Battery capacity how many hours. How to accurately determine the battery capacity and restore it? What is the battery capacity
A car battery is a device that has a number of characteristics by which it can be selected for a specific vehicle. This article will focus on such a battery parameter as capacity. Below you can find out how to independently determine the battery capacity and how this parameter is checked.
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What should a car owner know about battery capacity?
As you know, in total, any car battery has many parameters, including weight, period of use and storage, etc. However, one of the most important and key indicators is the battery capacity. For vehicles, this parameter is measured in ampere-hours. WITH Check your car's service manual to find out the capacity recommended by the manufacturer!
Calculation and determination
How to correctly calculate, check and determine the capacity of a car battery? By this indicator, marked on the battery label, you can determine the current level at which the device is discharged to a minimum voltage of 10.8 V. On average, the duration of traditional discharge cycles should be about 10-20 hours.
For example, if a car battery is labeled as 72 Ah, then this indicates that the battery can produce 3.6 amps of current for 20 hours. Accordingly, when the cycle ends, the voltage level at the terminal should be 10.8 V. However, it must be borne in mind that a car battery is not capable of delivering a current of 72 amperes for one hour. When it increases, the discharge time indicator decreases; these parameters are expressed as a power law.
Below is the dependency formula:
Cp = I k * t, where
- C p - battery capacity level;
- k is the Peukert number - the scientist who derived the formula;
- t – time.
As for the Baker's ratio, this is a constant parameter for a certain type of battery. When calculating the characteristics for lead devices, this value ranges from 1.15 to 1.35. This indicator is determined by the level of the battery's nominal capacity.
It can also be determined using another formula derived to calculate this indicator for an arbitrary discharge current parameter:
E =En(I n /I) (p-1) , where
- E n - level of nominal characteristics;
- E – real;
- I n—discharge current level.
Above we told you how to calculate and determine the nominal capacity of the device, but there is also such a thing as backup characteristics. If the calculation of the nominal indicator is determined by discharging with a small current, then the reserve characteristic parameter allows the calculation of the time value. We are talking about the time during which the car battery can function when the generator is not working. In this case, the discharge current is 25 amperes.
Calculation of the nominal parameter of a car battery can be done by analyzing various design and technological features. It should be noted that this value is quite strongly influenced by the conditions of use of the battery. The main characteristics that determine this indicator include the composition of the electrolyte, the volume of the active mass, and the level of thickness of the lead plates. The level of discharge capacity is directly affected by the magnitude of the discharge current, as well as the temperature of the electrolyte (video author - transistor815).
Examination
Many car owners are interested in the question of how to check the capacity measurement of this value independently. Some people are interested in this simply out of curiosity, while others want to check the value for compliance with what the manufacturer stated. In principle, checking it yourself is not so difficult.
Any verification is carried out on the basis of the data given above. For example, you can use a meter for this, conducting a control and training cycle. To properly build a meter, you will need a diagram.
The circuit diagram for the meter is shown below. As for the resistance for the meter, it is calculated using the following formula:
- U in this case is the battery voltage;
- I – discharge current value.
To equip the meter, the discharge current should be selected in accordance with the battery capacity, as well as the discharge cycle, which can be either 10 or 20 hours. In fact, in most cases, a car lamp with the required power is used for discharge. Using a multimeter, you can measure the exact indicator that passes through the circuit, and it is important to note the time until the voltage drops. Ultimately, the time that is multiplied by the current will correspond to the actual battery capacity.
Recovery
So, how is the recovery procedure carried out:
- To restore the value, a fresh electrolyte is taken, the density of which should be 1.28 k/cm3, in which a special desulfating additive is dissolved. It will take 48 hours for the additive to completely dissolve. For proper restoration, consider all the recommendations described in the instructions.
- Electrolyte is poured into the car battery, the density is measured using a hydrometer, this value should be 1.28 g/cm3.
- The next stage of restoration will be to unscrew the plugs on the device and connect it to the charger. For recovery to take place correctly, you will need to perform several charge and discharge cycles; a minimum current is used for charging, which should be no more than 10% of the maximum. When restoring the battery, it should not heat up or boil. If the voltage rises to 13.8 volts, you need to check the density of the water.
- Then the electrolyte is adjusted. Distillate is added to battery jars until the electrolyte density is 1.28 g/cm3.
- Then, for recovery, a discharge is carried out. A load in the form of a light bulb or a resistor should be connected to the device; the current in this case should be limited to 1 ampere, if the battery is six-volt - to 0.5 ampere. You need to wait until the voltage rises to 10.2 volts, and you need to note the time from the moment the load is connected. The resulting discharge characteristic must be multiplied by time - as a result you will receive the parameter of the required characteristic. If this characteristic is much less than the standard one, the discharge-charge procedure must be repeated. This process is repeated until the characteristic is nominal or at least close to it.
- At this point, the restoration procedure can be considered complete; additives can still be added to the electrolyte. If you did everything correctly, the device will serve you for many more years.
6. What determines the battery capacity?
Discharge current
ABOUT Typically, the manufacturer assigns the nominal capacity of a lead-acid battery for long-term (10, 20 or 100 hours) discharges.
The battery capacity at such discharges is designated as C 10, C 20 or C 100. 20 We can calculate the current flowing through the load during a 20-hour (for example) discharge - I 20: 20 I
[A] = E Does this mean that with a 15-minute (1/4 hour) discharge the current will be equal to E 20 x 4? No, that's not true. With a 15-minute discharge, the capacity of a lead-acid battery is typically just under half its rated capacity. Therefore, the current I 0.25 does not exceed E 20 x 2. That is The discharge current and discharge time of a lead battery are not proportional to each other.
[A] = E The dependence of the discharge time on the discharge current is close to a power law. In particular, Peukert's formula (law) is widespread - named after the German scientist Peukert. Peukert found that:
The battery capacity at such discharges is designated as C 10, C 20 or C 100. p * T = const
Here p is the Peukert number - an exponent that is constant for a given battery or type of battery. Peukert's formula also applies to modern sealed lead acid batteries.
D For lead-acid batteries, the Peukert number typically ranges from 1.15 to 1.35. The value of the constant on the right side of the equation can be determined from the nominal capacity of the battery. Then, after several transformations, we obtain a formula for the battery capacity E at an arbitrary discharge current I:
E = E n * (I n /I) p-1
Here E n is the nominal capacity of the battery, and I n is the discharge current at which the nominal capacity is set (usually a 20-hour or 10-hour discharge current).
Final discharge voltage
P As the battery discharges, the voltage on the battery drops. When the final discharge voltage is reached, the battery is disconnected. The lower the final discharge voltage, the greater the battery capacity. The battery manufacturer sets the minimum permissible final discharge voltage (it depends on the discharge current). If the battery voltage drops below this value (deep discharge), the battery may fail.
Temperature
P When the temperature rises from 20 to 40 degrees Celsius, the capacity of a lead battery increases by about 5%. When the temperature decreases from 20 to 0 degrees Celsius, the battery capacity decreases by approximately 15%. When the temperature decreases by another 20 degrees, the battery capacity drops by another 25%.
Battery wear
E The capacity of a lead-acid battery as delivered may be slightly more or slightly less than the nominal capacity. After several discharge-charge cycles or several weeks of being under a “floating” charge (in a buffer), the battery capacity increases. During further use or battery storage The battery capacity decreases - the battery wears out, and must eventually be replaced with a new battery. To replace the battery on time, it is better to monitor the battery wear using a modern battery capacity tester - Lead-acid battery capacity indicator "Pendant"
7. How to check the capacity of a lead-acid battery?
TO classical method battery check is the control digit. The battery is charged and then discharged with a constant current, recording the time to the final discharge voltage. Next, determine the residual capacity of the battery using the formula:
E [A*hour]= I [A] * T [hour]
T The discharge time is usually chosen so that the discharge time is approximately 10 or 20 hours (depending on the discharge time for which the nominal battery capacity is indicated). Now you can compare the remaining battery capacity with the nominal capacity. If the residual capacity is less than 70-80% of the nominal capacity, the battery is taken out of service, because with such wear, further battery aging
will happen very quickly. N
The disadvantages of the traditional method of monitoring battery capacity are obvious:
complexity and labor intensity;
removing the battery from use for a long period of time. For quick battery test
Now there are special devices that allow you to check the battery capacity in a few seconds. Battery capacity
- this is the amount of electrical energy that a fully charged battery can deliver at a certain discharge mode and temperature from the initial to the final voltage. The SI unit for electrical charge is the coulomb (1C), but in practice capacity is usually expressed in ampere-hours (Ah).
Capacity is measured in ampere hours and determined by the formula:
C=Iptp,
where C is capacity, Ah;
p - discharge current strength, A;
tp - discharge time, H.Nominal capacity
- the capacity that a new fully charged battery should give under normal discharge conditions specified in the standard for this battery. In this case, the voltage should not fall below a certain value.
An example of assessing the battery capacity using a 20-hour discharge mode with a current of 0.05C20 (current equal to 5% of the nominal capacity). E If the battery capacity is 55Ah, then discharging it with a current of 2.75A, it will be completely discharged in 20 hours. Similarly, for batteries with a capacity of 60Ah, a complete 20-hour discharge will occur at a slightly higher discharge current - 3A.
Charging capacity- the amount of electricity received by the battery during charging. The charging capacity of a battery is always greater than the discharge capacity due to energy losses due to side reactions and processes.
Capacity return is the ratio of the amount of electricity received from the battery during discharge to the amount of electricity required to charge the battery to its original state under certain conditions.
It depends on the completeness of the charge. Part of the charge is lost to gas formation, which reduces the recoil coefficient.
Residual capacity- a value corresponding to the amount of electricity that a partially discharged battery can give out when the discharge mode is set to the final discharge.
Battery reserve capacity- the time during which the battery can ensure the operation of consumers in emergency mode. The value of the reserve capacity, expressed in minutes, has recently been increasingly indicated by manufacturers of starter batteries after the value of the cold start current.
At a constant charging current l, the charging capacity C = It, where t is the charging time.
The capacity is measured until the voltage of at least one battery cell drops to a value regulated for a specific discharge mode.
Over the course of its service life, the battery capacity changes. At the beginning of the service life, it increases as the active mass of the plates develops. During operation, the capacity remains stable for some time, and then begins to gradually decrease due to the aging of the active mass of the plates.
The capacity of the battery depends on the amount of active material and the design of the electrodes, the amount and concentration of the electrolyte, the magnitude of the discharge current, the temperature of the electrolyte, the degree of wear of the battery, the presence and other factors.
As the discharge current increases, the battery capacity decreases. Batteries under forced discharge modes yield less capacity than when discharged under longer modes (low current). Therefore, batteries may have symbols for 3, 5, 6, 10, 20 and 100 hours of discharge. In this case, the capacities of the same battery will be completely different. The smallest will be with a 3-hour discharge, the largest with a 100-hour discharge.
With increasing capacity, the capacity increases, but at excessively high temperatures it decreases.This happens because, with increasing temperature, the electrolyte penetrates more easily into the pores of the active mass, as its viscosity decreases and internal resistance increases.Therefore, more active mass takes part in the discharge reaction than during a charge carried out at a lower temperature.
Battery Capacity Units
When choosing a portable battery charger (ROM), many people ask questions: “What do the mAh and Wh characteristics mean?”, “And why are they needed?”
We answer. Both values: mAh (milliamp-hour) and Wh (watt-hour) characterize the capacity of the charger. But it is most correct to focus on capacity, measured in watt-hours. And that's why.
Wh is an absolute constant capacity that most accurately describes the potential of a device.
And the capacity indicated in mAh is a relative value that describes the capacity of the device in relation only to a specific selected voltage. That is, for one voltage there is one capacitance, and for another voltage there is another capacitance. Often you can also see the designation “Ah” (ampere hour). 1 Ah = 1000 mAh. Thus, to get the Ah value, you need to divide the mAh value by 1000. Conversely, to get mAh, you need to multiply the Ah value by 1000.
For example, the CARKU E-Power-3 battery charger has a capacity of 29.6 Wh or 8000 mAh (8 Ah).
At the same time, 8000 mAh is the nominal capacity, and it is indicated relative to the nominal voltage of the batteries built into the body of the starter-charger. All lithium polymer (LiPo) and lithium ferrum phosphate (LiFePO4) batteries used in starter chargers have a nominal voltage of 3.7 V. Many will ask: “How so? If the nominal voltage = 3.7 V, then why are the ROM outputs marked with values of 5V, 12V and 19V?” The answer is simple: the voltage increase for one or another ROM output occurs due to the electronic filling of the device.
Thus, for a nominal voltage of 3.7V, the CARKU E-Power-3 ROM has a nominal capacity of 8000 mAh. From this value of nominal relative capacity, expressed in mAh, it is easy to obtain the value of absolute capacity, expressed in Wh:
1) first, convert the capacity value expressed in milliamp-hours to ampere-hours
8 Ah x 3.7 V = 29.6 Wh
Thanks to this ratio, it is easy to calculate the actual capacity in mAh of the CARKU ROM and any other battery at a specific operating voltage of a specific electrical consumer.
Let's make calculations using the example of the CARKU E-Power-3 ROM. This model has 2 outputs:
1) USB output for charging mobile phones, tablets, etc. with an operating voltage of 5 V. To calculate the actual capacity for this operating mode, it is necessary to divide the absolute capacity of 29.6 Wh by the voltage of 5 V, and then we get 5.92 Ah:
29.6 Wh / 5 V = 5.92 Ah (or 5920 mAh).
2) Output for starting a motor with an operating voltage of 12 V. Here the same formula is used to calculate the actual capacity:
29.6 Wh / 12 V = 2.467 Ah (or 2467 mAh).
As we can see from the calculations, the most obvious and correct value characterizing the capacity of the ROM is precisely Wh. And based on it, it is easy to calculate the capacity in mAh for a particular voltage and, therefore, approximately estimate the potential of the ROM for a specific electrical consumer.
The capacity values in mAh for the CARKU E-Power-3 ROM, when correctly calculated for 5V and 12V, are not as impressive as for a nominal voltage of 3.7V, but this does not detract from the high consumer performance of this little one. The compact and lightweight E-Power-3 allows, for example, to fully charge an iPhone4 3 times or a classic Nokia 106 6 times, as well as confidently start 4-liter gasoline engines in summer and 1.6-liter gasoline engines in winter, which is confirmed by real tests and numerous videos in Youtube.
Some into the forest, some for firewood
In ROM descriptions and passports, first of all, it is necessary to indicate the capacity in Wh. Additionally, you can indicate the nominal capacity of the ROM in mAh, paying tribute to the historically popular dimension, easily recognized by the mass consumer and widely used for power banks (external batteries), batteries for mobile phones, tablets, etc.
All CARKU ROMs have an absolute capacity in Wh and a nominal relative capacity in mAh. Some manufacturers incorrectly indicate the ROM capacity only in mAh, reflecting a secondary capacity characteristic and completely forgetting about the most important one.
There are also situations where some sites indicate inflated specifications in mAh. For example, the absolute capacity of the CARKU E-Power-Elite ROM is 44.4 Wh, which means its nominal capacity is 12000 mAh (44.4 Wh / 3.7 V = 12 Ah). Therefore, there cannot be a CARKU E-Power-Elite ROM with an absolute capacity of 44.4 Wh and at the same time with a nominal capacity of 14000 mAh or 15000 mAh, as some sales companies indicate.
It is also worth keeping in mind that the vast majority of portable starter-chargers currently presented on the Russian market have an actual capacity much less than the declared one. For example, 5000 mAh instead of 8000 mAh, 8000 mAh instead of 14000 mAh, etc. The difference between the declared and actual capacity sometimes reaches 2 or more times. This is a very common situation, because it is very difficult for the consumer to check the actual capacity, much less measure it. In turn, the actual capacity of the CARKU ROM fully corresponds to the declared one. This is confirmed, for example, by an independent review of the Russian ROM market and, in which the CARKU ROM demonstrates a greater number of launches than analogues with a larger capacity.
Why is it so important to pay attention to ROM capacity? Because the duration of autonomous operation of electrical consumers powered from the ROM directly depends on it. The capacity of the ROM is especially important in the winter when starting a vehicle engine, since the larger the capacity, the more attempts there will be to start the engine and their duration, and, consequently, the likelihood of a successful start. In addition, the battery is the main element of the ROM, so the cost of the ROM directly depends on its capacity. So keep this in mind when choosing a ROM for yourself.
What is the capacity of a car battery and what value should you choose?
A car battery has a number of parameters according to which it can be selected for a particular vehicle. And this is not only dimensions, weight, location of pins. These are also electrical characteristics by which one can judge the purpose of the battery. Today in stores you can find batteries for motorcycles, cars, trucks and special equipment. They are all different in their performance. Even for different classes of passenger cars, batteries differ in their electrical parameters. If you choose the wrong battery, problems may arise during subsequent operation. One of the key characteristics of a battery is capacity. We'll talk about it today.
The main characteristics of a car battery include the following:
- Electromotive force;
- Cold crank current;
- Capacity;
- Weight;
- Standard size;
- Polarity;
- Degree of charge;
- Lifetime;
- Self-discharge;
- Shelf life.
Car battery capacity
As already mentioned, battery capacity is measured in ampere-hours. This value is usually contained on the car battery sticker along with the starting current value. An example can be seen below.
What does the capacity indicated on the car battery label indicate? From it you can determine the amount of current that uniformly discharges the battery to the final voltage (10.8 volts). The duration of standard discharge cycles is 10 or 20 hours.
For example, a value of 72 Ah indicates that this car battery will be able to supply 3.6 amps of current for 20 hours. In this case, at the end of the cycle, the voltage at the terminals should be at least 10.8 volts. But it should be remembered that the same battery will not be able to carry a current of 72 amperes for 1 hour. As the current increases, the discharge time decreases, and this decrease is expressed by a power law.
One of the first to derive the formula for this dependence was Peukert, a German scientist. He derived the following formula:
Cp = I k * t, where
C p - battery capacity,
k - Peukert coefficient,
t – time.
The Peukert coefficient used in the formula is a constant value for a certain type of battery. For automobile lead-acid batteries, the Peukert number lies in the range of 1.15─1.35. This constant is determined by the nominal capacity of the battery.
As a result, a formula was derived for calculating the actual battery capacity at an arbitrary value of the discharge current:
E =En(I n /I) (p-1) , where
E n - nominal battery capacity,
E – actual battery capacity,
I n is the rated value of the discharge current at which the rated capacity is set. Current in a cycle of 10 or 20 hours. Typically this is 9 percent of E n.
Everything that was said above concerned the nominal capacity of a car battery. There is also the concept of reserve capacity. If the nominal value was determined as a result of discharge with a small current, then the reserve value shows how much the car battery will last if the generator fails. The discharge current is set to 25 amperes. Heating and lighting are taken into account here. In the event of a discharge with such a current, the reserve capacity is about two-thirds of the nominal value. If it is applied to the label of a car battery, then it is indicated in minutes.
The nominal capacity of the battery is determined by a number of technological and design characteristics. The operating conditions of the car battery also have a very strong influence. Among the primary characteristics that influence this parameter are the composition of the electrolyte, the amount of active mass, the geometry and thickness of the lead plates. The main technological characteristics that determine the size of the container are the composition and porosity of the active mass. In addition, the discharge capacity, as mentioned above, is affected by the magnitude of the discharge current and the temperature of the electrolyte.
The performance of a car battery can be assessed using the following formula:
Q = (E p /E o) * 100%, where
E p – battery capacity calculated during discharge, Ah,
E o – value calculated on the basis of its electrochemical parameters, Ah.
As follows from Faraday's law, to obtain a capacity of 1 Ah, in theory, 3.865 grams of Pb, 4.462 grams of PbO 2 and 3.659 grams of H 2 SO 4 are required. The total is about 11.986 grams per 1 Ah. But in reality, such values are impossible to achieve. It is impossible to achieve complete consumption of active substances in the ongoing chemical reaction. Only half of the active mass of the plates is available for reaction with the electrolyte. The other half simply provides the volumetric frame of the plates and the mechanical strength of the electrodes.
In real operating conditions, it turns out that the utilization rate of the active mass of the positive plate is about 50 percent, and that of the negative plate is 60 percent. Do not forget that the electrolyte is not pure sulfuric acid, but its aqueous solution (about 35 percent). Therefore, the actual consumption of materials is much higher, and the specific capacity is lower than the theoretical value.
How to check battery capacity
Some inquisitive car owners are interested in how to measure the capacity of a car battery with their own hands. Some people want to do this out of curiosity, others want to check whether the actual capacity value corresponds to what is written on the label. How to do this?
It's quite simple. All data for this has already been given above. For example, you can check the capacity of a car battery when carrying out. To do this, the following diagram is assembled.
The resistor resistance for the circuit is calculated by the formula:
Here U is the battery voltage,
I – discharge current.
The discharge current is selected depending on the capacity of the car battery and the discharge cycle (10 or 20 hours). In practice, a car light bulb of suitable power is usually used for the discharge. Using a multimeter, you can measure the exact amount of current passing in the circuit and note the time until the voltage drops to 10.8 volts. The resulting time multiplied by the current will be the actual capacity of the car battery.
