Maintaining the health of the car battery is an important component of ensuring the smooth operation of all electronics. The battery provides not only the start of the engine, but also performs a number of other functions: it stabilizes the voltage in the car's network, maintains the performance of electrical equipment when the engine is turned off, ensures the safety of the settings of the on-board computer, multimedia system, clock, climate system and other high-tech devices.

Obviously, to perform all tasks, it is necessary to maintain the battery charge and recharge it in a timely manner before it ends. A variety of indicators help to constantly monitor the parameter.

Built-in indicator

Modern batteries that use liquid electrolyte, as a rule, are equipped with a built-in float indicator of the battery charge. It is able to relatively accurately indicate the electrolyte level and the state of charge of the battery.

When charging the power source, the density of the electrolyte in it increases, the float (usually green) rises above the liquid level and is visible through the window (the charge is more than 65%). If it sinks in liquid, then the charge level is insufficient and the density of the float is less than that of the liquid mixture. The third option is to reduce the amount of electrolyte in the battery. In this case, the indicator (float) is not visible at all in the window, like the liquid, but a black tube is visible. So, depending on the color of the indicator (green, black or yellow / colorless), it is possible to reliably determine the degree of charge and the amount of liquid electrolyte.

Such a built-in battery indicator is not highly accurate, however, it is convenient and helps to determine important points in the health of the power source. You can refine them, if necessary, with the help of special devices. By the way, before considering the built-in indicator, it is recommended to lightly tap on it. So, when a car moves in a tube with a float, bubbles can form that can support the float on the surface, and by tapping the balloons rise up and do not interfere with seeing the real indicator.

Cabin indicator

Modern cars contain a huge number of electrical appliances that are connected to the network of the car. The battery not only ensures their performance while the engine is turned off, but also maintains all settings and instrument settings. Obviously, such a load on the battery gradually "eats" the degree of its charge. At the same time, it is paradoxical that many car models are not equipped with an elementary indicator of the battery charge level in the cabin. Therefore, it must be checked manually, which is not very convenient, especially in winter.

A simple indicator that you can simply assemble with your own hands will help to solve the problem in some way. Another undoubted advantage of this design is its low price. In comparison with cheap Chinese copies, the build quality will depend only on the skill and accuracy of the master. In general, if you have the minimum basic skills, then it will not be difficult to assemble an excellent indicator for checking the battery charge with your own hands.

The scheme of the device is quite simple.

The battery charge level will be shown by colored LEDs. You can choose any combination of colors. In the presented diagram, the diodes correspond to the following charge:

• green - 13 V and above;
• blue - 11-13 V;
• red - 6-11 V.

To assemble the indicator, you will need the following items:

• Resistors (2 pcs. 1KΩ, 3 - 220 Ω, 1 - 2KΩ);
• Transistors (VS547 and VS557);
• Three RGB LEDs of different colors;
• Two zener diodes (for 9.1 and 10 v).

Having tried on all the elements to the board, you need to cut out the corresponding fragment. It is better to output LEDs on wires, and not solder them directly to the board, so that you can then conveniently install them under the dashboard. Obviously, it is better to immediately provide a place in the car for it and proceed from this location to determine the length of the wires than after the assembly is completed.

The presented scheme, which allows you to assemble an LED battery indicator with your own hands, eliminates the need to manually check and monitor the status of the power source. Reliable and accurate readings will be displayed directly in the selected place on the panel and inform the car owner about the need to recharge the battery.

The circuit for assembling a battery charge indicator with your own hands was tested using a power supply with the ability to adjust the voltage. The only observed failure can be considered a slow switching from blue and red diodes. Rather, this is due to the fact that the tester did not respond to the rapid change in voltage. At the same time, a smooth decrease in the voltage at the battery terminals will ensure a fairly stable operation of the do-it-yourself device, which allows you to recharge the battery until the charge is complete.

What are car battery indicators

The battery plays a key role in starting a car engine. And how successful this launch will be depends largely on the degree of charge of the battery. And how many of us control the level of battery charge? It is called, answer yourself this question. Therefore, there is a high probability that one day you will not start the car due to a dead battery. Actually, the very check of the degree of charge is simple. You just need to periodically measure with a multimeter or voltmeter. But it would be much more convenient to have a simple indicator showing the state of charge of the battery. These indicators will be discussed in this article.

Technology does not stand still, and automotive manufacturers are trying their best to make car travel and its maintenance as comfortable as possible. Therefore, on modern cars in the on-board computer, among other functions, you can find data on the voltage of the battery. But such opportunities are not available on all cars. On older cars, there may be an analog voltmeter, which makes it difficult to understand what condition the battery is in. For beginners in the automotive business, we recommend that you familiarize yourself with the material on.

Therefore, all kinds of battery charge indicators began to appear. They began to be made, both on batteries in the form of hydrometers, and additional information displays on the car.

Such charge indicators are also available from third-party manufacturers. They are easy enough to place somewhere in the cabin and connect to the on-board network. In addition, on the Internet there are simple schemes for making charge indicators with your own hands.

Built-in battery charge indicator

Built-in charge indicators can be found mainly on. This is a float indicator, which is also called a hydrometer. Let's see what it consists of and how it works. In the photo below you can see how this indicator looks on the battery case.

And this is what it looks like when you take it out of the battery.

Schematically, the device of the built-in battery indicator can be represented as follows.

The principle of operation of most hydrometers is as follows. The indicator can show three different positions in the following situations:

• As the battery charges, the density of the electrolyte increases. In this case, the float in the form of a green ball rises up the tube and becomes visible through the light guide into the indicator eye. Typically, a green ball pops up when the battery is 65 percent or more charged;
• If the ball sinks in the electrolyte, then the density is below normal and the battery charge is insufficient. At this moment, a black indicator tube will be visible in the "peephole" of the indicator. This will indicate the need for charging. In some models, a red ball is added, which rises through the tube at a reduced density. Then the "eye" of the indicator will be red;
• And another option is to lower the electrolyte level. Then, through the "peephole" of the indicator, the surface of the electrolyte will be visible. This will indicate the need to top up with distilled water. True, in the case of a maintenance-free battery, this will be problematic.

Such a built-in indicator allows you to make a preliminary assessment of the degree of charge of the battery. Fully rely on the readings of the hydrometer should not be. If you read numerous reviews about the operation of these devices, it becomes clear that they often show inaccurate data and quickly fail. And there are several reasons for this:

• The indicator is installed in only one of the six battery cells. This means that you will have data on density and degree of charge for only one bank. Since there is no communication between them, one can only guess about the situation in other banks. For example, in this element, the electrolyte level may be normal, and in some others it is already insufficient. After all, the evaporation of water from the electrolyte in the banks is different (in the extreme, this process is more intense);
• The indicator is made of glass and plastic. Plastic parts may warp from heating or cooling. As a result, you will see distorted data;
• The density of an electrolyte depends on its temperature. The hydrometer does not take this into account in its readings. For example, on a cold electrolyte, it can show normal density, although it is reduced.

Factory battery indicators

Today on sale you can find quite interesting devices for monitoring the level of battery charge by its voltage. Let's look at some of them.

Battery Level Indicator DC-12V

This device is sold as a kit. It is suitable for those who are friends with electrical engineering and a soldering iron.

The DC-12 V indicator allows you to check the charge of the car battery and the functioning of the relay-regulator. The indicator is sold as a kit of spare parts and assembled independently. The cost of the DC-12 V device is 300-400 rubles.

The main characteristics of the DC-12V indicator:

• Voltage range: 2.5-18 volts;
• Maximum current consumption: up to 20 mA;
• PCB dimensions: 43 by 20 millimeters.

Do-it-yourself battery charge indicator on two LEDs- Properly maintained batteries will work well for you and share. Maintenance includes, in particular, regular monitoring of the battery voltage. The circuit shown in Figure 1 is suitable for most types of batteries. It contains a reference LED REF , which operates at a constant current of 1 mA and provides a reference light output of constant intensity, independent of battery voltage.

This constancy is provided by a resistor R1 connected in series with the LED. Therefore, even if the voltage of a fully charged battery drops to a full discharge, the current through it will change by only 10%. Thus, we can assume that the radiation intensity remains constant in the battery voltage range corresponding to the transition from the state of full charge to full discharge.

The luminous flux of the measurement LED VAR changes according to changes in the battery voltage. By placing the LEDs close to each other, you can easily compare the brightness of their glow, and thus determine the status of the battery. Use diffused lens LEDs as clear lens fixtures irritate your eyes. Provide sufficient optical isolation for the LEDs so that the light from one LED does not hit the lens of another.

Measuring LED operation

The meter LED operates at a current ranging from 10mA with a fully charged battery to less than 1mA with a fully discharged battery. A zener diode D z with a series resistor R 2 is necessary so that the current has a sharp dependence on the battery voltage. The sum of the zener voltage and the voltage drop across the LED should be slightly less than the lowest battery voltage. This voltage drops across the resistor R 2 . Changes in the battery voltage cause large changes in the current of the resistor R 2 . If the voltage is about 1V, 10mA of current flows through the LED VAR and it glows much brighter than the LED REF . If the voltage is lower than 0.1 V, the intensity of LED VAR var will be less than that of LED REF . indicating that the battery is low.

DIY battery charge indicator- immediately after the battery is charged, the voltage on it exceeds 13 V. This is safe for the circuit, since the current is limited to 10 mA. If the LEDs are bright, quickly release the S 1 1 button (to prevent damage to them (Figure 2). Although in the example in Figure 2 the charge indicator is connected to a 12-volt lead-acid battery, you can easily adapt this circuit to other battery types.Also, you can use it to monitor the voltage.

Two green LEDs induce the state when the battery charge exceeds 60%. A set of red LEDs indicates that the battery has fallen below 20%. The LED REFG and LED REFR are connected through resistors R 1 and R 2 with a resistance of 10 kOhm. Consistent measuring LEDs, the brightness of which changes, include zener diodes and resistors R 3 and R 4 with a resistance of 100 ohms. Diodes D 1 , D 2 and D 3 set the required clamping voltage. The dependence of the brightness of the LEDs on the state of the battery is shown in Table 1.

The following expression can be used to calculate the intensity of the green measurement LED:

V BATT = 10 G x 100 + V D1 + V D2 + V LEDG + V DZ1

V BATT =10 3 x 100+0.6+0.6+1.85+9.1=1225V.

The voltage drop across the LEDs used at a forward current of 1 mA is 1.85 V. If the characteristics of the LEDs differ, the resistances of the resistors must be recalculated. At this voltage, the LEDs glow the same, which corresponds to a battery charge of 60%. A description of lead-acid batteries can be found at. The following expression can be used to calculate the light intensity of the red measuring LED:

V BATT = I R x IOO + V D3 + V LEDR + V ZD2

At 1 mA green LED current

V BATT \u003d 10 -3 x 100 +0.6 + 1.85 + 9.1 \u003d 11.65 V.

Since both red LEDs glow the same at this voltage, it means that the battery is 20% charged. The LED VARG varg is off. Figure 3 shows that both measurement LEDs are brighter than the reference LEDs, indicating that the battery is 100% charged.

An LED indicator of the charge level of a conventional or rechargeable battery, where all thresholds are set using potentiometers, can be assembled according to the diagram given in this material. A huge plus is that it works with batteries from 3 to 28 V.

Low battery indicator circuit

The light emitting diode indicators themselves come in various types and colors, the recommended ones are shown on the diagram itself. Due to differences in forward voltage drop, current limiting resistors must be adjusted for best performance and uniformity. In the R18-R22 scheme, the same resistance is offered - note that these resistors do not have to be equal in the end. However, if they are all the same color, one resistor value will be enough.

LED color - charge level

• Red: 0 to 25%
• Orange : 25 - 50%
• Yellow : 50 - 75%
• Green : 75 - 100%
• Blue: >100% voltage

Here the LM317 acts as a simple 1.25 V reference. The minimum input voltage must exceed the output voltage by a couple of volts. Minimum input voltage = 1.25V + 1.75V = 3V. Although the LM317 has a minimum datasheet load of 5mA, not a single instance has been found that does not function at 3.8mA. It is the resistor R5 (330 ohms) that provides the minimum load.

During the tests, the charge level of 4.5 V of the battery was estimated, it is for it that the voltages on the diagram are given. The setting is as follows: first, the response voltages of each comparator must be determined in accordance with the level of battery discharge, then the voltage must be divided according to the division factor of the voltage divider. So, for a 4.5 V battery, it looks like this:

Threshold voltage

• 4.8V 1.12V
• 4.5V 1.05V
• 4.2 0.98V
• 3.9V 0.91V

Operation of the battery status indicator

The LM317 U3 chip is a 1.25 volt voltage reference. Resistors R5 and R6 form a voltage divider, which reduces the battery voltage to a level that is close to the reference voltage. The U2A element is an amplifier, so no matter how much current this node draws, the voltage remains stable. Resistors R8 - R11 provide high resistance to the comparator inputs. U1 consists of four comparators that compare the reference voltage of the potentiometers with the battery voltage. Op-amp LM358 U2B - also works as a kind of comparator that controls the lower-order LED.

At the limiting voltage values, the LEDs may not shine clearly, as a rule, flickering occurs between two adjacent LEDs. To prevent this, a small amount of positive feedback voltage is added across R14 - R17.

Indicator testing

If testing is done directly from the battery, please note that reverse polarity protection is not provided. It is better to initially connect the power circuits through a 100 ohm resistor in order to limit possible malfunctions. And after determining that the polarity is correct, this resistor can be removed.

Simplified version of the indicator

For those who want to build a simpler device, the U2 chip, all diodes and some resistors can be eliminated. We advise you to start with this version, and then, after making sure that it works normally, collect the full version of the battery discharge indicator. Good luck with your launch!

The successful start of an automobile engine largely depends on the state of charge of the battery. Regularly checking the voltage at the terminals with a multimeter is inconvenient. It is much more practical to use a digital or analog indicator located next to the dashboard. The simplest battery charge indicator can be made by hand, in which five LEDs help track the gradual discharge or charge of the battery.

circuit diagram

The considered circuit diagram of the charge level indicator is the simplest device that displays the charge level of the battery (battery) at 12 volts. Its key element is the LM339 chip, in the case of which 4 operational amplifiers (comparators) of the same type are assembled. The general view of the LM339 and the pin assignment is shown in the figure. The direct and inverse inputs of the comparators are connected via resistive dividers. 5 mm indicator LEDs are used as a load.

Diode VD1 serves as protection for the microcircuit from accidental polarity reversal. Zener diode VD2 sets the reference voltage, which is the standard for future measurements. Resistors R1-R4 limit the current through the LEDs.

Principle of operation

The LED battery indicator circuit works as follows. A voltage of 6.2 volts stabilized with the help of resistor R7 and a zener diode VD2 is fed to a resistive divider assembled from R8-R12. As can be seen from the diagram, reference voltages of different levels are formed between each pair of these resistors, which are fed to the direct inputs of the comparators. In turn, the inverse inputs are interconnected and connected to the battery terminals through resistors R5 and R6.

In the process of charging (discharging) the battery, the voltage at the inverse inputs gradually changes, which leads to alternate switching of the comparators. Consider the operation of the operational amplifier OP1, which is responsible for indicating the maximum battery charge level. Let's set the condition, if the charged battery has a voltage of 13.5 V, then the last LED starts to burn. The threshold voltage at its direct input, at which this LED will light up, is calculated by the formula:
U OP1+ \u003d U ST VD2 - U R8,
U ST VD2 \u003d U R8 + U R9 + U R10 + U R11 + U R12 \u003d I * (R8 + R9 + R10 + R11 + R12)
I \u003d U ST VD2 / (R8 + R9 + R10 + R11 + R12) \u003d 6.2 / (5100 + 1000 + 1000 + 1000 + 10000) \u003d 0.34 mA,
U R8 \u003d I * R8 \u003d 0.34 mA * 5.1 kOhm \u003d 1.7 V
U OP1+ = 6.2-1.7 = 4.5 V

This means that when a potential value of more than 4.5 volts is reached at the inverse input, the OP1 comparator will switch and a low voltage level will appear at its output, and the LED will light up. Using these formulas, you can calculate the potential at the direct inputs of each operational amplifier. The potential at the inverse inputs is found from the equality: U OP1- = I*R5 = U BAT - I*R6.

PCB and Assembly Parts

The printed circuit board is made of one-sided foil textolite 40 by 37 mm in size, which can be downloaded. It is designed for mounting DIP elements of the following type:

• MLT-0.125 W resistors with an accuracy of at least 5% (E24 series)
  R1, R2, R3, R4, R7, R9, R10, R11 - 1 kOhm,
  R5, R8 - 5.1 kOhm,
  R6, R12 - 10 kOhm;
• any low-power diode VD1 with a reverse voltage of at least 30 V, for example, 1N4148;
• low-power zener diode VD2 with a stabilization voltage of 6.2 V. For example, KS162A, BZX55C6V2;
• LEDs LED1-LED5 - indicator type