First, the fault phenomenon: in the case of access to the mains, each time the UPS is turned on, the relay will hear the repeated action of the relay. The battery voltage of the UPS panel is low and the buzzer sounds long.


Fault analysis: According to the above fault phenomenon, it can be judged that the fault is caused by the battery voltage being too low, which leads to unsuccessful UPS startup.


Remove the battery and perform equalization charging (all batteries are charged in parallel). If it is still unsuccessful, only replace the battery.




2. Fault phenomenon: When a backup UPS has utility power, it works normally. When there is no mains, the inverter has output, but the output voltage is low, and the transformer emits loud noise.


Fault analysis: The output of the inverter indicates that the final drive circuit is basically normal. The noise of the transformer indicates that the two arms of the push-pull circuit are asymmetrical. The detection steps are as follows:


1 Check if the power is normal.


2 If the power is normal, check whether the output signal of the pulse width output circuit is normal.


3 If the output of the pulse width output circuit is normal, check if the output of the drive circuit is normal.


Third, the fault phenomenon: the inverter power stage is damaged by a pair of power amplifier transistors. After replacing the transistor of the same type, it will burn out after running for a while.


Fault analysis: Judging from the phenomenon, the cause of the fault is that the current is too large, and the cause of excessive current is:


1 Overcurrent protection is invalid. The overcurrent protection circuit does not function when an overcurrent occurs at the inverter output.


2 pulse width modulation (PWM) component failure, the output of the two complementary waveforms is asymmetrical, one conduction time is long, and the other conduction time is short, so that the two arms work unbalanced, even the two arms are simultaneously turned on, resulting in two tubes damage.


3 The power tube parameters have a large difference. At this time, even if the input symmetrical waveform, the output will be asymmetrical. The waveform will be biased by the output transformer, that is, the magnetic flux is unbalanced. The accumulation will cause the transformer to saturate and the current will increase suddenly, and the power will burn out. Tube, while one burns out and the other burns out.


Fourth, the failure phenomenon: After the UPS is turned on, there is no display on the panel, and the UPS does not work.


Fault analysis: Judging from the fault phenomenon, its fault is in the mains input, battery and mains detection part and battery voltage detection loop:


1 Check if the mains input fuse is burnt.


2 If the mains input fuse is intact, check if the battery insurance is burnt, because some UPS will turn off all the output and display of the UPS when the self-test does not have the battery voltage.


3 If the battery is in good condition, check whether the mains detection circuit works normally. If the mains detection circuit is not working properly and the UPS does not have the mains start function, the UPS will also turn off all output and display.


4 If the city detection circuit works normally, check if the battery voltage detection circuit is normal.


V. Fault phenomenon: The UPS output is normal when there is mains, and the buzzer sounds when there is no mains, no output.


Fault analysis: Judging from the phenomenon that the battery and the inverter are partially faulty, the following procedures can be checked:


1 Check the battery voltage to see if the battery is not fully charged. If the battery is not fully charged, check whether the battery itself is faulty or the charging circuit is faulty.


2 If the battery working voltage is normal, check whether the inverter drive circuit works normally. If the output of the drive circuit is normal, the inverter is damaged.


3 If the inverter drive circuit is not working properly, check the waveform generation circuit for the presence of the PWM control signal output. If there is a control signal output, the fault is in the inverter drive circuit.


4 If the waveform generation circuit has no PWM control signal output, check whether the output is working due to the protection circuit, and if so, find out the cause of protection.


5 If the protection circuit is not working and the working voltage is normal, and the waveform generation circuit has no PWM waveform output, the waveform generation circuit is damaged.


The above troubleshooting sequence can also be reversed, sometimes finding faults faster.





Sixth, the fault phenomenon: the battery voltage is low, but the charge is still more than ten hours, the battery voltage is still not charged.


Fault analysis: If the battery or charging circuit is faulty from the phenomenon, you can check the following steps:


1 Check if the input and output voltage of the charging circuit is normal.


2 If the input of the charging circuit is normal, the output is not normal, disconnect the battery and test again. If it is still not normal, the charging circuit is faulty.


3 If the input and output of the charging circuit are normal after disconnecting the battery, it means that the battery has been damaged due to long-term uncharged, over-discharged or has reached the end of life.


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