What is the battery discharge current. The main characteristics of the batteries. From operating experience

From operating experience

NiMH cells are widely advertised as high-energy cells, cold-resistant and memoryless. Having bought a digital camera Canon PowerShot A 610, I naturally supplied it with a capacious memory for 500 high quality images, and to increase the duration of shooting I bought 4 NiMH cells with a capacity of 2500 mAh from Duracell.

Let's compare the characteristics of the elements produced by the industry:

Parameters		Lithium ion Li-ion	Nickel Cadmium NiCd	Nickel- metal hydride NiMH	Lead acid Pb
Duration of service, charge / discharge cycles		1-1.5 years	500-1000		3 00-5000
Energy capacity, W * h / kg
Discharge current, mA * battery capacity
Voltage of one element, V
Self-discharge rate		2-5% per month	10% for the first day, 10% for each subsequent month	2 times higher NiCd	40% in year
Range of permissible temperatures, degrees Celsius	charging
	detente		-20... +65
Allowable voltage range, V		2,5-4,3 (coke), 3,0-4,3 (graphite)			5,25-6,85 (for batteries 6 B), 10,5-13,7 (for batteries 12 V)

Table 1.

From the table we can see NiMH cells have a high energy capacity, which makes them the preferred choice.

To charge them, an intelligent charger DESAY Full-Power Harger was purchased, which provides charging of NiMH cells with their training. The cells were charged with high quality, but ... However, on the sixth charge, it ordered a long life. Electronics burned out.

After replacing the charger and several charge-discharge cycles, the batteries began to sit down in the second or third ten pictures.

It turned out that despite the assurances, NiMH cells also have memory.

And most modern portable devices that use them have built-in protection that turns off the power when a certain minimum voltage is reached. This prevents the battery from being fully discharged. This is where the memory of the elements begins to play its role. Incompletely discharged cells receive an incomplete charge and their capacity drops with each recharge.

Quality chargers allow charging without loss of capacity. But something I could not find on the sale of this for cells with a capacity of 2500mAh. It remains to periodically train them.

NiMH cell training

Everything written below does not apply to battery cells with strong self-discharge. ... They can only be thrown away, experience shows that they cannot be trained.

NiMH cell training consists of several (1-3) discharge - charge cycles.

Discharging is performed until the voltage on the battery cell drops to 1V. It is advisable to discharge the cells individually. The reason is that the ability to take charge can vary. And it gets stronger when you charge without training. Therefore, there is a premature operation of the voltage protection of your device (player, camera, ...) and the subsequent charging of an uncharged cell. The result is an increasing loss of capacity.

Discharging must be performed in a special device (Fig. 3), which allows it to be performed individually for each element. If there is no voltage control, then the discharge was carried out until a noticeable decrease in the brightness of the lamp.

And if you measure the burning time of the light bulb, you can determine the capacity of the battery, it is calculated by the formula:

Capacity \u003d Discharge current x Discharge time \u003d I x t (A * hour)

A battery with a capacity of 2500 mA hour is capable of delivering a current of 0.75 A to the load for 3.3 hours, if the time obtained as a result of discharge is less, respectively, and less residual capacity. And with a decrease in the capacity you need, you need to continue training the battery.

Now, to discharge the battery cells, I use a device made according to the scheme shown in Fig. 3.

It is made from an old charger and looks like this:

Only now there are 4 bulbs, as in Fig. 3. Bulbs must be mentioned separately. If the lamp has a discharge current equal to the nominal for the given battery or slightly less, it can be used as a load and indicator, otherwise the lamp is only an indicator. Then the resistor must be of such a value that the total resistance of El 1-4 and the parallel resistor R 1-4 is about 1.6 ohms. Replacing a light bulb with an LED is unacceptable.

An example of a bulb that can be used as a load is a 2.4V krypton flashlight bulb.

A special case.

Attention! Manufacturers do not guarantee the normal operation of batteries with charging currents exceeding the rapid charging current I charge should be less than the battery capacity. So for batteries with a capacity of 2500mA * hour, it should be below 2.5A.

It happens that NiMH cells after discharge have a voltage of less than 1.1 V. In this case, it is necessary to apply the technique described in the above article in the MIR PC magazine. An element or series of elements is connected to a power source through a 21 W automotive light bulb.

Once again I draw your attention! Self-discharge of such elements must be checked! In most cases, it is elements with reduced voltage that have increased self-discharge. These elements are easier to throw away.

Charging is preferable individual for each element.

For two cells with a voltage of 1.2 V, the charging voltage should not exceed 5-6 V. With forced charging, the light is also an indicator. When the brightness of the lamp decreases, you can check the voltage on the NiMH cell. It will be greater than 1.1 V. Typically, this initial boost charge takes 1 to 10 minutes.

If the NiMH cell, during forced charging for several minutes, does not increase the voltage, it heats up - this is a reason to remove it from the charge and discard it.

I recommend using chargers only with the ability to train (regenerate) the cells when recharging. If there are no such, then after 5-6 working cycles in the equipment, without waiting for a complete loss of capacity, train them and reject elements with a strong self-discharge.

And they won't let you down.

In one of the forums commented on this article "written stupidly, but nothing else". So this is not" stupid ", but simple and available for execution in the kitchen for everyone who needs help. That is, as simple as possible. Advanced can put a controller, connect a computer, ......, but that's another history.

So that it does not seem stupid

There are "smart" chargers for NiMH cells.

Such a charger works with each battery separately.

He can:

1. individually work with each battery in different modes,
2. charge batteries in fast and slow mode,
3. individual LCD display for each battery compartment,
4. independently charge each of the batteries,
5. charge one to four batteries of different capacities and sizes (AA or AAA),
6. protect the battery from overheating,
7. protect each battery from overcharging,
8. determination of the end of charging by voltage drop,
9. identify faulty batteries,
10. pre-discharge the battery to the residual voltage,
11. restore old batteries (charge-discharge training),
12. check the capacity of the batteries,
13. display on the LCD: - charge current, voltage, reflect the current capacity.

Most importantly, I emphasize, this type of device allows you to work individually with each battery.

According to user reviews, such a charger allows you to restore most of the neglected batteries, and serviceable ones to operate the entire guaranteed service life.

Unfortunately, I did not use such a charger, since it is simply impossible to buy it in the provinces, but in the forums you can find many reviews.

The main thing is not to charge at high currents, despite the declared mode with currents of 0.7 - 1A, this is still a small-sized device and can dissipate power of 2-5 watts.

Conclusion

Any recovery of NiMh batteries is strictly individual (with each individual element) work. With constant monitoring and rejection of elements that do not accept charging.

And it's best to rebuild them with smart chargers that allow you to individually reject and cycle charge-discharge with each cell. And since such devices do not automatically work with batteries of any capacity, they are intended for cells of a strictly defined capacity or must have controlled charging and discharging currents!

Consider the labeling of LiPo batteries using the example of a battery that has the following inscriptions:

• 3000 - capacity in mAh (mAh);
• 11.1V - nominal voltage;
• 3S - the number and order of connection of cans (individual batteries from which the battery is assembled) - this means that the battery is connected in series from 3 batteries, that is, the battery capacity will be 3000mAh, and the voltage will be 3.7x3 \u003d 11.1V;
• 20C - discharge current (on a 3000 mAh battery means that the maximum continuous discharge current is 20 * 3000 \u003d 60,000 mA \u003d 60A).

Voltage

Instead of voltage, the number of cans is written on the batteries.

The voltage of one can is 3.7 V. Accordingly, 3 banks are equal to 11.1 V.

The number of cans is indicated by the letter S.

Discharge current

Denoted by a letter C and the number of the capacity factor.

For example, if the battery says 20C, and its capacity is 3000 mAh (3 Ah),
then the recoil current is 3 Ah * 20 C \u003d 60 A

Peak discharge current

The current that the battery can deliver for a short period of time (which is also indicated in the characteristics). This is usually 10-30 seconds.

It is indicated in the same way as the discharge current, by the second number.

20C-30C means that the discharge current is 20C, and the peak current is 30C.

Capacity

It is indicated in mAh (milliampere-hour). 1000 mA / h \u003d 1 A / h.

Battery charging.

LiPo batteries are charged with a current of 1C (unless otherwise indicated on the battery itself, recently they have appeared with the ability to charge with a current of 2 and 5C). The nominal charging current of the battery is 1000 mAh - Ampere. For a 2200 battery, there will be 2.2 amperes, etc.
The computerized charger performs battery balancing (equalizing the voltage on each battery bank) during charging. Although it is possible to charge 2S batteries without connecting the balancing cable, we highly recommend always connect the balancing connector! Charge 3S and large assemblies only with the balance wire connected! If you don't plug it in and one of the cans picks up more than 4.4 volts, then you will have an unforgettable fireworks display!
The battery charges up to 4.2 volts per cell (usually a few millivolts less).

Storage mode.

On a computerized charger, you can put LiPo into storage mode, while the battery will be charged / discharged up to 3.85V per cell. Fully charged batteries will die when stored for more than 2 months (maybe less). They say that they are completely discharged too, but for a longer period.

Exploitation.

It is not recommended to discharge the LiPo battery by less than 3 volts per cell - it can die. Engine governors have a function to shut off the engine when this condition occurs. We use s or. We also recommend using. It is connected to the balancing connector and when it beeps, it's time to land.
When the motor consumes more current than the battery can give, LiPo tends to swell and die. So this must be monitored strictly!
Now there are nano-tech batteries with a current output of 25-50C.

Preparation for work.

Getting the LiPo ready for use is easy - just charge it and that's it! :)
This type of battery has no memory effect (no need to re-discharge before recharging), no need to cycle - do charge-discharge cycles before use.
If you are charging in the field, then you should look for batteries with accelerated charging, they write Fast charge 2C or 5C. In theory, they can be charged with a current of 33 Amperes!
The charger has a maximum of 5A, but this will also reduce charging from 50 minutes to 20! (battery 1000 mAh)

For the safe operation of batteries, you must adhere to the following rules:

• Do not create a short circuit between the battery terminals, as the significant short-circuit current of a charged battery can melt the terminal contacts and cause thermal burns.
• Do not store batteries in a discharged state. In this case, sulfation of the electrodes occurs and the batteries significantly reduce their capacity.
• Connect the battery to the device only in the correct polarity. A charged battery has a significant energy reserve and can damage the device if connected incorrectly.
• Do not open the battery case. The electrolyte gel contained inside can cause chemical burns to the skin.
• Dispose of the old battery in accordance with the recycling regulations for products containing heavy metals.

Specifications

Discharge characteristics of batteries

The most important indicators of AB quality are: capacity, voltage, dimensions, weight, cost, permissible depth of discharge, service life, efficiency, operating temperature range, permissible charge and discharge current. Also, it must be borne in mind that the manufacturer gives all the characteristics at a certain temperature - usually 20 or 25 ° C. With deviations from this voltage, the characteristics change, and usually for the worse.

Voltage and capacity values \u200b\u200bare usually included in the battery model name. For example: - a battery with a voltage of 12 volts and a capacity of 200 ampere * hours, gel, deep discharge. This means that the battery can supply energy to the load 12 x 200 \u003d 2400 W * h with a 10 hour discharge with a current of 1/10 of its capacity. With high currents and fast discharge, the battery capacity decreases. At lower currents, it usually increases. This can be seen on the graph of the discharge characteristics of the batteries. Also, you need to look at the discharge characteristics for specific batteries. Sometimes manufacturers in the name write an overestimated battery capacity, which occurs only under ideal conditions - for example, does Haze (Haze batteries have a real capacity of 10-20 percent lower than indicated in the name of the battery).

When discharged with a current of 0.1 C, the operating time is 10 hours and the battery will fully deliver the accumulated energy to the load. When discharging with a current of 2 C (20 times more), the operating time will be about 15 minutes (1/4 hour) and the battery will supply only half of the accumulated energy to the load. At high discharge currents, this value is even lower. Often, in uninterruptible power supplies, rechargeable batteries operate in even more severe modes, in which discharge currents reach 4 C. At the same time, the discharge time is comparable to 5 minutes and the battery delivers less than 40% of the energy to the load.

Battery capacity

The amount of energy that can be stored in a battery is called its capacity. It is measured in ampere hours. One battery with a capacity of 100 Ah can supply a load with a current of 1 A for 100 hours, or with a current of 4 A for 25 hours, etc., although the battery capacity decreases with increasing discharge current. Batteries with a capacity of 1 to 2000 Ah are sold on the market.

To extend the life of a lead-acid battery, it is advisable to use only a small part of its capacity before recharging. Each discharge-charge process is called a charge cycle, and it is not necessary to completely discharge the battery. For example, if you discharged the battery by 5 or 10% and then charged it again, this also counts as 1 cycle. Of course, the number of possible cycles will vary greatly for different depths of discharge (see below). If it is possible to use more than 50% of the energy stored in the battery before its charge, without a noticeable deterioration in its parameters, such a battery is called a "deep discharge" battery.

Recharging batteries can be damaged. The maximum voltage for acid batteries should be 2.5 volts per cell, or 15 volts for a 12 volt battery. Many photovoltaic batteries have a soft load characteristic, so when the voltage increases, the charge current decreases significantly. Therefore, it is always necessary to use a dedicated charge controller for. In the case of wind power plants or micro hydroelectric power plants, such controllers are also required.

Voltage

Battery voltage is often the main parameter by which you can judge the condition and state of charge of the battery. This is especially true for sealed batteries, in which it is not possible to measure the density of the electrolyte.

The voltages during charging, discharging and no current are very different. To determine the state of charge of the battery, measure the voltage at its terminals in the absence of both charging and discharge currents for at least 3-4 hours. During this time, the voltage usually has time to stabilize. The voltage value during charging or discharging does not tell anything about the state or state of charge of the battery. The approximate dependence of the state of charge of the battery on the voltage at its terminals in idle mode is shown in the table below. These are typical values \u200b\u200bfor liquid electrolyte starter batteries. For sealed batteries (AGM and gel), these voltages are usually slightly higher (you need to ask the manufacturer) - for example, AGM batteries are fully charged if the voltage is 13-13.2V (compare with the voltage of starter batteries with liquid electrolyte 12.5-12.7V ).

State of charge

The state of charge depends on many factors, and it can only be accurately determined by special chargers with memory and a microprocessor, which monitor both the charge and discharge of a particular battery over several cycles. This method is the most accurate, but also the most expensive. However, it can save a lot of money on maintenance and battery replacement. The use of special devices that control the operation of batteries according to their state of charge can greatly increase the service life of lead-acid batteries. A number of our solar controllers have built-in devices for calculating the state of charge of the battery and adjust the charge depending on its value.

To determine the state of charge, you can also use the following 2 simplified methods.

1. Battery voltage... This method is the least accurate, but only requires a digital voltmeter capable of measuring tenths and hundredths of a volt. Before taking measurements, disconnect all consumers and all chargers from the battery and wait at least 2 hours. You can then measure the voltage across the battery terminals. The table below shows the voltages for batteries with liquid electrolyte. For a fully charged new AGM or gel battery, the voltage is 13-13.2V (compare with the voltage of 12.5-12.7V wet starter batteries). As batteries age, this voltage decreases. You can measure the voltage on each bank of the battery to find the faulty bank (divide the voltage for 12V by 6 in order to determine the desired voltage on one bank).
2. Second method for determining the degree of charge - by the density of the electrolyte... This method is only suitable for batteries with liquid electrolyte.

Also, you need to wait 2 hours before taking measurements. A hydrometer is used for measurement. Be sure to wear rubber gloves and safety glasses! Keep baking soda and water nearby in case the water gets on your skin.

State of charge	Battery 12V	Battery 24V	Electrolyte density
100	12.70	25.40	1.265
95	12.64	25.25	1.257
90	12.58	25.16	1.249
85	12.52	25.04	1.241
80	12.46	24.92	1.233
75	12.40	24.80	1.225
70	12.36	24.72	1.218
65	12.32	24.64	1.211
60	12.28	24.56	1.204
55	12.24	24.48	1.197
50	12.20	24.40	1.190
40	12.12	24.24	1.176
30	12.04	24.08	1.162
20	11.98	23.96	1.148
10	11.94	23.88	1.134

Battery life

It is incorrect to define battery life in years or months. Battery life is determined by the number of charge-discharge cycles and greatly depends on the operating conditions. The deeper the battery is discharged, the longer it is in the discharged state, the fewer the number of possible operating cycles.

The very concept of "the number of working cycles of" charge-discharge "of the battery" is relative, as it strongly depends on various factors. In addition, the value of the number of operating cycles, for example for one type of battery, is not a universal concept, since it depends on the technology that is different for each manufacturer. Battery life is determined in cycles, therefore the operating time in years is approximate and calculated for typical conditions. work. Therefore, if, for example, an advertisement states that the battery life is 12 years, this means that the manufacturer has calculated the life for the buffer mode with an average of 8 charge-discharge cycles per month. For example, Haze AGM batteries have a 12-year lifespan and a maximum 1200 cycles at 20% discharge. There are 100 such cycles per year, about 8 per month.

Another important point - during operation, the useful capacity of the battery decreases. All characteristics in terms of the number of cycles are usually given not until the complete death of the battery, but until it loses 40% of its nominal capacity. That is, if the manufacturer gives the number of cycles 600 at a 50% discharge, this means that after 600 ideal cycles (i.e. at a temperature of 20C and a discharge with a current of the same magnitude, usually 0.1C) the useful capacity of the battery will be 60% of the initial ... With this loss of capacity, it is already recommended to replace the battery.

Lead-acid batteries intended for use in autonomous power supply systems have a service life of 300 to 3000 cycles, depending on the type and depth of discharge. In systems based on renewable energy sources, the battery can be discharged much more than in standby mode. To ensure a long service life, in a typical cycle, the discharge should not exceed 20-30% of the battery capacity, and the deep discharge should not exceed 80% of the capacity. It is very important to charge lead acid batteries immediately after discharge. Long-term presence (more than 12 hours) in a discharged or not fully charged state leads to irreversible consequences in the batteries and a decrease in their service life.

How can you tell if a battery is near the end of its life? It's very simple - the internal resistance of the battery increases, this leads to a faster increase in voltage during charging (and, accordingly, a decrease in the time required for charging), and a faster discharge of the battery. If the charge is produced with a current close to the maximum allowable current, the dying battery will heat up when charged more than before.

Maximum charge and discharge currents

The charge and discharge currents of any battery are measured relative to its capacity. Typically, for batteries, the maximum charge current should not exceed 0.2-0.3C. Excessive charging current will shorten the battery life. We recommend setting the maximum charging current no more than 0.15-0.2C. Refer to the specifications for the specific battery model for maximum charging and discharging currents.

Self-discharge

The phenomenon of self-discharge is more or less typical for all types of batteries and consists in the loss of their capacity after they have been fully charged in the absence of an external consumer of current.

For a quantitative assessment of self-discharge, it is convenient to use the value of the capacity lost by them over a certain time, expressed as a percentage of the value obtained immediately after charging. As a rule, a time interval is taken as a time interval equal to one day and one month. So, for example, for serviceable NiCD batteries, self-discharge is considered acceptable up to 10% during the first 24 hours after the end of the charge, for NiMH - a little more, and for Li-ION it is negligible and is estimated in a month. Self-discharge in sealed lead-acid batteries is significantly reduced and amounts to 40% per year at 20 ° C and 15% at 5 ° C. At higher storage temperatures, self-discharge increases: at 40 ° C, the batteries lose 40% of their capacity in 4-5 months.

It should be noted that the self-discharge of batteries is maximal precisely in the first 24 hours after charging, and then significantly decreases. Its deep discharge and subsequent charge increase the self-discharge current.

Self-discharge of batteries is mainly due to the release of oxygen at the positive electrode. This process is further enhanced at elevated temperatures. So, when the ambient temperature rises by 10 degrees in relation to room temperature, it is possible to double the self-discharge.

To some extent, self-discharge depends on the quality of the materials used, the manufacturing process, the type and design of the battery. Loss of capacity can be caused by damage to the separator when adhering crystals break through it. A separator is usually called a thin plate that separates the positive and negative electrodes. This usually occurs due to improper maintenance of the battery, its absence or the use of inappropriate or poor quality chargers. In a worn-out battery, the electrode plates swell, sticking to each other, which leads to an increase in the self-discharge current, while the damaged separator cannot be restored by carrying out charge / discharge cycles.

Kargiev Vladimir, "Your Solar House"
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GLOSSARY

Capacity (C) - the energy that the battery can give to the load, expressed in ampere-hours (Ah, mAh). It will be greater under the following conditions: lower discharge current, discharge with less interruptions, higher ambient temperature, and lower end voltage.

Rated capacity - nominal capacity value: the amount of energy that a fully charged battery is able to give when discharging under strictly defined conditions.

Self-discharge - loss of capacity in the absence of an external consumer of current.

Battery life- the operating time, at which the discharge capacity becomes less than a certain standardized value, is usually estimated by the operating number of charge-discharge cycles.

Autonomous power supplies - rechargeable batteries - are seen in modern technologies as an integral element of almost any project. For automotive technology, the battery is also a constructive part, without which full-fledged operation of transport is unthinkable. The general usefulness of batteries is obvious. But technologically these devices are still not completely perfect. For example, a clear imperfection is noted by frequent charging of the batteries. Of course, the question is, what voltage to charge the battery with in order to reduce the frequency of recharging and maintain all its working properties for a long period of time?

To thoroughly understand the intricacies of the charging / discharging processes of lead-acid batteries (automobile) will help to determine the basic parameters of batteries:

• capacity,
• electrolyte concentration,
• discharge current strength,
• electrolyte temperature,
• self-discharge effect.

Under the capacity of a battery of accumulators, electricity is received, given by each individual battery bank in the process of its discharge. Typically, the capacity is expressed in ampere hours (A / h).

On the case of the battery for the car, not only the nominal capacity is indicated, but also the starting current when the car is started on a cold one. An example of marking is a battery produced by the Tyumen plant

The discharge capacity of the battery, indicated on the technical label by the manufacturer, is considered a nominal parameter. In addition to this figure, the parameter of the charge capacity is also significant for operation. The required charge value is calculated by the formula:

Sz \u003d Iz * Tz

where: Ic - charging current; Tz - charge time.

The figure indicating the discharge capacity of the battery is directly related to other technological and design parameters and depends on the operating conditions. From the constructive and technological properties of the battery, the discharge capacity is influenced by:

• active mass,
• the electrolyte used,
• thickness of electrodes,
• geometrical dimensions of electrodes.

Among the technological parameters, the degree of porosity of active materials and the recipe for their preparation are also significant for the capacity of the battery.

The internal structure of a lead-acid car battery, which includes the so-called active materials - plates of negative and positive fields, as well as other components

Operational factors also do not stand aside. As practice shows, the strength of the discharge current paired with the electrolyte is also capable of influencing the battery capacity parameter.

Effect of electrolyte concentration

Excessive electrolyte concentration will shorten the battery life. Operating conditions of the battery with a high concentration of electrolyte lead to an intensification of the reaction, which results in the formation of corrosion on the positive electrode of the battery.

Therefore, it is important to optimize the value, taking into account the conditions in which the battery is operated and the manufacturer's requirements for such conditions.

Optimizing the concentration of the electrolyte of the battery is seen as one of the most important points in the operation of the device. Concentration control is essential

For example, for conditions with a temperate climate, the recommended level of electrolyte concentration for most car batteries is adjusted to a density of 1.25 - 1.28 g / cm 2.

And when the operation of devices is relevant in relation to a hot climate, the electrolyte concentration should correspond to a density of 1.22 - 1.24 g / cm 2.

Batteries - Discharge Current

It is logical to divide the battery discharge process conditionally into two modes:

1. Long.
2. Short.

The first event is characterized by a discharge at low currents over a relatively long time period (from 5 to 24 hours).

For the second event (short discharge, starter discharge), on the contrary, large currents in a short period of time (seconds, minutes) are characteristic.

An increase in the discharge current provokes a decrease in the capacity of the battery.

Charger Teletron, which is successfully used to work with lead-acid car batteries. Simple electronic circuit, but high efficiency

Example:

There is a battery with a capacity of 55 A / h with an operating current at the terminals of 2.75A. Under normal environmental conditions (plus 25-26 ° C), the battery capacity is within 55-60 A / h.

If the battery is discharged with a short-term current of 255 A, which is equivalent to an increase in the nominal capacity by 4.6 times, the nominal capacity will decrease to 22 A / h. That is, almost doubled.

Electrolyte temperature and battery self-discharge

The discharge capacity of storage batteries naturally decreases if the electrolyte temperature drops. A drop in the temperature of the electrolyte entails an increase in the degree of viscosity of the liquid component. As a consequence, the electrical resistance of the active substance increases.

Disconnected from the consumer, completely inactive, has the ability to lose capacity. This phenomenon is explained by chemical reactions inside the device, taking place even in conditions of complete disconnection from the load.

Both electrodes - negative and positive - fall under the influence of redox reactions. But to a greater extent, the self-discharge process involves the electrode of negative polarity.

The reaction is accompanied by the formation of hydrogen in gaseous form. With an increase in the concentration of sulfuric acid in the electrolyte solution, an increase in the density of the electrolyte from 1.27 g / cm 3 to 1.32 g / cm 3 is noted.

This is commensurate with a 40% increase in the rate of self-discharge effect on the negative electrode. An increase in the self-discharge rate is also provided by metal impurities included in the structure of the electrode of negative polarity.

Self-discharge of a car battery after long-term storage. With complete inactivity, with no load, the battery has lost a significant part of its capacity

It should be noted: any metals present in the electrolyte and other components of batteries enhance the self-discharge effect.

When these metals come into contact with the surface of the negative electrode, they cause a reaction, as a result of which hydrogen evolution begins.

Some of the existing impurities play the role of a charge carrier from the positive electrode to the negative one. In this case, the reactions of reduction and oxidation of metal ions take place (that is, again, the self-discharge process).

There are also cases when the battery loses its charge from contamination on the case. Contamination creates a conductive layer that closes the positive and negative electrodes

In addition to internal self-discharge, external self-discharge of the car battery is not excluded. The reason for this phenomenon can be a high degree of contamination of the surface of the battery case.

For example, electrolyte spilled on the case, water or other technical liquids. But in this case, the self-discharge effect is easily eliminated. You just need to clean the battery case and keep it always clean.

Car battery charging

Let's start from the situation of inactivity of the device (in the off state). What voltage or current to charge the car battery when the device is in storage?

In storage conditions, the main purpose of charging is aimed at compensating for self-discharge. In this case, charging is usually done with low currents.

The range of charge values \u200b\u200bis typically 25 to 100 mA. In this case, the charge voltage must be maintained within the range of 2.18 - 2.25 volts in relation to a single battery bank.

Selecting Battery Charge Conditions

The battery charging current is usually adjusted to a certain value depending on the set float time.

Preparation of a car battery for recharging in a mode that needs to be determined taking into account the technological properties and technical parameters during battery operation

So, if it is supposed to charge the battery for 20 hours, the optimal parameter of the charge current is a value equal to 0.05C (that is, 5% of the nominal capacity of the battery).

Accordingly, the values \u200b\u200bwill increase proportionally if you change one of the parameters. For example, after 10 hours of charging, the current will already be 0.1C.

Charge in a two-stage cycle

In this mode, initially (the first stage), the charge is carried out with a current of 1.5C until the voltage on an individual bank reaches 2.4 volts.

After that, the charger is switched to the charge current mode of 0.1C and continues to charge until the full capacity is set for 2 - 2.5 hours (second stage).

The charge voltage in the second stage mode varies from 2.5 to 2.7 volts for one can.

Boost charge mode

The principle of forced charging involves setting the value of the charging current at the level of 95% of the nominal battery capacity - 0.95C.

The method is quite aggressive, but it allows you to charge the battery almost completely in just 2.5-3 hours (in practice, 90%). Up to 100% capacity charging in a forced mode will take 4 - 5 hours.

Control training cycle

The practice of operating car batteries notes a positive result when the control-training cycle is applied to new batteries that have not yet been used.

For this option, charging with parameters calculated by a simple formula is optimal:

I \u003d 0.1 * C20;

Charge until the voltage on a single bank is 2.4 volts, after which the value of the charging current is reduced to the value:

I \u003d 0.05 * C20;

With these parameters, the process is continued until fully charged.

The control-training cycle also covers the practice of discharge, when the battery is discharged with a small current of 0.1C to a total voltage level of 10.4 volts.

In this case, the degree of density of the electrolyte is maintained at 1.24 g / cm 3. After the discharge, the device is charged according to the standard procedure.

General principles of charging lead-acid batteries

In practice, several methods are used, each of which has its own difficulties and is accompanied by a different amount of financial costs.

It is not difficult to decide in what way to charge the battery. Another question is what result will be obtained from the application of this or that method.

The most affordable and simplest method is considered to be a constant current charge at a voltage of 2.4 - 2.45 volts / bank.

The charging process continues until the current remains constant for 2.5-3 hours. The battery is considered fully charged under these conditions.

Meanwhile, the combined charge technique has received more recognition among motorists. In this version, the principle of limiting the initial current (0.1C) is applied until the specified voltage is reached.

Then the process continues at constant voltage (2.4V). For this circuit, it is permissible to increase the initial charge current to 0.3C, but no more.

It is recommended to charge batteries in buffer mode at low voltages. Optimal charge values: 2.23 - 2.27 volts.

Deep discharge - remediation

First of all, it should be emphasized: the restoration of the battery to the nominal capacity is possible, but on condition that no more than 2-3 deep discharges took place.

The charge in such cases is performed with a constant voltage equal to 2.45 volts per cell. It is also allowed to charge with a (constant) current of 0.05C.

The battery recovery process may require two to three separate charge cycles. Most often, to achieve full capacity, charging is carried out exactly in 2-3 cycles.

If the charge is carried out with a voltage of 2.25 - 2.27 volts, it is recommended to perform the process twice or three times. Since at low voltages, it is not possible to achieve the capacity rating in most cases.

Of course, the influence of the ambient temperature should be taken into account during the recovery process. If the ambient temperature is in the range of 5 - 35 ° C, the charge voltage does not need to be changed. Otherwise, charge adjustment will be required.

Video on the battery control and training cycle

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For normal operation of any battery, you must always remember "Rule of Three Rs":

1. Do not overheat!
2. Do not recharge!
3. Do not overdischarge!

The following formula can be used to calculate the charging time for a NiMH or multi-cell battery:

Charging time (h) \u003d Battery capacity (mAh) / Charger current (mA)

Example:
We have a battery with a capacity of 2000mAh. The charge current in our charger is 500mA. We divide the battery capacity by the charge current and get 2000/500 \u003d 4. This means that at a current of 500 milliamperes, our battery with a capacity of 2000 milliamperes will be charged to full capacity for 4 hours!

And now in more detail about the rules that you need to try to follow for normal operation of a nickel-metal hydride (Ni-MH) battery:

1. Store Ni-MH rechargeable batteries with a small amount of charge (30 - 50% of its nominal capacity).
2. Nickel-metal hydride batteries are more sensitive to heat than nickel-cadmium (Ni-Cd) batteries, so do not overload them. Overloading can adversely affect the current output of the battery (the ability of the battery to hold and deliver stored charge). If you have an intelligent charger with “ Delta Peak"(Interruption of battery charging upon reaching the peak voltage), then you can charge the batteries practically without the risk of overcharging and destruction thereof.
3. Ni-MH (nickel metal hydride) batteries can (but not necessarily!) Be "trained" after purchase. 4-6 charge / discharge cycles for batteries in a high-quality charger allows you to reach the limit of capacity, which was lost during the transportation and storage of batteries in questionable conditions after leaving the assembly line of the manufacturing plant. The number of such cycles can be completely different for batteries from different manufacturers. High-quality batteries reach their capacity limit already after 1-2 cycles, and batteries of questionable quality with artificially high capacity cannot reach their limit even after 50-100 charge / discharge cycles.
4. After discharging or charging, try to allow the battery to cool down to room temperature (~ 20 o C). Charging batteries in temperatures below 5 o C or above 50 o C can significantly affect battery life.
5. If you want to discharge a Ni-MH battery, do not discharge it to less than 0.9V for each cell. When the voltage of nickel batteries drops below 0.9V per cell, most chargers with "minimum intelligence" cannot activate the charge mode. If your charger cannot recognize a deeply discharged cell (discharged less than 0.9V), then you should use a more "dumb" charger or connect the battery for a short time to a power source with a current of 100-150mA until the voltage on the battery reaches 0.9V.
6. If you constantly use the same battery assembly in an electronic device in recharge mode, then sometimes it is worth discharging each battery from the assembly to a voltage of 0.9V and making it fully charged in an external charger. Such a complete cycling procedure should be performed once every 5-10 recharging cycles of batteries.

Charge table for typical Ni-MH batteries

Capacity of elements	Standard size	Standard charging mode	Peak charge current	Maximum discharge current
2000 mAh	AA	200mA ~ 10 hours	2000 mA	10.0A
2100 mAh	AA	200mA ~ 10-11 hours	2000 mA	15.0A
2500 mAh	AA	250mA ~ 10-11 hours	2500 mA	20.0A
2750 mAh	AA	250mA ~ 10-12 hours	2000 mA	10.0A
800 mAh	AAA	100mA ~ 8-9 hours	800 mA	5.0 A
1000 mAh	AAA	100mA ~ 10-12 hours	1000 mA	5.0 A
160 mAh	1/3 AAA	16mA ~ 14-16 hours	160 mA	480 mA
400 mAh	2/3 AAA	50mA ~ 7-8 hours	400 mA	1200 mA
250 mAh	1/3 AA	25mA ~ 14-16 hours	250 mA	750 mA
700 mAh	2/3 AA	100mA ~ 7-8 hours	500 mA	1.0 A
850 mAh	FLAT	100mA ~ 10-11 hours	500 mA	3.0 A
1100 mAh	2/3 A	100mA ~ 12-13 hours	500 mA	3.0 A
1200 mAh	2/3 A	100mA ~ 13-14 hours	500 mA	3.0 A
1300 mAh	2/3 A	100mA ~ 13-14 hours	500 mA	3.0 A
1500 mAh	2/3 A	100mA ~ 16-17 hours	1.0 A	30.0 A
2150 mAh	4/5 A	150mA ~ 14-16 hours	1.5 A	10.0 A
2700 mAh	A	100mA ~ 26-27 hours	1.5 A	10.0 A
4200 mAh	Sub C	420mA ~ 11-13 hours	3.0 A	35.0 A
4500 mAh	Sub C	450mA ~ 11-13 hours	3.0 A	35.0 A
4000 mAh	4/3 A	500mA ~ 9-10 hours	2.0 A	10.0 A
5000 mAh	C	500mA ~ 11-12 hours	3.0 A	20.0 A
10000 mAh	D	600mA ~ 14-16 hours	3.0 A	20.0 A

The data in the table is valid for fully discharged batteries.