Overview
ISO 8856:2014 - "Road vehicles - Electrical performance of starter motors - Test methods and general requirements" specifies standardized test methods and general requirements for determining the electrical characteristics of DC starter motors used to start internal combustion engines of road vehicles. The third edition (2014) updates the earlier 1995 edition and defines environmental/test conditions, test-bench arrangements, measurement procedures, correction methods and result presentation so manufacturers and test laboratories can produce comparable, repeatable performance data.
Key topics and technical requirements
- Scope and terms: Definitions include lock torque, nominal power, power output, reference temperature (20 °C), total resistance and power supply definitions.
- Test conditions:
- Reference temperature: 20 °C (default); cold cranking example −25 °C ± 2 °C.
- Run-in for new motors: example procedure of 40 cycles (2 s at 25% lock torque, 13 s rest).
- Measurement accuracy (Table 1 target and minimum accuracies):
- Current ±1% (target ±0.5%), Voltage ±1% (target ±0.5%)
- Rotational frequency ±2% (target ±1%), Torque ±2% (target ±1%)
- Temperature ±2 K
- Power supply characteristic: Starter motor supply is represented by a sloping straight voltage/current characteristic defined at 20 °C; standard supply points are provided (see table in standard) and can be adapted by agreement between motor and vehicle manufacturers.
- Test benches:
- Type 1: Pinion engaged with ring gear or equivalent; torque may be measured at drive gear.
- Type 2: Direct measurement at pinion or armature shaft using coaxial coupling.
- Test methods:
- Method A (continuous): Sweep load while recording torque, current, voltage, speed. Total test time ≤ 10 s.
- Method B (discrete points): Measure at selected torque/speed/current points; each point ≤ 3 s; cool to test temperature between points.
- Method C (cold cranking): Precondition at cold temperature and perform Method A within 3 min of removal.
- Measurement corrections: Procedures to correct torque for gear-train efficiency, inertia (deceleration), and temperature effects (magnet flux coefficient β). Rotational speed corrections for temperature and standard methods to compute power output and efficiency are included.
- Results presentation: Guidance for plotting characteristic curves and reporting nominal power at the reference temperature.
Applications and users
ISO 8856:2014 is used by:
- Starter motor manufacturers for design verification and specification of nominal power.
- Vehicle OEMs and engine manufacturers to validate starter selection and cold-cranking performance.
- Test laboratories and certification bodies to perform repeatable electrical performance tests.
- Component suppliers and quality engineers to ensure compliance with industry test methods for R&D and production testing.
Keywords: ISO 8856:2014, starter motor test methods, electrical performance, DC starter motors, road vehicles, torque correction, voltage-current characteristic, cold cranking.
Related information
- Developed by ISO/TC 22 (Road vehicles), Subcommittee SC 3 (Electrical and electronic equipment).
- This edition cancels and replaces ISO 8856:1995 (including Amendment ISO 8856:1995/Amd1:1997).
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