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ISO 26021-4: Road Vehicles — End-of-Life Activation — Part 4: Power Source
Power Supply Requirements for External Pyrotechnic Activation Tools in Vehicle Dismantling Operations
1. Power Source Classification and General Requirements
ISO 26021-4 specifies the power source requirements for external activation tools used to deploy pyrotechnic devices in end-of-life vehicles. The power source must deliver the energy required to fire all pyrotechnic squibs in a vehicle — potentially 20 to 50 individual devices — reliably and safely, under the environmental conditions encountered in vehicle dismantling and scrapyard operations. The standard defines three power source classes: Class A (vehicle battery powered, drawing power from the DLC pin 16), Class B (integral rechargeable battery), and Class C (external AC mains powered with galvanic isolation).
The total energy required to activate all pyrotechnic devices in a typical vehicle is approximately 200–500 J, delivered as sequential current pulses of 1.75–2.5 A at 12–24 V for 2–10 ms per squib. The peak power demand occurs during the firing interval but the energy storage and delivery system must be sized for the cumulative load across the full activation sequence.
Each power source class must meet minimum performance criteria: output voltage stability within ±5 % of nominal under load, maximum output current capability of at least 5 A continuous (Class A and B) or 10 A (Class C), and ripple voltage not exceeding 100 mV peak-to-peak during quiescent operation. The power source must also incorporate under-voltage lock-out to prevent partial activation — if the voltage drops below 9 V (for 12 V systems) or 18 V (for 24 V systems), the activation sequence must be automatically suspended.
| Parameter | Class A (Vehicle Battery) | Class B (Internal Battery) | Class C (AC Mains) |
|---|---|---|---|
| Nominal voltage | 9–16 V (12 V system) / 18–32 V (24 V system) | 12 V nominal (Li-ion or Ni-MH) | 100–240 V AC → 12/24 V DC isolated output |
| Continuous current | 5 A max (limited by DLC pin 16) | 5 A max (limited by internal BMS) | 10 A max (limited by PSE circuit) |
| Peak pulse current | 10 A for 50 ms (with bulk capacitor) | 15 A for 50 ms | 20 A for 100 ms |
| Energy storage | Vehicle battery (depends on state of charge) | ≥ 1000 J (sufficient for at least 2 full vehicles) | N/A (continuous supply from mains) |
| Isolation voltage | Not required (same vehicle ground) | Not required (floating output acceptable) | ≥ 1500 V AC (galvanic isolation mandatory) |
| Operating temperature | −20 °C to +60 °C | −10 °C to +50 °C | 0 °C to +40 °C |
Class A power sources (vehicle battery powered) carry a significant risk: the vehicle’s battery may be deeply discharged at end-of-life, having insufficient energy to complete the activation sequence. A partial activation — where some squibs fire but others do not — creates a more hazardous condition than no activation at all, because partially deployed airbag modules are mechanically unstable and may contain both live and spent pyrotechnic charges. ISO 26021-4 requires Class A tools to verify battery capacity before beginning any activation sequence.
2. Energy Storage Design and Pulse Delivery
The critical engineering challenge in pyrotechnic activation power source design is delivering the high pulse current required for squib initiation while maintaining voltage stability across the entire activation sequence. Each squib requires a firing current of 1.75–2.5 A for 2–10 ms, and multiple squibs may be fired in rapid succession. The power source must include a bulk energy storage element — typically an electrolytic capacitor bank of 10,000–50,000 µF total capacitance for Class B tools — that can supply pulse current without significant voltage droop.
The capacitor charging circuit must be designed with a controlled inrush current limiter to prevent excessive load on the battery or mains supply when recharging between firing pulses. A typical design uses a buck-boost converter to charge the capacitor bank to a regulated voltage 20–30 % above the nominal activation voltage, with a pre-charge resistor or active current limiter in the charging path. The discharge path must use a low-resistance semiconductor switch (MOSFET or IGBT) with a rated pulse current capability of at least 30 A for 100 ms.
An important safety feature mandated by ISO 26021-4 is a “bleed-down” circuit that automatically discharges the energy storage capacitors to below 1 V within 5 seconds of the activation sequence completing or aborting. This prevents stored energy hazards when the tool is disconnected from the vehicle or handled during maintenance. The bleed circuit must be fail-safe — normally closed relay or depletion-mode MOSFET that conducts when power is removed.
3. Fault Protection and Safety Interlock Design
ISO 26021-4 specifies multiple layers of fault protection for the activation power source. Overcurrent protection must be provided at three levels: the main power input, the energy storage charging circuit, and each individual firing channel output. The overcurrent protection must be of the resettable type (polymeric PTC or electronic current limiter) for the input and charging circuits, and one-shot fuse or electronic circuit breaker for the firing outputs.
Ground fault detection is required for Class C (mains-powered) tools, with automatic disconnection of the activation circuit within 40 ms of detecting a ground fault current exceeding 30 mA. The standard also requires reverse polarity protection on all external connections, transient voltage suppression on the firing output lines rated for automotive load-dump conditions (up to 60 V for 400 ms per ISO 7637-2 pulse 5), and electrostatic discharge protection on all user-accessible interfaces to ±8 kV contact discharge and ±15 kV air discharge per IEC 61000-4-2.
The most critical safety design requirement is the prevention of simultaneous firing of all pyrotechnic devices. A power source fault that causes all squibs to fire concurrently would subject vehicle occupants (if present) and nearby personnel to acoustic trauma from the combined pressure wave exceeding 170 dB SPL. ISO 26021-4 mandates that firing channel sequencing be implemented in hardware — not just software — using independent timing circuits or a hardware state machine that cannot be overridden by firmware.
FAQs
Q1: Can a standard vehicle battery charger be used as an ISO 26021-4 power source?
No. Standard battery chargers do not provide the regulated voltage, current limiting, and safety isolation required by ISO 26021-4. They may also introduce ripple and transient voltages that could interfere with CAN communication or trigger inadvertent squib firing. Only power sources specifically designed and tested to ISO 26021-4 should be used.
No. Standard battery chargers do not provide the regulated voltage, current limiting, and safety isolation required by ISO 26021-4. They may also introduce ripple and transient voltages that could interfere with CAN communication or trigger inadvertent squib firing. Only power sources specifically designed and tested to ISO 26021-4 should be used.
Q2: How is the power source verified for compliance?
Compliance testing includes measuring output voltage regulation under pulse load, verifying energy storage capacity, confirming timing of protection circuits (overcurrent, ground fault, bleed-down), and dielectric withstand testing (Class C only). Testing must be performed by an accredited laboratory per ISO 26021-4 Annex B test procedures.
Compliance testing includes measuring output voltage regulation under pulse load, verifying energy storage capacity, confirming timing of protection circuits (overcurrent, ground fault, bleed-down), and dielectric withstand testing (Class C only). Testing must be performed by an accredited laboratory per ISO 26021-4 Annex B test procedures.
Q3: What battery technology is recommended for Class B tools?
Lithium-ion (LiFePO4 chemistry recommended for its thermal stability and cycle life) or nickel-metal hydride (Ni-MH, for its robustness and lack of thermal runaway risk). Lithium-ion tools must include a battery management system that monitors cell voltage, temperature, and current with automatic shutdown on fault conditions.
Lithium-ion (LiFePO4 chemistry recommended for its thermal stability and cycle life) or nickel-metal hydride (Ni-MH, for its robustness and lack of thermal runaway risk). Lithium-ion tools must include a battery management system that monitors cell voltage, temperature, and current with automatic shutdown on fault conditions.
Q4: Can the same power source be used for 12 V and 24 V vehicle systems?
Yes, if the power source is designed with an auto-ranging input that accepts 9–32 V DC. Class C tools with universal AC input (100–240 V) and auto-ranging DC output can handle both voltage systems. Class A tools are limited to the vehicle’s native system voltage and cannot be used across different voltage classes without an intermediate converter.
Yes, if the power source is designed with an auto-ranging input that accepts 9–32 V DC. Class C tools with universal AC input (100–240 V) and auto-ranging DC output can handle both voltage systems. Class A tools are limited to the vehicle’s native system voltage and cannot be used across different voltage classes without an intermediate converter.
