Introduction of commonly used UPS batteries

There are three types of batteries used in UPS applications: open liquid lead-acid batteries, maintenance-free batteries, and nickel-cadmium batteries. The batteries currently provided by UPS manufacturers are generally maintenance-free batteries. The following mainly introduces the characteristics of three types of batteries:

1. Open liquid lead-acid battery

According to the battery structure, its service life can be 8-10 years or 15-20 years. Since the sulfuric acid electrolysis of this battery will produce corrosive gas, this type of battery must be installed in a ventilated room away from precision electronic equipment, and the battery room should be paved with anti-corrosion tiles.

Due to evaporation, open batteries require regular measurement of specific gravity and the addition of acid and water. This battery can withstand high temperatures, high pressure, and deep discharge. The battery room should be non-smoking and use open battery racks.

2. Maintenance-free battery

It is also known as valve regulated sealed lead-acid battery. The following principles should be followed in the use and maintenance:

A: The allowable operating range of sealed batteries is 15℃ to 50℃, but using it within 5℃ to 35℃ can extend the battery life. Below -15℃ the battery's chemical composition will change and the battery will not be able to charge. The longest life will be obtained when using it within the range of 20 to 25℃. The battery will have a long life but lower capacity when running at low temperatures, and a higher capacity but shorter life when running at high temperatures.

B: The relationship between battery life and temperature can be referred to by the following rule: after the temperature exceeds 25 degrees Celsius, the battery life will be halved for every 8.3 degree increase in temperature.

C: The float charge voltage of the maintenance-free battery is 2.3V/cell. A 12V battery should be 13.8V. It is recommended that the voltage of every cell be 2.25-2.3V. When 120 batteries are connected in series, the float charge voltage should be reduced by 3MV for every degree increase in temperature after the temperature rises above 25 degrees Celsius. Similarly, the voltage should be increased by 3MV for every degree increase in temperature to avoid insufficient charging. The discharge termination voltage is 1.67V per cell at full load (<30 minutes). In the case of a low discharge rate (low current and long-time discharge), the voltage should be increased to 1.7V-1.8V per cell. The charge voltage can be adjusted according to the load.

D: If the battery is not recharged within 72 hours after completing discharge, the sulfate will adhere to the plates and insulate the charge, thus damaging the battery.

E: When the battery is float-charged or equalized charged, the gas generated inside the battery is electrolyzed into the water at the negative plate, thereby maintaining the battery capacity without the need to add external water. However the corrosion of battery plates will reduce the battery capacity.

F: The battery separator life is only 5-6 months when the ambient temperature is 30-40 degrees. Batteries that are stored for a long time must be charged every 6 months. The battery must be stored in a dry and cool environment. The self-discharge rate of maintenance-free batteries at 20 degrees is 3-4% per month and varies with temperature.

G: Maintenance-free batteries are equipped with safety valves. When the internal air pressure of the battery rises to a certain level, the safety valves can automatically discharge excess gas, and the safety valve will automatically recover when the internal air pressure is restored.

H: The cycle life (number of charge and discharge cycles) of a battery depends on the discharge rate, discharge depth, and the recharging method, among which the most important factor is the discharge depth. When the discharge rate and time are constant, the shallower the discharge depth, the longer the battery cycle life. The cycle life of the maintenance-free battery is about 200 times under 100% deep discharge at 25 degrees.

I: When a battery reaches the end of its life, it will experience capacity decay, internal short circuit, shell deformation, plate corrosion, and reduced open circuit voltage.

J: IEEE defines the end of battery life as the capacity being less than 80% of the nominal capacity AH. There is a nonlinear relationship between nominal capacity and actual backup time. If the capacity is reduced by 20%, the corresponding backup time will be greatly reduced. Some UPS manufacturers define the end of battery life as when the capacity drops to 50-60% of the nominal capacity.

K: It is absolutely forbidden to mix batteries of different capacities and from different manufacturers, otherwise the battery life will be reduced.

L: If two battery groups are used in parallel, ensure that the battery connections and bus impedances are the same.

M: Maintenance-free batteries mean that there is no need to add fluid, but it is still necessary to regularly check whether there are cracks in the shell and whether there is electrolyte leakage.

3. Nickel-cadmium battery:

Unlike lead-acid batteries, these batteries produce hydrogen and oxygen during electrolysis instead of corrosive gases, so they can be installed next to electronic devices. The water consumption is very small, and generally, no maintenance is required. The normal lifespan is 20-25 years. Far more expensive than the previously mentioned batteries. The initial installation costs are approximately three times that of lead-acid batteries. The battery life will not be affected by high ambient temperature, nor will the battery capacity be affected by low ambient temperature. Generally, the voltage of each battery is 1.2V, so UPS needs to be designed with a higher charger voltage if using this type of battery.

Advantages and disadvantages:

1. Open lead-acid battery:

Advantages: less investment, longer life than maintenance-free batteries, and lower temperature requirements.

Disadvantages: Maintenance is more complicated, a dedicated battery room is required, corrosive gases are discharged, initial charging for 50-90 hours must be done on-site, and maintenance by a dedicated person is required.

2: Maintenance-free battery:

Advantages: No maintenance such as adding fluid is required, it can be transported in a fully charged state, and no special maintenance is required.

Disadvantages: Failure to perform recharging in time will damage the battery. More sensitive to temperature. Shorter life and is more expensive than lead-acid batteries.

3: Nickel-cadmium battery:

Advantages: Low maintenance requirements, long life, insensitive to temperature, no harmful gas emissions.

Disadvantages: Most expensive of the three batteries.

Commonly used batteries for UPS

At present, most computer centers generally use maintenance-free batteries, which are more convenient to maintain, but the following work is also required:

1: Discharge once every three to four months to prevent the plates from oxidation.

2: The ambient temperature should be kept at 20-25 degrees.

3: The connection cannot be too tight or too loose and needs to be checked frequently.

4: Check and replace in time after three years of use.