Equalizing battery charge. Fabulous battery voltage equalization or charging algorithm and miracle equalizer for batteries. Additional algorithms for charging batteries
- Carry out an external inspection of the battery. The top surface of the battery and terminal connections must be clean and dry, free from dirt and corrosion.
- If there is liquid on the top surface/of the flooded batteries, this may indicate that there is too much liquid in the battery. If there is liquid on the surface of a GEL or AGM battery, the battery is overcharged and its performance and life will be reduced.
- Check battery cables and connections. Replace damaged cables. Tighten loose connections.
Cleaning
- Make sure all protective caps are securely attached to the battery.
- Clean the top surface of the battery, terminals and connections using a rag or brush and a solution of baking soda and water. Do not allow cleaning solution to get inside the battery.
- Rinse with water and dry with a clean cloth.
- Apply a thin layer of petroleum jelly or terminal protectant, available from your local battery supplier.
- Keep the area around batteries clean and dry.
Adding water (ONLY batteries with liquid electrolyte)
It is forbidden to add water to gel or AGM batteries, since they do not lose it during operation. Water needs to be added periodically to flooded batteries. The frequency of topping up depends on the nature of battery use and operating temperature. New batteries should be checked every few weeks to determine the frequency of topping up water for a specific application. Batteries typically require more frequent toppings as they age.
- Fully charge the battery before adding water. Add water to discharged or partially charged batteries only if the plates are visible. In this case, add just enough water to cover the plates, then charge the battery and continue the water refill process described below.
- Remove the protective caps and turn them over to prevent dirt from getting on the inside surface. Check the electrolyte level.
- If the electrolyte level is significantly higher than the plates, then it is not necessary to add water.
- If the electrolyte level barely covers the plates, add distilled or deionized water to a level 3 mm below the ventilation well.
- After adding water, install the protective caps back on the battery.
- Tap water can be used if the level of contamination is within acceptable limits.
Charge and equalization charge
Charge
Proper charging is extremely important to get the most out of your battery. Both undercharging and overcharging a battery can significantly shorten its service life. For proper charging, see the instructions included with the equipment. Majority chargers-automatic and pre-programmed. Some chargers allow the user to set the voltage and current values. See charging recommendations in the Table.
- Make sure the charger is set to the correct program for wet, gel or AGM batteries, depending on the type of battery you are using.
- The battery must be fully charged after each use.
- Lead-acid batteries (wet, gel and AGM) do not have a memory effect and therefore do not require a complete discharge before recharging.
- Charging should only be carried out in well-ventilated areas.
- Before charging, check the electrolyte level to ensure that the plates are covered with water (wet batteries only).
- Before charging, make sure that all protective caps are securely attached to the battery.
- Batteries with liquid electrolyte will release gas (bubbles) before completing the charging process to ensure the electrolyte is properly mixed.
- Do not charge a frozen battery.
- Charging should be avoided at temperatures above 49°C.
Scheme 4
Scheme 4 and 5
Equalizing charge (ONLY for wet batteries)
An equalization charge is a battery overcharge performed on wet batteries after they have been fully charged. Trojan recommends performing an equalization charge only when batteries have a low specific gravity, less than 1.250, or a specific gravity that fluctuates within a wide range, 0.030, after the battery is fully charged. Do not equalize charge GEL or AGM batteries.
- You must make sure that the battery is a wet battery.
- Before starting charging, check the electrolyte level and make sure that the plates are covered with water.
- Make sure that all protective caps are firmly attached to the battery.
- Set the charger to equalizing charge mode.
- During the equalizing charge process, gas will be released in the batteries (bubbles will float to the surface).
- Measure the specific gravity every hour. The equalizing charge should be stopped when the specific gravity stops increasing.
ATTENTION! It is prohibited to perform an equalization charge on gel or AGM batteries.
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.
8.1. Constant charging mode.
All AB in electrical networks and substations must be operated in constant recharging mode.
A fully charged battery must be connected to the buses in parallel with a constantly running charging unit. The charging unit supplies the load direct current and at the same time recharges the battery, compensating for its self-discharge. End AEs must also operate in constant recharge mode.
When a powerful jolt load is turned on, as well as when the charging unit loses power from the alternating current side, the battery takes over the entire load of the DC network.
In emergency modes, the battery must also ensure operation necessary equipment ES or PS for at least 1 hour with the required voltage level of the design mode.
For an SK type battery, the charging voltage should be 2.20 ± 0.05 V per AE.
For SN type batteries, the recharge voltage should be 2.18 ± 0.04 V per AE at an ambient temperature not exceeding 35 °C. If the temperature is higher, the voltage should be 2.14 ± 0.04 V.
For batteries from different companies that use the main types of batteries (Vb VARTA, OPzS, GroE, etc.), the charging voltage should be 2.23 ± 0.005 V per AE at an ambient temperature of 20 ° C. For other types of branded AEs (FIAMM, OGi, etc.), the charging voltage must meet the requirements technical documentation to a specific type of AE of the manufacturer, supplier ((2.27 ± 0.03) V; 2.27 V ± 1%; 2.23 V ± 1%, etc.).
The voltage spread across individual AEs within the battery in the recharging mode should not exceed plus 0.1 V/minus 0.05 V from the recharging voltage.
The spread of electrolyte temperatures should be no more than 3°C compared to the average temperature of the battery electrolyte. The average temperature of the battery should not exceed the temperature of the ambient air (medium) by 3 °C.
The charging installation must ensure stabilization of the voltage on the battery with deviations that do not exceed the requirements established by the manufacturer, and for branded batteries - no more than ± 1% of the rated voltage (or the requirements established by supplier companies).
The specific current and voltage values required cannot be set ahead of time. It is necessary to establish and maintain an average value of the charging voltage and monitor the battery. A decrease in electrolyte density in most batteries indicates insufficient recharging current. In this case, as a rule, the required recharging voltage is 2.25 V for SK type batteries and not lower than 2.20 V for CH type batteries.
8.2 Charge mode.
Subject to compliance with operating requirements, and also depending on the condition of the battery, local conditions, the availability of appropriate types of chargers (units), and the availability of time, it is permissible to use any known charging methods and their modifications:
- at constant current;
- with a smoothly descending current strength;
- at constant voltage, etc.
The charging method is established by the company's instructions.
In this case, there should be no conditions under which, for specific types of AE, unacceptable voltages and charge currents, excess of the electrolyte temperature and processes of intense gas formation may occur.
During charging, the necessary parameters to monitor the condition of the batteries should be measured and recorded at appropriate intervals.
Charging at a constant current must be performed in one or two degrees.
With a two-stage charge, the first stage current should not exceed 0.25C10 for SK type batteries, 0.2C10 for CH type batteries, and 0.7C10 for branded batteries, depending on the type (until a voltage of 2.40 V is reached at the AE).
When the voltage increases (reaches) up to 2.30-2.35 V/cell. for conventional and 2.40 V on AE for branded ones, the charge is transferred to the second stage, the charge current should be no more than: for batteries of type SK - 0.12C10, for batteries of type SN - 0.05C10 and for branded batteries - 0, 35С10.
With a single-stage charge, the current should not exceed a value equal to 0.12C10 for batteries of types SK and CH and 0.15C10 for branded batteries. Charging SN type batteries with a current of 0.12C10 is allowed only after emergency discharges.
The charge is carried out to a constant voltage and electrolyte density for 1 hour for SK type batteries and for 2 hours for SN type batteries.
Branded batteries are charged to a constant voltage of 2.6-2.8 V/cell. and electrolyte density 1.24 ± 0.010 g/cm3 (reduced to a temperature of 20 °C) for 2 hours.
When charging branded batteries using a gradually decreasing current method until a voltage of 2.4 V/cell is reached. charging current is not limited. At a voltage of 2.40 V/cell. the charge current should not exceed 0.15C10, and at a voltage of 2.65 V/cell. - 0.035С10.
Charging at a constant voltage must be carried out in one or two degrees.
The charge in one stage is carried out at a constant voltage of 2.15-2.35 V on AEs of conventional types SK and SN. In this case, the initial charge current may exceed the value of 0.25C10, but then it automatically decreases to the level of 0.05C10.
Branded batteries are charged at a constant voltage of 2.25-2.30 V/cell, with the initial charge current being (0.1-0.3)C10.
Charging in two stages of conventional types is carried out in the first stage with a current that does not exceed 0.25C10, up to a voltage of 2.15-2.35 V on the AE, and then at a constant voltage - from 2.15 to 2.35 V/cell.
Branded batteries at the first stage are charged with a current of (0.1-0.15)C10 until a voltage of 2.35 V/cell is reached, and at the second stage a constant charge voltage of 2.23 V ± 1% is maintained, while the charging current automatically gradually decreases. The charge ends when the voltage and density of the electrolyte on the AE reach constant values for 2 hours.
Charging batteries with an elemental switch must be carried out in accordance with the instructions of the enterprise.
During charging, the voltage at the end of the charge can reach 2.60-2.70 V/cell; the charge is accompanied by strong “boiling” of the battery electrolyte, which will cause increased wear of the electrodes and a reduction in service life, especially for branded batteries.
For all charges, the batteries must have at least 115% of the capacity removed from the previous discharge.
During charging, it is necessary to measure the voltage, temperature and density of the battery electrolyte in accordance with Table 8.
Before turning on, 10 minutes after turning on and after the end of charging, before turning off the charging unit, it is necessary to measure and record the parameters of each battery, and during charging - of the control batteries. The charge current, cumulative capacity and charge date are also recorded.
The electrolyte temperature during charging of SK type batteries should not exceed 40°C. At a temperature of 40°C, the charging current must be reduced to a value that will ensure the specified temperature.
The electrolyte temperature during charging of CH type batteries should not exceed 35°C. At temperatures above 35°C, the charge is carried out with a current that does not exceed 0.05C10, and at temperatures above 45°C - with a current of 0.025C10.
In branded batteries such as Vb VARTA, OPzS, GroE, etc. In accordance with the requirements of the specifications and technical documentation, during charging the electrolyte temperature is not allowed to rise above 55 °C.
When charging CH type batteries (as well as branded batteries that use special filters and valve-controlled linings) with a constant or gradually decreasing current, it is necessary to remove the ventilation filter plugs.
8.3. Equalizing charge.
The same charging current, even at the optimal battery charging voltage, due to the difference in self-discharge of individual batteries, may be insufficient to maintain all batteries in a fully charged state.
To bring all SK type batteries to a fully charged state and to prevent sulfation of the electrodes, it is necessary to carry out an equalizing charge with a voltage of 2.30-2.35 V/cell. until the electrolyte density in all batteries reaches a constant value of 1.20-1.21 g/cm3 at a temperature of 20 °C.
The frequency of battery equalization charges and their duration depend on the condition of the battery. An equalizing charge must be carried out at least once a year for at least 6 hours.
For those batteries where, due to the operating conditions of the electrical installation, the charging voltage can only be maintained at a level of 2.15 V per battery, an equalizing charge must be carried out quarterly.
For branded batteries, the need, frequency and conditions for equalizing charges are determined (agreed upon) in accordance with the technical documentation of the supplier companies for specific types of batteries.
When the electrolyte level drops to 20 mm above the protective shield of SN type batteries, add water and carry out an equalizing charge to completely mix the electrolyte and bring all batteries to a fully charged state.
The equalizing charge is carried out at a voltage of 2.25-2.40 V/cell. until the electrolyte density in all batteries reaches a constant value of 1.240 ± 0.005 g/cm3 at a temperature of 20°C and its level is 35-40 mm above the safety shield.
The duration of the equalizing charge is approximately:
- at a voltage of 2.25 V - 30 days;
- at a voltage of 2.40 V - 5 days.
If, when monitoring the voltage on the AE, its deviation exceeds the average value by ± 0.05 V, it is necessary to additionally monitor the density of the electrolyte in this AE (and correct it if necessary).
If the battery has single batteries with reduced voltage and reduced electrolyte density (lagging batteries), then an additional equalizing charge is carried out for them from a separate rectifier device.
8.4. Battery discharge.
Batteries that operate in constant recharge mode are practically not discharged under normal conditions. They are discharged only in the event of a malfunction or disconnection of the recharging device, in emergency conditions or during control discharges.
Individual batteries or groups of batteries are subject to discharge during repairs or troubleshooting.
For a battery on a substation, the estimated duration of emergency discharge is set to at least 1 hour. To ensure the specified duration, the discharge current should not exceed the values of 18.50 x No. A and 25 x No. A, respectively.
For branded batteries, the calculated discharge current is determined according to the technical documentation for a specific type of battery.
When discharging batteries with currents less than the 10-hour discharge mode, it is not allowed to determine the end of the discharge only by voltage. The end of the discharge is determined by the following conditions:
- reduction in electrolyte density to 1.15 g/cm3 (by 0.03-0.06 g/cm3 compared to the electrolyte density at the beginning of the discharge);
- voltage reduction to 1.80 V;
- removing the container after 10 hours.
8.5. Control digit.
Control discharges of one of the most lagging AEs or checking the performance of the AE with a jog current must be performed according to a duly approved program.
Control discharges must be performed to determine the actual capacity of the battery and carried out in a 10-hour or 3-hour discharge mode.
The discharge current value should be the same each time, but not higher than the maximum permissible for a particular type of battery.
For batteries (AE), which are used in the industry, the final voltage of control discharges is 1.80 V/cell. during discharges with 10-, 5-, three-hour discharge current and 1.75 V/el. — during discharges with one-hour and 0.5-hour discharge current.
Branded batteries allow deeper discharges at final voltages, however, in order to unify the requirements for the period of mastering and gaining operational experience, the final voltage of the 10-hour control discharge is set to 1.80 V/cell.
At the PS, control discharges are carried out if necessary. In cases where the number of batteries is insufficient to ensure the voltage on the busbars at the end of the discharge within the specified limits, it is allowed to discharge a portion of the main batteries.
Control discharges of branded batteries type Vb VARTA, OPzS, etc. are carried out in accordance with the requirements of technical documentation (TS) of supplier companies, but at least once every five years. If a trend towards a decrease in the actual capacity of the battery below the nominal is detected, control discharges can be performed every six months.
Before the control discharge, it is necessary to equalize the batteries.
The measurement results of the control discharge must be compared with the measurement results of the previous discharges. For a more correct assessment of the condition of the battery, it is necessary that all control discharges of a given battery be carried out in the same mode and entered into the battery log.
Before starting the discharge, it is necessary to record the discharge date, voltage, electrolyte density of each battery and the temperature in two or three control batteries.
During discharge on control and lagging batteries, voltage, temperature and electrolyte density should be measured in accordance with Table 9.
Table No. 9
During the last hour of discharge, the battery voltage must be measured every 15 minutes.
The test discharge must be carried out to a voltage of 1.8 V on at least one battery. For some types of branded batteries, the company's instructions may state that the control discharge should be stopped after the terminals of the battery poles reach the final discharge voltage n x 1.8 V or after the corresponding time has elapsed (10 hours).
At the end of the discharge, it is necessary to take electrolyte samples from control batteries for chemical analysis and checking the content of impurities in accordance with GOST 667-73, GOST 6709-72, PUE or in accordance with the requirements of supplier companies.
After the first year of operation of batteries of type SK, SN, electrolyte analysis must be performed from all batteries.
At the end of the discharge, the voltage, temperature and density of the electrolyte, as well as the voltage between the battery poles and between the battery poles and the ground, should be measured and recorded for all AEs.
If the average temperature of the electrolyte during discharge differs from 20 °C, then the resulting actual capacity must be reduced to the capacity at a temperature of 20 °C according to the formula:
C20 = SF/1+ α(t-20), where
C20 - capacity reduced to a temperature of 20°C, A x hour;
SF - capacity actually released during discharge, A x hour;
α - temperature coefficient, in accordance with table 10;
t is the average temperature of the electrolyte during discharge, °C.
Table No. 10.
8.6. Topping up batteries.
The electrodes in the AE must always be completely recessed into the electrolyte.
The electrolyte level in SK type batteries must be maintained 10-15 mm above the top edge of the electrodes. If the electrolyte level decreases, you need to top up the batteries with distilled water, tested to be free of chlorine and iron. It is allowed to use steam condensate in accordance with GOST 6709-72. Water can be supplied to the bottom of the tank through a tube or to its upper part. In the latter case, it is recommended to recharge the battery with “boiling” to equalize the density of the electrolyte.
Batteries with an electrolyte density below 1.20 g/cm3 can be topped up with an electrolyte with a density of 1.18 g/cm3 only if the reasons for the decrease in density are identified.
The electrolyte level in SN type batteries should be between 20 and 40 mm above the safety shield. If topping up occurs when the level drops to the minimum limit, it is necessary to carry out an equalizing charge.
Under normal operating conditions, some batteries (Monolit type, SMG, etc.), especially those with valve regulation (VRLA type, etc.), do not need to be topped up with electrolyte throughout their entire service life. For some types of batteries (VARTA, etc.), refill intervals can be more than three years.
It must be borne in mind that most often, at a lower electrolyte level, the density of the electrolyte increases, so distilled water of the appropriate quality should be added (GOST 6709-72). It is necessary to add water no later than when the electrolyte level drops to the lower permissible level. In branded batteries, the electrolyte is added to a level that is 5-10 mm below the applied maximum permissible level “max”.
To achieve homogeneity of the electrolyte, it is necessary to perform an equalizing charge.
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 discharge of the battery by too high a 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 gratings and internal short circuit with irreversible destruction of the battery.
Factors that increase the risk of thermal runaway:
- intermittent or "pulsating" charge due to unstable external source energy or 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 efficiency 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 lead-acid rechargeable batteries 12V in batteries rated 24V and 48V.
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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).
Sihua Wen, Battery Application Engineer, Texas Instruments
Usually in any system consisting of several batteries connected in series, a charge imbalance problem arises separate batteries. Charge equalization is a design technique that improves battery safety, runtime, and service life. The latest battery protection ICs and charge indicators from Texas Instruments - the BQ2084, BQ20ZXX family, BQ77PL900 and BQ78PL114, included in the company's product line - are essential for implementation of this method.
WHAT IS BATTERY UNBALANCE?
Overheating or overcharging will accelerate battery wear and may cause fire or even explosion. Software and hardware protections reduce the danger. In a bank of many batteries connected in series (usually such blocks are used in laptops and medical equipment), there is a possibility of the batteries becoming unbalanced, which leads to their slow but steady degradation.
No two batteries are the same, and there are always slight differences in battery state of charge (SOC), self-discharge, capacity, resistance and temperature characteristics, even if we are talking about batteries of the same type, from the same manufacturer and even from the same production batch. When forming a block of several batteries, the manufacturer usually selects batteries that are similar in SSB by comparing the voltages on them. However, differences in the parameters of individual batteries still remain, and may increase over time. Most chargers determine the full charge by the total voltage of the entire chain of batteries connected in series. Therefore, the charging voltage of individual batteries can vary widely, but not exceed the voltage threshold at which overcharge protection is activated. However, the weak link - a battery with low capacity or high internal resistance - may experience higher voltages than other fully charged batteries. The defectiveness of such a battery will appear later during a long discharge cycle. The high voltage of such a battery after charging is complete indicates its accelerated degradation. When discharged for the same reasons (high internal resistance and low capacity), this battery will have the lowest voltage. This means that when charging at weak battery The overvoltage protection may operate while the remaining batteries in the unit are not yet fully charged. This will result in underutilization of battery resources.
BALANCING METHODS
Battery imbalance has a significant adverse effect on battery life and service life. It is best to equalize the voltage and SSB of batteries when they are fully charged. There are two methods of balancing batteries - active and passive. The latter is sometimes called "resistor balancing". The passive method is quite simple: batteries that need balancing are discharged through bypass circuits that dissipate power. These bypass circuits can be integrated into the battery pack or placed in an external chip. This method is preferable for low-cost applications. Almost all excess energy from batteries with a large charge is dissipated in the form of heat - this is the main disadvantage of the passive method, because it reduces the battery life between charges. The active balancing method uses inductors or capacitors, which have negligible energy losses, to transfer energy from highly charged batteries to less charged batteries. Therefore, the active method is significantly more effective than the passive one. Of course, increasing efficiency comes at a cost - the use of additional, relatively expensive components.
PASSIVE BALANCING METHOD
The simplest solution is to equalize the battery voltage. For example, the BQ77PL900 IC, which provides protection for battery packs with 5-10 batteries in series, is used in leadless tools, scooters, uninterrupted sources food and medical equipment. The microcircuit is a functionally complete unit and can be used to work with a battery compartment, as shown in Figure 1. Comparing the battery voltage with programmed thresholds, the microcircuit, if necessary, turns on the balancing mode. Figure 2 shows the operating principle. If the voltage of any battery exceeds a specified threshold, the charge stops and bypass circuits are connected. Charging is not resumed until the battery voltage drops below the threshold and the balancing procedure stops.
Rice. 1.BQ77PL900 chip used in stand-alone
operating mode to protect the battery pack
When applying a balancing algorithm that uses only voltage deviation as a criterion, incomplete balancing is possible due to the difference in the internal impedance of the batteries (see Fig. 3). The fact is that internal impedance contributes to the voltage spread during charging. The battery protection chip cannot determine whether the voltage imbalance is caused by different battery capacities or differences in their internal resistance. Therefore, with this type of passive balancing there is no guarantee that all batteries will be 100% charged. The BQ2084 charge indicator IC uses an improved version of voltage balancing. To minimize the effect of internal resistance variation, the BQ2084 performs balancing closer to the end of the charging process, when the charging current is low. Another advantage of the BQ2084 is the measurement and analysis of the voltage of all batteries included in the unit. However, in any case, this method is only applicable in charging mode.
Rice. 2.Passive method based on voltage balancing
Rice. 3.Passive voltage balancing method
uses battery capacity inefficiently
Microcircuits of the BQ20ZXX family use the proprietary Impedance Track technology to determine the charge level, based on determining the SSB and battery capacity. In this technology, for each battery, the charge Q NEED required to achieve a fully charged state is calculated, after which the difference ΔQ between the Q NEED of all batteries is found. Then the microcircuit turns on the power switches, through which the battery is balanced to a state of ΔQ = 0. Due to the fact that the difference in the internal resistance of the batteries does not affect this method, it can be used at any time: both when charging and discharging the batteries. Using Impedance Track technology, more accurate battery balancing is achieved (see Figure 4).
Rice. 4.
ACTIVE BALANCING
In terms of energy efficiency, this method is superior to passive balancing, because To transfer energy from a more charged battery to a less charged one, instead of resistors, inductances and capacitances are used, in which there are practically no energy losses. This method is preferred in cases where maximum battery life is required.
Featuring proprietary PowerPump technology, the BQ78PL114 is TI's latest active battery balancing component and uses an inductive converter to transfer power. PowerPump uses an n-channel p-channel MOSFET and an inductor that is located between a pair of batteries. The circuit is shown in Figure 5. The MOSFET and inductor make up the intermediate buck/boost converter. If the BQ78PL114 determines that the top battery needs to transfer energy to the bottom battery, a signal of about 200 kHz with a duty cycle of about 30% is generated at the PS3 pin. When the Q1 key is open, energy from the upper battery is stored in the throttle. When switch Q1 closes, the energy stored in the inductor flows through the flyback diode of switch Q2 into the lower battery.
Rice. 5.
Energy losses are small and mainly occur in the diode and inductor. The BQ78PL114 chip implements three balancing algorithms:
- by voltage at the battery terminals. This method is similar to the passive balancing method described above;
- by open circuit voltage. This method compensates for differences in the internal resistance of batteries;
- according to SZB (based on predicting the battery condition). The method is similar to that used in the BQ20ZXX family of microcircuits for passive balancing by SSB and battery capacity. In this case, the charge that needs to be transferred from one battery to another is precisely determined. Balancing occurs at the end of the charge. Using this method it is achieved best result(see Fig. 6)
Rice. 6.
Due to the large balancing currents, PowerPump technology is much more efficient than conventional passive balancing with internal bypass switches. When balancing a laptop battery pack, the balancing currents are 25...50 mA. By selecting the value of the components, you can achieve balancing efficiency 12-20 times better than with the passive method with internal keys. A typical unbalance value (less than 5%) can be achieved in one or two cycles.
In addition, PowerPump technology has other obvious advantages: balancing can occur in any operating mode - charge, discharge, and even when the battery delivering energy has a lower voltage than the battery receiving energy. Compared to the passive method, much less energy is lost.
DISCUSSION OF THE EFFECTIVENESS OF ACTIVE AND PASSIVE BALANCING METHOD
PowerPump technology performs balancing faster. When unbalancing 2% of 2200 mAh batteries, it can be done in one or two cycles. With passive balancing, the power switches built into the battery pack limit the maximum current value, so many more balancing cycles may be required. The balancing process can even be interrupted if there is a large difference in battery parameters.
The speed of passive balancing can be increased by using external components. Figure 7 shows a typical example of such a solution that can be used in conjunction with the BQ77PL900, BQ2084 or BQ20ZXX family of chips. First, the internal battery switch is turned on, which creates a small bias current flowing through resistors R Ext1 and R Ext2 connected between the battery terminals and the microcircuit. The gate-source voltage across resistor RExt2 turns on external key, and the balancing current begins to flow through the open external switch and resistor R Bal.
Rice. 7.Schematic diagram of passive balancing
using external components
The disadvantage of this method is that an adjacent battery cannot be balanced at the same time (see Fig. 8a). This is because when the internal switch of the adjacent battery is open, no current can flow through resistor R Ext2. Therefore, key Q1 remains closed even when the internal key is open. In practice this problem does not have of great importance, because With this balancing method, the battery connected to Q2 is quickly balanced, and then the battery connected to the Q2 key is balanced.
Another problem is the occurrence high voltage drain-source V DS, which can occur when every second battery is balanced. Figure 8b shows the case when the upper and lower batteries are balanced. In this case, the voltage V DS of the middle key may exceed the maximum permissible. The solution to this problem is limitation maximum value resistor R Ext or eliminating the possibility of simultaneous balancing of every second battery.
The fast balancing method is a new way to improve battery safety. With passive balancing, the goal is to balance the battery capacity, but due to the low balancing currents, this is only possible at the end of the charge cycle. In other words, overcharging a bad battery can be prevented, but this will not increase the operating time without recharging, because too much energy will be lost in the bypass resistive circuits.
When using PowerPump active balancing technology, two goals are simultaneously achieved - capacity balancing at the end of the charge cycle and minimal voltage difference at the end of the discharge cycle. The energy is stored and transferred to the weak battery rather than dissipated as heat in the bypass circuits.
CONCLUSION
Correctly balancing battery voltage is one of the ways to increase the safety of battery operation and increase their service life. New balancing technologies monitor the condition of each battery, which increases their service life and improves operational safety. PowerPump's fast active balancing technology increases battery life and allows batteries to be balanced as efficiently and effectively as possible at the end of the discharge cycle.