| Scenario | Voltage (V) | Current (A) | R (mΩ) | Duty (%) | Time (min) | Mass (kg) | Cp (J/kg·K) | G (W/°C) | Ambient (°C) | Initial (°C) | Expected rise (°C) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Commuter burst | 48 | 30 | 10 | 60 | 15 | 0.7 | 900 | 2.0 | 25 | 25 | ~1–3 |
| Continuous climb | 52 | 60 | 8 | 100 | 20 | 1.2 | 950 | 1.5 | 30 | 30 | ~4–10 |
| Adiabatic stress test | 60 | 80 | 6 | 100 | 10 | 1.0 | 900 | 0 | 25 | 25 | ~3–7 |
- Enter current, resistance, and duty cycle for your load profile.
- Set duration and choose seconds, minutes, or hours.
- Provide mass and specific heat to represent the heated pack mass.
- Add ambient and initial temperatures; set conductance for cooling strength.
- Press Submit to view final temperature and rise above initial.
- Use the download buttons to export the report as CSV or PDF.
Why temperature rise matters in pack design
Temperature rise drives cell aging, imbalance, and power derating. A few degrees can reduce usable energy, trigger protective cutbacks, and accelerate electrolyte breakdown. For packs in vehicles, tools, or cabinets, estimating heat early helps size conductors, choose cell format, and plan airflow or cold plates. It highlights hot spots, guiding sensor placement and prototype cooling checks.
Estimating I²R losses under pulsed loads
Most heating comes from resistive loss: I²R. The calculator multiplies current squared by pack resistance and scales it by duty cycle for pulsed operation. If your load switches between two currents, use a weighted average of I² over each interval, not average current. Resistance changes with temperature and state of charge, so measure near your operating point. For PWM drives, include ripple only if it is significant.
Selecting realistic thermal mass and heat capacity
Thermal mass converts watts into degrees. Mass and specific heat represent the portion of the pack that warms during the event. Short bursts heat cells and busbars; long runs heat enclosure and mounts. If unsure, run two cases: 'cells only' and 'whole pack' to bracket reality. Effective heat capacity for lithium-ion assemblies often sits near 800–1100 J/kg·K; metals and potting shift the composite value.
Interpreting conductance, time constant, and steady state
Cooling is modeled with a single conductance to ambient. Higher conductance means stronger heat rejection, lower final temperature, and a shorter time constant τ = m·Cp/G. The steady-state value is ambient plus Pheat/G, useful for continuous loads. If τ is much larger than your duration, rise is close to adiabatic. Estimate conductance from a cooldown test by fitting an exponential decay, then computing G = m·Cp/τ. This simplification assumes near-linear cooling over the range.
Using results to set limits and improve cooling
Use the results to compare mitigations. Lower current, reduce resistance, engage more mass, or improve conductance using fins, thermal pads, or forced convection. Check final temperature against your limit, then iterate until margin is acceptable. Re-run at worst-case ambient and conservative resistance. Voltage is for context. Export CSV and PDF to record assumptions and compare revisions across teams.
FAQs
What temperature does the calculator output?
It reports the estimated final average pack temperature and the rise from the initial value. Local cell hot spots can be higher, especially with poor thermal contact or uneven current distribution.
How do I choose internal resistance?
Use a measured pack DC resistance at the expected state of charge and temperature. If you only have a datasheet value, add margin because resistance increases with aging, colder conditions, and higher interconnect losses.
Why is duty cycle included?
Heating depends on I squared, so pulsed loads can produce more heat than the same average current. Duty cycle scales the ON-time contribution, giving a practical approximation for PWM or intermittent operation.
When should I set thermal conductance to zero?
Use zero when cooling is negligible over the event, such as a short bench pulse or insulated pack. The result becomes an adiabatic estimate, useful as a conservative upper bound.
What does steady-state temperature mean?
With conductance enabled, the model approaches a stable temperature where heat generated equals heat rejected. That steady-state value helps evaluate continuous loads and shows whether added cooling will meaningfully reduce long-run temperature.
Is this suitable for safety certification decisions?
No. It is an engineering screening tool for comparisons and early sizing. For compliance, use validated thermal testing, detailed models, and the exact limits from your cell supplier and system safety requirements.