March 2016
As is known, the operation of a lead-acid battery is based on the occurrence of a potential difference between two electrodes immersed in the electrolyte. The active substance of the negative cathode is pure lead, and the active substance of the positive anode is lead dioxide. In backup and autonomous power supply systems, batteries manufactured according to different technologies: serviced bulk, sealed gel or AGM. Regardless of the technology, the chemical processes occurring in lead-acid batteries are similar:
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During operation, the so-called aging of the battery inevitably occurs, that is, a gradual loss of capacity - up to the permissible operating limit, usually taken to reduce the capacity to 60% of the original. Under ideal conditions, the actual battery life in buffer mode can be close to the nominal life. |
The aging process of a battery can be significantly accelerated due to the following destructive processes:
- Sulfation of plates;
- Corrosion of plates and shedding of active mass;
- Evaporation of the electrolyte or the so-called “drying out” of the battery;
- Electrolyte stratification (typical only for liquid batteries).
Sulfation of plates
 | When the battery is discharged, the loose active mass turns into solid microcrystals of lead sulfate. If the battery is not charged for a long time, the microcrystals become larger, the deposit thickens and blocks the access of the electrolyte to the plates, which makes charging the battery impossible. Factors that increase the risk of sulfation:
Sulfation of the plates can be partially eliminated by special battery charging modes. |
Corrosion and shedding of the active substance
 | During corrosion, pure lead of the plate grid, interacting with water, is oxidized into lead oxide. Lead oxide conducts electric current worse to the active substance of the plate lubricant, increases internal resistance and reduces the battery's resistance to high discharge currents. On the positive plates, corrosion weakens the adhesion of the grid to the active substance. In addition, the active substance of the positive plate itself gradually loses strength. With each cycle of spreading, the layer of the plate changes state from a bulk mass of microcrystals of lead oxide to a hard crystalline structure of lead sulfate. Alternating compression and expansion reduces the physical strength of the spread layer, which, combined with a weakening of adhesion, leads to sliding and shedding of the active substance to the bottom of the battery. Corrosion and accumulation of detached active substance can lead to deformation of the battery plates and, in the worst case scenario, to short circuit. |
Factors that increase the risk of corrosion and shedding of the active mass:
- charge too high voltage;
- charging with insufficient current - that is, staying under high voltage for a long time during the filling phase;
- staying in the absorption phase for too long (“overcharge”);
- charging the battery with too much current;
- accelerated battery discharge with too much current.
Shedding (sliding) of the active mass of the electrolyte is an irreversible phenomenon. The most dangerous consequence of sliding of the active mass is the shorting of the plates.
Electrolyte evaporation
 | When the positive plate of the battery is discharged, oxygen is formed from the water. Under normal float charge conditions, oxygen recombines with hydrogen on the negative plate of the battery, restoring the original amount of water in the electrolyte. But oxygen diffusion in the separator is difficult, so the recombination process cannot be 100% effective. Reducing the proportion of water changes the charging characteristics of the battery and, at a certain threshold, makes charging completely impossible. Factors that increase the risk of “battery drying out”:
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Electrolyte evaporation is an irreversible phenomenon for gel andAGM batteries. The main reason for drying out, especially forAGM – “overcharging” of batteries.
Thermal runaway and thermal breakdown of batteries
Battery aging, due to the processes listed above, occurs at an accelerated pace, but still quite slowly and often unnoticeably.
The recombination of gases in a sealed battery is a chemical process that produces heat. When recombination occurs at the correct voltage and charge current values, heating does not create problems. However, when the battery is overcharged, the internal temperature rises faster than the battery can be cooled externally. An increase in temperature reduces the charging voltage, which in the absorption stage leads to a simultaneous increase in current. This in turn increases the temperature again.
A self-sustaining cycle of increasing current and heat generation starts, leading, in the worst case scenario, to deformation of the grids and an internal short circuit with irreversible destruction of the battery.
Factors that increase the risk of thermal runaway:
- intermittent or “pulsating” charge due to an unstable external power source or a poor-quality charger;
- staying in the absorption phase for too long – “overcharge”;
- poor heat dissipation or elevated ambient temperature.
Specifics of destructive processes in the battery chain
 | It is easy to see that when charging a separate battery, all risk factors can be eliminated by ensuring the correct operating conditions and charging algorithm. However, power backup systems rarely use less than two batteries. With a parallel-serial connection, the charger “sees” the values of charging current and voltage only at the terminal terminals, so the voltages on individual batteries may differ significantly from the recommended values. A battery that has a higher level of self-discharge (higher leakage current) can cause overcharging of cells connected to it in series and incomplete charging of cells connected to it in parallel. Overcharging and undercharging increase the risk of almost all destructive processes. Therefore, to reduce the danger, all batteries in the chain must have the same state of charge and capacitance values as close as possible. For new installations, it is recommended to use batteries not only of the same brand, but also of the same factory batch. However, practice shows that even in one batch There are not even two batteries with exactly the same characteristics capacity, state of charge and internal leakage currents. Moreover, the requirement of identical characteristics is unattainable when it is necessary to replace a damaged battery in an already used battery. |
A slight variation in the degree of charge of new batteries is most often smoothed out during the running-in process over several discharge and charge cycles. But if there is a significant scatter or difference in capacity characteristics imbalancebetween individual batteries of the array only increases over time.
Systematic recharging of batteries with a lower capacity and possible reversal of the polarity of undercharged batteries during deep discharges lead to the accumulation of damage and failure of individual batteries. Due to the thermal runaway effect, even one failed battery can destroy the entire battery array.
Active battery equalization
You can smooth out differences in battery parameters using a special device called a battery charge balancer or imbalance leveler.
IMPORTANT! The use of charge balancers reduces the risk of destructive processes, but cannot fix an already seriously damaged battery.
Physically, the battery charge equalization device is a compact electronic module connected to each pair of series-connected elements:
- for 24V battery required one charge balancer to the chain (scheme 1).
- for a 48V battery required three charge balancers to the chain (Scheme 2).
The SBB is powered from the battery itself or from a charge source. SBB's own power consumption is low and comparable to self-discharge losses.
Level efficiency SBB2-12-A fundamentally higher than that of other charge balancers, the operation of which is based either on shunting excess charging power (so-called passive balancers, creating direct energy losses), or on selective recharging of elements (equalization occurs only during charging). Maximum equalization current SBB2-12-A– 5A, which exceeds the capabilities of all alternative devices on the market.
The effect of using a charge balancer:
1) Improved overall reliability and increasing battery life.
2) Increased energy output battery, because When batteries are deeply discharged, the capacity of all batteries in a series circuit is more fully used.
SBB balancers work continuously, keeping the batteries in a balanced state even when the charger is turned off.
Connection diagram
Connection diagram for a level (balancer) to a 24V and 48V battery.
Below are the charge level connection diagrams SBB2-12-A to 12V lead-acid batteries in 24V and 48V batteries.
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Scheme 1. 24V battery from two 12V batteries | Scheme2. 48V battery from four 12V batteries |
Connecting a level (balancer) to a battery of several parallel circuits.
It is allowed to operate one charge equalization balancer SBB on 2-3 parallel chains of batteries - if the imbalance is small and the maximum equalization current is not exceeded. Separate balancing of each chain gives better results due to the selectivity of the corrective action.
When using one level for several chains, it is necessary to use a diagram for connecting batteries with DC buses and connecting midpoints (Scheme 3).
When using a separate level in each chain, you can use the usual battery connection diagram (Scheme 4).
When battery stacks operate in buffer or cyclic mode, as well as when such systems are expanded, an uneven distribution of electrical energy output is possible, which leads to faster battery aging. Read this article on how to properly level the battery charge.
Periodic leveling electric charge batteries in the system is a necessary process to ensure proper operation of the equipment. If several batteries are connected in a circuit, imbalance may occur over time - a noticeable change in the voltage of individual batteries. To avoid this, it is recommended to rebalance once every six months. It is usually carried out using increased voltage for twenty-four hours. You can find out the specific voltage from the battery specification on our website, look at the data on the manufacturer’s website, or check with the seller.
Multi-level systems - brief description and purpose
Systems using multiple batteries, are widely used in everyday life and in production. About battery connection diagrams multi-level systems. Here it must be said that they are very useful for long-term provision uninterruptible power supply heating boilers, as well as for creating “green” energy systems powered by solar panels and wind generators. After all, in addition to generating electricity, it must also be accumulated and stored somewhere. It is for these purposes that systems of several rechargeable batteries are needed, with the help of which a system of any capacity and voltage can be assembled from 12-volt batteries.
As mentioned above, during long-term operation problems arise related to battery imbalance; later we will talk about this in more detail.
In order to avoid charge imbalance in new batteries, it is recommended to buy all batteries from the same manufacturer, the same series, type and capacity with the same release date. If these rules are violated or the system is expanded, the battery charge must be equalized!
If during system service uninterruptible power supply If there is a need to expand the capacity, then the most ideal option would be to select an additional battery based on the above requirements, no more than a year apart in the date of release.
The fact is that a year after the operation of such a system, irreversible processes may occur in deep-discharge lead-acid batteries and their normal joint operation is not guaranteed. Those. A new battery can be damaged by older ones. If there is a significant difference in the production date of a year or more, the manufacturer's after-sales warranty for the new battery may be lost!
Imbalance - what is it and how to deal with it
From time to time, in all systems using batteries with serial, parallel or mixed connection types, charge imbalance occurs. Because of this, battery performance deteriorates, capacity decreases, and individual batteries fail before their design date.
The problem is that all batteries are slightly different from each other, even if they are the same brand. When creating a battery pack, these differences may increase. Suppose there is a battery in the system with a resistance slightly higher than its neighbors. Naturally, when charging, the voltage on it will be slightly higher, and the overvoltage protection may even work. When discharging electricity, the voltage of this battery will be the lowest, as will its capacity. All this leads to the fact that the resource of the entire system will not be fully used. The result is degradation and strengthening of the defect over time. A weak link will degrade the performance of the entire battery pack. You can, of course, buy another battery, but this is not a panacea. What to do if the batteries are relatively new? And the cost is not cheap.
There are two ways to equalize battery charge:
- Passive;
- Active.
The first method uses bypass circuits that disperse energy. These devices can be built into the UPS system, or located in a separate chip. Most often, this method is used in budget equipment. Almost all excess electrical energy from a battery with a superior charge is converted and dissipated - this is the main limitation of the passive method. It reduces the life of the system without charging.
With the active balancing method, inductance is used to transfer electricity from batteries with a higher charge to weak batteries, therefore, losses are not high. Thanks to this, the active method is much more effective than the passive one. But you still have to pay extra for quality; active equipment is more expensive.
Battery charge equalization - practice
A system that equalizes the battery charge is necessary for the maintenance of batteries with a serial connection type, when charging them from a single source. Batteries connected in series form a single circuit or line. There may be several of them, depending on the nature of the system. The equipment is capable of regulating currents on individual batteries in several circuits simultaneously.
The system consists of a controller, which is responsible for regulating the charge. It connects to the general power source of the circuit. There are also separate sensors installed on the battery. This equipment is switched using a special loop.
Batteries in one circuit must be of equal capacity, otherwise the equipment will not cope with the task of balancing the charge on the batteries. The greater the difference in capacitance characteristics, the more charge and discharge cycles will be required to equalize the battery charge.
How the charge balancer works
The controller analyzes the voltage and starts if it increases. The system calculates the average and, using special loops, takes information from each individual battery. If the battery voltage exceeds the average, the controller issues a command for load compensation. If it is lower, the load is removed. These actions are tied to charge-discharge cycles, and, with each new cycle, the voltage is brought to the average.
If the total electrical voltage does not increase within three working hours, the controller signals that the work is completed and sends a command to turn off the sensors on the battery. But, the analysis of electrical voltage does not stop.
All batteries are equipped with a voltage sensor-controller. It is best to do this next to the contacts, then connect the plus to the plus, the minus to the minus. When installed correctly, the sensor flashes. If there is no signal, either it was connected incorrectly, or the battery is faulty. Via the COM port, the controller can output information on each battery to a personal computer.
In addition, the controller signals when the battery voltage drops or rises below 10.5 Volts and above 15 Volts.
conclusions
Equalizing battery charges is a necessary technical measure. It increases the safety of using batteries and increases their service life. Modern battery balancing controllers test the technical condition of each battery and make it possible to use the system while minimizing losses. In general, this is useful for safety reasons and ensures reliable and trouble-free operation of the equipment.
Wonderful chargers, desulfators, equalizers, and do you know that what many attribute to them out of ignorance are called in a simple word,charging algorithm. I’ve been talking about this for a long time, and yet I hear more and more wonderful devices and wonderful stories about such devices. It’s strange why, after just a month of observation, I, an ordinary engineer, express and talk about these algorithms, and it turns out they can coincide with other types of devices. That is, the algorithm of the equalizer and, for example, the charging algorithm, or the charging algorithm of an inverter with a charge equalization effect, can coincide with each other.
Attention: here I do not mean and do not say that they are identical, since in most cases it can be completed or written on the body of the MP microprogram by everyone independently from scratch. The shapes of the pulses and the timing of the pulses, and the pulse of voltage and current changes may differ and have a different time range. But often, in 50% of cases they can be similar. If not by time, then by signal shapes, if not by signal shape, but close to it.
So that each manufacturer relies on its own observations and data.
So this method itself works for the memory, the equalizer, and the inverter memory. A very useful microprogram that allows the battery to last at least 50% longer, but there is a 10% chance to increase their life.
In general, if the battery fails, many people still tell and believe in fairy tales. They buy devices like the ones described above and wait for a miracle. But, unfortunately, this device does not resurrect anything and does not restore anything. Its task is to carry out battery prevention in real time. It is precisely because of this prevention that the batteries begin to behave more stable, they do not go away, for example, when connected in series, one is overcharged and the other is not fully charged.
As they say, it is better to do prevention in time than to try to eliminate the consequences later.
Yes, I heard enough fairy tales about these miracle devices, I collected my statistics for 4 years, and finally everything came together. Of course, disassembling the device will definitely dot the I’s and the presence of a choke or watt resistances will indicate that there is buildup. But this does not mean that one battery should be discharged while charging the other, this guys is complete nonsense :)
Because the task of these devices is to equalize the voltage of the battery banks, of which there are 6 for a 12-volt battery, 10 for an alkaline battery, and accordingly twice as much for a 24-volt battery, and so on.
Honestly, at first I thought that this device was discharging a charged battery, but after looking at the results in the second year, I gave up on it. The principle is similar to a desulfator, but the algorithms are different. In general, in the future I’ll dig it up and do a full test. Nobody gave me the device and it was purchased with personal funds and this is my opinion. More information, more and more accurate data. But the fact is that they no longer coincide with the opinion of the majority - that’s for sure.
As an example, we consider the classic battery of the German concern Hawker Gmbh - Perfect Plus. There is nothing difficult about caring for the battery. You only need to strictly follow the instructions and within a certain time frame to carry out a number of operations that will allow the battery you purchased to operate for as long as possible, which means it will save you money.
Special properties of lead batteries:
The capacity is 5 hours, i.e. rated capacity can be obtained by discharging DC for 5 hours until the final discharge voltage is set at 1.7 V/cell at the initial temperature of 30 °C.
Voltage The rated voltage of one battery is 2 V. The rated voltage standards for traction batteries are: 24 V, 48 V, 72 V, 80 V.
The operating voltage of one traction battery depends on the magnitude of the discharge current, the degree of discharge and temperature. The specified final discharge voltage for a 5-hour discharge is 1.7 V/cell.
The density of the electrolyte in a fully charged state, at a temperature of 30°C, is 1.29 kg/l.
Battery durability and service life. Durability refers to the result of a long-term test in laboratory conditions, in which the battery is subjected to charge-discharge cycles in a precise manner. specific program. A minimum number of cycles should be obtained that will not reduce the capacity below 80% of its rated value. The corresponding procedure is described in DIN 43539, part 3.
The actual service life may be greater or less than the durability, as numerous operating factors lead to loads different from those under laboratory conditions.
Impact factors leading to increased battery life:
impeccable care and service
normal operating temperatures (from 20 C to 40 C)
flawless charging device
avoid deep discharges
timely troubleshooting
Impacts leading to a reduction in service life:
frequent deep discharges, i.e. removal of more than 80% of the nominal capacity
elevated operating temperatures (> 40 C) for a long time
charge with an unacceptably high current after reaching the gassing voltage (2.4 V/cell)
the battery is in a discharged state
the presence of an impurity that has entered the electrolyte (for example, water for topping up that does not meet the requirements)
overload or short circuit
Maintenance and care of traction batteries General rules operation:
Never leave the battery in a discharged state, but immediately recharge it.
To achieve optimal service life, avoid discharging more than 80% of the rated capacity; in this case, the density of the electrolyte should not be lower than 1.13 kg/l (300C).
To avoid deep discharges, it is necessary to monitor the discharge of vehicle batteries.
The operating temperature should be 20 C – 40 C.
To avoid damage to the battery, the maximum permissible electrolyte temperature of 55 C must not be exceeded.
Before charging and during intermediate charges, it is necessary to remove or open the container lid or battery closing device. Close no earlier than 1/2 hour after the end of charging.
Chargers must match the battery capacity and required charging time.
For topping up, use only distilled water in accordance with DIN 43530 part 4; no acid or additives should be used.
Battery charge (daily operation):
You must disconnect the battery by disconnecting the plug from the outlet. remove the battery cover. At the same time, the plugs remain closed.
Check the electrolyte level at the “min” mark.
After this, it is necessary to measure the temperature of the electrolyte. If the temperature exceeds 45 C, cool.
Connect the plug. If necessary, connect the electrolyte mixing system (for plugs without an integrated air outlet system).
Turn on the charger or check if the device is turned on.
Start the battery charging process.
After charging, disconnect the charger or check if the device is turned off, then disconnect the battery from the charger. If necessary, check the final results.
If the charge is insufficient or after a deep charge, carry out an equalizing charge.
Cleaning (daily work):
Dirt and dust that accumulate on the surface of the elements during operation must be removed depending on the needs and operation of the battery (rags, damp steam from 100 C to 150 C, using a hose with a nozzle).
Topping up water (weekly work):
It is also necessary to monitor the electrolyte level. At least once a week. If there is no automatic topping up, top up with purified water according to DIN 43530 part 4 at the end of the charge.
After charging, it is necessary to check the electrolyte level in all cells and top it up with distilled water.
It is also necessary to carry out an equalizing charge once a week.
Voltage, density and temperature (monthly work):
Once a month it is necessary to carry out work to check all elements for uniform gas emission.
After charging is complete or equalizing charge Acid density and temperature should be measured and deviations from standard values should be selectively entered into the battery flow sheet.
If significant differences between elements have been identified, then such elements should be examined separately.
It is also necessary to measure the voltage, density and temperature of the elements.
Work performed every six months and every year: .
check the correct functioning of the charger, first of all, the charge current at the beginning of gas evolution (2.4 V/cell) and at the end of the charge.
Check the plug and plug device.
repair minor damage to the container insulation (applied layer) immediately after removing or neutralizing traces of acid (follow the manufacturer's recommendations).
The insulation resistance of the batteries in relation to ground should be measured in accordance with DIN 43539 part 1 with the external electrical circuit open.
measure insulation resistance: 50 ohms per volt of rated voltage.
Clean the battery if the insulation resistance is poor.
Storage
If the batteries are not planned to be used for a long period, they should be stored in a fully charged state in a dry room at a temperature above 0 C.
To maintain the battery's operational readiness, the following charging modes should be used:
Monthly equalization charge
Maintenance charge at charging voltage 2.23 V x number of cells (30 C)
How to avoid damage and accidents?
To avoid damage, short circuits, sparks, do not place metal objects or tools on batteries.
Transport batteries only using suitable lifting devices (according to VDE 3616).
When working with batteries, the relevant safety regulations as well as DIN VDE 0510 and VDE 0105 part 1 must be observed.
Shelf life
The effect of storage time on battery life should be considered. It should be remembered that properly selected lifting devices prevent deformation of the battery case and thus protect the container coating. Lifting devices must match the geometry of the battery.
We are talking about batteries that are used in areas of increased explosion hazard. The battery case covers must be open during charging and subsequent removal of gases so that the resulting explosive gas mixture, with sufficient ventilation, loses its ability to ignite.
Category: Charger support Published 05/04/2016 12:06Most stationary batteries use a lead-acid electrochemical system, which requires some maintenance, including an equalizing charge. Periodic application of an equalizing charge allows the characteristics of all cells to be equalized to the same level by applying a charging voltage of 2.50 V per cell, which is about 10 percent higher than the normal value.
An equalization charge is nothing more than a deliberate overcharge to remove lead sulfate crystals from the plates that have accumulated over time. If you do not control the battery condition, the processes sulfation may reduce the overall capacity or even damage the battery. The equalizing charge also combats acid stratification- a condition in which the acid concentration at the bottom of the battery becomes higher than at the top.
Experts recommend performing a maintenance equalization charge once or twice a year. The best method to find out about its necessity is to use full charging in saturation mode, with further comparison specific gravity each cell of a flooded lead-acid battery using a hydrometer. If the difference between the specific densities of different elements is more than 0.030, then this indicates the need to use an equalizing charge.
During the equalization charge, check the specific gravity of the cells every hour and do not stop charging until the density stops increasing. Stopping the increase in density will indicate that no further improvements in the battery are possible, and further charging can only do harm.
The battery being charged must be kept in a cool place and under constant attention - excessive heat and gas formation is possible. Moderate gas formation is normal, but in any case the battery must be charged in a ventilated area, since only a 4 percent concentration of hydrogen in the air is already explosive.
I do not find the feasibility of using an equalizing charge for VRLA and other sealed batteries general opinion. Some manufacturers recommend equalizing the charge of such batteries monthly for 2-16 hours. But it should be remembered that overcharging sealed batteries leads to excessive gas formation and activation of the 34 kPa valve, which can result in electrolyte depletion.
Not all chargers have an equalizing charge function. Such a charge should not be carried out with a device not intended for this purpose.
