An essential characteristic for a battery is internal resistance- denoted by the letter “R”. It affects a lot, and its measurement is one of the main stages of battery diagnostics. This parameter is divided into several types. Perhaps the most significant is the internal resistance of the battery. It's helpful to understand what it means and how it is measured.
Parameter description
To begin with, it is worth saying that there is a total resistance of the battery. This is the sum of ohmic R and R polarization. At the same time, ohmic is the sum of the electrolyte resistances, connections between battery elements, negative and positive terminals, electrodes, separators.
Battery internal resistance- such R, which turns out to be a battery for the current flowing inside it. It does not matter whether the current is charging or discharging. However, it will vary in different battery elements. The elements will have their own indicator:
- electrode arrays;
- electrolyte;
- separators.
The indicator in these cells is influenced by several factors, due to which it can vary greatly between different batteries. That's why it wouldn't hurt to measure the battery's resistance.
Related factors
There is practically no difference between the performance of sponge lead and the negative electrode grid. However, the resistance of lead peroxide is 10,000 times greater than that of the positive electrode array on which it is applied.
The electrodes of the device themselves can be made in different ways, which causes differences in performance. May vary, including:
- quality of electrical contact of coating and gratings;
- electrode design;
- lattice design;
- the presence of alloying components in the battery.
The R of separators is affected by changes in porosity and thickness. For an electrolyte it depends on its temperature and concentration. If the electrolyte freezes, the indicator will reach infinity.
It must be said that whatever the internal resistance of the battery, it will depend on the frequency.
Resistance measurement
This value is conditional. It changes depending on the degree of charge of the battery, the load size, and temperatures. That is why, when making accurate calculations regarding the battery, it is customary to use not the value of internal resistance, but the so-called discharge curves.
However, there are situations when you need to find out the internal resistance car battery. For these purposes, you can use an incandescent lamp from a headlight.
This option will give a completely accurate result. For example, this could be a halogen lamp with a power of 60 watts.
A parallel connection is made to the voltmeter battery and the above lamp. Next you need to remember the voltage value. Then the lamp turns off. Naturally, after this the tension will increase. If the latter increased by no more than 0.02 volts, then the battery is in satisfactory condition. That is, internal R is no more than 0.01 Ohm.
Finding out this parameter yourself is not difficult at all. The main thing is- do not use LED lamps. The entire procedure will take a few minutes.
Experience of car enthusiasts
I never do this on my own. And in general, I rarely take care of the battery the way I should. Therefore, difficulties with ignition often arise. You have to go to car repair shops to get rid of them. I pay money, but I don’t waste my time and energy.
Igor Slabkin
Of course, you need to measure. But do not rely on absolute indicators taken from the Internet. It is much more relevant to compare new results with old ones, because they will greatly depend not only on the model, but also on natural conditions. Of course, certain frameworks and standards still exist, but they should only be taken from the official specifications presented on the device body or in its original packaging.
Kirill Semenov
I regularly measure this parameter. One day it got too big. It took me a long time to figure out the reason, and then I realized that something had happened to the coating. I didn’t understand why, but I quickly corrected it. I just replaced the element. The ignition is still fine, so you can do this.
Alexander Rasskazov
I constantly take care of my car’s battery, because I’m afraid that it won’t start in the most inappropriate situation. I measure all parameters, including this one. This is the only way to fully understand the situation and track changes. This is important for diagnosis possible problems and malfunctions.
Victor Kuznetsov
Previously, I didn’t understand how to find out what the internal resistance of a battery is. As it turned out, the procedure is very simple - certainly no more difficult than measuring the full capacity. The procedure takes only a few minutes. Only the lamps you need are not LED, but ordinary ones.
If you take a new one lithium ion battery, let's say a standard size 18650 with a nominal capacity of 2500mAh, bring its voltage to exactly 3.7 volts, and then connect it to an active load in the form of a 10-watt resistor with a nominal value of R = 1 Ohm, then what magnitude of direct current do we expect to measure through this resistor ?
What will happen there at the very first moment, until the battery practically begins to discharge? In accordance with Ohm's law, it would seem that there should be 3.7A, since i=U/R=3.7/1 = 3.7[A]. In fact, the current will be slightly less, namely in the region of I = 3.6A. Why will this happen?
The reason is that not only the resistor, but also the battery itself has a certain internal resistance, since chemical processes inside it cannot occur instantly. If you imagine a battery in the form of a real two-terminal network, then 3.7V will be its emf, in addition to which there will also be an internal resistance r, equal, for our example, to approximately 0.028 Ohm.
Indeed, if you measure the voltage across a resistor of R = 1 Ohm attached to the battery, it will turn out to be approximately 3.6 V, and 0.1 V will therefore drop at the internal resistance r of the battery. This means that if a resistor has a resistance of 1 ohm, the voltage measured across it was 3.6 V, therefore the current through the resistor is equal to I = 3.6A. Then, if u = 0.1V went to the battery, and our circuit is closed, in series, then the current through the battery is I = 3.6A, therefore, according to Ohm’s law, its internal resistance will be equal to r = u / I = 0.1/3.6 = 0.0277 Ohm.
What determines the internal resistance of a battery?
In reality, the internal resistance of batteries different types is not constant all the time. It is dynamic and depends on several parameters: on the load current, on the battery capacity, on the degree of charge of the battery, as well as on the temperature of the electrolyte inside the battery.
The higher the load current, the lower, as a rule, the internal resistance of the battery, since the charge transfer processes inside the electrolyte are more intense in this case, more ions are involved in the process, and the ions move more actively in the electrolyte from electrode to electrode. If the load is relatively small, then the intensity of chemical processes on the electrodes and in the battery electrolyte will also be less, which means the internal resistance will seem greater.
Batteries with a larger capacity have a larger electrode area, which means the area of interaction between the electrodes and the electrolyte is larger. Hence large quantity ions participate in the charge transfer process, more ions create a current. A similar principle is demonstrated - the larger the capacitance, the more charge can be used in the vicinity of a given voltage. So, the higher the battery capacity, the lower its internal resistance.
Now let's talk about temperature. Each battery has its own safe operating temperature range, within which the following applies. The higher the temperature of the battery, the faster the diffusion of ions inside the electrolyte occurs, therefore, at a higher operating temperature, the internal resistance of the battery will be lower.
First lithium batteries, which did not have protection against overheating, even exploded because of this, since the oxygen formed due to the rapid disintegration of the anode (as a result of a rapid reaction on it) was released too actively. One way or another, batteries are characterized by an almost linear dependence of internal resistance on temperature in the range of acceptable operating temperatures.
As the battery discharges, its active capacity decreases, since the amount of active substance in the plates that can still participate in creating current becomes less and less. Therefore, the current becomes less and less, and accordingly the internal resistance increases. The more charged the battery, the lower its internal resistance. This means that as the battery discharges, its internal resistance becomes greater.
4.2 - 0.22 = 3.98 Volts.
And this is a completely different matter... If we take and connect five such parallel sections in series, we will get a battery with a voltage -
Ubat=3.98V*5=19.9 Volts, capacity -
Sbat=2.2A/h*5=11A/h….
capable of delivering a current of 10 Amperes to the load....
Something like that…
P.S. ….I caught myself thinking that pleasure can also be measured in A/h…..
____________________
I agree that the method described above can lead to a large error in measuring internal resistance, but..., in fact, the absolute value of this resistance is of little interest to us - what is important to us is the method itself, which will make it possible to objectively and quickly assess the “health” of each element …Practice has shown that the resistances of elements differ significantly…, and knowing only the value of internal resistance, you can easily find “simulators”….
Measuring the internal resistance of LiFePO4 elements designed for very high discharge currents may cause some difficulties associated with the need to load them with very high currents... but I can’t say anything about this, since I practically haven’t done this....
How to measure the internal resistance of a battery
If we close the plus and minus of the battery, we get current short circuit Ie = U/Re, as if there is resistance inside Re. Internal resistance depends on the electrochemical processes inside the element, including current.
If the current is too high, the battery will deteriorate and may even explode. Therefore, do not short the plus and minus. Enough thought experiment.
Size Re can be estimated indirectly by changes in current and voltage across the load Ra. With a slight decrease in load resistance Ra to Ra‑dR, the current increases from Ia to Ia+dI. The voltage at the output of the element Ua=Ra×Ia decreases by the amount dU = Re × dI. Internal resistance is determined by the formula Re = dU / dI
To estimate the internal resistance of a battery or battery, I added a 12-ohm resistor and a toggle switch (a button is shown in the diagram below) to change the current by dI = 1.2 V / 12 Ohm = 0.1 A. At the same time, you need to measure the voltage on the battery or resistor R .
Can be done simple diagram only for measuring internal resistance according to the pattern shown in the figure below. But it’s still better to first discharge the battery a little and then measure the internal resistance. In the middle, the discharge characteristic is flatter and the measurement will be more accurate. The result is an “average” value of internal resistance, which remains stable for quite a long time.
Example of determining internal resistance
We connect the battery and voltmeter. Voltmeter shows 1.227V. Press the button: the voltmeter shows 1.200V .
dU = 1.227V – 1.200V = 0.027V
Re = dU / dI = 0.027V / 0.1A = 0.27 Ohm
This is the internal resistance of the element at a discharge current of 0.5A
The tester does not show dU, but simply U. In order not to make mistakes in the mental calculation, I do this.
(1) I press the button. The battery begins to discharge and the voltage U begins to decrease.
(2) At the moment when the voltage U reaches a round value, for example 1.200V, I press the button and immediately see the value U+dU, for example 1.227V
(3) New numbers 0.027V - and there is the desired dU difference.
As batteries age, their internal resistance increases. At some point you will find that the capacity of even a freshly charged battery cannot be measured, since when you press the button Start The relay does not turn on and the clock does not start. This happens because the battery voltage immediately drops to 1.2V or less. For example, with an internal resistance of 0.6 ohms and a current of 0.5 A, the voltage drop will be 0.6 × 0.5 = 0.3 volts. Such a battery cannot operate at a discharge current of 0.5A, which is required, for example, for a ring LED lamp. This battery can be used at a lower current to power a watch or wireless mouse. It is precisely because of the large value of internal resistance that modern charging device, like the MH-C9000, determine that the battery is faulty.
Internal resistance of a car battery
To evaluate the internal resistance of the battery, you can use a lamp from a headlight. It should be an incandescent lamp, for example, a halogen, but not an LED. A 60W lamp consumes 5A current.
At a current of 100A, the internal resistance of the battery should not lose more than 1 Volt. Accordingly, at a current of 5A, more than 0.05 Volts (1V * 5A / 100A) should not be lost. That is, the internal resistance should not exceed 0.05V / 5A = 0.01 Ohm.
Connect a voltmeter and a lamp in parallel to the battery. Remember the voltage value. Turn off the lamp. Notice how much the voltage has increased. If, say, the voltage increases by 0.2 Volt (Re = 0.04 Ohm), then the battery is damaged, and if by 0.02 Volt (Re = 0.004 Ohm), then it is working. At a current of 100A, the voltage loss will be only 0.02V * 100A / 5A = 0.4V
Internal battery resistance. What is the internal resistance of a battery? |
|
1. What is the internal resistance of a battery?Let's take a lead acid battery with a capacity of 1 A*hour and a rated voltage of 12 V. In a fully charged state, the battery has a voltage of approximately U= 13 V. What is the current I will flow through the battery if a resistor with resistance is connected to it R=1 Ohm? No, not 13 amperes, but somewhat less - about 12.2 A. Why? In their calculations, electricians are accustomed to composing electrical circuits from elements with several poles. Conventionally, one can imagine a battery as a two-terminal network with EMF (electromotive force - voltage without load) E and internal resistance r. It is assumed that part of the battery EMF drops at the load, and the other part drops at the internal resistance of the battery. In other words, it is assumed that the formula is correct: Why is the internal resistance of a battery a conditional value? Because a lead battery is a fundamentally nonlinear device and its internal resistance does not remain constant, but changes depending on the load, battery charge and many other parameters, which we will talk about a little later. Therefore, accurate calculations of battery performance must be made using the discharge curves provided by the battery manufacturer, and not the internal resistance of the battery. But to calculate the operation of circuits connected to the battery, the internal resistance of the battery can be used, each time being aware of what value we are talking about: the internal resistance of the battery when charging or discharging, the internal resistance of the battery at direct current or alternating current, and if variable, then what frequency, etc. Now, returning to our example, we can roughly determine the internal resistance of a 12 V, 1 Ah DC battery. r = (E - U) / I = (13V - 12.2V) / 1A = 0.7 Ohm. 2. How are the internal resistance of a battery and the conductivity of a battery related?By definition, conductivity is the reciprocal of resistance. Therefore, the conductivity of the battery S is the inverse of the internal resistance of the battery r. The SI unit of battery conductivity is Siemens (Sm). 3. What does the internal resistance of a battery depend on?The voltage drop across a lead battery is not proportional to the discharge current. At high discharge currents, ion diffusion |
As you know, high-capacity batteries are larger and more massive than small-capacity batteries. They have a larger working surface of the plates and more space for diffusion of electrolyte inside the battery.  Therefore, the internal resistance of high-capacity batteries is less than the internal resistance of smaller-capacity batteries. Measurements of the internal resistance of batteries at constant and alternating current show that the internal resistance of the battery is highly dependent on frequency. Below is a graph of battery conductivity versus frequency, taken from the work of Australian researchers.
At high temperatures, the rate of diffusion of electrolyte ions is higher than at low temperatures. This dependence is linear. It determines the dependence of the internal resistance of the battery on temperature. During battery discharge, the amount of active mass on the battery plates decreases, which leads to a decrease in the active surface of the plates. 4. Can the internal resistance of the battery be used to test the battery?Devices for testing batteries have been known for quite some time, the operating principle of which is based on the relationship between the internal resistance of the battery and the battery capacity. Some devices (load forks and similar devices) offer to evaluate the condition of the battery by measuring the voltage of the battery under load (which is similar to measuring the internal resistance of a battery at direct current). The use of others (alternating current battery internal resistance meters) is based on the connection of internal resistance with the state of the battery. The third type of devices (spectrum meters) allows you to compare the spectra of internal resistance of batteries running on alternating current of different frequencies and draw conclusions about the condition of the battery based on them. The internal resistance (or conductivity) of the battery itself allows only a qualitative assessment of the condition of the battery. In addition, manufacturers of such devices do not indicate at what frequency the conductivity is measured and with what current the test is performed. And, as we already know, the internal resistance of the battery depends on both frequency and current. Consequently, conductivity measurements do not provide quantitative information that would allow the user of the device to determine how long the battery will last the next time it is discharged to the load. This drawback is due to the fact that there is no clear relationship between the battery capacity and the internal resistance of the battery. The most modern battery testers are based on analyzing the oscillogram of the battery's response to a special waveform. They quickly estimate the battery capacity, which allows you to monitor the wear and aging of a lead battery, calculate the duration of the battery discharge for a given condition, and make a forecast of the remaining life of the lead battery. |
Protect the environment. Do not throw away worn-out batteries - take them to a specialized company for recycling. |
|
If we measure the voltage on the battery to which the resistor is connected, we will see that it is approximately equal to 12.2 V - the voltage on the battery has dropped due to the fact that the diffusion rate of ions in the electrolyte is not infinitely high.
electrolyte occurs in 
It follows from the graph that the internal resistance of a lead-acid battery has a minimum at frequencies of the order of hundreds of hertz.
At higher temperatures, the internal resistance of the battery is lower than at low temperatures.
Therefore, the internal resistance of a charged battery is less than the internal resistance of a discharged battery.Add to Anti-Banner
The operation of a digital camera with nickel-cadmium and nickel-metal hydride alkaline sealed cylindrical batteries of size AA pushed me to realize the need to manufacture a device to determine the internal resistance of the battery. In a digital camera, the battery operates at fairly high discharge currents - 300 - 600 mA. Practice has determined that the automation of digital cameras incorrectly determines the remaining battery capacity and turns off the camera. And batteries removed from the camera still have to be discharged in less fastidious devices: flashlights, toys, players.
Determining the internal resistance of a battery, I hope, will give me the opportunity to determine in practice the suitability of a particular battery for use in a digital camera. Advertising in this matter turned out to be a bad clue, given that the electromotive force of nickel-cadmium batteries is 1.2 volts, and the electromotive force of nickel-metal hydride batteries is 1.25 volts (according to Wikipedia).
I mainly used the methodology for measuring the internal resistance of batteries from the document - GOST R IEC 60285-2002 “Nickel-cadmium sealed cylindrical batteries”.
I used 12 ohm resistance. I assembled 2 bit circuits from them and a toggle switch. The discharge currents turned out to be about 100 mA, 300 mA. To measure the voltage across the resistances, I used an APPA93N multimeter in the 2 Volt range. I put together a diagram from what I had. I couldn't find any lower resistance resistors. I used the case from an old microcalculator. I installed the resistance on a piece of breadboard. I found out empirically that to assess the quality of power supplies, it is better to increase the discharge currents.
Diagram of an internal resistance meter for nickel-cadmium, nickel-metal hydride alkaline sealed cylindrical batteries and AA alkaline batteries:
Ready-made internal resistance meter for nickel-cadmium, nickel-metal hydride alkaline sealed cylindrical batteries and AA alkaline batteries:
The first test was nickel - metal hydride alkaline sealed cylindrical AA batteries from Pleomax with a capacity of 2300 mAh. The voltage (U1) across the battery loaded with a 12 Ohm resistor was 1.271 Volts. Using Ohm's law, we determine the current strength in the circuit (I1). The current is 0.105917 Ampere or 105.917 mA. We switch the toggle switch. The voltage (U2) across the battery loaded with a 4 Ohm resistor was 1.175 Volts. Using Ohm's law, we determine the current strength in the circuit (I2). The current is 0.29375 Ampere or 293.75 mA. Using the formula for determining the internal resistance of a battery from GOST R IEC 60285-2002 “Nickel-cadmium sealed cylindrical batteries” (Uin = U1-U2/I2-I1), we calculate it - 0.511 Ohm. I automated the calculations. To do this, I created a Wicrosoft Excel file – calculations.xlsx.
Calculations.rar
In this file, you can substitute the measured voltage values U1, U2 and your load resistance values and get the result of the calculation - the internal resistance of the accumulator or battery.
I have a small amount of batteries accumulated. I decided to test them. I entered the test results into a table.
The voltage of a car battery is the potential difference across the pole terminals. For greater accuracy, it is recommended to measure the voltage when the transients caused by the charging or discharging current have ended. Their duration can be several hours, and the voltage change can reach 0.6-1.8 Volts. Although it is generally accepted that car starter batteries have a nominal voltage of 12 Volts, in reality the voltage of a new charged battery is in the range of 12.7-13.3 Volts.
The capacity of the battery is characterized by the amount of electricity, measured in ampere-hours, received from the battery when it is discharged to a set final voltage of 10.5 Volts and a temperature of 20 degrees. During normal operation, it is not recommended to discharge a car battery below its final voltage. Otherwise, its service life is sharply reduced.
The value of the battery capacity allows you to calculate the approximate time it delivers (or operates) the average current to the load. The capacity depends on the strength of the discharge current, so during testing the discharge conditions are standardized. The discharge current is set to 0.05 Cp for a 20-hour discharge mode and 0.1 Cp for 10 hours. For a battery with a capacity of 60 Ah, it is, respectively, 3 Amperes and 6 Amperes. At such currents, the capacity of the new one corresponds to the nominal value. And for a discharge current of 25 Amps, the typical capacity of this battery is 40 Ah. This capacity will provide power to electrical equipment for 96 minutes.
40 Ah x 60 minutes / 25 Ampcr = 96 minutes.
The current value of 25 A was not adopted in the tests by chance. It is believed that this is the current consumption of the electrical equipment of a typical passenger car. With starter currents, the capacity of a car battery can drop 5 times relative to the nominal value. So, for a 6ST-55A battery with a starter current of 250 A and a temperature of minus 18 degrees, the capacity is only 10 Ah instead of 55 Ah. And yet this value will provide a total starter cranking time of 2.4 minutes.
10 Ah x 60 minutes / 250 Amps = 2.4 minutes.
The capacity of a car battery decreases very sharply at negative temperatures and already at minus 20 degrees it decreases to 40-50%
Reducing the cold cranking current and the capacity of the 6ST-55 battery as the temperature drops.
With a larger capacity, a car battery also produces a higher cold cranking current. For example, a 55 Ah capacity provides a current of 420-480 Ampere according to the EN standard and 250-290 Ampere according to DIN, a battery with a capacity of 62 Ah provides a current of 510 Ampere according to the EN standard and 340 Ampere according to DIN, and a 77 Ah battery already provides 600 Ampere according to EN and 360 Amps according to DIN.
Cold start current (Cold Cranking Ampere - CCA) of a car battery, requirements of DIN 43539 T2, EN 60095-1, SAE, IEC 95-1 (IEC 95-1).
The cold start current of a car battery determines its maximum starting capacity, that is, how much current the battery can deliver at a temperature of minus 18 degrees at the end specified interval until the battery voltage drops to the required minimum level. The DIN and EN standards provide for two checks on the process of discharging a car battery to a voltage of 6 Volts.
The first check is carried out 30 seconds from the start of the discharge, and it measures the voltage U30 of the battery, which for the DIN standard must be greater than 9 Volts, and for the EN standard - greater than 7.5 Volts. The second check consists of measuring the duration of the T6v discharge until the battery voltage reaches 6 Volts, which should be at least 150 seconds.
There are four standards, DIN 43539 T2, EN 60095-1, SAE, IEC 95-1, which define the duration of the test interval and the permissible minimum voltage of a car battery, the requirements for which are indicated in the table below
The SAE and IEC standards only define the limiting voltage value U30. For ease of comparison, the cold cranking current values of a car battery can be converted from one standard to another. Currents are recalculated using the following formulas.
Isae = 1.5Idin + 40 (A)
Iiec = Idin/0.85 (A)
Ien = Idin/0.6 (A)
Idin = 0.6Ien (A)
Values in the EN standard are rounded.
— At a current of less than 200 A in 10 A increments.
— At a current of 200-300 A in steps of 20 A (220, 240, 260, 280 A).
- At a current of 300-600 A in steps of 30 A (330, 360, 390 A, etc.).
For example, a VARTA battery with a capacity of 55 Ah has a DIN current of 255 Amperes. Using the above formulas, we get for Isae = 422.5 Ampere, Iiec = 300 Ampere, Ien = 425 Ampere, rounding - 420 A.
Typically, the cold start current of a car battery is 6.5-7.5 times higher than the nominal capacity. The number of possible engine starts over the entire service life of a car battery ranges from 4,000 for low-maintenance batteries and up to 12,000 for specially designed batteries, such as the Optima battery, according to the manufacturer.
It is believed that in one year, during operation of moderate intensity, from 1,000 to 2,000 engine starts are made. Thus, the service life of a car battery can be from 4 to 2 years. We note in view of the importance that the cold start current CCA, in accordance with the standards, is standardized by each car battery manufacturer only for a temperature of minus 18 degrees. The manufacturer does not provide data for lower temperatures.
For fully charged and new battery with a capacity of 50-60 Ah, the cold cranking current is in the range of 300-500 Amperes. If the starting current of a typical 6ST-55 battery at a temperature of plus 25 degrees is 400 Amperes, then at a temperature of minus 30 degrees it will drop to 200 A. With each new attempt at an unsuccessful start, its value will be less and less. Although production technologies batteries and are improving, but these changes had almost no effect on the degree of reduction in their starter current at negative temperatures.
Reserve capacity (RC - residual capacity) of a car battery.
The reserve capacity or residual capacity of a car battery is rarely indicated in the battery data sheet, but it is important for the consumer because it shows the time during which the battery will provide operation of the car if the car fails. At the same time, current consumption by all vehicle systems is normalized to 25 Amperes.
The reserve capacity of a car battery is defined as the period of time in minutes during which the battery can maintain a discharge current of 25 Amps until the voltage drops to 10.5 Volts. The standards do not establish a requirement for the amount of reserve capacity. For many batteries with a capacity of 55 Ah, the reserve capacity reaches 100
minutes, which is a good indicator.
Internal resistance of a car battery.
Typical internal resistance values for a new car battery are 0.005 ohms at room temperature. It consists of the resistance between the electrodes and the electrolyte and the resistance of the internal connections. Towards the end of its service life, the internal resistance of a car battery increases many times, which leads to the fact that the battery cannot crank.
Based on materials from the book “Tutorial for installing car theft protection systems.”
Naiman V. S., Tikheev V. Yu.