The battery (battery) is one of the most important components of the car. It provides electric power to the starter when the motor starts, and is also responsible for the operation of many other devices when the engine is idle: backlight lamps for the instrument panel and interior, radio, signal, fuel pump, etc. Normal operation of all systems is possible only with a charged battery. That is why it must be serviced and charged on time.
But often the opposite happens. You come to the garage or to the parking lot, trying to start the engine, but in response the starter gives you either the sounds of his incredible efforts to turn the flywheel at least a little, or just clicks on the retractor relay. And in addition to everything, a lamp is lit on the dashboard, indicating a low battery.
In order not to fall into such situations, it is necessary to systematically diagnose the battery, but first, let's figure out why it discharges.
Reasons for low battery
There may be several reasons for the battery to discharge. Here are some of them:
- the battery has completely exhausted its resource;
- generator malfunction;
- current leakage;
- increased load on the electrical system;
- unauthorized operation of electrical appliances with the engine off.
Why is this happening
Any battery has a certain resource, even with timely maintenance. Modern batteries, depending on operating conditions, can last from 3 to 7 years. After this period, the car battery voltage gradually begins to decrease. This is due to the destruction of lead plates, which, unfortunately, can not be avoided over time. Of course, you can try to restore the battery, however, it will not work like the new one.
In case of generator malfunctions, the vehicle’s battery charging voltage jumps, drops or is completely absent. In this case, the battery operates in emergency mode, which can lead not only to its discharge, but also to its failure.
Current leakage is one of the main causes of battery drain. It is easily determined using an ammeter or multimeter included in its mode. By measuring the current between the removed ground terminal and the negative terminal of the battery, we determine the amount of leakage. If it is above 80 mA, you should immediately contact the service to find the leak and fix the problem.
Often, car owners themselves install additional electrical appliances (speakers, subwoofers, lighting elements, various electronic devices), without even realizing that they significantly exceed the network load value provided for by the passport data of the car. This inevitably leads to the fact that the generator ceases to cope with this load, and part of it is blocked by the battery.
It happens that unlucky drivers, sometimes leaving the car, simply forget to turn off the dimensions, radio, interior lighting or other devices that consume electricity. Such inattention also causes the battery to drain quickly.
A battery that is not serviced on time will also never work for a long time. Even if an unattended battery is installed in your car, you need to constantly look after it and periodically charge it.
Ways to check battery status
It is impossible to determine the state of the battery in one way. You should not listen to “specialists” who claim that by measuring the voltage of the car’s battery or its current, we can conclude that it is working. This is a comprehensive process, including the following activities:
- visual inspection;
- determination of electrolyte level;
- determination of electrolyte density;
- battery voltage measurement.
Visual inspection of the battery
The first thing you can do to establish the battery’s performance is to inspect it. Appearance is able to tell a lot.
Dirt mixed with moisture and automotive fluids at the terminals is not permitted. It leads to the oxidation of metal parts and the loss of electrical contact. As a result, at best we can get self-discharge, at worst - a short circuit. If the battery is dirty, do not be lazy to check the self-discharge current to make sure that it is necessary to maintain cleanliness under the hood. To do this, take an ammeter, disconnect the wires from the battery, touch one probe to one of the terminals, and simply slide the other along the battery case. The value indicated on the screen of the ammeter will be the self-discharge current.
Next, take a look at the battery case. The presence of cracks and sag on it indicates mechanical damage, which caused the leakage of electrolyte. If this happens, it is not practical to use this battery further. When there are drips from under the plugs, it is necessary to check the amount of electrolyte in each of the cans and eliminate the cause of its pouring.
How to set the electrolyte level
Checking the level is possible only in serviced batteries. It is strongly discouraged to violate the integrity of the maintenance-free battery case for unintended “maintenance”.
If the battery is serviced, it must be removed, cleaned of dirt and unscrew the plugs. Level measurement is carried out using a special tube with a millimeter scale. It is lowered into the jar until it contacts the top plate of the separator, the hole on the top is clamped with a finger. When pulled out, you can easily determine the electrolyte level. It should not be less than 10 mm. If the electrolyte level is less than the specified value, it is necessary to determine the reason for its decrease. Usually it falls due to the usual boiling and evaporation. In this case, you just need to add distilled water to the jars.
If the level has decreased due to electrolyte spills, you need to add the finished electrolyte. After refilling, the battery must be recharged.
How to determine the density of electrolyte
The main factor affecting the operating voltage of a car’s battery is the density of the electrolyte. It can be measured only with the help of a special device - a hydrometer. It is a large dropper with a rubber bulb at the top, a scale and a float inside. Density measurement, of course, can also be done only in serviceable batteries. But what should be its size?
The electrolyte density for a fully charged battery at a temperature of 20 0 C is 1.27 g / cm 3 . When the battery is low, this indicator decreases.
Battery voltage measurement
What voltage must the car battery have to be able to start the engine? There is no definite answer here and cannot be.
It is known that the voltage of a charged car battery should be 12.6-12.7 V. Depending on various conditions, this indicator may vary slightly, but if the charge drops below 12 V, the battery can be considered discharged by 50%. It urgently needs to be charged, since deep discharge will inevitably lead to sulfation of lead plates. But even with such an indicator, starting the engine is quite possible. Provided that the battery does not need repair, and the generator provides charging, you can safely ride. But if the voltage does not exceed 11.6 V, the battery is considered completely discharged, and its further operation without diagnostics and charging is impossible.
Measuring the battery voltage is easy. To do this, you need to disconnect the wires from it, and connect the terminals of the voltmeter or multimeter in its mode to the terminals, setting a limit of 20 V.
What determines the voltage of the car battery. Battery discharge level
Now let's try to figure out how the main battery parameters are interconnected. The voltage of the car battery depends on the density of the electrolyte. When the battery is discharged, it consumes acid, which is part (36%) of the electrolyte. As a result, its density decreases. The reverse process occurs when charging the battery: water consumption leads to the formation of acid, as a result of which the density of the electrolyte increases.
The voltage of a charged car battery (12.7 V) corresponds to a density of 1.27 g / cm 3 . When one of the indicators decreases, the other decreases.
Table of battery voltage versus electrolyte density
The density of the electrolyte, g / cm 3 | Vehicle battery charge voltage, V | The degree of discharge of the battery,% |
1.27 | 12.7 | 0 |
1.25 | 12.54 | 13.5 |
1.23 | 12,42 | 25.0 |
1,2 | 12.24 | 45.0 |
1.15 | 11.94 | 75.0 |
1,11 | 11.6 | 100.0 |
How does electrolyte density and battery voltage depend on ambient temperature?
Car owners often hear that the voltage of a car’s battery in winter can be significantly reduced. Leave, they say, the car for several days in the cold, and that's it, then you won’t start. That is why some of them remove and take the battery home.
What happens inside the battery at low temperatures and what can it lead to? In fact, the voltage of the car’s battery does not drop in winter. Yes, the density of the electrolyte changes, but for a charged battery it grows, and for a discharged battery it drops. In other words, if the battery is discharged, you must either charge it or carry it with you. Otherwise, it will not only not be able to start the engine in frost, it may freeze the electrolyte, which will lead to rupture of the housing.
A charged battery is not in danger. Yes, sometimes there are problems with the engine starting, but only due to the fact that at low temperatures chemical processes are much slower, so the battery may not produce the required power to start. But it’s enough to bring it into the heat and withstand a little, and again it will be ready to work as before. Therefore, the normal voltage of a car’s battery for the winter period is no different from that for summer.
How to charge the battery
There are four ways to charge the battery. Each of them has its own advantages and disadvantages. Let's take them apart.
- DC charging method. The only drawback is the constant control over the process. Its essence lies in the fact that a current equal to a tenth of the nominal capacity of the battery is set on the charger. Charging takes 20 hours. Due to the fact that the battery, while charging, will gain current, the charging current will decrease, so it needs to be adjusted every 1.5-2 hours.
- Constant voltage charging method. This method also involves a charging process during the day. Here it is necessary to take into account that the charging voltage of the car battery will depend on the magnitude of the supplied voltage. For example, with a continuous charge of 14.5 V for 24 hours, the battery will charge only 75-80%, at 15 V - about 90%, and only with an indicator of 16.3-16.5 V the battery will be able to fully charge. This method is considered the safest and most effective.
- The combined method. To charge in this way you will need a special charger. The process is fully automated and requires neither control nor presence. Simply connect the terminals and turn on the device. When the normal battery voltage of the car is reached during charging, the device will turn off automatically.
- Fast charge. This method is not recommended for use under normal conditions. It is used in extreme cases when the battery needs to be charged in the shortest possible time. To do this, the maximum current is set on the device, by which the battery should be charged for no more than 20 minutes. Of course, we are not talking about a full charge, but this will be enough to start the engine.