Normal battery voltage of the car. Voltage of a charged car battery

A rechargeable battery (battery) is one of the most important parts of a car. It provides electricity to the starter when the motor is started, and also is responsible for the operation of many other devices when the engine is not running: the lamps of the instrument panel and interior, the radio, the signal, the fuel pump, etc. The normal operation of all systems is possible only with a charged battery. That's why it must be serviced and loaded on time.

But often it happens quite the opposite. Come to the garage or parking lot, try to start the engine, but in response, the starter gives you either the sounds of incredible efforts to slightly crank the flywheel, or simply the clicks of the retractor relay. And in addition to everything, a lamp on the dashboard indicates the discharge of the battery.

In order not to fall into such situations, it is necessary to systematically diagnose the battery, but first let's see why it is discharged.

Causes of battery discharge

Causes, due to which there is a discharge of the battery, may be several. Here are some of them:

• The battery has completely expended its life;
• Generator malfunction;
• Current leakage;
• Increased load on the onboard electric grid;
• Unauthorized operation of electrical appliances when the engine is not running.

Why is this happening

Any battery has a certain resource, even with timely maintenance. Modern batteries, depending on operating conditions, can serve from 3 to 7 years. At the end of this period, the voltage of the car battery gradually begins to decrease. This is due to the destruction of lead plates, which, unfortunately, can not be avoided with time. Of course, you can try to restore the battery, but work the way it is new, it will not be.

In the event of a generator failure, the charging voltage of the vehicle's battery rides, falls, or is completely absent. In this case, the battery works 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 discharge. It is easily determined by means of an ammeter or a multimeter included in its mode. By measuring the current between the removed ground terminal and the negative terminal of the battery, determine the leakage value. If it is above 80 mA, you should immediately contact the service to find a leak and fix the problem.

Often the owners of cars independently install additional electrical appliances (speakers, subwoofers, lighting elements, various electronic devices) without even realizing that they exceed the amount of the network load provided for by the car's passport data. 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 tape recorder, interior lighting or other appliances that consume electricity. This inattention also causes a rapid discharge of the battery.

In time, a non-serviced battery will also never work long. Even if your car has a maintenance-free battery, you need to constantly look after it and periodically charge it.

Methods for checking the status of the battery

Determine the state of the battery in one way is impossible. Do not listen to "experts" who say that by measuring the voltage of the car battery or its current, you can conclude that it works. This is a complex process, which includes the following activities:

• Visual inspection;
• Determination of the electrolyte level;
• Determination of electrolyte density;
• Battery voltage measurement.

Visual inspection of the battery

The first thing you can do to establish the efficiency of the battery is to inspect it. Appearance is able to tell about a lot.

Mud alternating with moisture and car fluids on the terminals is an unacceptable phenomenon. It leads to the oxidation of metal parts and the loss of electrical contact. In the end, 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 you need to keep the hood clean. To do this, take an ammeter, disconnect the battery from the battery, touch one probe to one of the terminals, and simply swipe the other on the battery case. The value indicated on the ammeter screen is the self-discharge current.

Next, look at the battery case. The presence of cracks and streaks on it indicates a mechanical damage that caused the leakage of the electrolyte. If this happens, use of this battery is further impractical. When there are stains from the plugs, you need to check the amount of electrolyte in each of the cans and eliminate the cause of its pouring.

How to set the electrolyte level

Check the level is possible only in the serviced batteries. It is strongly recommended not to break the integrity of the battery-free battery case for unintended "maintenance".

If the battery is serviced, it needs to be removed, cleaned of dirt and unscrewed plugs. Measurement of the level is made using a special tube with a millimeter scale. It is lowered into the jar until it comes into contact with the upper plate of the separator, the hole from above is clamped with a finger. When pulling out, you can easily determine the level of electrolyte. It should not be less than 10 mm. If the electrolyte level is less than the specified value, you need to determine the cause of 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 spillage of the electrolyte, you need to top up the finished electrolyte. After topping up the battery, you need to recharge it.

How to determine the density of electrolyte

The main factor affecting the working voltage of the car battery is the density of the electrolyte. It can be measured only by means of a special device - a hydrometer. It is a large pipette with a rubber pear at the top, a scale and a float inside. Density measurement, of course, can also be made only in serviced batteries. But what should be its value?

The density of the electrolyte for a fully charged battery at a temperature of 20 ^° C is 1.27 g / cm ³ . When the battery is low, this indicator decreases.

Battery voltage measurement

What is the battery voltage of the car so that you can start the engine? There is no definite answer and can not be.

It is known that the voltage of a charged car battery should be 12.6-12.7 V. Depending on various conditions, this figure may vary slightly, but if the charge falls below 12 V, the battery can be considered discharged by 50%. It urgently needs to be recharged, since a deep discharge inevitably leads to sulfation of the lead plates. But even with this indicator, starting the engine is quite possible. Provided that the battery does not need repair, and the generator gives 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.

It is not difficult to measure the battery voltage. 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. Degree of battery discharge

Now let's try to understand how the basic parameters of the battery are interconnected. The voltage of the car battery directly depends on the density of the electrolyte. When the battery is discharged, the acid that is part of the (36%) electrolyte is consumed. As a consequence, its density decreases. The reverse process occurs when the battery is charged: the flow of water leads to the formation of an 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 the battery voltage versus the electrolyte density

How does the density of the electrolyte and the battery voltage depend on the ambient temperature

From car owners often hear that the battery voltage of the car in winter can be significantly reduced. Leave, they say, the car for a few days in the cold, and everything, then you will not get. That's why some of them take pictures and take the battery home.

What happens inside the battery at low temperatures and what can it lead to? In fact, the battery voltage of the car does not fall in winter. Yes, the density of the electrolyte varies, but for a charged battery it increases, and for a discharged battery it falls. In other words, if the battery is discharged, it must either be charged, or carried with itself. Otherwise, it not only can not start the engine in the frost, it can freeze the electrolyte, which will lead to rupture of the body.

Charged battery does not threaten anything like this. Yes, sometimes there are problems with starting the engine, but only because of the fact that at low temperatures, chemical processes are much slower, so the battery may not give out the power required to start. But it is enough to bring it into the heat and to withstand a little, and it will again be ready to work as before. Therefore, the normal voltage of the car battery for the winter period does not differ from the parameters for the summer.

How to charge the battery

There are four ways to charge the battery. Each of them has its advantages and disadvantages. Let's analyze them.

1. Charging method with direct current. The only drawback is the constant control over the process. Its essence lies in the fact that the charger is set to a current equal to a tenth of the nominal capacity of the battery. Charging is carried out within 20 hours. Due to the fact that the battery will charge while charging, the charging current will decrease, so it needs to be adjusted every 1.5-2 hours.
2. Charging method with constant voltage. 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 amount of the applied voltage. For example, with a continuous charge of 14.5 V for 24 hours, the battery will be charged only by 75-80%, at 15 V - about 90%, and only at 16.3-16.5 V the battery will have time to fully charge. This method is considered the safest and most effective.
3. Combined method. To charge this way you need a special charger. The process is fully automated and requires neither control nor presence. Simply connect the terminals and turn on the machine. When the normal voltage of the car battery is reached during the charging process, the device will turn off automatically.
4. Fast charging. This method is not recommended for use under normal conditions. It is used in extreme cases, when you need to charge the battery in the shortest possible time. To do this, the device sets the maximum current that the battery should charge no more than 20 minutes. Of course, we are not talking about full charging here, but it will be enough to start the engine.