What is UPS? Why use UPS? All the knowledge about UPS power supply is here(Part 3 - 8)

Time of issue:2021-10-11


UPS basic maintenance


1. General requirements for UPS maintenance 


An operation guide should be placed on the UPS host site to guide on-site operations.


The parameter setting information of UPS shall be fully recorded, properly archived and kept updated in time.


Check whether various automatic, alarm and protection functions are normal.


Perform various UPS functional tests on a regular basis.


Regularly check the contact of the lead wires and terminals of the host, battery and power distribution part, check whether the connection of the feeder bus, cable and flexible connector is reliable, and measure the voltage drop and temperature rise.


Frequently check the operation of the equipment and whether the fault indication is normal.


Regularly check the appearance of the internal components of the UPS, and deal with it promptly if any abnormalities are found.


Regularly check whether the operating temperature of the main UPS modules and fan motors are abnormal.


Keep the machine clean, and clean the vents, fans and filters regularly.


Carry out UPS battery pack load test regularly.


Each locality should select an appropriate tracking rate according to the changes in the frequency of the local mains. When the input frequency fluctuates frequently and the rate is high, beyond the UPS tracking range, inverter/bypass switching operation is strictly prohibited. When powering the diesel engine, special attention should be paid to avoid this situation.


The UPS should use an open battery rack to facilitate the operation and maintenance of the battery.


2. UPS maintenance items and periodic table


UPS daily inspection items:


The main contents are: check the control panel, confirm that all indications are normal, all indication parameters are normal, and there is no alarm on the panel; check for obvious high temperature and abnormal noise; make sure that the ventilation grid is not blocked; call up the measured parameters and observe whether there is any Does not match the normal value, etc.


UPS weekly inspection items:


The main contents of the weekly inspection are: measuring and recording battery charging voltage, battery charging current, UPS three-phase output voltage, and UPS output line current. If the measured value is significantly different from the previous one, the size, type and location of the new load should be recorded.


UPS monthly, quarterly, and annual maintenance items:


Battery management of UPS power supply


The battery is an important part of the UPS. A large proportion of UPS failures are caused by battery problems. The performance of the battery directly affects the reliability of the system. In order to ensure the service life of the battery, in addition to maintaining the normal temperature and routine maintenance, the automatic management of the battery is a crucial factor.


UPS power supply automatic battery management includes automatic equalization and floating charge conversion control, battery pre-warning shutdown, regular automatic maintenance, manual battery self-check and many other advanced functions that can improve battery life. It also has battery failure detection and battery discharge backup time. Forecast and battery characteristic curve management.


Automatic battery charging and floating charging conversion


The battery charging process can automatically switch between equal charge and float charge according to the battery current. The set criterion for equal charge to float charge is: I≤0.01C.


Battery float voltage temperature compensation: (take 2V battery as an example)


When the battery is in the floating charge state, the floating charge voltage can be compensated according to the temperature. The temperature compensation takes 20°C as the center point and fully compensates within 10°C-40°C. The calculation formula:


Temperature T>40, T=40; if T<10, T=10


The average cell voltage of the battery should be adjusted to: V=V0+(20-T)×0.003


Among them, V0 is the single float voltage at 20°C given by the battery manufacturer, which can be set according to different batteries when the battery is first powered on, and the default is 2.23V. The equalization voltage is not compensated, and the default monomer equalization voltage is 2.35V.


Equal charge time limit:


If you are in the equalizing charge state for 12 consecutive hours, the control system will forcefully switch to the floating charge state. The condition for this setting is that when the equalizing charge time reaches the set value, it will automatically switch to the floating charge state.


Battery discharge management:


Set the cut-off voltage of battery discharge to 1.8V per single battery. The actual cut-off voltage will fluctuate around this value depending on the degree of battery aging. The cut-off voltage is selected as 1.8V per single battery. High-power discharge has been taken into consideration. The decay of the battery capacity under the circumstances.


UPS battery automatic test:


The UPS battery capacity test can be done manually or by using the UPS battery automatic test function. The manual test method can refer to the battery capacity test method in the DC power supply system. The automatic test function of UPS is introduced below.


The test can only be carried out under the following conditions:


The inverter is running.
The inverter is not overloaded.
The backup power supply (bypass power supply) exists and meets the requirements.
The inverter is synchronized with the bypass power supply.
The battery must be fully charged.


The UPS battery automatic test function is set according to the following three points:


Time interval (test period can be set to 10 days-150 days).
The date and time of the automatic battery test.
The default alarm mode when there is a battery problem.


When starting the battery test, the rectifier voltage will drop below the rated voltage of the battery pack, and above the inverter shutdown voltage, if the battery can be discharged as required within the specified load and within the specified time, the UPS will give an affirmative signal, indicating that the battery Yes; if the battery cannot be discharged as required within the specified load and within the specified time, the UPS will give a negative signal, indicating that the battery needs to be replaced. But at this time, because the rectifier/charger voltage is greater than the inverter shutdown voltage value, the rectifier/charger voltage still supplies power to the inverter, so that the output voltage is uninterrupted.


3. Common UPS fault and handle methods


When the mains power is on, the UPS has a mains power failure alarm. Possible reasons:


The mains input air switch tripped.
The input AC line is in poor contact.
The mains input voltage is too high, too low, or the frequency is abnormal.
The UPS input MCB or switch is damaged or the fuse is blown.
The mains detection circuit inside the UPS is faulty.




Check the input MCB.
Check the input wiring.
If the utility power is abnormal, do not deal with it or start the generator to supply power.
Replace the damaged MCB, switch or fuse.
Check the UPS mains detection circuit.


When the mains power is normal, the UPS output is normal; after the mains power is cut off, the load is also cut off. Possible Causes:


Because the mains is often low voltage, the battery is under voltage.
The UPS charger is damaged and the battery cannot be charged.
The battery is aging and damaged.
Load overload, UPS bypass output.
The load is not connected to the UPS output.
The battery pack of the long-time back-up model is not connected or has poor contact.
The UPS inverter is not started (the UPS panel control switch is not turned on), and the load is supplied by the mains bypass.
The inverter is damaged and the UPS bypasses the output.




When the mains voltage is normal, the battery is fully charged, the generator is started to charge the battery, and a voltage stabilizer is added to the UPS input.
Check the charger.
Replacement battery.
Reduce the load.
Connect the load to the output of the UPS.
Check whether the battery pack is properly connected.
Start the inverter to supply power to the load (open the panel control switch).
Check the inverter.


The UPS cannot start, possible reasons:


The battery is not used for a long time, and the voltage is low.
The input AC and DC power cables are not connected properly.
The internal startup circuit of the UPS is faulty.
The internal power circuit of the UPS is faulty or the power is short-circuited.
The internal power components of the UPS are damaged.



Fully charge the battery.
Check whether the input AC and DC wires are in good contact.
Check the UPS startup circuit.
Check the UPS power circuit.
Check whether the internal rectifier, booster, inverter and other parts of the UPS are damaged.


When the UPS is in normal use, a long buzzer alarm occurs suddenly. Possible reasons:


The user starts with a large load or a large impact load.
The output terminal is suddenly short-circuited.
The UPS internal inverter circuit is faulty.
UPS protection and detection circuit malfunction.




When the load is turned on, increase the power capacity of the UPS in the order of large first and then small.
Check whether the output of the UPS is short-circuited.
Check the UPS inverter.
Check the internal control circuit of the UPS.


The UPS works normally but the load equipment is abnormal. Possible reasons:


The UPS output zero-ground voltage is too high.
The UPS ground wire and the load equipment ground wire are not connected at the same point.
The load equipment is abnormally disturbed.




Check the grounding of the UPS. If necessary, connect a 1-3kΩ resistor between the zero and ground of the output terminal of the UPS.
Connect the UPS ground and load ground to the same point.
Restart the load equipment.


What is UPS? Why use UPS? All the knowledge about UPS power supply is here(Part 1 - 8)- UPS types, functions and principles
What is UPS? Why use UPS? All the knowledge about UPS power supply is here(Part 2 - 8)- UPS quality selection and configuration selection
What is UPS? Why use UPS? All the knowledge about UPS power supply is here(Part 4 - 8)- 10 basic problems of UPS power supply