Inputs
Example Data Table
Sample screening scenarios for quick comparison. Adjust values to match your cell and enclosure.
| Scenario | Chemistry | Mass (g) | Rth (K/W) | Power (W) | Duration (s) | Initial (°C) | Ambient (°C) | Outcome (screening) |
|---|---|---|---|---|---|---|---|---|
| Warehouse charge incident | NMC | 45 | 1.20 | 35 | 180 | 25 | 25 | Moderate: evaluate ventilation and detection. |
| High ambient enclosure | NCA | 48 | 1.80 | 55 | 240 | 45 | 45 | High: improve cooling and add propagation barriers. |
| Robust cooling test | LFP | 52 | 0.60 | 40 | 300 | 25 | 25 | Low: validate with measured heat rates. |
Formula Used
The calculator uses a first-order lumped thermal model suitable for early-stage screening.
- Thermal mass: m·cp (J/K), where m is cell mass and cp is specific heat.
- Time constant: τ = Rth · (m·cp) (s).
- Steady-state temperature: Tss = Ta + P·Rth (°C).
- Temperature vs time: T(t) = Tss + (T0 − Tss) · e^(−t/τ).
- Energy screening: Wh = Ah · Vnom · SOC (SOC as fraction), and kJ = Wh · 3.6.
How to Use This Calculator
- Select chemistry to prefill typical screening thresholds.
- Enter cell mass, thermal resistance, and starting temperatures.
- Provide a net heat generation power and duration window.
- Press Calculate to see predicted temperatures and times.
- Use CSV/PDF exports to document assumptions and outcomes.
Screening Objective
This calculator provides a rapid early screen for overheating pathways that can precede venting and thermal runaway. It converts a constant heat‑generation assumption into a temperature‑versus‑time estimate, then compares that estimate to user‑defined venting and runaway thresholds. Typical use cases include charger fault scenarios, enclosure hot‑soak checks, and sensitivity studies during design reviews. Treat the results as triage, not final certification.
Thermal Model Inputs
The core inputs map to a lumped thermal network. Cell mass and specific heat define thermal inertia as m·cp in J/K. Thermal resistance to ambient, Rth in K/W, represents the path through can, interface material, and enclosure airflow. Heat generation power P in watts should represent net heat into the cell during the event window. Initial and ambient temperatures set boundary conditions for the transient response.
Interpreting Temperature Outputs
The model predicts an approach to a steady temperature Tss = Ta + P·Rth with time constant τ = Rth·(m·cp). If duration is short compared with τ, the predicted rise will be limited; if it is long, the estimate moves closer to Tss. The calculator also estimates time to reach each threshold when reachable. If venting or runaway is “Not reached,” your parameters imply margin for that scenario.
Energy and Pack Context
Electrical energy is reported as a screening metric because stored energy often correlates with consequence severity. Per‑cell energy uses Wh = Ah·Vnom·SOC, while pack energy scales by series and parallel counts. For example, a 5 Ah, 3.7 V cell at 90% SOC stores about 16.7 Wh, or 60 kJ. Higher pack kJ values may warrant stronger propagation barriers, vent routing, and spacing even when the per‑cell temperature result looks acceptable.
Documentation and Limitations
Use the risk category and score to prioritize follow‑up work. When results approach thresholds, refine assumptions with measured heat‑rate data, improved Rth estimates, or a time‑varying profile. Export the CSV or PDF to capture inputs, outputs, and notes for audits, lessons‑learned, or change control. Limitations include constant P, single‑node temperature, and no modeling of exothermic reaction escalation, gas venting, or cell‑to‑cell propagation.
FAQs
What does thermal resistance (Rth) represent?
Rth approximates how strongly the cell couples to its surroundings. It combines internal conduction, interface materials, and external convection. Lower Rth means better cooling and a lower steady‑state temperature for the same heat generation.
How should I estimate heat generation power (P)?
Use a net heat rate over the event window. For charge or discharge faults, start with measured calorimetry data when available. Otherwise, use a conservative average and run sensitivity cases, such as ±25%, to understand margin.
Why can the predicted temperature be below the steady‑state value?
Tss is the long‑time limit under constant P. If the duration is shorter than the time constant τ, the transient does not fully settle, so the temperature remains below Tss.
What do “Not reached” times to venting or runaway mean?
Under the current inputs, the math indicates the temperature trajectory does not cross that threshold. It does not guarantee safety; changes in heat rate, cooling, or reaction onset can shift thresholds and invalidate the assumption.
How do I choose venting and runaway thresholds?
Start with supplier data or internal test results for your exact cell model. Use chemistry as a rough guide only. When uncertain, set lower thresholds to create a conservative screen, then refine with validated measurements.
Can I use this calculator for module or pack temperatures?
The thermal model is per‑cell and lumped into one node. For modules, use it as a quick bound by mapping an effective mass, cp, and Rth. For detailed design, use multi‑node models and enclosure testing.