions documented so reviews stay consistent for each revision cycle.
1) Which method should I use: efficiency or resistance?
Use efficiency when you know pack efficiency at the target power. Use resistance when you have DCIR at the correct SOC and temperature. Resistance is more sensitive at high current.
2) What coolant ΔT is reasonable for a first pass?
Many liquid loops start with 6–10 °C coolant rise across the pack. Smaller ΔT increases flow but can improve cell uniformity. Validate with hotspot measurements and radiator capability.
3) Does the flow result include radiator performance?
No. The flow is an energy-balance requirement at the pack. Radiator effectiveness, fan power, ambient airflow, and coolant approach temperatures must be checked separately during system sizing.
4) How should I choose the safety factor?
Use 1.10–1.30 for concept work, higher if data is uncertain. Lower it after testing confirms resistance growth, coolant fouling rates, and hotspot distribution. Safety factor should reflect verified margins.
5) Why does the resistance method sometimes give lower heat?
Because it depends on assumed voltage and DCIR. If voltage is high or DCIR is low, I²R losses drop. Ensure DCIR matches the operating temperature and includes busbar and interconnect contributions.
6) Can I use this for air cooling instead of liquid?
Yes for heat load. Treat design heat as the required removal rate, then estimate airflow using air specific heat and an allowable air temperature rise. Ducting losses and fan curves still apply.