The reason for the low DC voltage output of the charger
The DC voltage output of the charger of electric vehicle is too low. According to the maintenance experience, besides the voltage stabilization control circuit will cause the output voltage to be too low, there are several reasons as follows:
(1) the output voltage terminal rectifier and the filter capacitor fail, and can be judged by substitution method.
(2) The performance of the switching power transistor decreases, which leads to the failure of the switching power transistor to conduct normally, which increases the internal resistance of the power supply and decreases the load carrying capacity.
(3) the source of the switch power tube usually has a resistance which is very small but has a high power. The resistance value of the resistor is like 0.2 to o.8 Omega. If the resistance changes or opens and welds, poor contact will cause the output voltage to be too low.
(4) High frequency pulse transformer is not good, not only causes the output voltage to drop, but also causes the switch power transistor to excite insufficiently, thus repeatedly losing the switch tube.
(5) HVDC filter capacitor is poor, resulting in poor power load capability.
(6) the power output line is not in good contact, and there is a definite contact resistance which causes the output voltage to be too low.
(7) the voltage of the power grid is too low. Although the charger can still output rated charging voltage under low jade, the output voltage is too low when the grid voltage is lower than the minimum voltage limit of the charger. Maintenance method: First of all, use a multimeter to check whether the low voltage DC filter capacitor is deteriorated, whether the capacity is reduced, whether the normal charge and discharge. If there are no above problems, we measure the current limiting resistance of the electrode of the switch power pipe and the change value of the overcurrent protection of the source, the metamorphic or the open welding, and the bad contact. If there is no problem, check again if the core of the HF transformer is intact. In addition to this Z, it may be the output filter capacitor capacity reduction, or open welding, virtual connection; power output current limiting resistance variable value or virtual connection; power output line virtual connection and other trapped elements should not be released, should be carefully checked to ensure no - loss.