Automobile fuse is the key protective element in automobile circuit. Its core function is to automatically fuse circuits in the event of an abnormal increase in current, preventing equipment from breaking down or catching fire. The following is a detailed description of the automobile fuse, including its function, inspection methods, size specification and type classification:
I. Functions of Automotive Fuses
Overload Protection: When the current in the circuit exceeds the fuse's rated value (e.g., short circuit, equipment failure or use of multiple high-power appliances at once), the fuse will melt due to overheating, cutting off the current and preventing damage to wiring harnesses, battery or electrical components due to overheating.
Fault Isolation: A single fuse does not affect other circuits, making it easy to fault location quickly (for example, if the headlight does not work, check the corresponding fuse).
Compliance with safety standards: Automotive electrical systems require rigorous safety certifications, and fuses are central to compliance with regulatory requirements (e.g. ISO 8820, SAE J2352).
II. Inspection Methods for Automotive Fuses
Visual: Signs of Blown Fuse: After melting, the central sheet metal will break or change color (e.g., blackening, coking).
Transparent Housing: Some fuses use clear plastic housings that allow direct observation of the inner metal contacts to check their integrity.
Multimeter Test
Steps:
Disconnect the vehicle's power supply (e.g. unplug the key or disconnect the negative pole of the battery).
Set the multimeter to resistance range (Ω). Connect the two probes to either end of the fuse.
If the reading is infinite, the fuse explodes; if it's close to zero omega, it's normal.
Replacement testing
If the fuse's condition cannot be determined, test it with a new fuse of the same specification. Please note, however, that only temporary replacement is possible, and the original specification fuse must be used when a fault is confirmed.
Avoid large rated fuses as they can be a safety hazards.
III. Automotive Fuse Size Specifications
The size of the car fuse must match the fuse box slot. Common specifications are as follows:
Type Size (Length × Width × Height) Applicable Scenarios
10.9mm x 3.6mm x 16.3mm
Modern car mainstream size, used in most circuits (such as headlights, radio).
Standard (ATO) 19.1mm x 5.1mm x 18.5mm applies to conventional vehicles and high power circuits (e.g. air conditioning, power seats).
Large (Maxi) 29.2mm x 8.5mm x 34.3mm for high current circuits (e.g. AC generator, starter).
Medium (JCASE) 18.5mm × 6.3mm × 30.2mm for high voltage circuits (e.g. battery management systems) in hybrid / electric vehicles.
IV. INTRODUCTION Automotive Fuses can be classified into the following types according to their characteristics, installation methods and applications:
1. By Melting Characteristics
Fast-Acting Fuses
Features: Sensitive to overload current and quick to fuse (usually in seconds).
Purpose: To protect precision electronic equipment (e.g. ECU, sensors) from sudden current shocks.
Time-Delay Fuses
Features: Allows short-term overload (such as gushing at motor startup) and delayed fuse burnout.
Uses: Protection motor, compressor and other equipment (e.g., wiper motors, air conditioning compressors).
2. By Installation Method
Blade Fuse
Features: Inserts the fuse box through the metal strip, replaces the convenience, low cost.
Application: Most automotive circuits (e.g. headlights, sound system).
Bolt-Down Fuse
Features: Bolt fastening, low contact resistance, can withstand large current.
Application: High voltage or high power circuit (e.g., generator output, battery positive pole).
PCB Fuse
Features: Direct welding on circuit board, small size, strong shock resistance.
Application: Automotive electronics module (e.g., BCM, ABS control unit).
3. By Special Purpose
High-Voltage Fuse (HV Fuse)
Features: High voltage rating (e.g. 600V, 1000V) for high voltage battery pack in electric vehicles.
Example: a high-voltage fuse used in a Tesla Model 3 battery pack.
Pulse Fuse
Features: High frequency pulse current resistance (e.g. ignition coil, injector drive circuit).
Purpose: Engine control unit (ECU) -related circuit.
Purpose-Resettable Fuse (PPTC)
Features: Automatically resets after cooling, but not commonly used in the automotive industry (due to high reliability requirements).
Application: Some low-power auxiliary circuits (e.g., interior reading lights).
