UPS (Uninterruptible Power System) is an uninterruptible power supply system with constant voltage and constant frequency output containing energy storage devices (usually batteries) and inverters as the main components. It is mainly used in occasions that require 24-hour power supply for equipment, such as communication equipment, computer network systems or other power electronic equipment.
A friend in the background asked about UPS, and related knowledge was pushed one after another. Today, let's learn about UPS common faults and analysis.
UPS common faults and analysis
1. The UPS output is normal when there is mains power, and the buzzer beeps for a long time when there is no mains power, and there is no output.
Failure Analysis:
Judging from the phenomenon, it is a partial fault of the battery and inverter, which can be checked according to the following procedures:
1) Check the battery voltage to see if the battery is undercharged, if the battery is not charged enough, it is necessary to check whether the battery itself is faulty or the charging circuit fault.
2) If the battery working voltage is normal, check whether the inverter drive circuit is working normally, if the output of the drive circuit is normal, it means that the inverter is damaged.
3) If the inverter drive circuit is not working properly, check whether the waveform generation circuit has PWM control signal output, if there is control signal output, it means that the fault is in the inverter drive circuit.
4) If the waveform generation circuit does not have PWM control signal output, check whether its output is blocked due to the operation of the protection circuit, and if so, find out the protection reason.
5) If the protection circuit does not work and the working voltage is normal, and the waveform generating circuit has no PWM waveform output, it means that the waveform generating circuit is damaged.
The above troubleshooting sequence can also be reversed, and faults can sometimes be found more quickly.
2. The battery voltage is low, but the battery voltage still cannot be charged after more than ten hours of charging.
Failure Analysis:
If the phenomenon is judged to be a battery or charging circuit fault, it can be checked as follows:
1) Check whether the input and output voltages of the charging circuit are normal.
2) If the input of the charging circuit is normal, the output is abnormal, disconnect the battery and test again, if it is still abnormal, it is the charging circuit fault.
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 its life.
3. A pair of power amplifier transistors in the power stage of the inverter are damaged, and after replacing the transistors of the same type, they will burn out after running for a period of time.
Failure Analysis:
Judging from the phenomenon, the cause is excessive current, and the causes of excessive current are:
1) The over-current protection fails. When an overcurrent occurs at the inverter output, the overcurrent protection circuit does not work.
2) The pulse width modulation (PWM) component is faulty, and the output of the two complementary waveforms is asymmetrical, one has a long on-time, while the other has a short on-time, so that the two arms work unbalanced, and even both arms are turned on at the same time, resulting in damage to the two tubes.
3) The parameters of the power tube are quite different, even if the input symmetrical waveform, the output will be asymmetrical, the waveform through the output transformer, resulting in bias magnetism, that is, the magnetic flux is unbalanced, and the accumulation leads to the saturation of the transformer and the sudden increase in current, which burns out the power tube, and one burns out, and the other burns out.
4. After the UPS is turned on, there is no display on the panel, and the UPS does not work.
Failure Analysis:
Judging from the fault phenomenon, the fault is in the mains input, the battery and the mains detection part and the battery voltage detection loop:
1) Check whether the mains input fuse is burned out.
2) If the mains input fuse is intact, check whether the battery fuse is burned, because some UPSs will turn off all the output and display of the UPS when the battery voltage cannot be self-tested.
3) If the battery insurance is intact, check whether the mains detection circuit is working normally, if the mains detection circuit is not working normally and the UPS does not have the function of starting without mains, the UPS will also turn off all outputs and displays.
4) If the city detection circuit is working normally, check whether the battery voltage detection circuit is normal.
5. In the case of connecting to the mains, every time you turn on the UPS, you can hear the repeated action sound of the relay, and the indicator light of the battery voltage is too low on the UPS panel and the buzzer is always ringing.
Failure Analysis:
According to the above fault phenomenon, it can be judged that the fault is caused by the battery voltage is too low, which leads to the unsuccessful start of UPS. Remove the battery, first carry out equalization charging (all batteries are connected in parallel for charging), if it is still unsuccessful, the only way to replace the battery is to replace it.
6. A backup UPS works normally when there is mains, and the inverter has output when there is no mains, but the output voltage is low, and the transformer emits loud noise.
Failure Analysis:
The output of the inverter indicates that the final stage drive circuit is basically normal, and the noise of the transformer indicates that the two arms of the push-pull circuit work asymmetrically, and 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 whether the output of the drive circuit is normal.
7. Turn on the UPS when the mains power supply is normal, the inverter working indicator flashes, and the buzzer makes an intermittent sound, the UPS can only work in the inverter state, and cannot be converted to the mains working state.
Failure Analysis:
If the conversion of inverter power supply to mains power supply cannot be carried out, it means that there is a fault in the conversion part of inverter power supply to mains power supply, and it should be focused on detection:
1) Whether the mains input fuse is damaged.
2) If the mains input fuse is intact, check whether the output of the mains rectifier filter circuit is normal.
3) If the output of the mains rectifier filter circuit is normal, check whether the mains detection circuit is normal.
4) If the mains detection circuit is normal, check whether the conversion control output of the inverter power supply to the mains power supply is normal.
8. When the load of the backup UPS is close to full load, the mains power supply is normal, and the battery fuse blows when the battery is powered.
Failure Analysis:
If the battery fuse is blown out, it means that the battery power supply current is too large, and the detection steps are as follows:
1) Whether the inverter breaks down.
2) Whether the battery voltage is too low.
3) If the battery voltage is too low, check whether the battery charging circuit is normal.
4) If the battery charging circuit is normal, then check whether the battery voltage detection circuit is working normally.
9. UPS can only be powered by mains power and cannot be converted to inverter power supply.
Failure Analysis:
The conversion of mains power to inverter power supply cannot be carried out, indicating that the conversion part of mains power to inverter power supply is faulty, and it is necessary to focus on detection:
1) Whether the battery voltage is too low and whether the battery fuse is in good condition.
2) If the battery part is normal, check whether the battery voltage detection circuit is normal.
3) If the battery voltage detection circuit is normal, check whether the mains power conversion control output is normal.
Two cases of UPS uninterruptible power supply maintenance
The MUS1000L UPS is a kind of power supply equipment used by the majority of users, and the output sine wave is synchronized with the mains, the distortion coefficient is small, the performance is stable and reliable, and it is an ideal long-term backup power supply for the microcomputer. Here are two examples of troubleshooting methods for reference.
Fault phenomenon 1: no-load energized, can not be transferred to mains, there is no inverter, the machine has no operation, and the buzzer has no sound.
Check the analysis and processing results:
First of all, check the AC insurance and battery insurance, all of which are normal. Check the battery voltage again, the measured voltage value is 48V, and the battery is normal. Therefore, it is concluded that the fault is in the control part.
According to the working principle of the backup UPS, in the case of no mains input, the UPS outputs 220V voltage by the control circuit and the battery inverter, and the buzzer constantly alarms. This fault indicates that the control circuit is not working, and the working voltage of the control circuit is provided by the battery.
After inspection, it was found that the three-terminal regulator block "7812" was damaged, and after replacing the new three-terminal regulator block "7812", the mains power was turned on normally, and the inverter was also normal after the power was off.
Fault symptom 2: The mains power is working normally, and the backup working time with normal load is seriously insufficient.
Detection & Analysis:
From the fault symptom analysis, the fault may have:
(1) The battery voltage is too low and not fully charged.
(2) The inverter control loop is faulty.
(3) Part of the battery is damaged.
(4) The charger circuit is faulty.
(5) The output plug is subject to moisture and dust invasion, resulting in leakage.
Check first:
(1) Clear the output connector to eliminate the possibility of leakage.
(2) Charge the UPS for a long time, and the boot fault still exists after charging.
(3) Use a multimeter to detect the battery pack voltage, which is 48V normal.
(4) Check the charging circuit, it is normal.
(5) Check the inverter control loop, normal.
(6) Check the electrical performance of the battery with a multimeter and an ammeter, and find that the electrical performance of the battery pack decreases, which is caused by the increase of the internal resistance of the battery. Without a 50Ω resistor, the measured battery voltage is 48V. After connecting the resistor, the current is 800mA, and the voltage at both ends of the resistor is 40V.
The test data shows that the internal resistance of the battery increases, that is, the power consumption of the 8V voltage drop on the internal resistance is 6.4W, if the increase of the internal resistance of the battery is related to the power supply time of 30 minutes, it proves that the electrical performance of the battery decreases.
Result:
Replace the battery, which is normal after starting, and can achieve the long backup time of UPS. The cost of the battery is high, accounting for more than 30% of the total cost of UPS. Therefore, in order to save costs, some battery chargers with reduced performance can be forcibly charged, and they can still be used if the charging is successful. This fault is sometimes caused by damage to the cooling fan of the inverter control loop, please pay attention to it when maintaining.
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