How to use and maintain UPS power supply correctly

At present, there are many types of UPS introduced in my country, and different products come from different countries and manufacturers. The working principles and specific circuit designs of these UPS are not the same. In particular, some manufacturers often erase the logo of the integrated circuit model for commercial needs. All these factors bring certain difficulties to the use and maintenance of UPS. Despite this, some common points can still be found in some commonly used UPS usage rules. The following are some clues for the correct use and maintenance of UPS for your reference.

(I) In the design of backup UPS, in order to reduce production costs, it uses the same main power transformer when powered by AC power and battery power. When this type of UPS is powered by battery, the positions of its AC output live wire and neutral wire are fixed, and the user cannot change their mutual order. And because the neutral wire of the AC input terminal of this UPS is the ground wire of the UPS control circuit, when using this UPS, the user must comply with the relevant regulations in the manufacturer's product manual.

(II) The actual available capacity of the battery in all UPS is closely related to the discharge current of the battery, the ambient operating temperature of the battery, the length of storage time and the nature of the load (resistance, inductance, capacitance). If the UPS is not used correctly, the actual available capacity of the battery will often be only a small part of the nominal capacity of the battery. Therefore, users should pay attention to the following points when using the battery:

A. Over-discharge of the battery and long-term open circuit idleness will cause a large amount of lead sulfate to be generated inside the battery and adsorbed onto the cathode of the battery, forming the so-called cathode "sulfation", which results in an increase in the internal resistance of the battery and a deterioration in the charge and discharge performance of the battery. The service life of the commonly used M-type sealed lead-acid battery is about 3-5 years.

B. For most current UPS, after each discharge of the battery, the battery can be float charged using the battery charging circuit inside the UPS. To ensure that the battery is placed in a saturated charging state again, the charging time is generally required to be 10 to 12 hours. Insufficient charging time will cause the battery to be in an insufficiently charged state. At this time, the actual available capacity of the battery is far lower than the nominal capacity of the battery. For some UPS, when the mains voltage is lower than 200V, it is impossible to use the charging circuit inside the UPS to saturate the battery.

C. Some users reduce the actual load power of the UPS or increase the battery capacity to extend the battery discharge time.

D. When the UPS battery encounters one of the following situations during use, in order to restore the battery's charge and discharge characteristics, balanced charging should be used to solve the problem. The so-called balanced charging is to connect each battery unit in parallel and charge it with a uniform charging voltage. The situations in which balanced charging of batteries is required are:

• Over-discharge makes the battery terminal voltage lower than the allowable discharge termination voltage of the battery. For a 12V M-type lead-acid battery, its discharge termination voltage is about 10.5V;

E. To ensure that the battery has good charge and discharge characteristics, for UPS that has been idle for a long time (empirical data is UPS shutdown for more than 10 days), it is best not to add load before restarting it, and let the UPS use the charging circuit inside the machine to float charge the battery for 10 to 12 hours before using it. For users of backup UPS, if the UPS works in the backup working state for a long time, it is recommended to put the UPS in the inverter working state for at least 2-3 minutes every month to activate the battery.

(III) For most UPS, when they are in the inverter power supply state, it is generally required that its load characteristics are purely resistive or capacitive. When the load is capacitive, its power factor is required to be greater than about 0.8. Therefore, for those users with inductive loads, they should pay attention to adjusting their total load reactance to meet the condition of power factor greater than 0.9 as much as possible. Otherwise, the actual load power that the UPS can bear will decrease. Manufacturers recommend: The maximum starting load of the UPS is best controlled within 80% of the rated output power of the UPS. For UPS with sine wave output, when its load is less than 30% of the rated output power of the UPS, its output voltage waveform distortion coefficient will increase slightly. Practice has proved that for most UPS, controlling its load within the range of 30% to 60% of the rated output power of the UPS is the best working mode. Therefore, users who have requirements for the AC input waveform should pay attention to this.

(IV) For a backup UPS, when it is in the backup working state powered by the mains, although it has the function of anti-interference automatic voltage stabilization, it does not have the function of automatic output short circuit protection (generally, the AC input fuse is used to achieve current limiting). Therefore, for users of this type of UPS, the capacity of the fuse in the AC input circuit shall not be increased at will. Only when this power supply is in the inverter power supply state, it has both the automatic voltage stabilization and output short circuit automatic protection functions.

(V) For a backup square wave output UPS, since there is no technical means to accurately adjust its square wave operating frequency in its control circuit, when this power supply is in the inverter power supply state, its square wave operating frequency may sometimes deviate significantly from 50Hz. In addition, for a square wave output UPS, when it is in the inverter power supply state, it is not suitable to run it without load for a long time.

(VI) For backup UPS, the following potentiometers are generally set to adjust the working point:

•Adjust the voltage of UPS mains power supply-inverter power supply conversion;

•Adjust the output AC voltage of the UPS inverter;

•Adjust the charging voltage of the battery charging circuit.

For online UPS, generally only one potentiometer is provided to adjust the UPS AC output voltage. Which potentiometer should be adjusted? Generally, users should not easily adjust other potentiometers in the machine, otherwise it will cause the UPS control circuit to be out of adjustment and the machine cannot work normally.

(VII) Most UPS currently on the market have anti-interference automatic voltage stabilization function. Therefore, under normal circumstances, there is no need to add an anti-interference AC voltage stabilizer. If the user must use an AC voltage stabilizer, the AC voltage stabilizer can be used as the input stage of the UPS.

(VIII) When purchasing a long-delay UPS, in order to ensure that the battery can be used efficiently, increase its effective available capacity and extend the battery life, a charger with improved constant current charging characteristics should be selected. If a general cut-off constant voltage charger is used, the battery performance will inevitably deteriorate rapidly. For a long-delay UPS, the cost of the battery pack often exceeds the cost of the UPS host, so users should pay attention to this.

(IX) If the user uses a small diesel generator to supply power during a power outage, since the internal resistance of the diesel generator is much greater than that of the mains power grid, it is possible that the output voltage value of the AC voltage stabilization circuit of the backup UPS will be greatly different when it is powered by the mains and the diesel generator. In this case, the user should readjust the AC voltage stabilization working point of the UPS.

(10) For a square wave output backup UPS, the conversion time between the mains power supply and the inverter power supply is about 4 to 9 ms. This cannot guarantee 100% reliable power supply to the load. For this power supply, if a fault occurs occasionally and the computer's working program is interrupted or damaged, that is, the computer's "self-check" operation does not mean a fault. Therefore, square wave output UPS is not suitable for use in the power supply system of computer networks.

(XI) If a square wave output UPS is used as the host in a long-delay UPS, the computer hardware failure rate will increase. In principle, a sine wave output UPS should be used as the host in a long-delay UPS system.