To determine whether the fuse of an electric vehicle is damaged and to identify the signals indicating the need for replacement, a comprehensive judgment should be made by combining visual inspection, functional testing, and system diagnosis. The following are the specific methods and common signals:
1. Visual Inspection: Direct observation of physical damage
Fusion marks
Metal fusion: The internal metal wire (fusible element) of the fuse breaks, usually accompanied by blackening and deformation of the glass tube or plastic casing.
Casing damage: When a high-voltage fuse (above 250V) melts, it may be accompanied by casing explosion, arc burn marks, and immediate replacement is required.
Color change or char marks: The fuse terminals or casing show color change (such as brown or black) due to overheating, indicating long-term overload or short circuit.
Poor contact signs
Terminal oxidation: The surface of the fuse terminal is covered with white or green oxide, causing an increase in contact resistance and possible local overheating.
Looseness or displacement: The fuse is not fully inserted into the socket, or the spring clips of the socket are aged and cause insufficient contact pressure. It needs to be reinserted tightly or replaced with a new socket.
II. Function Testing: Verifying Circuit Conductivity
Multimeter measurement
Power-off test: Disconnect the vehicle power supply (e.g., remove the negative terminal of the low-voltage battery), and use the multimeter set to the resistance setting (Ω) to measure the resistance between the two ends of the fuse.
Normal: The resistance is close to 0Ω (conducting).
Damaged: The resistance is infinity (open circuit), and replacement is required.
Live test (careful operation): In the low-voltage circuit, use the multimeter set to the voltage setting to measure the voltage between the two ends of the fuse.
Normal: The voltage difference between the two ends is close to 0V (no voltage drop).
Damaged: One end has voltage, while the other end has no voltage, indicating that the fuse has blown.
Special testing tools
Fuse testing pen: Insert into the fuse socket, and quickly determine the conductive state through the LED indicator light, suitable for rapid on-site troubleshooting.
Circuit diagnostic instrument: Some high-end diagnostic instruments can read the fuse status codes in the BMS (Battery Management System) or ECU (Electronic Control Unit), directly locating the fault.
III. System Diagnosis: Inferring Faults Based on Vehicle Performance
Function Failure Signals
Equipment Not Working: Such as no response at the charging port, inability to start the motor, no cooling from the air conditioner, etc., and related circuit fuses have blown.
Intermittent Faults: The equipment works intermittently and then stops, possibly due to poor contact of the fuse or slight overload.
Odor or Strange Noise: When the fuse blows, there may be a burnt smell or a slight cracking sound, requiring immediate inspection.
Dashboard Warning
Fault Light On: Such as "High Voltage System Fault" or "Charging System Fault", possibly accompanied by fuse blowout.
Voltage Abnormality Alert: BMS detects that the battery pack voltage is too low or too high, possibly due to fuse blowout causing the voltage sampling circuit to be interrupted.
Data Stream Analysis
Current Overload Record: By reading historical data from the BMS or motor controller using the diagnostic instrument, if a continuous overload is detected (such as the current exceeding the fuse rating by more than 20%), it may have triggered fuse blowout.
Temperature Abnormality: Abnormal increase in temperature sensor data around the fuse indicates long-term overload or poor contact.
