Therefore, the transformer was carefully disassembled and the number of turns of each group of windings was recorded. The number of turns on the secondary side was 18. Because the charging voltage of the 12V battery was about 14V, the winding on the secondary side was removed for 9 turns. After reinstallation, the test found that the output voltage of the charger dropped from 27V to 12.8V. At this time, the resistance of R22 needed to be increased. After the test, the resistance of R22 was finally set at 15kΩ, no-load output of the charger is 14.2V. Because the first two stages of this three-stage charger are controlled according to the charging current. Therefore, the control and charging state indication loop formed by LM324 need not be changed, only the step-down resistor R23 supplying power to LM324 is reduced from 2.6kΩ to 220Q, and the R24 connected in series on the charging indication light emitting diode LED1 is reduced to 10kΩ.

The R27 position is 2.2K, and the resistance value on R39 R34 is about 7.3K. Use a multi-turn potentiometer to replace it. After adding the battery (10Ah), adjust it carefully, and the voltage is 14.1~14.3V during charging (red light, phase). Basically OK.

--★1. The electric vehicle charger will display the charging state according to the output current. The green light is on, indicating that the charger has no output current (for example, the battery is fully charged or the battery is not connected).

--★2. Under normal circumstances, even if the green light is on, there should be voltage output. If there is no voltage output, it should be: ①, the rectifier diode at the output end is damaged; ②, the output cable has an open circuit; ③, the voltmeter is not normal.

In order to facilitate maintenance, the common fault maintenance will now inform friends:

1 fault phenomenon: primary input insurance burned, black. The load is seriously short-circuited. Focus on checking the rectifier tube and switch tube. After the switch tube is damaged, the current detection resistor connected to the ground pin will also burn out at the same time. Pay attention to replacing it with a resistor of the same specification when changing. The error cannot be too large, otherwise the newly replaced switch tube will be blown up. Pay special attention!!

2 There is no voltage at the output, and the power supply and saturation indicator lights are on, which is mainly caused by short circuit of the output circuit. The common one is "Charge Your Electric Vehicle with Chargers of Other Output Polarities" caused by the positive and negative connection of the power supply. Focus on checking the output insurance resistance 3W0.1 ohm green or gray white. After replacement, check whether the anti-connection diode is mostly 1N5408 or 6A10 for damage.

3 The output voltage is normal, the charging time is long, the green light is not changed, and the battery is heated seriously. After eliminating the battery failure, the common charger reason is that the voltage detection and conversion integrated circuit LM324 part of the unit is damaged, which can be checked by replacement method.

4 The power supply has no indicator light and the switch tube has no problem. Most of the power supply drive circuit UC3842 is damaged. The inspection method is to measure the power supply voltage of 3842 7 pins to be about 15V, 6 pins to float about 1-2V, and 8 pins to output 5V. If the above three conditions are met, it can be basically considered that the 3842 is free of faults. If the 3842 is damaged, check whether the power supply resistor 150K3W is damaged,

5 If it is damaged by rain, most of it is 3842 damage, 8N60 damage 3842 6 pins to the control pole resistance of the switch tube damage "about 120 ohms" power supply resistance 150K3W resistance damage current detection