Equalizing battery charge. Battery charge equalization ensures long operating time and extends service life. Factors that increase the risk of “battery drying out”

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 voltage separate 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 industry. About diagrams for connecting batteries in multi-level systems. Here it must be said that they are very useful for long-term provision of uninterrupted power supply to 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 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:

  1. Passive;
  2. 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

Charge equalizing system battery necessary for Maintenance battery with serial type connections when charging them from a single source. Batteries, with serial connection form a single chain 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 controllers Battery balancing tests the technical condition of each battery and makes 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.

Sihua Wen, Battery Application Engineer, Texas Instruments

Typically, in any system consisting of several batteries connected in series, the problem of unbalancing the charge of the individual batteries arises. 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 predetermined 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 values ​​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.

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.

Category: Charger support Published 05/04/2016 12:06

Most 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 need is to use a full charge in saturation mode, with further comparison specific gravity each element of the 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.

There is no general agreement on the advisability of applying an equalizing charge to VRLA and other sealed batteries. 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 depletion of the electrolyte.

Not all chargers have an equalizing charge function. Such a charge should not be carried out with a device not intended for this purpose.

  • 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, this means excess battery charge, and its performance and service 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. Most chargers are automatic and pre-programmed. Some chargers allow the user to set the voltage and current values. See charging recommendations in the Table.

  • Make sure that Charger set to the desired program for wet, gel or AGM batteries, depending on the type of battery used.
  • 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.