Not all cars have an indicator showing the battery charge level. The car enthusiast must independently monitor this indicator, periodically checking it with a voltmeter, having previously disconnected the battery from the car's mains. However, a simple electronic device will allow you to get approximate values without leaving the salon.
Choice of circuit and components
Finished construction
Structurally, a self-made battery charge control indicator consists of an electronic unit, on the case of which there are three LEDs: red, blue and green. The choice of color may be different - it is important that when one of them is activated, the information received is correctly interpreted.
Due to the small size of the device, you can use an ordinary breadboard. The optimal device layout is preselected. Several models can be found, but the most common and therefore workable version of the battery charge indicator is shown in the figure.
Diagram of the board and its components
Before installing the components, it is necessary to arrange them on the printed circuit board according to the diagram. Only then can you cut it to the desired size. It is important that the indicator is as small as possible. If you plan to install it in the case, you should take into account its internal dimensions.
This circuit is designed to monitor the operation of a car battery with a mains voltage from 6 to 14 V. For other values of this parameter, the characteristics of the components must be changed. Their list is shown in the table.
The successful start of a car engine is highly dependent 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 indicator can be made by hand, in which five LEDs help track the gradual discharge or charge of the battery.
Schematic diagram
The considered schematic diagram of the charge level indicator is a simple device that displays the charge level of a 12 volt battery (accumulator). Its key element is the LM339 microcircuit, 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 are shown in the figure. 
Direct and inverse inputs of the comparators are connected through resistive dividers. Indicator LEDs 5 mm are used as a load.
The VD1 diode protects the microcircuit from accidental polarity reversal. Zener diode VD2 sets the reference voltage, which is a reference for future measurements. Resistors R1-R4 limit the current through the LEDs.
Principle of operation
The battery charge indicator circuit on LEDs works as follows. Stabilized with a resistor R7 and a Zener diode VD2, a voltage of 6.2 volts 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 combined with each other and through the resistors R5 and R6 are connected to the terminals of the storage battery (AKB).
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 light up. The threshold voltage at its direct input, at which this LED will light up, is calculated by the formula:
U OP1 + = U СТ VD2 - U R8,
U ST VD2 = U R8 + U R9 + U R10 + U R11 + U R12 = I * (R8 + R9 + R10 + R11 + R12)
I = U CT VD2 / (R8 + R9 + R10 + R11 + R12) = 6.2 / (5100 + 1000 + 1000 + 1000 + 10000) = 0.34 mA,
U R8 = I * R8 = 0.34 mA * 5.1 kΩ = 1.7 V
U OP1 + = 6.2-1.7 = 4.5V
This means that when a potential 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 40 x 37 mm single-sided foil-coated PCB, which can be downloaded. It is designed for mounting DIP elements of the following type:
- resistors MLT-0.125 W with an accuracy of at least 5% (series E24)
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;
- LED1-LED5 LEDs - indicator type
The battery charge indicator is a must-have item in the household of any motorist. The relevance of such a device increases many times, when, for some reason, the car refuses to start on a cold winter morning. In this situation, it is worth deciding whether to call a friend so that he would come and help start up from his battery, or the battery ordered to live a long time, being discharged below a critical level.
Why monitor battery health?
The car battery consists of six batteries connected in series with a supply voltage of 2.1 - 2.16V. Normally, the battery should produce 13-13.5V. A significant discharge of the battery should not be allowed, since this decreases the density and, accordingly, the freezing temperature of the electrolyte rises.
The more the battery is worn out, the less time it will hold a charge. In the warm season, this is not critical, but in winter the parking lights forgotten when they are on by the time they return can completely "kill" the battery, turning the contents into a piece of ice.
In the table, you can see the freezing temperature of the electrolyte, depending on the state of charge of the unit.
| Dependence of the freezing temperature of the electrolyte on the degree of battery charge | ||||
|---|---|---|---|---|
| Electrolyte density, mg / cm cub. | Voltage, V (no load) | Voltage, V (with a load of 100 A) | Battery charge level,% | Freezing point of electrolyte, gr. Celsius |
| 1110 | 11,7 | 8,4 | 0,0 | -7 |
| 1130 | 11,8 | 8,7 | 10,0 | -9 |
| 1140 | 11,9 | 8,8 | 20,0 | -11 |
| 1150 | 11,9 | 9,0 | 25,0 | -13 |
| 1160 | 12,0 | 9,1 | 30,0 | -14 |
| 1180 | 12,1 | 9,5 | 45,0 | -18 |
| 1190 | 12,2 | 9,6 | 50,0 | -24 |
| 1210 | 12,3 | 9,9 | 60,0 | -32 |
| 1220 | 12,4 | 10,1 | 70,0 | -37 |
| 1230 | 12,4 | 10,2 | 75,0 | -42 |
| 1240 | 12,5 | 10,3 | 80,0 | -46 |
| 1270 | 12,7 | 10,8 | 100,0 | -60 |
A drop in the charge level below 70% is considered critical. All automotive electrical appliances do not consume voltage, but current. Without load, even a highly discharged battery can show normal voltage. But at a low level, during engine start, there will be a strong voltage drop, which is an alarm signal.
It is possible to notice an impending disaster in time only if an indicator is installed directly in the cabin. If, while the car is running, it constantly signals discharging, it is time to go to the service station.
What are the indicators
Many batteries, especially maintenance-free ones, have a built-in sensor (hygrometer), the principle of which is based on measuring the density of the electrolyte.
This sensor monitors the state of the electrolyte and the value of its indicators is relative. It is not very convenient to climb under the hood of the car several times to check the state of the electrolyte in different operating modes.
Electronic devices are much more convenient to monitor the state of the battery.
Types of battery charge indicators
Many such devices are sold in car dealerships, differing in design and functionality. Factory appliances are conventionally divided into several types.
By connection method:
- to the cigarette lighter socket;
- to the on-board network.
By the way the signal is displayed:
- analog;
- digital.
The principle of operation is the same for them, determining the battery charge level and displaying information in a visual form.
Schematic diagram indicator How to make a battery charge indicator on LEDs?
There are dozens of different control schemes, but the results are identical. Such a device can be assembled independently from scrap materials. The choice of the circuit and components depends solely on your capabilities, imagination and the range of the nearest radio store.
Here is a diagram for understanding how the LED battery indicator works. Such a portable model can be assembled on the knee in a few minutes.
D809- a 9V zener diode limits the voltage across the LEDs, and the differentiator itself is assembled on three resistors. Such led indicator triggered by the current in the circuit. At a voltage of 14V and above, the current strength is sufficient for the glow of all LEDs, at a voltage of 12-13.5V they glow VD2 and VD3, below 12V - VD1.
A more advanced version with a minimum of parts can be assembled on a budget voltage indicator - chip AN6884 (KA2284).
Circuit of a led battery charge level indicator on a voltage comparator
The circuit works on the principle of a comparator. VD1- 7.6V zener diode, it serves as a reference voltage source. R1- voltage divider. During the initial setup, it is set in such a position that at a voltage of 14V all LEDs are lit. The voltage supplied to inputs 8 and 9 is compared through a comparator, and the result is decoded into 5 levels by lighting up the corresponding LEDs.
Battery charging controller
To monitor the state of the battery while the charger is operating, we make a battery charge controller. The circuit of the device and the components used are maximally accessible, at the same time provide full control over the process of recharging the batteries.
The principle of operation of the controller is as follows: while the voltage on the battery is lower than the charge voltage, the green LED is on. As soon as the voltage equals, the transistor opens, lighting up the red LED. Changing the resistor in front of the base of the transistor changes the voltage level required to open the transistor.
It is a versatile control circuit that can be used for both high-power car batteries and miniature lithium batteries.
DIY battery indicator on two LEDs- properly maintained batteries will work well for you. Maintenance includes regular monitoring of the battery voltage. The diagram shown in Figure 1 is suitable for most types of batteries. It contains a reference LED REF, which operates at direct current 1 mA and provides a reference luminous flux of constant intensity, independent of battery voltage.
This constancy is provided by a resistor R1 in series with the LED. Therefore, even if the voltage of a fully charged battery drops to full discharge, the current through it will change by only 10%. Thus, we can assume that the radiation intensity remains constant in the range of battery voltages corresponding to the transition from a state of full charge to full discharge.
The luminous flux of the measuring LED VAR changes according to changes in the battery voltage. By placing LEDs close to each other, you will be able to easily compare their brightness, and thus determine the status of the battery. Use LEDs with a diffusely diffusing lens as clear lens devices irritate your eyes. Provide sufficient optical isolation of the LEDs so that light from one LED does not hit the lens of another.
Measurement LED operation
The metering LED operates at a current ranging from 10 mA with a fully charged battery to less than 1 mA with a full discharge. Zener diode D z with series resistor R 2 are necessary in order for the current to have 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 resistor R 2. Changes in battery voltage cause large changes in the current of resistor R 2. If the voltage is approximately 1 V, a current of 10 mA flows through the LED VAR and is 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 discharged.
DIY battery indicator- immediately after the end of charging the battery, the voltage on it exceeds 13 V. For the circuit, this is safe, since the current is limited to 10 mA. If the LEDs are brightly on, quickly release the S 1 1 button (to avoid damaging 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, and you can also use it to monitor voltage.
Two green LEDs induce a state when the battery charge exceeds 60%. A set of red LEDs indicates that the battery has dropped below 20%. LEDs REFG and LED REFR are connected through 10 kΩ resistors R 1 and R 2. Sequential measuring LEDs, the brightness of which changes, included 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 clipping 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 luminous 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 = 1225B.
The voltage drop across the LEDs used with 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 light up in the same way, which corresponds to a 60% charge of the battery. A description of lead acid batteries can be found in. The following expression can be used to calculate the glow intensity of the red measurement LED:
V BATT = I R x IOO + V D3 + V LEDR + V ZD2
With a green LED current of 1 mA
V BATT = 10 -3 x 100 +0.6 + 1.85 + 9.1 = 11.65 V.
Since both red LEDs glow the same at this voltage, this means that the battery is 20% charged. LED LED VARG varg is off. Figure 3 shows that both meter LEDs are brighter than the reference LEDs, indicating that the battery is 100% charged.
With a discharged battery, starting the car is quite problematic. To avoid such an unpleasant "surprise", it is enough just to use a voltmeter from time to time. However, not all motorists and not always do this, because it is much more convenient to have some kind of device showing how long the battery charge will last.
What are the indicators
The storage battery (or joint stock bank) consists of six interconnected elements, the voltage in each should normally be about 2.15 volts, that is, the total battery voltage is suitable for 13.5 volts. If the charge falls below critical values (about 9.5 volts), this can lead to a deep discharge of the battery and, as a result, its complete failure.
Modern technologies "meet" motorists and make their life as easy as possible. For example, many cars already have on-board computers that also monitor the battery charge level.
However, while this option is not available to everyone, one has to use other types of indicators of this important indicator. So, you can find individual crystal displays on the dashboard, there are hygrometer indicators, you can also (if you have the appropriate skills) make a battery charge indicator yourself. Many signaling devices of this type must be connected to the vehicle's on-board network so that they can monitor the battery charge level.
Built-in charge indicator
The most common type of indicator on maintenance-free batteries is the hydrometer. It consists of an eye, a light guide, a leg and a float (therefore it is called a float). The leg with the light guide is located inside the battery; a float is attached to the leg, with the help of which the electrolyte level in the battery is determined. There is a peephole on the battery case, which shows the three main states of the battery:
- a green float ball shines through the peephole, which means that the battery is more than half charged;
- the peephole remains black (the indicator tube shines through), this is a signal that the float is completely immersed in the electrolytic liquid, therefore, its density is reduced, and the battery needs to be charged;
Additional Information. Some models of hydrometers have a red float, which can be seen in the "window" when the charge and density of the electrolyte decreases.
- if only the surface of the liquid inside the battery is visible in the "eye", it means that it "wants to drink" - the electrolyte level is critical, it is urgently necessary to top up with distilled water (and it is rather difficult to do this, since such batteries are maintenance-free).
Note! Although the built-in battery indicator of this type allows you to instantly determine the existing problem (or lack thereof), judging by some user reviews, the readings of such devices are quite often false, and they themselves quickly break down.
As a rule, this is due to the following reasons:
- data comes from only one battery cell out of six, and the liquid level in them can vary significantly;
- indicator parts made of plastic do not withstand temperature regime battery life, so the data is incorrect;
- float indicators do not in any way determine the temperature of the electrolytic liquid, and the density also depends on it, therefore the electrolyte of a lowered temperature will show a normal level of density, while it will also be low.
Factory indicators in the form of panels
In specialized stores, you can find many different control devices for the battery, each car owner can choose the design and functions for himself. The indicators also differ in the method of connection: to the cigarette lighter or to the on-board network of the car. However, the main task for all devices is the same - to determine how much the battery is charged, and to signal this.
There are indicators that you need to assemble yourself, like a constructor. As an example - DC-12 V. It makes it possible to control the battery charge, as well as the operation of the regulating relay.
Such a small control device operates in the range from 2.5 to 18 volts, consumes very little electricity - up to 20 milliamps, the size of the indicator window is 4.3 by 2 cm.
If you put a second battery in the car, you can use the indicator from TMC - this is a small panel made of industrial aluminum on LEDs with a built-in voltmeter and a switch between adjacent batteries.
Of the expensive models (and unreasonably expensive, at the price of a new battery) voltage controllers of the American company "Faria Euro Black Style" can be distinguished. The color of the case is usually black, the diameter of the display window is 5.3 cm, the screen is backlit in white. The power supply requires 12 volts.
How to assemble a charge indicator yourself
If the car owner is friends with a soldering iron, he can assemble the analyzer with his own hands, you can find many assembly schemes. With the help of one, the simplest, you can assemble a charge indicator that resembles the above-described DC-12 V. It works according to the same principles: it is connected to the on-board network and determines the battery voltage within 6-14 volts.
To assemble the device, you will need transistors, resistors, zener diodes, a printed circuit board and one red, blue and one green LED. After assembly, according to the diagram, the board is inserted on the dashboard, and the ends of the LEDs are held in a place convenient for viewing. In this case, a fully charged battery will be indicated in green, blue - with normal charge (11 to 13 volts), and if the battery is close to discharge, the red LED will light up.
It is unpleasant when the car cannot start simply because the battery is discharged at the most inopportune moment. A voltage indicator bought in a store or soldered on your own will help to avoid unpleasant "surprises" and will warn you in advance that the battery needs recharging.
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