How to make a low battery indicator. DIY battery charge indicator
Hello to all radio amateurs! Today I want to tell you about my successful repetition of one battery charge indicator. On that site, it was already tested and posted by the respected Maxim Vorobyov. It does not contain scarce components and can be assembled even by novice radio amateurs, because it does not need to be tuned. With serviceable parts and proper installation, it starts working immediately. Here is the diagram itself:
Only I changed it a little to fit my details. Since there was no 5.6 volt zener diode, I set it to 6.8 volts, I had to change R1 to 82 kOhm. And in parallel, HL3 put a 1.2 kΩ resistor, because there was some illumination of the LED.
Operational amplifiers used those that were available (in my case kr140ud708). The resistors were in SMD. Here's what actually happened:
The only thing I forgot is about the capacitor C1, so I soldered it to the power leads on the reverse side:
Now this device will work on my father's homemade tractor. The board in Lay6 format is attached. Good luck to everyone in repeating this not a tricky device.
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
Not all cars have an indicator that displays the battery charge level. The motorist must independently monitor this indicator, periodically checking it with a voltmeter, after disconnecting the battery from the machine's electrical network. However, a simple electronic device will allow you to get approximate figures without leaving the cabin.
The choice of circuit and components
Finished construction
Structurally, a self-made battery charge control indicator consists of an electronic unit, on the body 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 prototyping board. The optimal scheme of the device is preselected. You can find several models, 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 has a minimum size. If you plan to install it in a housing, you should take into account its internal dimensions.
This circuit is designed to control the operation of a car battery with a mains voltage of 6 to 14 V. For other values of this parameter, the characteristics of the components should be changed. Their list is shown in the table.
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, will eliminate 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.
In modern practice, there are still cars on which there is neither an on-board computer nor a display with a battery charge indicator. Movement without an indicator is fraught with a complete stop of the engine and the inability to start it in the future.
The battery charge indicator performs two functions: it shows the charging current of the battery from the generator and informatively the amount of battery charge. There are several ways to fix this defect in the car. One of them is the simplest, do-it-yourself device showing battery charging.
In available sources, there are many proposals for the manufacture of a digital current circuit of such a device. It has a fairly simple look. This requires skills in soldering radio components and the desire to assemble the device with your own hands. Select LED, zener diode, breadboard and resistors. The diagram of the battery charge indicator is shown in the figure below.
Principle of operation
The LED indicator, thanks to the presence of three colors of LEDs, can show the various phases of the charging current. Start charging. Working middle. End of process warning. This circuit gives us the ability to control the entire operating cycle of the battery.
Soldering parts with your own hands is not difficult, but first check with a tester. If all the details are in order, you can assemble according to the scheme. Nicknamed tester LED output. We determine the output of low voltage current from six to eleven volts.
This is a red LED. From eleven to thirteen volts - yellow. More than thirteen - there will be a green LED. The circuit has a simple set of parts and works reliably.
Interesting! The battery outputs a certain voltage to the LED. It lights up. So we determine the beginning and end of the battery charge.
If you do not have any components, then you need to look on the Internet for similar schemes and modify the device with your own hands. The circuit will also show a reliable indication of the charge current of the battery.
It is important for the car that the circuit does not work all the time, but only when the driver is driving. It is recommended that after finishing work with your own hands, mount the resulting device under the steering wheel and connect it to the ignition switch. In this case, the indicator will only work when the vehicle ignition is on.
We see that after the completion of work, with your own hands you can create a convenient and necessary battery indicator for reliable operation of the car. The cost of such a product will not be high.
Important! The reliability of the indicator and the convenience of its placement can effectively eliminate the lack of refinement of designers - car manufacturers.
On the one hand, any device, whether it be a vehicle or simple kitchen utensils, seems to be perfect and refined from a technical point of view. Not requiring the intervention of human thought and competent hands.
On the other hand, there will always be competent "Kulibins" for whom this device seems not perfect and requires improvement and technical refinement.
This is what progressive technological progress is based on. It seems simple, but at the same time a vital visual indication of the process of charging a car battery, not designed by designers, found its simple development by simple admirers of the world of science and technology.