UPS (Uninterruptible Power System), that is, uninterruptible power system, is an uninterruptible power supply system with constant voltage and constant frequency output that contains energy storage devices (usually batteries) and uses inverter as the main component. 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 of
asked about UPS, and related knowledge was pushed one after another. Let us learn about the common faults and analysis of UPS today.
ups common faults and analysis
1, UPS output is normal when there is mains , but when there is no mains buzzer long beeps, no output.
fault analysis:
judges from the phenomenon that the battery and inverter are partially faulty, and can be checked according to the following procedures:
1) Check the battery voltage to see if the battery is insufficiently charged. Or the charging circuit is faulty.
2) If the working voltage of the battery is normal, check whether the drive circuit of the inverter works normally. If the output of the drive circuit is normal, the inverter is damaged.
3) If the inverter drive circuit does not work normally, check whether the waveform generating circuit has PWM control signal output, if there is a control signal output, it means that the fault is in the inverter drive circuit.
4) If the waveform generating circuit has no PWM control signal output, check whether its output is blocked due to the protection circuit, and if so, find out the reason for the protection.
5) If the protection circuit does not work and the working voltage is normal, but 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 sometimes the fault can be found faster.
2. The voltage of the battery is low, but the battery voltage still cannot be charged after charging for more than ten hours.
fault analysis:
judges from the phenomenon that the battery or the charging circuit is faulty, and can be checked according to the following steps:
1) Check whether the input and output voltages of the charging circuit are normal.
2) If the input of the charging circuit is normal, but the output is abnormal, disconnect the battery and test again. If it is still abnormal, the charging circuit is faulty.
3) If the input and output of the charging circuit are normal after the battery is disconnected, it means that the battery has been damaged due to long-term non-charging, over-discharging, or the end of its service life.
3. A pair of power amplifier transistors in the power stage of the inverter are damaged. After replacing the transistors of the same type, they burn out after running for a period of time.
fault analysis:
judges from the phenomenon that the cause is excessive current, and the causes of excessive current are:
1) overcurrent protection fails. When the inverter output overcurrent occurs, the overcurrent protection circuit does not work.
2) The pulse width modulation (PWM) component is faulty. The two complementary waveforms output are asymmetrical. One conducts for a long time, while the other conducts for a short time. The tube is damaged.
3) The parameters of the power tubes are quite different. At this time, even if a symmetrical waveform is input, the output will be asymmetrical. The waveform passes through the output transformer, resulting in biased magnetism, that is, the magnetic flux is unbalanced, and the accumulation will cause the transformer to saturate and the current will increase sharply, burning out Power tube, and one burns out, and the other burns out thereupon.
4. After the UPS is turned on, there is no display on the panel, and the UPS does not work.
fault analysis:
judges from the fault phenomenon, the fault is in the mains input, battery and mains detection part and battery voltage detection circuit:
1) Check whether the mains input fuse is burnt.
2) If the mains input fuse is intact, check whether the battery fuse is burnt, because some UPS will turn off all UPS outputs and displays when the battery voltage cannot be detected by itself.
3) If the battery is in good condition, check whether the mains detection circuit is working normally. If the mains detection circuit is not working properly 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 works normally, then check whether the battery voltage detection circuit is normal.
5. When the UPS is connected to the mains, every time you turn on the UPS, you will hear the repeated action of the relay, the battery voltage indicator on the UPS panel is always on and the buzzer beeps.
fault analysis:
can judge according to the above fault phenomenon: the fault is caused by the battery voltage being too low, which leads to the failure to start the UPS. Remove the battery and perform equalization charging first (all batteries are charged in parallel), if it still fails, only replace the battery.
6. A backup UPS works normally when there is mains power. When there is no mains power, the inverter has output, but the output voltage is low, and the transformer makes a lot of noise.
fault analysis: The output of the
inverter indicates that the final drive circuit is basically normal, and the noise of the transformer indicates that the two arms of the push-pull circuit work asymmetrically. The detection steps are as follows:
1) Check whether the power is normal.
2) If the power is normal, then 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, then 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 light flashes, and the buzzer sounds intermittently. The UPS can only work in the inverter state, and cannot switch to the mains work state.
fault analysis:
cannot convert the inverter power supply to the mains power supply, indicating that there is a fault in the conversion part of the inverter power supply to the mains power supply, and it is necessary to focus on checking:
1) Whether the mains input fuse is damaged.
2) If the mains input fuse is intact, check whether the mains rectification filter circuit output is normal.
3) If the output of the mains rectification filter circuit is normal, check whether the mains detection circuit is normal.
4) If the mains power detection circuit is normal, then check whether the inverter power supply to the mains power supply conversion control output is normal.
8. When the backup UPS is close to full load, the mains power supply is normal, but the battery fuse blows when the battery supplies power.
fault analysis:
battery fuse is blown, indicating that the battery supply current is too large, the detection steps are as follows:
1) Whether the inverter has broken 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, 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.
fault analysis:
cannot convert mains power to inverter power supply, indicating that there is a fault in the conversion part of mains power to inverter power supply. It is important to check:
1) whether the battery voltage is too low, and whether the battery fuse is intact.
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, then check whether the control output of the mains to inverter power conversion is normal.
UPS uninterruptible power supply repair two examples
Baoshen brand MUS1000L UPS is a kind of power supply equipment widely used by users. Its output sine wave is synchronous with the mains, with small distortion coefficient and stable and reliable performance. It is an ideal computer for microcomputers. A long backup power supply. Here are two troubleshooting methods for your reference.
Symptom 1: No-load power on, can not transfer to mains, and there is no inverter, the machine does not operate, and the buzzer has no sound.
check analysis and processing results:
first check the AC insurance, battery insurance, are normal. Check the battery voltage again, the measured voltage value is 48V, and the battery is also normal. Therefore, it is concluded that the fault is in the control part.
According to the working principle of backup UPS, when there is no mains input, the UPS will output 220V voltage from the control circuit and battery inverter, and the buzzer will keep alarming. This fault phenomenon shows 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 voltage stabilizing block "7812" was damaged. After replacing the new three-terminal voltage stabilizing block "7812", the mains power was turned on normally, and the inverter was normal after the power was cut off.
Symptom 2: Mains works normally, and the backup working time with normal load is seriously insufficient.
detection and analysis:
From the fault phenomenon analysis, the faults may include:
(1) The battery voltage is too low and not fully charged.
(2) The inverter control circuit is faulty.
(3) Partial battery damage.
(4) There is a fault in the charger circuit.
(5) The output plug is invaded by damp and dust, causing leakage.
checks first:
(1) Clear the output connector to eliminate the possibility of leakage.
(2) After charging the UPS for a long time, the startup fault still exists after charging.
(3) Check the voltage of the battery pack with a multimeter, it is 48V and it is normal.
(4) Check the charging circuit, it is normal.
(5) Check the inverter control circuit, it is normal.
(6) Use a multimeter and an ammeter to check the electrical performance of the battery, and find that the electrical performance of the battery pack has declined, which is specifically caused by the increase in the internal resistance of the battery in and . The measured battery voltage is 48V without the 50Ω resistor. After connecting the resistor, the current is 800mA, and the voltage across the resistor is 40V. The test data of
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 internal resistance of the battery increases and the power supply time is 30 minutes, it proves that the electrical performance of the battery has declined.
processing result:
replaces the battery, it works normally after starting up, and can reach the long backup time of UPS. The cost of batteries is very high, accounting for more than 30% of the total cost of UPS. Therefore, in order to save money, some batteries with degraded performance can be forcibly charged with a charger. If the battery is successfully charged, it can still be used. This fault is sometimes caused by damage to the cooling fan of the inverter control circuit, please pay attention to it during maintenance.
