I. Overview
Battery is an important part of UPS, EPS, DC screen and other systems. It is widely used in important fields such as industry, communication, railway (including subway), banking, securities, military, aviation, etc. Its advantages and disadvantages directly affect The reliability of power supply systems in various fields.
Second, the meaning and classification
Battery: A device that converts chemical energy and DC power into one another and can be recharged after being discharged by charging. It is called a battery. (Common batteries are lead acid, cadmium nickel, hydrogen nickel and lithium ion batteries. Below, we will focus on Lead-acid maintenance-free battery); the battery is the shortest device with the lowest MTBF in the whole UPS, EPS, DC screen and other systems. If the user can use and maintain it correctly, it can prolong its service life, otherwise its service life will be greatly shortened, so that it will be retired early, causing unnecessary losses to the users themselves.
The types of batteries can generally be divided into:
1. According to the purpose classification, it can be divided into: A> start-up (for various cars, tractors, diesel engines, starting and ignition, lighting; high-current discharge is required at start-up, low-temperature start is required, battery internal resistance is small); B> fixed acid-proof (for power plants, substations, communications, hospitals, etc. as protection, automatic control, accident lighting, communication and other backup power; dilute electrolyte, long life, floating charge); C> traction (for various Battery car, **** car, forklift, mining motor car, etc. As electric traction and lighting power supply; requires thick plate, large capacity, charge and discharge cycle with 3h~5h rate); D> other use ( Different sizes and capacities, various discharge rates)
2. According to the state of charge of the lead-acid battery, it is divided into: A> dry discharge state (the plate is in the discharge state, placed in the battery tank without electrolyte; the electrolyte should be poured into the initial use, and the initial time is long B> can be used after charging); B> dry state (the plate is in the dry state of the electrolyte-free battery tank, when used, the electrolyte can be used without initial charge); C> with liquid charging State (charged state charged battery); D> wet state (charge state, part of the electro-hydraulic suction in the plate and diaphragm, when used, the electro-hydraulic, do not need to charge. Storage time is not as dry-charged battery Long time); E> maintenance-free battery (charged state with liquid battery, no need to maintain water during the specified working life, self-discharge rate is very small); F> less maintenance battery (charged state with liquid battery, in the specified work Only a small amount of maintenance is required during the lifetime, and water is added for a long time)
3. According to the structure of the battery cover and the exhaust vent, it is divided into: A> open type (no permanent cover, the generated gas can escape freely, only the cover plate not fixed to the housing; to reduce acid mist. Obsolete) B>Exhaust type (battery case and cover are fixed together; the acid injection port of the cover is equipped with exhaust æ‹´) C> Acid-proof explosion-proof type (the battery cover is equipped with acid-proof fire retardant, allowing the battery row Gas, but the acid mist does not escape; when there is outside fire source, the battery does not burn inside, does not explode) D> Acid-proof dehydrogenation type (with catalytic enthalpy, the hydrogen and oxygen released from the battery can be re-formed into water, return to the battery At the same time, it has anti-acid and anti-riot function. E> Valve-controlled closed battery (battery sealed, no need to add water, equipped with safety valve, gas can be exhausted when the pressure inside the battery is too large, outside gas can not enter the inside of the battery; Maintenance battery)
Third, the use of lead-acid batteries
Lead-acid battery: The electrode is mainly made of lead, and the electrolyte is a kind of battery of sulfuric acid solution. Generally, it consists of a positive electrode plate, a negative electrode plate, a separator, a battery tank, an electrolyte, and a terminal. It was invented by the French scientist Plant in 1859 and has a history of 148 years. Calculation of the capacity of a lead-acid battery: Under the specified conditions, the amount of electricity that can be supplied by a fully charged battery is usually expressed in ampere-hours (Ah). Capacity = single positive plate number × single plate capacity
Some equipments such as UPS, EPS, DC screen, etc., generally consider lead-acid maintenance-free batteries, such as German Sunshine, German Pine, GNB, Guangdong Yuasa, Guangdong Zhicheng Champion, taking into account load conditions, usage environment, service life and cost. , Shenyang Panasonic, Shanghai Hercules, and other brands of quality maintenance-free batteries. Users should never use inferior batteries because they are cheap, because this will affect the reliability of the entire system and may cause even greater losses.
1. Lead-acid maintenance-free battery inspection before use
Lead-acid maintenance-free batteries have self-discharge (SELF-D1SCHARGE). If they are not used for a long time (usually placed for more than six months, self-discharge is 50%), energy will be lost, so regular charge and discharge are required. Maintenance personnel can judge the battery's open circuit voltage to judge whether the battery is good or bad. Take the 12V battery as an example. If the open circuit voltage is higher than 12.5V, it means that the battery has more than 80% energy storage and must be charged for more than 10 hours; if the open circuit voltage is Between 12V-12.5V, it should be recharged immediately, and must be charged for 13-24 hours or more; if the open circuit voltage is lower than 12V, it means that the battery storage energy is less than 20%, and it must be charged for more than 48 hours. After charging, the open circuit voltage should be around 13V. Therefore, it is recommended that the user not be placed for too long, and the qualified user recommends charging and discharging for 3 months to ensure that the battery capacity reaches the desired value. Before use, check the appearance to see if the wiring column is oxidized. If it is polished, it will affect the conductivity. Then look at the battery surface for cleanness. If there is dust, wipe it with a dry cloth.
2. Lead-acid maintenance-free battery inspection
Since the maintenance-free battery adopts the absorption electrolyte system, it will not generate any gas during normal use. However, if the user uses it improperly, the battery will be overcharged, and gas will be generated. At this time, the internal pressure of the battery will increase, and the battery will be increased. The upper pressure valve is opened, which will cause the battery to rise, deform, leak or even rupture. These phenomena can be judged from the appearance. If the above situation is found, the battery should be replaced immediately. If available, the battery online detection system can be installed to check the battery voltage, internal resistance, temperature and other changes.
3. Maintenance of lead-acid maintenance-free battery in use
Although the maintenance-free battery does not require manual maintenance work when it is used, it still has certain requirements when it is used. If it is used improperly, it will affect the service life of the battery.
Factors affecting battery life are as follows: installation, temperature, charge and discharge current, charging voltage, depth of discharge, and long-term charging.
1) Battery installation
The battery should be installed in a clean, cool, ventilated, dry place as far as possible, and protected from sunlight, heaters or other radiant heat sources. The battery should be placed upright and not tilted. The terminal connections between each battery should be firm. When connecting, different capacities, different performances, different old and new, batteries of different manufacturers should not be used together. When the battery is connected, an insulating tool should be used to prevent accidental short circuit of the positive and negative electrodes and burn the battery. When the battery is connected to the charger or load, the circuit switch must be in the off position. The positive pole of the battery should be connected to the positive pole of the charger or load. The negative pole of the battery should be connected to the negative pole of the charger or load. The nuts, bolts, washers and connecting wires for coupling should be loose and moderate, and the screws should be loose and too tight.
2) Ambient temperature
The ambient temperature has a great influence on the battery. If the ambient temperature is too high, the battery will overcharge and generate gas. If the ambient temperature is too low, the battery will be undercharged, which will cause the battery to last. Therefore, the ambient temperature is generally required to be around 25 °C.
3) Charging
Charging is divided into initial charging, normal charging, and balanced charging.
At the initial charge, the first charge of the new battery is called initial charge, and the purpose is to reduce the active material of the plate which is oxidized during the assembly process, increase the active material content, and improve the discharge performance of the battery.
Normal charging, charging a battery that has been discharged is called normal charging.
Floating charging, the battery pack and the power supply are connected in parallel to the load. When the AC power is normal, the rectifier rectifies the alternating current into direct current, and then charges the battery while re-converting the direct current to alternating current to supply power to the load. When the AC power supply is interrupted, the DC power of the battery is immediately converted into AC power by the inverter to supply power to the load to ensure the continuity of the power supply. This type of battery charging is called floating charging.
Balanced charging, in the process of using the battery, there will often be imbalances in specific gravity, capacity, voltage, etc. The output voltage of the battery pack is too low and the output power is too small. To this end, the battery pack is overcharged so that each of the battery cells in the battery pack is fully charged. This charging process is called equalization charging.
Regardless of the charging method used, care should be taken to control the charging voltage and current in accordance with the manufacturer's product description to prevent over-voltage and over-current charging from degrading battery performance and shortening or damaging the life.
In the power system, the battery is always on-line, so that the battery is basically in a long-term floating state. The selection of the float voltage plays a vital role in the long-term reliable operation of the battery. As seen earlier, The high float voltage will cause the battery to lose water slowly and cause thermal runaway to make the battery fail. The low float voltage will cause the battery to be fully charged for a long time, causing the battery to sulphate and cause the battery to fail. The correct float voltage should be selected at 2.23V/cell. It should be adjusted accordingly with the battery operating temperature. Due to the different battery manufacturers, this parameter will have some differences, and should be selected according to the parameters provided by the manufacturer.
In a battery pack, the batteries are always charged in series. Due to the individual differences in the batteries, the terminal voltage of each battery will not be strictly consistent. To ensure the long-term safe operation of each battery in the battery pack, each battery pack must be guaranteed. The floating voltage of the battery is in the correct range. Balanced charging is a commonly used method to ensure sufficient battery power in the battery pack through proper overcharging. This method should limit the use of the battery pack because it should be overcharged. Instead of equalizing the charging, a single battery should be used. If the battery pack must be balanced, the equalized charging voltage must be strictly controlled. The voltage of the balanced charging should be selected in strict accordance with the regulations of the battery manufacturer.
4) Discharge
The discharge current should not be too large, and it is necessary to avoid short-circuit discharge. Generally, according to C10-C20 ampere-hour discharge, specifically, such as 50AH battery, discharge with C10 (5 ampere current), up to 10 hours, can achieve the purpose of fully activating the battery, and at the same time can test the battery Whether the capacity is sufficient (some battery manufacturers require C20 to discharge, and the corresponding discharge time is doubled).
When discharging, the battery terminal voltage should not be lower than the termination voltage, in case the battery is over-discharged, resulting in a decrease in battery performance and a shortened life. After discharge, it should be charged in time. The battery is not allowed to stand for a long time in the discharged state.
5) Depth of discharge
The depth of discharge has a great influence on the service life of the battery. The deeper the discharge depth of the battery, the less the cycle is used, so when it is used.
Deep discharge should be avoided.
6) Regular maintenance
After using the battery for a certain period of time, it should be checked regularly, such as observing whether its appearance is abnormal, measuring whether the voltage of each battery is average, etc. If the battery is not charged for a long time, the battery will always be in a state of charge, which will make the battery's activity worse, so even if it is not In the event of a power outage, the UPS also needs to perform periodic discharge tests to keep the battery active. The discharge test can usually be carried out once every three to six months if the conditions permit. The practice is that the UPS is loaded - ** is more than 50%, then the mains is disconnected, so that the UPS is in the battery discharge state, and the discharge duration depends on the battery capacity. Generally, it takes several minutes to several tens of minutes. After the discharge, the mains supply is restored and the battery is continuously charged.
Fourth, the failure mechanism of lead-acid batteries (ie common faults)
1 Battery water loss: The loss of water in the lead-acid battery will lead to an increase in the specific gravity of the electrolyte, causing corrosion of the positive grid of the battery, reducing the active material of the battery, thereby reducing the capacity of the battery and failing.
The difficulty in sealing lead-acid batteries is the electrolysis of water during charging. When the charge reaches a certain voltage (generally 2.30V / monomer or more), oxygen is released on the positive electrode of the battery, and hydrogen gas is released from the negative electrode. On the one hand, the release of gas brings out the acid mist to pollute the environment, on the other hand, the water in the electrolyte is reduced, and it is necessary to perform additional water maintenance at intervals. The valve-regulated lead-acid battery is a product developed to overcome these shortcomings. Its product features are:
(1) Using a multi-quality high-quality grid alloy to increase the overpotential of gas release. That is, the ordinary battery grid alloy releases gas when it is above 2.30 V/cell (25 ° C). After using a high-quality multi-component alloy, the gas is released at 2.35 V/monomer (25 ° C) or more, thereby relatively reducing the amount of gas released.
(2) Let the negative electrode have excess capacity, that is, 10% more capacity than the positive electrode. At the later stage of charging, the oxygen released from the positive electrode comes into contact with the negative electrode, reacts, and regenerates water, so that the negative electrode is under-charged due to the action of oxygen, and thus no hydrogen gas is generated. The oxygen of this positive electrode is absorbed by the lead of the negative electrode, and the process of synthesizing water is further developed, that is, the so-called cathode absorption.
(3) In order to allow the oxygen released from the positive electrode to flow to the negative electrode as quickly as possible, a new ultra-fine glass fiber separator different from the microporous rubber separator used in the ordinary lead-acid battery must be used. The porosity is increased from 50% to more than 90% of the rubber separator, so that oxygen is easily circulated to the negative electrode, and the synthetic water is regenerated. In addition, the ultra-fine fiberglass board has the function of adsorbing sulfuric acid electrolyte, so the valve-regulated sealed lead-acid battery adopts a lean liquid design, and even if the battery is dumped, there is no electrolyte overflow.
(4) The sealed valve is used to control the acid-filtering structure, so that the acid mist can not escape, and the purpose of safety and environmental protection is achieved.
In the above cathode absorption process, since the generated water can not overflow under the condition of sealing, the valve-regulated sealed lead-acid battery can be spared from the supplementary water maintenance, which is also the origin of the valve-regulated sealed lead-acid battery called the dimension-free battery.
Valve-regulated sealed lead-acid batteries are equipped with a filter acid pad to prevent acid mist from escaping. However, it is conditional that the sealed battery does not escape gas, that is, the battery should not escape during the storage period; no charge should escape when the charging voltage is below 2.35V/monomer (25°C); no gas escapes during the discharge period. . However, when the charging voltage exceeds 2.35 V/cell, it is possible to cause gas to escape. Because at this time, the battery body generates a large amount of gas in a short time and can not be absorbed by the negative electrode. When the pressure exceeds a certain value, it starts to be exhausted through the one-way exhaust valve, and the exhausted gas is filtered by the acid pad to filter out the acid mist. The battery is lost in gas, so the valve-regulated sealed lead-acid battery has a very strict charging voltage requirement and cannot cause overcharging.
2 negative plate sulfation
The main active material of the negative grid of the battery is sponge-like lead. When the charge of the valve-regulated sealed lead-acid battery is insufficient, the sponge lead on the negative grid of the battery will lose its activity and can no longer participate in the chemical reaction. One phenomenon is called sulfation of the active material. Sulfation reduces the active material of the battery, reduces the effective capacity of the battery, and also affects the gas absorption capacity of the battery. The battery will be ineffective for a long time.
To prevent the formation of sulphation, the battery must always be in a fully charged state.
3 positive plate corrosion
As the battery loses water, the specific gravity of the electrolyte increases, and the excessive acidity of the electrolyte exacerbates the corrosion of the positive electrode plate, so that the porosity of the positive electrode plate is increased, the electrolyte is relatively less, the active material of the electrode plate is reduced, and the battery capacity is lowered. To prevent corrosion of the plates, care must be taken to prevent battery water loss.
4 thermal runaway
Thermal runaway means that the battery has a cumulative enhancement of charging current and battery temperature during constant voltage charging, and gradually damages the battery. The root cause of thermal runaway is:
Ordinary rich liquid lead-acid batteries are filled with liquid between the positive and negative plates, and there is no gap. Therefore, the oxygen generated by the positive electrode cannot reach the negative electrode during the charging process, so that the negative electrode is not depolarized, and hydrogen gas is easily generated, and escapes with oxygen. battery.
Because heat cannot be dissipated by water loss, VRLAB batteries generate more heat during overcharging than rich liquid lead-acid batteries. It is more prone to thermal runaway.
Therefore, the float voltage should be reasonably selected. The float voltage is the charging voltage used by the battery for a long time, which is a factor that is critical to the battery life. In general, it is appropriate to set the float charge to 2.23V/cell (25°C). If you do not work according to this float range, but use 2.35V / monomer (25 ° C), then there will be thermal runaway after 4 months of continuous charging; or 2.30V / monomer (25 ° C), continuous charging 6~ If there is a thermal runaway in 8 months, if it is 2.28V/monomer (25°C), there will be a serious capacity drop for 12 to 18 months, which will lead to thermal runaway. The direct consequence of thermal runaway is that the battery casing is bulged, leaking, and the battery capacity is reduced, eventually failing.
V. Conclusion
Lead-acid batteries (especially maintenance-free) are becoming more and more important in all walks of life. I hope this article can provide reference for the majority of users, so that they can better use the battery, make it last longer, and create higher for the enterprise. Benefits.
Battery is an important part of UPS, EPS, DC screen and other systems. It is widely used in important fields such as industry, communication, railway (including subway), banking, securities, military, aviation, etc. Its advantages and disadvantages directly affect The reliability of power supply systems in various fields.
Second, the meaning and classification
Battery: A device that converts chemical energy and DC power into one another and can be recharged after being discharged by charging. It is called a battery. (Common batteries are lead acid, cadmium nickel, hydrogen nickel and lithium ion batteries. Below, we will focus on Lead-acid maintenance-free battery); the battery is the shortest device with the lowest MTBF in the whole UPS, EPS, DC screen and other systems. If the user can use and maintain it correctly, it can prolong its service life, otherwise its service life will be greatly shortened, so that it will be retired early, causing unnecessary losses to the users themselves.
The types of batteries can generally be divided into:
1. According to the purpose classification, it can be divided into: A> start-up (for various cars, tractors, diesel engines, starting and ignition, lighting; high-current discharge is required at start-up, low-temperature start is required, battery internal resistance is small); B> fixed acid-proof (for power plants, substations, communications, hospitals, etc. as protection, automatic control, accident lighting, communication and other backup power; dilute electrolyte, long life, floating charge); C> traction (for various Battery car, **** car, forklift, mining motor car, etc. As electric traction and lighting power supply; requires thick plate, large capacity, charge and discharge cycle with 3h~5h rate); D> other use ( Different sizes and capacities, various discharge rates)
2. According to the state of charge of the lead-acid battery, it is divided into: A> dry discharge state (the plate is in the discharge state, placed in the battery tank without electrolyte; the electrolyte should be poured into the initial use, and the initial time is long B> can be used after charging); B> dry state (the plate is in the dry state of the electrolyte-free battery tank, when used, the electrolyte can be used without initial charge); C> with liquid charging State (charged state charged battery); D> wet state (charge state, part of the electro-hydraulic suction in the plate and diaphragm, when used, the electro-hydraulic, do not need to charge. Storage time is not as dry-charged battery Long time); E> maintenance-free battery (charged state with liquid battery, no need to maintain water during the specified working life, self-discharge rate is very small); F> less maintenance battery (charged state with liquid battery, in the specified work Only a small amount of maintenance is required during the lifetime, and water is added for a long time)
3. According to the structure of the battery cover and the exhaust vent, it is divided into: A> open type (no permanent cover, the generated gas can escape freely, only the cover plate not fixed to the housing; to reduce acid mist. Obsolete) B>Exhaust type (battery case and cover are fixed together; the acid injection port of the cover is equipped with exhaust æ‹´) C> Acid-proof explosion-proof type (the battery cover is equipped with acid-proof fire retardant, allowing the battery row Gas, but the acid mist does not escape; when there is outside fire source, the battery does not burn inside, does not explode) D> Acid-proof dehydrogenation type (with catalytic enthalpy, the hydrogen and oxygen released from the battery can be re-formed into water, return to the battery At the same time, it has anti-acid and anti-riot function. E> Valve-controlled closed battery (battery sealed, no need to add water, equipped with safety valve, gas can be exhausted when the pressure inside the battery is too large, outside gas can not enter the inside of the battery; Maintenance battery)
Third, the use of lead-acid batteries
Lead-acid battery: The electrode is mainly made of lead, and the electrolyte is a kind of battery of sulfuric acid solution. Generally, it consists of a positive electrode plate, a negative electrode plate, a separator, a battery tank, an electrolyte, and a terminal. It was invented by the French scientist Plant in 1859 and has a history of 148 years. Calculation of the capacity of a lead-acid battery: Under the specified conditions, the amount of electricity that can be supplied by a fully charged battery is usually expressed in ampere-hours (Ah). Capacity = single positive plate number × single plate capacity
Some equipments such as UPS, EPS, DC screen, etc., generally consider lead-acid maintenance-free batteries, such as German Sunshine, German Pine, GNB, Guangdong Yuasa, Guangdong Zhicheng Champion, taking into account load conditions, usage environment, service life and cost. , Shenyang Panasonic, Shanghai Hercules, and other brands of quality maintenance-free batteries. Users should never use inferior batteries because they are cheap, because this will affect the reliability of the entire system and may cause even greater losses.
1. Lead-acid maintenance-free battery inspection before use
Lead-acid maintenance-free batteries have self-discharge (SELF-D1SCHARGE). If they are not used for a long time (usually placed for more than six months, self-discharge is 50%), energy will be lost, so regular charge and discharge are required. Maintenance personnel can judge the battery's open circuit voltage to judge whether the battery is good or bad. Take the 12V battery as an example. If the open circuit voltage is higher than 12.5V, it means that the battery has more than 80% energy storage and must be charged for more than 10 hours; if the open circuit voltage is Between 12V-12.5V, it should be recharged immediately, and must be charged for 13-24 hours or more; if the open circuit voltage is lower than 12V, it means that the battery storage energy is less than 20%, and it must be charged for more than 48 hours. After charging, the open circuit voltage should be around 13V. Therefore, it is recommended that the user not be placed for too long, and the qualified user recommends charging and discharging for 3 months to ensure that the battery capacity reaches the desired value. Before use, check the appearance to see if the wiring column is oxidized. If it is polished, it will affect the conductivity. Then look at the battery surface for cleanness. If there is dust, wipe it with a dry cloth.
2. Lead-acid maintenance-free battery inspection
Since the maintenance-free battery adopts the absorption electrolyte system, it will not generate any gas during normal use. However, if the user uses it improperly, the battery will be overcharged, and gas will be generated. At this time, the internal pressure of the battery will increase, and the battery will be increased. The upper pressure valve is opened, which will cause the battery to rise, deform, leak or even rupture. These phenomena can be judged from the appearance. If the above situation is found, the battery should be replaced immediately. If available, the battery online detection system can be installed to check the battery voltage, internal resistance, temperature and other changes.
3. Maintenance of lead-acid maintenance-free battery in use
Although the maintenance-free battery does not require manual maintenance work when it is used, it still has certain requirements when it is used. If it is used improperly, it will affect the service life of the battery.
Factors affecting battery life are as follows: installation, temperature, charge and discharge current, charging voltage, depth of discharge, and long-term charging.
1) Battery installation
The battery should be installed in a clean, cool, ventilated, dry place as far as possible, and protected from sunlight, heaters or other radiant heat sources. The battery should be placed upright and not tilted. The terminal connections between each battery should be firm. When connecting, different capacities, different performances, different old and new, batteries of different manufacturers should not be used together. When the battery is connected, an insulating tool should be used to prevent accidental short circuit of the positive and negative electrodes and burn the battery. When the battery is connected to the charger or load, the circuit switch must be in the off position. The positive pole of the battery should be connected to the positive pole of the charger or load. The negative pole of the battery should be connected to the negative pole of the charger or load. The nuts, bolts, washers and connecting wires for coupling should be loose and moderate, and the screws should be loose and too tight.
2) Ambient temperature
The ambient temperature has a great influence on the battery. If the ambient temperature is too high, the battery will overcharge and generate gas. If the ambient temperature is too low, the battery will be undercharged, which will cause the battery to last. Therefore, the ambient temperature is generally required to be around 25 °C.
3) Charging
Charging is divided into initial charging, normal charging, and balanced charging.
At the initial charge, the first charge of the new battery is called initial charge, and the purpose is to reduce the active material of the plate which is oxidized during the assembly process, increase the active material content, and improve the discharge performance of the battery.
Normal charging, charging a battery that has been discharged is called normal charging.
Floating charging, the battery pack and the power supply are connected in parallel to the load. When the AC power is normal, the rectifier rectifies the alternating current into direct current, and then charges the battery while re-converting the direct current to alternating current to supply power to the load. When the AC power supply is interrupted, the DC power of the battery is immediately converted into AC power by the inverter to supply power to the load to ensure the continuity of the power supply. This type of battery charging is called floating charging.
Balanced charging, in the process of using the battery, there will often be imbalances in specific gravity, capacity, voltage, etc. The output voltage of the battery pack is too low and the output power is too small. To this end, the battery pack is overcharged so that each of the battery cells in the battery pack is fully charged. This charging process is called equalization charging.
Regardless of the charging method used, care should be taken to control the charging voltage and current in accordance with the manufacturer's product description to prevent over-voltage and over-current charging from degrading battery performance and shortening or damaging the life.
In the power system, the battery is always on-line, so that the battery is basically in a long-term floating state. The selection of the float voltage plays a vital role in the long-term reliable operation of the battery. As seen earlier, The high float voltage will cause the battery to lose water slowly and cause thermal runaway to make the battery fail. The low float voltage will cause the battery to be fully charged for a long time, causing the battery to sulphate and cause the battery to fail. The correct float voltage should be selected at 2.23V/cell. It should be adjusted accordingly with the battery operating temperature. Due to the different battery manufacturers, this parameter will have some differences, and should be selected according to the parameters provided by the manufacturer.
In a battery pack, the batteries are always charged in series. Due to the individual differences in the batteries, the terminal voltage of each battery will not be strictly consistent. To ensure the long-term safe operation of each battery in the battery pack, each battery pack must be guaranteed. The floating voltage of the battery is in the correct range. Balanced charging is a commonly used method to ensure sufficient battery power in the battery pack through proper overcharging. This method should limit the use of the battery pack because it should be overcharged. Instead of equalizing the charging, a single battery should be used. If the battery pack must be balanced, the equalized charging voltage must be strictly controlled. The voltage of the balanced charging should be selected in strict accordance with the regulations of the battery manufacturer.
4) Discharge
The discharge current should not be too large, and it is necessary to avoid short-circuit discharge. Generally, according to C10-C20 ampere-hour discharge, specifically, such as 50AH battery, discharge with C10 (5 ampere current), up to 10 hours, can achieve the purpose of fully activating the battery, and at the same time can test the battery Whether the capacity is sufficient (some battery manufacturers require C20 to discharge, and the corresponding discharge time is doubled).
When discharging, the battery terminal voltage should not be lower than the termination voltage, in case the battery is over-discharged, resulting in a decrease in battery performance and a shortened life. After discharge, it should be charged in time. The battery is not allowed to stand for a long time in the discharged state.
5) Depth of discharge
The depth of discharge has a great influence on the service life of the battery. The deeper the discharge depth of the battery, the less the cycle is used, so when it is used.
Deep discharge should be avoided.
6) Regular maintenance
After using the battery for a certain period of time, it should be checked regularly, such as observing whether its appearance is abnormal, measuring whether the voltage of each battery is average, etc. If the battery is not charged for a long time, the battery will always be in a state of charge, which will make the battery's activity worse, so even if it is not In the event of a power outage, the UPS also needs to perform periodic discharge tests to keep the battery active. The discharge test can usually be carried out once every three to six months if the conditions permit. The practice is that the UPS is loaded - ** is more than 50%, then the mains is disconnected, so that the UPS is in the battery discharge state, and the discharge duration depends on the battery capacity. Generally, it takes several minutes to several tens of minutes. After the discharge, the mains supply is restored and the battery is continuously charged.
Fourth, the failure mechanism of lead-acid batteries (ie common faults)
1 Battery water loss: The loss of water in the lead-acid battery will lead to an increase in the specific gravity of the electrolyte, causing corrosion of the positive grid of the battery, reducing the active material of the battery, thereby reducing the capacity of the battery and failing.
The difficulty in sealing lead-acid batteries is the electrolysis of water during charging. When the charge reaches a certain voltage (generally 2.30V / monomer or more), oxygen is released on the positive electrode of the battery, and hydrogen gas is released from the negative electrode. On the one hand, the release of gas brings out the acid mist to pollute the environment, on the other hand, the water in the electrolyte is reduced, and it is necessary to perform additional water maintenance at intervals. The valve-regulated lead-acid battery is a product developed to overcome these shortcomings. Its product features are:
(1) Using a multi-quality high-quality grid alloy to increase the overpotential of gas release. That is, the ordinary battery grid alloy releases gas when it is above 2.30 V/cell (25 ° C). After using a high-quality multi-component alloy, the gas is released at 2.35 V/monomer (25 ° C) or more, thereby relatively reducing the amount of gas released.
(2) Let the negative electrode have excess capacity, that is, 10% more capacity than the positive electrode. At the later stage of charging, the oxygen released from the positive electrode comes into contact with the negative electrode, reacts, and regenerates water, so that the negative electrode is under-charged due to the action of oxygen, and thus no hydrogen gas is generated. The oxygen of this positive electrode is absorbed by the lead of the negative electrode, and the process of synthesizing water is further developed, that is, the so-called cathode absorption.
(3) In order to allow the oxygen released from the positive electrode to flow to the negative electrode as quickly as possible, a new ultra-fine glass fiber separator different from the microporous rubber separator used in the ordinary lead-acid battery must be used. The porosity is increased from 50% to more than 90% of the rubber separator, so that oxygen is easily circulated to the negative electrode, and the synthetic water is regenerated. In addition, the ultra-fine fiberglass board has the function of adsorbing sulfuric acid electrolyte, so the valve-regulated sealed lead-acid battery adopts a lean liquid design, and even if the battery is dumped, there is no electrolyte overflow.
(4) The sealed valve is used to control the acid-filtering structure, so that the acid mist can not escape, and the purpose of safety and environmental protection is achieved.
In the above cathode absorption process, since the generated water can not overflow under the condition of sealing, the valve-regulated sealed lead-acid battery can be spared from the supplementary water maintenance, which is also the origin of the valve-regulated sealed lead-acid battery called the dimension-free battery.
Valve-regulated sealed lead-acid batteries are equipped with a filter acid pad to prevent acid mist from escaping. However, it is conditional that the sealed battery does not escape gas, that is, the battery should not escape during the storage period; no charge should escape when the charging voltage is below 2.35V/monomer (25°C); no gas escapes during the discharge period. . However, when the charging voltage exceeds 2.35 V/cell, it is possible to cause gas to escape. Because at this time, the battery body generates a large amount of gas in a short time and can not be absorbed by the negative electrode. When the pressure exceeds a certain value, it starts to be exhausted through the one-way exhaust valve, and the exhausted gas is filtered by the acid pad to filter out the acid mist. The battery is lost in gas, so the valve-regulated sealed lead-acid battery has a very strict charging voltage requirement and cannot cause overcharging.
2 negative plate sulfation
The main active material of the negative grid of the battery is sponge-like lead. When the charge of the valve-regulated sealed lead-acid battery is insufficient, the sponge lead on the negative grid of the battery will lose its activity and can no longer participate in the chemical reaction. One phenomenon is called sulfation of the active material. Sulfation reduces the active material of the battery, reduces the effective capacity of the battery, and also affects the gas absorption capacity of the battery. The battery will be ineffective for a long time.
To prevent the formation of sulphation, the battery must always be in a fully charged state.
3 positive plate corrosion
As the battery loses water, the specific gravity of the electrolyte increases, and the excessive acidity of the electrolyte exacerbates the corrosion of the positive electrode plate, so that the porosity of the positive electrode plate is increased, the electrolyte is relatively less, the active material of the electrode plate is reduced, and the battery capacity is lowered. To prevent corrosion of the plates, care must be taken to prevent battery water loss.
4 thermal runaway
Thermal runaway means that the battery has a cumulative enhancement of charging current and battery temperature during constant voltage charging, and gradually damages the battery. The root cause of thermal runaway is:
Ordinary rich liquid lead-acid batteries are filled with liquid between the positive and negative plates, and there is no gap. Therefore, the oxygen generated by the positive electrode cannot reach the negative electrode during the charging process, so that the negative electrode is not depolarized, and hydrogen gas is easily generated, and escapes with oxygen. battery.
Because heat cannot be dissipated by water loss, VRLAB batteries generate more heat during overcharging than rich liquid lead-acid batteries. It is more prone to thermal runaway.
Therefore, the float voltage should be reasonably selected. The float voltage is the charging voltage used by the battery for a long time, which is a factor that is critical to the battery life. In general, it is appropriate to set the float charge to 2.23V/cell (25°C). If you do not work according to this float range, but use 2.35V / monomer (25 ° C), then there will be thermal runaway after 4 months of continuous charging; or 2.30V / monomer (25 ° C), continuous charging 6~ If there is a thermal runaway in 8 months, if it is 2.28V/monomer (25°C), there will be a serious capacity drop for 12 to 18 months, which will lead to thermal runaway. The direct consequence of thermal runaway is that the battery casing is bulged, leaking, and the battery capacity is reduced, eventually failing.
V. Conclusion
Lead-acid batteries (especially maintenance-free) are becoming more and more important in all walks of life. I hope this article can provide reference for the majority of users, so that they can better use the battery, make it last longer, and create higher for the enterprise. Benefits.
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