The UPS (uninterruptible power supply) battery is the core component of the UPS system, and its charging and discharging principle is based on electrochemical energy conversion, which achieves the mutual conversion of electrical energy and chemical energy through reversible oxidation-reduction reactions. The following provides a detailed introduction to battery types, structural composition, charging and discharging processes, management strategies, and influencing factors:
1、 The main types and structures of UPS batteries
1. Common battery types
Valve regulated sealed lead-acid batteries (VRLA) are the most widely used, characterized by low cost, high reliability, and simple maintenance. They are divided into colloidal batteries and AGM (adsorption glass fiber felt) batteries.
Lithium ion batteries (Li ion): In recent years, they have gradually become popular, with high energy density, small size, and light weight, but the cost is high and strict management of charging voltage is required.
Nickel cadmium battery (Ni Cd): resistant to overcharging and overdischarging, with good low-temperature performance, but there is a "memory effect" and cadmium is toxic, so its application is gradually decreasing.
2. Core structure composition
Taking lead-acid batteries as an example:
Positive electrode plate: The main component is lead dioxide (PbO ₂).
Negative electrode plate: The main component is sponge like metallic lead (Pb).
Electrolyte: Dilute sulfuric acid solution (H ₂ SO ₄).
Diaphragm: isolates positive and negative electrodes, prevents short circuits, and allows ions to pass through.
Shell: Sealed container to prevent electrolyte leakage.
2、 The discharge principle of UPS batteries (chemical energy → electrical energy)
1. Electrochemical reaction process
When the UPS load requires power supply, the battery discharges as follows: Negative electrode (oxidation reaction): \ (Pb+HSO4 ^ - \ rightarrow PbSO4+H ^+2e ^ - \) Positive electrode (reduction reaction): \ (PbO2+HSO4 ^ -+3H ^+2e ^ - \ rightarrow PbSO4+2H2O \) Total reaction: \ (Pb+PbO2+2H2SO4 \ rightarrow 2PbSO4+2H2O \)
2. Energy conversion mechanism
During discharge, the negative electrode lead (Pb) loses electrons to generate lead sulfate (PbSO ₄), which flows to the positive electrode through an external circuit to supply power to the load.
The positive electrode lead dioxide (PbO ₂) combines with electrons under the action of sulfuric acid, also generating lead sulfate, while consuming sulfuric acid, resulting in a decrease in electrolyte concentration.
The electromotive force of a battery is determined by the electrode potential difference between the positive and negative electrode materials, and the individual voltage of a lead-acid battery is about 2V.
3、 The charging principle of UPS batteries (electrical energy → chemical energy)
1. Electrochemical reaction process
When UPS is connected to the mains power, the charger charges the battery, and the reaction is opposite to discharge: negative electrode (reduction reaction): \ (PbSO4+H ^+2e ^ - \ rightarrow Pb+HSO4 ^ - \) positive electrode (oxidation reaction): \ (PbSO4+2H2O \ rightarrow PbO2+HSO4 ^ -+3H ^+2e ^ - \) total reaction: \ (2PbSO4+2H2O \ rightarrow Pb+PbO2+2H2SO4 \)
2. Charging stage and management strategy
UPS charging is usually divided into three stages, taking lead-acid batteries as an example:
Constant current charging stage: In the initial stage, the battery is charged with a constant current (such as 0.1C~0.3C, where C is the battery capacity) to quickly replenish power, and the voltage gradually increases.
Constant voltage charging stage: When the voltage reaches the set value (such as about 2.35V~2.4V for lead-acid battery cells), it switches to constant voltage charging, and the current gradually decreases until it approaches zero.
Floating charging stage: After charging is completed, maintain a low voltage (such as 2.23V~2.25V per cell) to keep the battery fully charged and compensate for self discharge losses.
4、 Special management requirements for UPS battery charging and discharging
1. Overcharge protection
Excessive charging voltage can cause electrolyte decomposition (water is electrolyzed into hydrogen and oxygen), accelerate electrode aging, and even cause explosions (lead-acid batteries).
UPS avoids overcharging by setting voltage thresholds and controlling charging time, while lithium-ion batteries also rely on battery management systems (BMS).
2. Overdischarge protection
Excessive discharge can cause the lead sulfate crystals on the electrode plate to become coarse and difficult to reduce through charging, leading to irreversible sulfurization and shortening the battery life.
UPS usually sets the discharge cut-off voltage (such as about 1.75V for lead-acid battery cells), and cuts off the load or alarms when the voltage is below the threshold.
3. Temperature compensation
The temperature affects the internal resistance and chemical reaction rate of the battery, and UPS will automatically adjust the charging voltage according to the temperature:
When the temperature rises, reduce the charging voltage to avoid overcharging;
When the temperature decreases, increase the voltage appropriately to ensure charging efficiency.
5、 Maintenance points in practical applications
Regular charge and discharge tests: To avoid long-term float charging causing "plate passivation", perform a deep discharge (to 80% capacity) every 3-6 months and fully charge.
Balanced charging: Regularly perform balanced charging on the series connected battery pack (increasing the voltage to 2.35V~2.4V per cell for 4-6 hours) to eliminate voltage differences between cells.
Environmental control: Maintain temperature between 20 ℃~25 ℃, humidity below 60%, avoid direct sunlight and dust accumulation.
Status monitoring: Real time monitoring of battery voltage, current, temperature, and internal resistance through the UPS monitoring system, and timely replacement of aging units.
summarize
The charging and discharging principle of UPS batteries is essentially an electrochemical reversible reaction. Through reasonable charging management (constant current constant voltage float charging) and discharge protection (cut-off voltage control), the battery life and reliability can be maximized. In practical applications, maintenance strategies should be developed based on battery types such as lead-acid and lithium batteries, while paying attention to the impact of temperature, current, and other factors on performance to ensure stable power supply for UPS in the event of a power outage.
