How to measure the resistance of a 18650 battery with a multimeter. Selecting and using personal GPS navigators
Voltage car battery is the potential difference across the terminals. For greater accuracy, it is recommended to measure the voltage when the transients caused by the charge or discharge 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 starter car 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 battery capacity is characterized by the amount of electricity, measured in ampere-hours, received from the battery when it is discharged to the set final voltage of 10.5 volts and a temperature of 20 degrees. It is not recommended to discharge the vehicle battery below the end voltage during normal use. AT otherwise the resource of its work is sharply reduced.
The value of the battery capacity allows you to calculate the approximate time of return (or operation) of its average current to the load. The capacitance depends on the strength of the discharge current, therefore, during testing, the discharge conditions are normalized. The discharge current is set to 0.05 Cp for 20 hours of discharge 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 capacitance of the new one corresponds to the nominal value. And for a discharge current of 25 Amperes, the typical capacity of this battery is 40 Ah. Such a capacity will provide a power supply time for electrical equipment within 96 minutes.
40 Ah x 60 minutes / 25 Ampcr = 96 minutes.
The current value of 25 A was adopted in tests not 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 by 5 times relative to the nominal one. 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 scroll 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 scroll current and capacity of the 6ST-55 battery with a decrease in temperature.
With a larger capacity, a car battery also gives a greater cold scrolling current. For example, with a capacity of 55 Ah provides a current of 420-480 Amp according to EN and 250-290 Amp according to DIN, a battery with a capacity of 62 Ah provides a current of 510 Amp according to EN and 340 Amp according to DIN, and a 77 Ah battery is already 600 Amp according to EN and 360 Amp DIN.
Cold start current (Cold Cranking Amper - CCA) of a car battery, requirements of DIN 43539 T2, EN 60095-1, SAE, IEC 95-1 (IEC 95-1) standards.
The cold start current of a car battery determines its maximum starting capacity, that is, what current the battery can give at a temperature of minus 18 degrees at the end specified interval time until the battery voltage drops to the required minimum level. The DIN and EN standards provide two checks for the process of discharging a car battery to a voltage of 6 volts.
The first check is made 30 seconds after the start of the discharge, and it measures the voltage U30 of the battery, which for the DIN standard must be more than 9 Volts, and for the EN standard it must be more than 7.5 Volts. The second check is to measure the duration of the discharge T6v 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 (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
In the SAE and IEC standards, only the voltage limit U30 is defined. For ease of comparison, the cold scroll current values of a car battery can be converted from one standard to another. Recalculation of currents occurs according to the following formulas.
Isae = 1.5Idin + 40 (A)
IIec = Idin/0.85 (A)
Ien \u003d Idin / 0.6 (A)
Idin = 0.6Ien (A)
Values in the EN standard are rounded off.
— For currents less than 200 A in 10 A steps.
- 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 55 Ah VARTA battery has a DIN current of 255 amps. Using the above formulas, we get for Isae \u003d 422.5 Amps, Iiec \u003d 300 Amps, Ien \u003d 425 Amps, rounding - 420 A.
Typically, the value of the cold start current of the CCA of a car battery exceeds the numerically rated capacity by 6.5-7.5 times. The number of possible engine starts over the life of a car battery ranges from 4,000 for and low maintenance batteries to 12,000 for batteries of a special design, such as an Optima battery, according to the manufacturer.
It is believed that in one year, with moderate intensity operation, from 1,000 to 2,000 engine starts are made. Thus, the 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 normalized by each manufacturer of a car battery only for a temperature of minus 18 degrees. The manufacturer does not provide data for lower temperatures.
For a fully charged and new battery with a capacity of 50-60 Ah, the cold scroll current is in the range of 300-500 Amps. If the starter 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 battery production technologies are improving, these changes have almost no effect on the degree of reduction in their starter current at sub-zero 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 passport, but it is important for the consumer because it shows the time during which the battery will ensure the operation of the car if the car fails. At the same time, the current consumption by all vehicle systems is normalized at 25 amperes.
The reserve capacity of a car battery is defined as the period of time in minutes that 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. By 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 spin.
Based on the materials of the book "Self-tuition manual for the installation of car anti-theft protection systems."
Naiman V. S., Tikheev V. Yu.
What is the internal resistance of a battery and what is it used for?
The impedance of a lead acid battery is the sum of polarization resistance and ohmic resistance. Ohmic resistance is the sum of the resistances of the battery separators, electrodes, positive and negative terminals, connections between cells and electrolyte.
The resistance of the electrodes is influenced by their design, porosity, geometry, grid design, the state of the active substance, the presence of alloying components, the quality of the electrical contact between the grids and the coating. The resistance values of the grids of negative electrodes and spongy lead (Pb) on them are approximately the same. At the same time, the resistance of lead peroxide (PbO2), which is deposited on the positive electrode grid, is 10,000 times greater.
During the discharge of a lead-acid battery, lead sulfate (PbSO4) is released on the surface of the electrodes. This is a poor conductor, which significantly increases the resistance of the electrode plates. In addition, lead sulfate is deposited in the pores of the coating of the plates and significantly reduces the diffusion of sulfuric acid from the electrolyte into them. As a result, by the end of the discharge cycle of a lead-acid battery, its resistance increases by 2-3 times. During the charging process, lead sulfate dissolves, and the battery resistance returns to its original value.
The value of electrolyte resistance has a significant effect on the resistance of a lead-acid battery. This value, in turn, strongly depends on the concentration and temperature of the electrolyte. As the temperature decreases, the resistance of the electrolyte increases, and reaches infinity when it freezes.
At an electrolyte density of 1.225 g/cm3 and a temperature of +15 C, it has a minimum resistance value. With a decrease or increase in density, the resistance increases, which means that the internal resistance of the battery also increases.
The resistance of separators varies depending on changes in their thickness and porosity. The amount of current that flows through the battery affects the polarization resistance. A few words about polarization, and the reasons why it occurs. The first reason is that the electrode potentials change in the electrolyte and on the surface of the electrodes (double electrical layer). The second reason is that during the passage of current, the electrolyte concentration changes in the immediate vicinity of the electrodes. This leads to a change in the electrode potentials. When the circuit opens and the current disappears, the electrode potentials return to their original values.
The characteristics of lead-acid batteries include a small internal resistance compared to other types of batteries. Due to this, they can deliver a large current (up to 2 thousand amperes) in a short time. Therefore, their main field of application is starter batteries on vehicles with internal combustion engines.
It is also worth noting that the internal resistance of the battery with alternating or direct current is highly dependent on its frequency. There are a number of studies, the authors of which observed the internal resistance of a lead-acid battery at a current frequency of several hundred hertz.
How can you estimate the internal resistance of a battery?
As an example, consider a 55 Ah lead-acid car battery with a nominal voltage of 12 volts. A fully charged battery has a voltage of 12.6-12.9 volts. Let's say that a resistor with a resistance of 1 ohm is connected to the battery. Let the open battery voltage be 12.9 volts. Then the current theoretically should be 12.9 V / 1 ohm = 12.9 amps. But in reality, it will be below 12.5 volts. Why is this happening? This is explained by the fact that the ion diffusion rate in the electrolyte is not infinitely large.
On the image accumulator battery presented as a 2-pole power supply. He has electromotive force(emf), which corresponds to the open circuit voltage, and internal resistance. In the diagram, they are designated E and Rin. When the circuit closes, the battery EMF drops partly across the resistor as well as through the internal resistance itself. That is, what is happening in the circuit can be described by the following formula.
E \u003d (R + Rin) * I.
In the images below, you can see the values \u200b\u200bof the EMF of a car battery in an open circuit and the voltage when a load is connected in the form of two car bulbs connected in parallel.
As already mentioned, the internal resistance of the battery is a conditional value. A lead-acid battery is a non-linear device whose internal resistance varies with temperature, load, state of charge, electrolyte concentration, and other parameters listed above. So, for accurate calculations of the battery, discharge curves are used, and not the value of internal resistance.
However, in the calculations electrical circuits with batteries, the internal resistance value can be used. Naturally, the value of internal resistance is always taken taking into account the factors on which it depends (charge or discharge, direct or alternating current, current frequency, etc.).
So, based on the formula above, you can calculate the internal resistance of a battery with an EMF of 12.6 volts during discharge direct current 2 amps.
r \u003d (E ─ U) / I \u003d (12.9 V - 12.5 V) / 2 A \u003d 0.2 Ohm.
By the way, some charging device allow you to measure the internal resistance of a battery. For example, below you can see the value of the internal resistance of a charged car battery, measured by charging the SkyRC iMax B6 mini. True, it is not known by what principle the device calculates this value.
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If we close the plus and minus of the battery, we get short circuit current Ie = U / Re as if there is resistance inside Re. The internal resistance depends on the electrochemical processes inside the element, including the current.
If the current is too high, the battery will deteriorate, and may even explode. Therefore, do not close the plus and minus. Enough thought experiment.
the value Re can be estimated indirectly from the change in current and voltage across the load Ra. With a slight decrease in the 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 in this case decreases by dU = Re × dI . Internal resistance is determined by the formula Re = dU / dI
To evaluate the internal resistance of a battery or battery, I added a 12 ohm resistor and a toggle switch to the capacitance meter circuit (the 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 on the resistor R .
Can do a simple circuit only for measuring the internal resistance on the sample shown in the figure below. But still, it is 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 "average" value of the internal resistance will be obtained, which remains stable for a sufficiently long time.
Example for determining internal resistance
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 a mistake 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 I see the value U + dU, for example 1.227V
(3) New numbers 0.027V - and there is the desired difference dU.
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, because when you press a button start The relay does not turn on and the clock does not start. This is because the voltage on the battery 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 an annular LED lamp. This battery can be used at a lower current - to power a clock or wireless mouse. It is by the large value of internal resistance that modern chargers, like the MH-C9000, determine that the battery is faulty.
Car battery internal resistance
To assess the internal resistance of the battery, you can use a lamp from the headlight. It must be an incandescent lamp, for example, halogen, but not LED. A 60W lamp consumes a current of 5A.
At a current of 100A, more than 1 Volt should not be lost on the internal resistance of the battery. 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 lamp in parallel with the battery. Take note of the voltage. Turn off the lamp. Notice how much the voltage has increased. If, for example, the voltage increased by 0.2 Volts (Re = 0.04 Ohm), then the battery is damaged, and if by 0.02 Volts (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
Any electrical receiver has internal resistance. The concept includes ohmic resistance and polarization resistance, depends on the materials for the manufacture of internal structures, the properties of the electrolyte, the state of current conductors. The internal resistance of the battery is a variable value, it depends on the temperature, the degree of sulfation, the condition of the terminals and contacts inside the battery case. The norm is determined by extrapolating the discharge curve. The abstract value of internal resistance is not used in the calculations.
Let's figure out how to measure the internal resistance of starting acid batteries. We use a halogen car lamp with a power of 60 W, a current of 5 A as a resistance with known parameters. Provided that the losses due to internal resistance should not exceed 1%, we will take measurements.
In parallel with the battery, you need to connect a voltmeter and a lamp. Record voltage. Turn off the lamp, record the voltage. A lamp resistance of 5A should create a voltage loss of 0.05V at a current of 100A. (1V * 5A / 100A)
If, during measurements, the resistance increased to 0.05 V, the battery is good. A value greater than 0.2 V indicates that the internal resistance is high in the battery, you need to look for the cause.
The measurement of the internal measurement of a lead battery varies little from structural elements, negative electrodes, and spongy lead. But the active putty and the positive electrode resist the passage of current 10 thousand times more. With an increase in the degree of sulfation, resistance increases, with constant voltage the current drops. Upon receipt of the charging current, the crystals are destroyed, the resistance decreases.
It is important that the temperature of the electrolyte has a direct effect on the internal resistance. When the electrolyte freezes, it acts as an insulator. Ideally, the electrolytic reaction proceeds at 15 0 C and an electrolyte density of 1.25 g/cm3. An increase in temperature also negatively affects the charge-discharge permeability in the car battery. What should be the internal resistance at the moment under consideration depends on the temperature and the degree of charge of the battery.
Separately, you need to consider the resistance of the separator - gaskets between the positive and negative plates. It is not an obstacle to the movement of the dissipated electrolyte mass, but creates a resistance to polarization. A double electric layer is created on the surface, which is an obstacle to the passage of charge.
The property of starter batteries to accumulate and deliver a large current is due to the low internal resistance of this type of battery. The indicator also depends on the frequency of the supply current.
The norm of internal resistance of a new battery is 0.005 Ohm at a temperature of 15-20 0 C, but since the moment of operation, the value has been steadily increasing. What state of the device is currently possible to determine using the load plug.
Internal resistance of a car battery - table
From the internal resistance of each lead battery and battery depend specifications pulsed current and energy return time. You can approximately determine the parameter using a tool - a load fork.
However, there are other ways - indirect. Curves of dependence of electrolyte temperature and resistance, a graph of resistance increase depending on the degree of charge of the battery. This indicator can be determined by the density of the electrolyte or voltage. Therefore, there are no tables; you can check the internal resistance both from the graphs and from indirect characteristics. In this case, it should be borne in mind that the frequency of the current has a great influence on the resistance. In household analysis, tables are used for a current of 50 Hz.
Most often, as a meter of internal resistance of batteries, a load plug is used. You can use the measurement program in the Imax B6 universal charger.
18650 battery internal resistance
The 18650 form factor battery is a cylinder in which cans are spirally coiled, consisting of pairs of tapes with different poles, separated by separators. The internal filling can be nickel-cadmium, metal hydride or lithium-ion. Depending on the active pair, the batteries have different capacities and potential differences at the terminals.
What should be the internal resistance in 18650 lithium-ion batteries? Does resistance change with loss of capacitance. All this can be determined by drawing up a scheme for measurement.
Ra - active resistance 18650
Cdv is the capacitance of the electrical double layer
R0 is the charge transfer resistance at the electrolyte-electron interface
Zw is the Warburg diffusion impedance
In this case, the measurement is carried out with a current of 1000 Hz, according to international standards. This is due to the battery device, which is both a capacitor and a resistor. Standard internal resistance of new lithium batteries 18650 is about 100mΩ. This is the norm. Over time, the battery inevitably loses capacity, internal resistance increases.
Video
We offer you to watch a video material on how to practically measure the internal resistance with a special device.
