External Short Circuit
The external short-circuit test is an electrical abuse test. It is a standard safety test used to evaluate how a battery behaves when its positive and negative terminals are directly shorted by a very low-resistance path outside the cell. The minimum assembly level for the test is a cell, though it’s also relevant at module or pack levels.
External short circuit resistance, also called a load, is defined relative to DC resistance
Test Procedure:
| Short Circuit | Short Circuit Resistance |
|---|---|
| Hard Short | 0.1 – 1 x Cell DC resistance |
| Medium Short | 5 – 10 x Cell DC resistance |
| Soft Short | >100 x Cell DC resistance |
| For very low-resistance cells | Practical short of 1–5 mΩ |
| Cell with unknown internal resistance | 1 (+/-10%) mΩ load resistance |
Standards:
SANDIA 6925 followed here. Similar standards UN 38.3, IEC 62133, UL 1642 / UL 2054, ISO 12405 / SAE J2464 (EV batteries)
Equipment used:
Inhouse BSI setup to perform external short circuit test or battery cycler
Frequently Asked Questions (FAQ)
1. How does external short circuit differ from an internal short test?
External short: Applies a controlled short across the terminals; easier to reproduce.
Internal short: Simulates defect-driven shorts inside the cell; very difficult to standardize and often uses nail penetration or artificial shorting devices.
Internal short: Simulates defect-driven shorts inside the cell; very difficult to standardize and often uses nail penetration or artificial shorting devices.
2. What SOC should the battery be tested at?
Generally, at 100% SOC, or the manufacturer’s maximum specified charge level, because this is the worst-case condition for failure severity.
3. What parameters must be recorded during the test?
- Voltage
- Current
- External temperature of the test cell in multiple locations
- Applied short duration
- Visual observations: venting, smoke, fire
- Audio (pop, vent sounds)
- Gas release/flammability (for advanced testing)
4. Why is the short required to be applied in <1 second?
- Real accidental shorts happen suddenly, and this is performed to simulate a real-life accidental short.
- To avoid pre-heating or intermediate resistance states. This ensures a clean, instantaneous fault condition, matching Sandia’s recommended practice.
5. Why do we define short levels relative to DC resistance?
By defining hard, medium, and soft short levels relative to a cell’s DC resistance, testing can realistically simulate different real-world failure scenarios.
- Batteries vary in size, chemistry, and internal resistance.
- A fixed-resistance short might be too mild for large cells or too severe for small cells.
| HSL | Description | Classification Criteria and Effect |
|---|---|---|
| 0 | No effect | No effect. No loss of functionality. |
| 1 | Passive protection activated | No damage or hazard; reversible loss of function. Replacement or re-setting of protection device is sufficient to restore normal functionality. |
| 2 | Defect/Damage | No hazard but damage to RESS; irreversible loss of function |
| 3 | Minor Leakage or Minor Vent | Visual or audible evidence of leaking or venting. Leak without significant pooling or collection of free liquid. Venting without significant smoke or loss of particulate material. No visual obstruction of the RESS |
| 4 | Major Leakage or Major Vent | Visual evidence of leaking or venting. Leaking with significant pooling or observed free liquid. Venting with significant smoke, solvent vapor, and/or loss of particulate material. Visual obstruction of the RESS by vent gases and/or smoke. Total RESS mass loss < 30% |
| 5 | Rupture | Loss of mechanical integrity of the RESS package, resulting in release of contents. The kinetic energy of released material is not sufficient to cause physical damage external to the RESS. Rupture may be the result of a RESS thermal runaway (but not necessarily). Total RESS mass loss 30 – 55% |
| 6 | Fire or Flame | Ignition and sustained combustion of flammable gas or liquid (≥1 s sustained fire). Sparks or incandescent material is not considered a fire or a flame |
| 7 | Energetic Failure | Fast release of energy sufficient to cause pressure waves (slower than the speed of sound) and/or projectiles that may cause considerable structural and/or bodily damage, depending on the size of the RESS. The kinetic energy of flying debris from the RESS may be sufficient to cause damage as well. Total RESS mass loss ≥ 55% |
6. Can an external short circuit test cause thermal runaway?
Yes, especially for high-energy Li-ion cells under hard shorts at high SOC.
7. What is Hazard Severity Level (HSL) Rating Table?
An HSL Rating Table is a structured way to categorize how serious the consequences of a hazard can be. It helps determine how severe injury, damage, or environmental impact could be if a hazardous event occurs.
| HSL | Description | Classification Criteria and Effect |
|---|---|---|
| 0 | No effect | No effect. No loss of functionality. |
| 1 | Passive protection activated | No damage or hazard; reversible loss of function. Replacement or re-setting of protection device is sufficient to restore normal functionality. |
| 2 | Defect/Damage | No hazard but damage to RESS; irreversible loss of function |
| 3 | Minor Leakage or Minor Vent | Visual or audible evidence of leaking or venting. Leak without significant pooling or collection of free liquid. Venting without significant smoke or loss of particulate material. No visual obstruction of the RESS |
| 4 | Major Leakage or Major Vent | Visual evidence of leaking or venting. Leaking with significant pooling or observed free liquid. Venting with significant smoke, solvent vapor, and/or loss of particulate material. Visual obstruction of the RESS by vent gases and/or smoke. Total RESS mass loss < 30% |
| 5 | Rupture | Loss of mechanical integrity of the RESS package, resulting in release of contents. The kinetic energy of released material is not sufficient to cause physical damage external to the RESS. Rupture may be the result of a RESS thermal runaway (but not necessarily). Total RESS mass loss 30 – 55% |
| 6 | Fire or Flame | Ignition and sustained combustion of flammable gas or liquid (≥1 s sustained fire). Sparks or incandescent material is not considered a fire or a flame |
| 7 | Energetic Failure | Fast release of energy sufficient to cause pressure waves (slower than the speed of sound) and/or projectiles that may cause considerable structural and/or bodily damage, depending on the size of the RESS. The kinetic energy of flying debris from the RESS may be sufficient to cause damage as well. Total RESS mass loss ≥ 55% |