Charger insurance burned out.
I. Electric vehicle charger failure and maintenance methods:
Blown fuse tube: under normal circumstances, the blown fuse tube indicates that there is a short circuit or overcurrent fault in the charger's internal circuit. This is because the charger works in the state of high voltage and high current for a long time, and the failure rate of the internal components is high. In addition, the fluctuation of power grid voltage and surge will cause the current in the charger to increase instantaneously and blow the fuse.
Repair method: First carefully check the various components on the circuit board to see whether the appearance of these components is burned or there is electrolyte overflow, smell - smell no difference. Then measure the resistance value of the power input, if less than 20OkΩ, it indicates that there is a local short circuit phenomenon at the back end, and then measure the positive and reverse resistance value of the 4 rectifier diodes and the resistance value of the two current limiting resistors to see whether there is short circuit or burned out; Finally, measure whether the power filter capacitor can be charged and discharged normally, whether the switching power tube is broken down and damaged, whether UC3842 and the surrounding components are broken down and burned out. It should be noted that because the measurement is on the road, the measurement results may be wrong or cause misjudgment, so the components can be welded down to measure if necessary. If there is still no such situation, measure whether the input power cable and output power cable are short circuited. In general, in the fuse fuse failure, the rectifier diode, power filter capacitor, switching power tube, UC3842 are vulnerable parts, the probability of damage can reach 95% or more, to focus on checking these components, it is easy to eliminate the fault.
2. No DC voltage output or voltage output is unstable: if the fuse is intact, in an idle condition with load. The reasons for this kind of failure are: overvoltage, overcurrent protection circuit open circuit, short circuit phenomenon; The vibration circuit is not working; The power supply load is too heavy, the rectifier diode in the high-frequency rectifier filter circuit is broken down: filter capacitor leakage, etc.
Maintenance method: First, use a multimeter to measure whether the various components of the high-frequency pulse transformer are damaged: After eliminating the high-frequency rectifier diode breakdown and load short circuit, then measure the DC voltage of each output, if the output is still zero, it can be sure that the control circuit of the power supply is faulty, and finally use a multimeter to statically measure whether the rectifier diode and low-voltage filter capacitor in the high-frequency filter circuit are damaged, if the above components are damaged, replace the new components. General faults can be eliminated. However, it should be noted that the output line break or open welding, virtual welding will also cause this fault, and attention should be paid to this situation during maintenance.
3. No DC voltage output, but the fuse is intact: this phenomenon indicates that the charger is not working, or entered the protection state after work.
Maintenance method: First of all, we should determine whether the charger's change control chip UC3842 is in working condition or has been damaged. The specific judgment method is as follows: power on and measure the voltage of pin 7 to ground of UC3842. If pin 7 has normal voltage and pin 8 has 5∨ voltage, pin 1, pin 2, pin 4, pin 6 also has different voltage, it indicates that the circuit has started and the UC3842 is basically normal. If pin 7 has low voltage and other pins have no voltage, the UC3842 is damaged. The most common damage is 7-pin to ground breakdown, 6-7 pin to ground breakdown, and 1-7 pin to ground breakdown. If these feet are not broken down, and the charger still cannot start normally, it also indicates that the UC3842 has been damaged and should be replaced directly. If it is judged that the chip is not broken, it is checked whether the current limiting resistance of the gate of the switch is welded, welded or changed, and whether the switching power tube itself is poor performance. In addition, the power output line break or poor contact will also cause this failure, so it should also be paid attention to during maintenance.
4. Dc voltage output is too high: This fault is often caused by the voltage regulator sampling and voltage regulator control circuit abnormal, in the charger, DC output, sampling resistance, error sampling amplifier, optical coupler, power control chip together to form a closed control loop, any problem will cause the voltage to rise.
Maintenance method: Because the charger has an overvoltage protection circuit, the output voltage is too high, which will first make the overvoltage protection circuit act. Therefore, in the event of such a fault, we can disconnect the overvoltage protection circuit, so that the voltage protection circuit does not work, and then measure the main voltage of the power supply at the moment of startup. If the measured value is more than 1V higher than the normal value, the reason for the high output voltage is indeed in the control loop. At this time, it should be emphasized to check whether the sampling resistance is variable or damaged, and whether the precision reference voltage source (TL431) or the optocoupler (PC817) has poor performance, deterioration or damage. The precision reference voltage source (TL431) is easy to be damaged. We can distinguish the precision voltage regulator amplifier by the following method: connect the reference end (Ref) of TL431 to its Cathode, string a 1OkΩ resistor, and connect 5∨ voltage. If the Anode (Anode) and the cathode between 2.5V, and wait for a moment and still 2.5∨, it is a good tube, otherwise it is a bad tube.
5. Dc voltage output is too low: According to maintenance experience, in addition to the voltage regulator control circuit will cause the output voltage is too low, there are the following reasons:
(1) The rectifier tripole Ju and filter capacitor at the output voltage end are invalid, which can be judged by substitution method.
(2) The performance of the switching power tube is reduced, resulting in the switching tube can not be normally switched on, so that the internal resistance of the power supply increases, and the load capacity decreases.
(3) The source pole of the switching power tube is usually connected with a small resistance value but a large power resistor, which is used as an overcurrent protection detection resistor. The resistance value of the resistance - generally in 0.2 ~ O.8Ω. Such as the resistance change value or welding, poor contact will also cause the output voltage is too low.
(4) The high frequency pulse transformer is poor, which not only causes the output strider pressure to drop, but also causes the switching power tube to be insufficient and thus repeatedly damaged the switching tube.
(5) The high voltage DC filter capacitance is poor, resulting in poor load capacity of the power supply.