Battery(element) - consists of positive and negative electrodes (lead plates) and separators separating these plates, installed in a housing and immersed in an electrolyte (solution of sulfuric acid). The accumulation of energy in the battery occurs during the course of a chemical reaction of oxidation - reduction of the electrodes.
Accumulator battery consists of 2 or more series or (and) parallel sections (batteries, cells) connected to each other to provide the required voltage and current.It is able to accumulate, store and distribute electricity, provide engine start, and also power electrical appliances when the engine is not running.
Lead Acid Battery- a battery in which the electrodes are made mainly of lead, and the electrolyte is a solution of sulfuric acid.
active mass- this is an integral part of the electrodes, which undergoes chemical changes during the passage of electric current during the charge-discharge.
Electrode A conductive material capable of producing an electric current when reacting with an electrolyte.
Positive electrode (anode) - an electrode (plate) whose active mass in a charged battery consists of lead dioxide (PbO2).
Negative electrode (cathode) - an electrode whose active mass in a charged battery consists of spongy lead.
Electrode grid serves to hold the active mass, as well as to supply and remove current to it.
Separator - material used to isolate electrodes from each other.
Pole terminals serve to supply the charging current and to return it under the total voltage of the battery.
Lead -(Pb) - a chemical element of the fourth group of the periodic system of D. I. Mendeleev, serial number 82, atomic weight 207.21, valency 2 and 4. Lead is a bluish-gray metal, its specific gravity, in solid form, is 11.3 g /cm 3 decreases during melting depending on the temperature. The most ductile among metals, it rolls well to the thinnest sheet and is easily forged. Lead is easily machined and is one of the fusible metals.
Lead(IV) oxide(lead dioxide) PbO 2 is a dark brown heavy powder with a subtle characteristic smell of ozone.
Antimony is a silver-white metal with a strong luster, crystalline structure. In contrast to lead, it is a hard metal, but very brittle and easily broken into pieces. Antimony is much lighter than lead, its specific gravity is 6.7 g/cm 3 . Water and weak acids do not affect antimony. It slowly dissolves in strong hydrochloric and sulfuric acids.
Cell plugs cover the cell openings in the battery cover.
Central ventilation plug serves to block the gas outlet in the battery cover.
Monoblock- this is a polypropylene battery case, divided by partitions into separate cells.
Distilled water added to the battery to compensate for its losses as a result of water decomposition or evaporation. For topping up batteries only distilled water should be used!
Electrolyte is a solution of sulfuric acid in distilled water, which fills the free volumes of cells and penetrates into the pores of the active mass of electrodes and separators.
It is capable of conducting electric current between electrodes immersed in it. (For central Russia with a density of 1.27-1.28 g/cm3 at t=+20°C).
Slow-moving electrolyte: To reduce the danger from the electrolyte spilled out of the battery, agents are used that reduce its fluidity. Substances can be added to the electrolyte that turn it into a gel. Another way to reduce electrolyte mobility is to use glass mats as separators.
open battery
- a battery with a plug with a hole through which distilled water is added and gaseous products are removed. The hole can be provided with a ventilation system.
closed accumulator- an accumulator that is closed under normal conditions, but has a device that allows gas to be released when the internal pressure exceeds a set value. Usually, additional filling of electrolyte into such a battery is not possible.
Dry charged battery- a rechargeable battery stored without electrolyte, the plates (electrodes) of which are in a dry charged state.
Tubular (shell) plate- positive plate (electrode), which consists of a set of porous tubes filled with active mass.
Safety valve- part of the vent plug, which allows gas to escape in case of excessive internal pressure, but does not allow air to enter the accumulator.
Ampere hour (Ah)- this is a measure of electrical energy, equal to the product of current strength in amperes and time in hours (capacity).
Battery voltage- potential difference between the terminals of the battery during discharge.
Battery capacity- the amount of electrical energy given off by a fully charged battery when it is discharged until the final voltage is reached.
Internal resistance- resistance to current through the element, measured in ohms. It consists of the resistance of the electrolyte, separators and plates. The main component is the resistance of the electrolyte, which changes with temperature and sulfuric acid concentration.
Electrolyte density - e then the characteristic of a physical body, equal to the ratio of its mass to the occupied volume. It is measured, for example, in kg/l or g/cm3.
Battery Life- the useful life of the battery under given conditions.
Outgassing- gas formation in the process of electrolyte electrolysis.
self-discharge- spontaneous loss of battery capacity at rest. The self-discharge rate depends on the material of the plates, chemical impurities in the electrolyte, its density, the purity of the battery and the duration of its operation.
battery emf(electromotive force) is the voltage at the pole terminals of a fully charged battery in an open circuit, that is, in the absence of charge or discharge currents.
Cycle- one sequence of charge and discharge of the element.
The formation of gases on the electrodes of a lead battery. It is especially abundantly released in the final phase of the charge of a lead battery.
Gel batteries- these are sealed lead-acid batteries (not sealed, because a small release of gases does occur when the valves are opened), closed, completely maintenance-free (not topped up) with a gel-like acid electrolyte (Dryfit and Gelled Electrolite-Gel technologies).
AGM Technology(Absorbed Glass Mat) - absorbent fiberglass pads.
Energy return- the ratio of the amount of energy given off when the battery is discharged to the amount of energy required to charge it to its original state under certain conditions. The energy return for acid batteries under normal operating conditions is 65%, and for alkaline batteries 55 - 60%.
Specific energy- the energy given off by the battery during discharge per unit of its volume V or mass m, i.e. W \u003d W / V or W \u003d W / m. The specific energy of acid batteries is 7-25, nickel-cadmium 11-27, nickel-iron 20-36, silver-zinc 120-130 W*h/kg.
Short circuit in batteries happens when electrical connection plates of different polarity.
Battery - Battery EMF - Electromotive Force
The emf of a battery not connected to the load is on average 2 volts. It does not depend on the size of the battery and the size of its plates, but is determined by the difference in the active substances of the positive and negative plates.Within small limits, the emf can vary from external factors, of which the density of the electrolyte, i.e., more or less acid content in the solution, is of practical importance.
The electromotive force of a discharged battery with a high density electrolyte will be greater than the emf of a charged battery with a weaker acid solution. Therefore, the degree of charge of a battery with an unknown initial density of the solution should not be judged on the basis of the readings of the device when measuring the emf without a connected load.
Batteries have an internal resistance that does not remain constant, but changes during charging and discharging, depending on the chemical composition of the active substances. One of the most obvious factors in battery resistance is the electrolyte. Since the resistance of the electrolyte depends not only on its concentration, but also on temperature, the resistance of the battery also depends on the temperature of the electrolyte. As the temperature increases, the resistance decreases.
The presence of separators also increases the internal resistance of the elements.
Another factor that increases the resistance of the elements is the resistance of the active material and gratings. In addition, the state of charge affects the resistance of the battery. Lead sulfate, formed during discharge on both the positive and negative plates, does not conduct electricity, and its presence greatly increases the resistance to the passage of electric current. Sulphate closes the pores of the plates when they are in a charged state, and thus prevents the free access of the electrolyte to the active material. Therefore, when the element is charged, its resistance is less than in the discharged state.
If you close the external circuit of a charged battery, an electric current will appear. In this case, the following reactions take place:
at the negative plate
at the positive plate
where e - the charge of an electron is
For every two molecules of acid consumed, four water molecules are formed, but at the same time two water molecules are consumed. Therefore, in the end, only two water molecules are formed. Adding equations (27.1) and (27.2), we obtain the final discharge reaction:
Equations (27.1) - (27.3) should be read from left to right.
When the battery is discharged, lead sulfate is formed on the plates of both polarities. Sulfuric acid is consumed by both the positive and negative plates, while the positive plates consume more acid than the negative ones. At the positive plates, two water molecules are formed. The electrolyte concentration decreases when the battery is discharged, while it decreases to a greater extent at the positive plates.
If you change the direction of the current through the battery, then the direction of the chemical reaction will be reversed. The battery charging process will begin. The charge reactions at the negative and positive plates can be represented by equations (27.1) and (27.2), and the total reaction can be represented by equation (27.3). These equations should now be read from right to left. When charging, lead sulfate at the positive plate is reduced to lead peroxide, at the negative plate - into metallic lead. In this case, sulfuric acid is formed and the concentration of the electrolyte increases.
The electromotive force and voltage of the battery depend on many factors, of which the most important are the acid content in the electrolyte, temperature, current and its direction, and the degree of charge. The relationship between electromotive force, voltage and current can be written
san as follows:
at discharge 
where E 0 - reversible EMF; E p - EMF of polarization; R - internal resistance of the battery.
Reversible EMF is the EMF of an ideal battery, in which all types of losses are eliminated. In such a battery, the energy received during charging is fully returned when discharging. The reversible EMF depends only on the acid content in the electrolyte and temperature. It can be determined analytically from the heat of formation of the reactants.
A real battery is in conditions close to ideal if the current is negligible and the duration of its passage is also short. Such conditions can be created by balancing the battery voltage with some external voltage (voltage standard) using a sensitive potentiometer. The voltage measured in this way is called the open circuit voltage. It is close to the reversible emf. In table. 27.1 shows the values of this voltage, corresponding to the density of the electrolyte from 1.100 to 1.300 (refer to a temperature of 15 ° C) and a temperature of 5 to 30 ° C.
As can be seen from the table, at an electrolyte density of 1.200, which is common for stationary batteries, and a temperature of 25 ° C, the battery voltage with an open circuit is 2.046 V. During the discharge, the density of the electrolyte decreases slightly. The corresponding voltage drop in an open circuit is only a few hundredths of a volt. The change in open circuit voltage due to temperature change is negligible and is of more theoretical interest.
If some current passes through the battery in the direction of charge or discharge, the battery voltage changes due to an internal voltage drop and a change in EMF caused by side chemical and physical processes at the electrodes and in the electrolyte. The change in the EMF of the battery, caused by these irreversible processes, is called polarization. The main causes of polarization in the battery are the change in the electrolyte concentration in the pores of the active mass of the plates in relation to its concentration in the rest of the volume and the resulting change in the concentration of lead ions. When discharged, acid is consumed, when charged, it is formed. The reaction takes place in the pores of the active mass of the plates, and the influx or removal of acid molecules and ions occurs through diffusion. The latter can take place only if there is a certain difference in electrolyte concentrations in the region of the electrodes and in the rest of the volume, which is set in accordance with the current and temperature, which determines the viscosity of the electrolyte. A change in the electrolyte concentration in the pores of the active mass causes a change in the concentration of lead ions and EMF. During discharge, due to a decrease in the electrolyte concentration in the pores, the EMF decreases, and during charging, due to an increase in the electrolyte concentration, the EMF increases.
The electromotive force of polarization is always directed towards the current. It depends on the porosity of the plates, current and
temperature. The sum of the reversible EMF and the polarization EMF, i.e. E 0 ± E P , represents the EMF of the battery under current or dynamic EMF. When discharged, it is less than the reversible emf, and when charged, it is greater. The battery voltage under current differs from the dynamic EMF only by the value of the internal voltage drop, which is relatively small. Therefore, the voltage of an energized battery also depends on current and temperature. The influence of the latter on the battery voltage during discharge and charge is much greater than with an open circuit.
If the battery circuit is opened while discharging, the battery voltage will slowly increase to the open circuit voltage due to continued diffusion of the electrolyte. If you open the battery circuit while charging, the battery voltage will slowly decrease to the open circuit voltage.
The inequality of electrolyte concentrations in the area of the electrodes and in the rest of the volume distinguishes the operation of a real battery from an ideal one. When charged, the battery behaves as if it contained a very dilute electrolyte, and when charged, it behaves as if it contains a very concentrated one. A dilute electrolyte is constantly mixed with a more concentrated one, while a certain amount of energy is released in the form of heat, which, provided that the concentrations are equal, could be used. As a result, the energy given off by the battery during discharge is less than the energy received during charging. Energy loss occurs due to the imperfection of the chemical process. This type of loss is the main one in the battery.
Battery internal resistanceTorah. The internal resistance is made up of the resistances of the plate frame, active mass, separators and electrolyte. The latter accounts for most of the internal resistance. The resistance of the battery increases during discharge and decreases during charging, which is a consequence of changes in the concentration of the solution and the content of sulphate.
veil in the active mass. The resistance of the battery is small and noticeable only at a large discharge current, when the internal voltage drop reaches one or two tenths of a volt.
Battery self-discharge. Self-discharge is the continuous loss of chemical energy stored in the battery due to side reactions on the plates of both polarities, caused by accidental harmful impurities in the materials used or impurities introduced into the electrolyte during operation. Of greatest practical importance is self-discharge caused by the presence in the electrolyte of various metal compounds that are more electropositive than lead, such as copper, antimony, etc. Metals are released on negative plates and form many short-circuited elements with lead plates. As a result of the reaction, lead sulfate and hydrogen are formed, which is released on the contaminated metal. Self-discharge can be detected by slight outgassing at the negative plates.
On the positive plates, self-discharge also occurs due to the normal reaction between base lead, lead peroxide and electrolyte, which results in the formation of lead sulfate.
Self-discharge of the battery always occurs: both with an open circuit, and with discharge and charge. It depends on the temperature and density of the electrolyte (Fig. 27.2), and with an increase in the temperature and density of the electrolyte, self-discharge increases (the loss of charge at a temperature of 25 ° C and an electrolyte density of 1.28 is taken as 100%). The capacity loss of a new battery due to self-discharge is about 0.3% per day. As the battery ages, self-discharge increases.
Abnormal plate sulfation. Lead sulfate is formed on plates of both polarities with each discharge, as can be seen from the discharge reaction equation. This sulfate has
fine crystalline structure and charging current is easily restored into lead metal and lead peroxide on plates of the appropriate polarity. Therefore, sulfation in this sense is a normal phenomenon that is an integral part of battery operation. Abnormal sulfation occurs if batteries are over-discharged, systematically undercharged or left in a discharged state and inactive for a long time, and also if they are operated with excessively high electrolyte density and at high temperatures. Under these conditions, fine crystalline sulfate becomes denser, crystals grow, greatly expanding the active mass, and are difficult to recover when charged due to high resistance. If the battery is inactive, temperature fluctuations contribute to the formation of sulfate. As the temperature rises, small sulfate crystals dissolve, and as the temperature decreases, the sulfate slowly crystallizes out and the crystals grow. As a result of temperature fluctuations, large crystals are formed at the expense of small ones.
In sulfated plates, the pores are clogged with sulfate, the active material is squeezed out of the grids, and the plates often warp. The surface of sulfated plates becomes hard, rough, and when rubbed
The material of the plates between the fingers feels like sand. The dark brown positive plates become lighter, and white spots of sulfate appear on the surface. Negative plates become hard, yellowish gray. The capacity of the sulfated battery is reduced.
Beginning sulfation can be eliminated by a long charge with a light current. With strong sulfation, special measures are necessary to bring the plates back to normal.
Battery voltage, along with the capacity and density of the electrolyte, allows you to draw a conclusion about the condition of the battery. By voltage car battery one can judge the degree of its charge. If you want to be aware of the status of your battery and take proper care of it, then you definitely need to learn how to control the voltage. What's more, it's quite easy. And we will try to explain in an accessible way how this is done and what tools are needed.
First you need to decide on the concepts of voltage and electromotive force (EMF) of a car battery. EMF ensures the flow of current through the circuit and provides a potential difference at the terminals of the power supply. In our case, this is a car battery. The battery voltage is determined by the potential difference.
EMF is a value that is equal to the work expended on moving a positive charge between the terminals of a power source. The values of voltage and electromotive forces are inextricably linked. If there is no electromotive force in the battery, then there will be no voltage at its terminals. It should also be said that voltage and EMF exist without the passage of current in the circuit. In the open state, there is no current in the circuit, but an electromotive force is still excited in the battery and there is voltage at the terminals.
Both quantities, emf and car battery voltage, are measured in volts. It is also worth adding that the electromotive force in a car battery arises due to the flow of electrochemical reactions inside it. The dependence of EMF and battery voltage can be expressed by the following formula:
E = U + I*R 0 where
E is the electromotive force;
U is the voltage at the battery terminals;
I is the current in the circuit;
R 0 - internal resistance of the battery.
As can be understood from this formula, the EMF is greater than the battery voltage by the amount of voltage drop inside it. In order not to fill your head with unnecessary information, let's put it simply. The electromotive force of the battery is the voltage at the battery terminals without taking into account the leakage current and external load. That is, if you remove the battery from the car and measure the voltage, then in such an open circuit it will be equal to the EMF.
Voltage measurements are made with instruments such as a voltmeter or multimeter. In a battery, the EMF value depends on the density and temperature of the electrolyte. With an increase in the density of the electrolyte, the voltage and EMF also increase. For example, at an electrolyte density of 1.27 g / cm 3 and a temperature of 18 C, the battery bank voltage is 2.12 volts. And for a battery consisting of six cells, the voltage value will be 12.7 volts. This is the normal voltage of a car battery that is charged and not under load.
Normal car battery voltage
The voltage on the car battery should be 12.6-12.9 volts if it is fully charged. Measuring the battery voltage allows you to quickly assess the degree of charge. But the real condition and deterioration of the battery by voltage cannot be known. To get reliable data on the state of the battery, you need to check its real and carry out a test under load, which will be discussed below. We advise you to read the material on how.
However, with the help of voltage, you can always find out the state of charge of the battery. Below is a table of the state of charge of the battery, which shows the voltage, density and freezing point of the electrolyte, depending on the battery charge.
| The degree of battery charge,% | ||||
|---|---|---|---|---|
| Electrolyte density, g/cm. cube (+15 gr. Celsius) | Voltage, V (in the absence of load) | Voltage, V (with a load of 100 A) | The degree of battery charge,% | Freezing point of electrolyte, gr. Celsius |
| 1,11 | 11,7 | 8,4 | 0 | -7 |
| 1,12 | 11,76 | 8,54 | 6 | -8 |
| 1,13 | 11,82 | 8,68 | 12,56 | -9 |
| 1,14 | 11,88 | 8,84 | 19 | -11 |
| 1,15 | 11,94 | 9 | 25 | -13 |
| 1,16 | 12 | 9,14 | 31 | -14 |
| 1,17 | 12,06 | 9,3 | 37,5 | -16 |
| 1,18 | 12,12 | 9,46 | 44 | -18 |
| 1,19 | 12,18 | 9,6 | 50 | -24 |
| 1,2 | 12,24 | 9,74 | 56 | -27 |
| 1,21 | 12,3 | 9,9 | 62,5 | -32 |
| 1,22 | 12,36 | 10,06 | 69 | -37 |
| 1,23 | 12,42 | 10,2 | 75 | -42 |
| 1,24 | 12,48 | 10,34 | 81 | -46 |
| 1,25 | 12,54 | 10,5 | 87,5 | -50 |
| 1,26 | 12,6 | 10,66 | 94 | -55 |
| 1,27 | 12,66 | 10,8 | 100 | -60 |
We advise you to periodically check the voltage and charge the battery as needed. If the voltage of the car battery drops below 12 volts, it must be recharged from the mains. charger. Its operation in this state is highly discouraged.
Battery operation in a discharged state leads to an increase in sulphation of the plates and, as a result, a drop in capacity. In addition, it can lead to deep discharge, which for calcium batteries like death. For them, 2-3 deep discharges is a direct path to a landfill.
Well, now about what kind of tool a motorist needs to control the voltage and condition of the battery.
Car Battery Voltage Monitoring Tools
Now that you know what normal car battery voltage is, let's talk about measuring it. To control the voltage, you need a multimeter (also called a tester) or a regular voltmeter.
To measure voltage with a multimeter, you need to switch it to voltage measurement mode, and then attach the probes to the battery terminals. The battery must be removed from the car or the terminals removed from it. That is, measurements are taken on an open circuit. The red probe goes to the positive terminal, the black one to the negative terminal. The display will show the voltage value. If you mix up the probes, nothing bad will happen. Just a multimeter will show a negative voltage value. Read more about the article at the link provided.
There is also such a device as a load fork. They can also measure voltage. To do this, the load plug has a built-in voltmeter. But much more interesting for us is that the load plug allows you to measure the voltage of the battery in a closed circuit with resistance. Based on these readings, you can judge the state of the battery. In fact, the load fork creates an imitation of starting a car engine.
To measure the voltage under load, connect the terminals of the load plug to the battery terminals and turn on the load for 5 seconds. At the fifth second, look at the readings of the built-in voltmeter. If the voltage dipped below 9 volts, then the battery has already failed and should be replaced. Of course, provided the battery is fully charged and in an open circuit it produces a voltage of 12.6-12.9 volts. On a working battery, when a load is applied, the voltage will first drop somewhere up to 10-10.5 volts, and then begin to grow slightly.
What should be remembered?
In conclusion, here are some tips that will save you from mistakes when operating the battery:
- periodically measure the battery voltage and regularly (once every 3 months) recharge it from a mains charger;
- keep the alternator, wiring and voltage regulator of the car in good condition to properly charge the battery when traveling. The value of the leakage current must be checked regularly. and its measurement are described in the article by reference;
- check the density of the electrolyte after charging and refer to the table above;
- keep the battery clean. This will reduce the leakage current.
Attention! Never short-circuit the terminals of a car battery. The consequences will be sad.
That's all I wanted to say about the voltage of the car battery. If you have additions, corrections and questions, write them in the comments. Happy battery life!
Published inBatteries are filled with sulfuric acid and produce explosive gases (hydrogen and oxygen) during the normal charge-discharge cycle. To avoid personal injury or vehicle damage, always follow the following safety instructions:
- Before working on any electrical components of the vehicle, disconnect the power cable from the negative battery terminal. When the negative power cable is disconnected, all electrical circuits in the vehicle will be open, which will ensure that any electrical component is not accidentally shorted to ground. An electrical spark creates a potential risk of injury and fire.
- Any work related to the battery must be carried out with safety goggles.
- Wear protective clothing to protect against contact with the sulfuric acid filled in the battery.
- Do not violate the safety regulations specified in the maintenance procedures when handling equipment used for maintenance and testing of batteries.
- It is strictly forbidden to smoke or use open flames in the immediate vicinity of the battery.
Battery maintenance
Current Maintenance battery cleaning consists in checking the cleanliness of the battery case and, if necessary, adding clean water to it. All battery manufacturers recommend the use of distilled water for this purpose, but if this is not available, clean drinking water with a low salt content can be used. Since water is the only consumable battery component, do not add acid to the battery. Part of the water from the electrolyte evaporates during the process of charging and discharging the battery, but the acid contained in the electrolyte remains in the battery. Do not overfill the battery with electrolyte, because in this case, the normal bubbling (gas formation) that occurs in the electrolyte during battery operation will lead to electrolyte leakage, causing corrosion of the battery terminals, its mounting brackets and the pallet. Batteries should be filled with electrolyte to a level approximately one and a half inches (3.8 cm) below the top of the filler neck.
The contacts of the power cables connected to the battery and the terminals of the battery itself must be inspected and cleaned to avoid a voltage drop on them. One of the most common reasons an engine won't start is loose or corroded contacts in the power cables connected to the battery terminals.
Rice. Heavily corroded battery terminal
Rice. This power cable connected to the battery was found to be heavily corroded under the insulation. Although corrosion had eroded through the insulation, it remained unnoticed until the cable was carefully examined. This cable needs to be replaced
Rice. Carefully check all battery terminals for signs of corrosion. In this vehicle, two power cables are connected to the positive battery terminal with a long bolt. This is a common cause of corrosion that causes electrical start failure.
Battery EMF measurement
Electromotive force(EMF) is the potential difference between the positive and negative electrodes of the battery when the external circuit is open.
The value of the EMF depends mainly on the electrode potentials, i.e. on the physical and chemical properties of the substances from which the plates and electrolyte are made, but does not depend on the size of the battery plates. The EMF of an acid battery also depends on the density of the electrolyte.
Electromotive force measurement(EMF) of the battery with a voltmeter is in a simple way determining the degree of its charge. The EMF of the battery is not an indicator that guarantees the performance of the battery, but this parameter characterizes the condition of the battery more fully than just examining it. The battery, which appearance quite functional, in fact, it may not be as good as it seems.
This test is called voltage measurement in mode idle move(checking the EMF) of the battery because the measurement is carried out at the battery terminals without a load connected to it, at zero current consumption.
- If the test is performed immediately after the end of the battery charging or in the car at the end of the trip, before the measurement, it is necessary to free the battery from the polarization EMF. The polarization emf is an increased, compared to normal, voltage that occurs only on the surface of the battery plates. The polarization emf disappears quickly when the battery is under load, so it does not give an accurate assessment of the state of charge of the battery.
- To release the battery from the polarization EMF, turn on the headlights in high beam mode for one minute, and then turn them off and wait a couple of minutes.
- With the engine and all other electrical equipment turned off, with the doors closed (so that the interior lights are turned off), connect a voltmeter to the battery terminals. Connect the red, positive, wire of the voltmeter to the positive terminal of the battery, and the black, negative, wire to its negative terminal.
- Record the voltmeter reading and compare it with the battery charge chart. The table below is suitable for evaluating the state of charge of a battery by EMF value at room temperature - 70°F to 80°F (21°C to 27°C).
Table
| Battery EMF (V) | Degree of charge |
| 12.6V and above | 100% charged |
| 12,4 | 75% charged |
| 12,2 | 50% charged |
| 12 | 25% charged |
| 11.9 and below | discharged |
Rice. The voltmeter shows the battery voltage one minute after the headlights are turned on (a). After turning off the headlights, the voltage measured at the battery quickly recovered to 12.6 V (b)
NOTE
If the voltmeter gives a negative reading, then either the battery is charged in reverse polarity (and then must be replaced), or the voltmeter is connected to the battery in reverse polarity.
Battery voltage measurement under load
One of the most accurate ways to determine battery health is to measure the battery voltage under load. Most automotive battery start and charge testers use a carbon rheostat as a battery load. The load parameters are determined by the nominal capacity of the tested battery. The nominal capacity of a battery is the amount of starting current that the battery can provide at 0°F (-18°C) for 30 seconds. Previously, the characteristic of the nominal capacity of batteries in ampere-hours was used. Measurement of the battery voltage under load is carried out at a discharge current value equal to half of the rated CCA current of the battery or three times the rated battery capacity in ampere-hours, but not less than 250 amperes. The measurement of the battery voltage under load is carried out after checking the degree of its charge using the built-in hydrometer or by measuring the EMF of the battery. The battery must be at least 75% charged. An appropriate load is connected to the battery and after 15 seconds of battery operation under load, the voltmeter readings are recorded with the load connected. If the battery is good, then the voltmeter reading should remain above 9.6 V. Many battery manufacturers recommend measuring twice:
- the first 15 seconds of battery operation under load are used to release the polarization EMF
- the second 15 seconds - to get a more reliable assessment of the condition of the battery
Between the first and second cycles under load, a delay of 30 seconds must be made to give the battery time to recover.
Rice. Bear Automotive's Automotive Battery Starting and Charging Tester automatically puts the battery under test on load for 15 seconds to remove polarization EMF, then disconnects the load for 30 seconds to restore the battery, and reconnects the load for 15 seconds. seconds. The tester displays information about the battery status
Rice. Sun Electric VAT 40 tester (Model 40 voltammeter) connected to a battery for load testing. The operator, using the load current regulator, sets the value of the discharge current, equal to half the nominal CCA current of the battery, according to the ammeter reading. The battery runs under load for 15 seconds and after this time interval, the battery voltage, measured with the load connected, must be at least 9.6 V
NOTE
Some battery charge and health testers measure the capacity of the battery. Follow the test procedure specified by the test equipment manufacturer.
If the battery fails the load test, recharge it and retest. If the second test fails, the battery must be replaced.
Charging the battery
If the battery is heavily discharged, it must be recharged. Charging the battery, in order to avoid damage due to overheating, is best done in the standard charging mode. Explanations regarding the standard battery charging mode are shown in the figure.
Rice. This battery charger is set to charge the battery with a rated charging current of 10 A. Charging the battery in the standard mode, as shown in the photo, does not affect the battery as much as the boost charge mode, which does not prevent the battery from overheating and warping of battery plates
It must be remembered that it may take eight hours or more to charge a completely discharged battery. Initially, it is necessary to maintain the charging current at a level of about 35 A for 30 minutes in order to facilitate the start of the battery charging process. In the accelerated charging mode, the battery is heated up and the risk of warping of the battery plates increases. Boost charging also causes increased gas generation (release of hydrogen and oxygen), which creates a health hazard and a fire hazard. The battery temperature should not exceed 125°F (52°C, battery hot to the touch). As a rule, it is recommended to charge rechargeable batteries with a charging current equal to 1% of the CCA current rating.
- Boost charge mode - 15A maximum
- Standard charge mode - 5A maximum
It can happen to anyone!
Owner Toyota car disconnected the battery. After connecting a new battery, the owner noticed that on dashboard the yellow airbag warning light came on and the radio was disabled. The owner purchased a used car from a dealer and did not know the secret four-digit code needed to unlock the radio. Forced to find a way to solve this problem, he randomly tried to enter three different four-digit numbers in the hope that one of them would fit. However, after three unsuccessful attempts, the radio turned off completely.
The frustrated owner turned to the dealer. It cost over $300 to fix the problem. To reset the airbag alarm, a special device was required. The radio had to be taken out of the car and sent out of state to an authorized service center and reinstalled in the car upon return.
Therefore, before disconnecting the battery, be sure to coordinate this with the car owner - you must make sure that the owner knows the secret code for turning on the encoded radio, which is simultaneously used in the car's security system. It may be necessary to use the radio's memory backup device when the battery is disconnected.
Rice. Here's a good idea. The technician made a memory backup power supply from an old rechargeable flashlight and a cable with an adapter to the cigarette lighter socket. He simply connected the wires to the battery terminals of his rechargeable flashlight. The flashlight battery is more convenient to use than a conventional 9-volt battery - in case someone comes up with the idea of opening a car door at a time when the memory backup power source is connected to the circuit. A 9-volt battery, which has a small capacity, would quickly be discharged in this case, while the capacity of the flashlight battery is large enough to provide the necessary memory power even when the interior lighting is turned on.