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Maintenance method for common faults of electric vehicle charger

Date: 2017-06-01
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 Maintenance of common troubles
As the input circuit of the electric vehicle charger works in the state of high voltage and too high current, the fault rate is the highest. Such as high voltage high current transistor, rectifier filter capacitor, power switch tube; the second is easy to damage is part of the output rectifier diode rectifier, diode protection, filter capacitor, a current limiting resistor; then the PWM controller and feedback protection circuit.
1. fuse tube fuse
In general, fuse tube fuses indicate that the internal circuit of the charger has a short circuit or overcurrent fault. This is because the charger for a long time to work in high voltage, high current status, the higher the failure rate of internal components. In addition, the power grid voltage fluctuations, surge will cause the instantaneous increase in the charger and fuse fuse.
Maintenance method: first, carefully look at the circuit board on the various components, to see whether the appearance of these components are burned, or electrolyte overflow, smell and smell. To measure the resistance value of the input power, if less than 20Ok Omega, the back-end local short-circuit phenomenon, then measuring 4 rectifier diode, anti resistance value and two current limiting resistance, there is no short-circuit or burned out; finally, the measurement of the power filter capacitor will discharge, normal switch power tube breakdown damage, UC3842 and surrounding elements of breakdown, burn etc.. It should be noted that due to road measurements, it is possible to make the measurements error or cause miscarriage of justice, so if necessary, the components can be welded down to measure. If there is still no such condition, measure whether the input power line and the output power line are internally short circuited. In general, the fuse fault, rectifier diode, power supply filter capacitor and switch power tube, UC3842 is wearing parts, the above damage probability is up to 95%, to check on these components, it is easy to troubleshoot.
2. no DC voltage output or voltage output instability
If the fuse is in good condition, in a load condition. The fault reasons are: overvoltage and overcurrent protection circuit open circuit, short circuit phenomenon; vibration TB not work; power overload, high frequency rectifier diode rectifier filter circuit breakdown: filter capacitor leakage etc..
Maintenance method: first, with a multimeter measuring each component of high frequency pulse transformer is damaged: the exclusion of the high frequency rectifier diode breakdown, load short circuit, to measure DC voltage of the output, if the output is zero, it can be sure the power source control circuit is out of order, finally multimeter static measurement of high frequency filter circuit in low voltage rectifying diodes and filter capacitor is damaged, if the components are damaged, replace the components, the general failure can be ruled out. But take note: output line disconnection or open welding, weld will cause this failure, maintenance should pay attention to this situation.
3. no DC voltage output, but the fuse is intact
This phenomenon indicates that the charger is not working or has entered a protective state after work.
Maintenance methods: first of all, should determine whether the charger control chip UC3842 is in the king's state or has been damaged. To determine the specific method is: UC3842 electrical measuring 7 feet to ground voltage, if the voltage is normal and 7 feet 8 feet +5 V voltage, 1, 2, 4, 6 feet will have different voltage, the circuit has been basically normal startup, UC3842. If the voltage at the 7 pin is low and the rest of the pins are free of voltage, the UC3842 is corrupted. The most common damage is the breakdown of 7 foot to ground, 6 and 7 foot grounding and 1 and 7 foot grounding breakdown. If these feet are not broken, and the charger is still not normally started, but also shows that UC3842 has been damaged, should be replaced directly. To determine if the chip is not bad, is a check switch this gate limiting resistor is open welding, weld or variable value and switch power tube itself is bad performance. In addition, the disconnection or bad contact of the power line will cause this kind of fault, so attention should be paid during the maintenance.
4. the DC voltage output is too high
This failure is often to voltage sampling and voltage control circuit abnormality in the charger, DC output, sampling resistor, error sampling amplifier, optical coupler, power control chip constitute a closed loop control, any problems will lead to higher voltage.
Maintenance method: because the charger has over-voltage protection circuit, the output voltage is too high, first of all will make over-voltage protection circuit action. Therefore, in case of this fault, we can disconnect the overvoltage protection circuit to make the voltage protection circuit fail to function, and then measure the main power supply voltage at the start of the switch. If the measured value is more than 1V higher than the normal value, the reason for the excessive output voltage is indeed in the control loop. At this point, emphasis should be placed on checking whether the sampling resistance is variable or damaged. Whether the precision reference voltage source (TL431) or the optocoupler (PC817) is defective, deteriorated or damaged. The precision voltage reference (TL431) can be easily damaged, we can use the following methods to identify precision voltage amplifiers: TL431 reference terminal (Ref) and the cathode (Cathode) connected on a 1Ok resistor, connected to 5 V voltage. Ruo Yangji (Anode) and 2.5V as the cathode, and wait until the moment is still 2.5 V, is good or bad tube, tube.
5. DC voltage output is too low
According to the maintenance experience, in addition to the voltage regulator circuit will cause output voltage is too low, there are several reasons:
(1) output voltage rectifier triode Chu, filter capacitor failure, can pass

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