How to make a battery charge indicator with your own hands. We make a battery voltage indicator ourselves: high quality at minimal cost

What could be sadder than a suddenly dead battery in a quadcopter during a flight or a metal detector turning off in a promising clearing? Now, if only you could find out in advance how charged the battery is! Then we could connect the charger or install a new set of batteries without waiting for sad consequences.

And this is where the idea is born to make some kind of indicator that will give a signal in advance that the battery will soon run out. Radio amateurs all over the world have been working on the implementation of this task, and today there is a whole car and a small cart of various circuit solutions - from circuits on a single transistor to sophisticated devices on microcontrollers.

Attention! The diagrams presented in the article only indicate low voltage on the battery. To prevent deep discharge, you must manually turn off the load or use.

Option #1

Let's start, perhaps, with a simple circuit using a zener diode and a transistor:

Let's figure out how it works.

As long as the voltage is above a certain threshold (2.0 Volts), the zener diode is in breakdown, accordingly, the transistor is closed and all the current flows through the green LED. As soon as the voltage on the battery begins to drop and reaches a value of the order of 2.0V + 1.2V (voltage drop at the base-emitter junction of transistor VT1), the transistor begins to open and the current begins to be redistributed between both LEDs.

If we take a two-color LED, we get a smooth transition from green to red, including the entire intermediate gamut of colors.

The typical forward voltage difference in bi-color LEDs is 0.25 Volts (red lights up at lower voltage). It is this difference that determines the area of ​​complete transition between green and red.

Thus, despite its simplicity, the circuit allows you to know in advance that the battery has begun to run out. As long as the battery voltage is 3.25V or more, the green LED lights up. In the interval between 3.00 and 3.25V, red begins to mix with green - the closer to 3.00 Volts, the more red. And finally, at 3V only pure red lights up.

The disadvantage of the circuit is the complexity of selecting zener diodes to obtain the required response threshold, as well as the constant current consumption of about 1 mA. Well, it is possible that colorblind people will not appreciate this idea with changing colors.

By the way, if you put a different type of transistor in this circuit, it can be made to work in the opposite way - the transition from green to red will occur, on the contrary, if the input voltage increases. Here is the modified diagram:

Option No. 2

The following circuit uses the TL431 chip, which is a precision voltage regulator.

The response threshold is determined by the voltage divider R2-R3. With the ratings indicated in the diagram, it is 3.2 Volts. When the battery voltage drops to this value, the microcircuit stops bypassing the LED and it lights up. This will be a signal that the complete discharge of the battery is very close (the minimum permissible voltage on one li-ion bank is 3.0 V).

If a battery of several lithium-ion battery banks connected in series is used to power the device, then the above circuit must be connected to each bank separately. Like this:

To configure the circuit, we connect an adjustable power supply instead of batteries and select resistor R2 (R4) to ensure that the LED lights up at the moment we need.

Option #3

And here is a simple circuit of a li-ion battery discharge indicator using two transistors:
The response threshold is set by resistors R2, R3. Old Soviet transistors can be replaced with BC237, BC238, BC317 (KT3102) and BC556, BC557 (KT3107).

Option No. 4

A circuit with two field-effect transistors that literally consumes microcurrents in standby mode.

When the circuit is connected to a power source, a positive voltage at the gate of transistor VT1 is generated using a divider R1-R2. If the voltage is higher than the cutoff voltage of the field-effect transistor, it opens and pulls the gate of VT2 to ground, thereby closing it.

At a certain point, as the battery discharges, the voltage removed from the divider becomes insufficient to unlock VT1 and it closes. Consequently, a voltage close to the supply voltage appears at the gate of the second field switch. It opens and lights up the LED. The LED glow signals to us that the battery needs to be recharged.

Any n-channel transistors with a low cutoff voltage will do (the lower the better). The performance of the 2N7000 in this circuit has not been tested.

Option #5

On three transistors:

I think the diagram needs no explanation. Thanks to the large coefficient. amplification of three transistor stages, the circuit operates very clearly - between a lit and not lit LED, a difference of 1 hundredth of a volt is sufficient. Current consumption when the indication is on is 3 mA, when the LED is off - 0.3 mA.

Despite the bulky appearance of the circuit, the finished board has fairly modest dimensions:

From the VT2 collector you can take a signal that allows the load to be connected: 1 - allowed, 0 - disabled.

Transistors BC848 and BC856 can be replaced with BC546 and BC556, respectively.

Option #6

I like this circuit because it not only turns on the indication, but also cuts off the load.

The only pity is that the circuit itself does not disconnect from the battery, continuing to consume energy. And thanks to the constantly burning LED, it eats a lot.

The green LED in this case acts as a reference voltage source, consuming a current of about 15-20 mA. To get rid of such a voracious element, instead of a reference voltage source, you can use the same TL431, connecting it according to the following circuit*:

*connect the TL431 cathode to the 2nd pin of LM393.

Option No. 7

Circuit using so-called voltage monitors. They are also called voltage supervisors and detectors. These are specialized microcircuits designed specifically for voltage monitoring.

Here, for example, is a circuit that lights up an LED when the battery voltage drops to 3.1V. Assembled on BD4731.

Agree, it couldn’t be simpler! The BD47xx has an open collector output and also self-limites the output current to 12 mA. This allows you to connect an LED to it directly, without limiting resistors.

Similarly, you can apply any other supervisor to any other voltage.

Here are a few more options to choose from:

• at 3.08V: TS809CXD, TCM809TENB713, MCP103T-315E/TT, CAT809TTBI-G;
• at 2.93V: MCP102T-300E/TT, TPS3809K33DBVRG4, TPS3825-33DBVT, CAT811STBI-T3;
• MN1380 series (or 1381, 1382 - they differ only in their housings). For our purposes, the option with an open drain is best suited, as evidenced by the additional number “1” in the designation of the microcircuit - MN13801, MN13811, MN13821. The response voltage is determined by the letter index: MN13811-L is exactly 3.0 Volts.

You can also take the Soviet analogue - KR1171SPkhkh:

Depending on the digital designation, the detection voltage will be different:

The voltage grid is not very suitable for monitoring li-ion batteries, but I don’t think it’s worth completely discounting this microcircuit.

The undeniable advantages of voltage monitor circuits are extremely low power consumption when turned off (units and even fractions of microamps), as well as its extreme simplicity. Often the entire circuit fits directly on the LED terminals:

To make the discharge indication even more noticeable, the output of the voltage detector can be loaded onto a flashing LED (for example, L-314 series). Or assemble a simple “blinker” yourself using two bipolar transistors.

An example of a finished circuit that notifies of a low battery using a flashing LED is shown below:

Another circuit with a blinking LED will be discussed below.

Option No. 8

A cool circuit that makes the LED blink if the voltage on the lithium battery drops to 3.0 Volts:

This circuit causes a super-bright LED to flash with a duty cycle of 2.5% (i.e. long pause - short flash - pause again). This allows you to reduce the current consumption to ridiculous values ​​- in the off state the circuit consumes 50 nA (nano!), and in the LED blinking mode - only 35 μA. Can you suggest something more economical? Hardly.

As you can see, the operation of most discharge control circuits comes down to comparing a certain reference voltage with a controlled voltage. Subsequently, this difference is amplified and turns the LED on/off.

Typically, a transistor stage or an operational amplifier connected in a comparator circuit is used as an amplifier for the difference between the reference voltage and the voltage on the lithium battery.

But there is another solution. Logic elements - inverters - can be used as an amplifier. Yes, it's an unconventional use of logic, but it works. A similar diagram is shown in the following version.

Option No. 9

Circuit diagram for 74HC04.

The operating voltage of the zener diode must be lower than the circuit's response voltage. For example, you can take zener diodes of 2.0 - 2.7 Volts. Fine adjustment of the response threshold is set by resistor R2.

The circuit consumes about 2 mA from the battery, so it must also be turned on after the power switch.

Option No. 10

This is not even a discharge indicator, but rather an entire LED voltmeter! A linear scale of 10 LEDs gives a clear picture of the battery status. All functionality is implemented on just one single LM3914 chip:

Divider R3-R4-R5 sets the lower (DIV_LO) and upper (DIV_HI) threshold voltages. With the values ​​​​indicated in the diagram, the glow of the upper LED corresponds to a voltage of 4.2 Volts, and when the voltage drops below 3 volts, the last (lower) LED will go out.

By connecting the 9th pin of the microcircuit to ground, you can switch it to point mode. In this mode, only one LED corresponding to the supply voltage is always lit. If you leave it as in the diagram, then a whole scale of LEDs will light up, which is irrational from an economical point of view.

As LEDs you need to take only red LEDs, because they have the lowest direct voltage during operation. If, for example, we take blue LEDs, then if the battery runs down to 3 volts, they most likely will not light up at all.

The chip itself consumes about 2.5 mA, plus 5 mA for each lit LED.

A disadvantage of the circuit is the impossibility of individually adjusting the ignition threshold of each LED. You can set only the initial and final values, and the divider built into the chip will divide this interval into equal 9 segments. But, as you know, towards the end of the discharge, the voltage on the battery begins to drop very rapidly. The difference between batteries discharged by 10% and 20% can be tenths of a volt, but if you compare the same batteries, only discharged by 90% and 100%, you can see a difference of a whole volt!

A typical Li-ion battery discharge graph shown below clearly demonstrates this circumstance:

Thus, using a linear scale to indicate the degree of battery discharge does not seem very practical. We need a circuit that allows us to set the exact voltage values ​​at which a particular LED will light up.

Full control over when the LEDs turn on is given by the circuit presented below.

Option No. 11

This circuit is a 4-digit battery/battery voltage indicator. Implemented on four op-amps included in the LM339 chip.

The circuit is operational up to a voltage of 2 Volts and consumes less than a milliampere (not counting the LED).

Of course, to reflect the real value of the used and remaining battery capacity, it is necessary to take into account the discharge curve of the battery used (taking into account the load current) when setting up the circuit. This will allow you to set precise voltage values ​​corresponding to, for example, 5%-25%-50%-100% of residual capacity.

Option No. 12

And, of course, the widest scope opens up when using microcontrollers with a built-in reference voltage source and an ADC input. Here the functionality is limited only by your imagination and programming ability.

As an example, we will give the simplest circuit on the ATMega328 controller.

Although here, to reduce the size of the board, it would be better to take the 8-legged ATTiny13 in the SOP8 package. Then it would be absolutely gorgeous. But let this be your homework.

The LED is a three-color one (from an LED strip), but only red and green are used.

The finished program (sketch) can be downloaded from this link.

The program works as follows: every 10 seconds the supply voltage is polled. Based on the measurement results, the MK controls the LEDs using PWM, which allows you to obtain different shades of light by mixing red and green colors.

A freshly charged battery produces about 4.1V - the green indicator lights up. During charging, a voltage of 4.2V is present on the battery, and the green LED will blink. As soon as the voltage drops below 3.5V, the red LED will start blinking. This will be a signal that the battery is almost empty and it is time to charge it. In the rest of the voltage range, the indicator will change color from green to red (depending on the voltage).

Option No. 13

Well, for starters, I propose the option of reworking the standard protection board (they are also called), turning it into an indicator of a dead battery.

These boards (PCB modules) are extracted from old mobile phone batteries on an almost industrial scale. You just pick up a discarded mobile phone battery on the street, gut it, and the board is in your hands. Dispose of everything else as intended.

Attention!!! There are boards that include overdischarge protection at unacceptably low voltage (2.5V and below). Therefore, from all the boards you have, you need to select only those copies that operate at the correct voltage (3.0-3.2V).

Most often, a PCB board looks like this:

Microassembly 8205 is two milliohm field devices assembled in one housing.

By making some changes to the circuit (shown in red), we will get an excellent li-ion battery discharge indicator that consumes virtually no current when turned off.

Since transistor VT1.2 is responsible for disconnecting the charger from the battery bank when overcharging, it is superfluous in our circuit. Therefore, we completely eliminated this transistor from operation by breaking the drain circuit.

Resistor R3 limits the current through the LED. Its resistance must be selected in such a way that the glow of the LED is already noticeable, but the current consumed is not yet too high.

By the way, you can save all the functions of the protection module, and make the indication using a separate transistor that controls the LED. That is, the indicator will light up simultaneously with the battery turning off at the moment of discharge.

Instead of the 2N3906, any low-power pnp transistor you have on hand will do. Simply soldering the LED directly will not work, because... The output current of the microcircuit that controls the switches is too small and requires amplification.

Please take into account the fact that the discharge indicator circuits themselves consume battery power! To avoid unacceptable discharge, connect indicator circuits after the power switch or use protection circuits, .

As is probably not difficult to guess, the circuits can be used vice versa - as a charge indicator.

The most surprising thing is that the battery charge level indicator circuit does not contain any transistors, microcircuits, or zener diodes. Only LEDs and resistors connected in such a way that the level of the supplied voltage is indicated.

Indicator circuit

The operation of the device is based on the initial turn-on voltage of the LED. Any LED is a semiconductor device that has a voltage limit point, only exceeding which it begins to work (shine). Unlike an incandescent lamp, which has almost linear current-voltage characteristics, the LED is very close to the characteristics of a zener diode, with a sharp slope of the current as the voltage increases.
If you connect LEDs in a circuit in series with resistors, then each LED will start to turn on only after the voltage exceeds the sum of the LEDs in the circuit for each section of the circuit separately.
The voltage threshold for opening or starting to light an LED can range from 1.8 V to 2.6 V. It all depends on the specific brand.
As a result, each LED lights up only after the previous one lights up.

I assembled the circuit on a universal circuit board, soldering the outputs of the elements together. For better perception, I took LEDs of different colors.
Such an indicator can be made not only with six LEDs, but, for example, with four.
The indicator can be used not only for the battery, but to create a level indication on music speakers. By connecting the device to the output of the power amplifier, parallel to the speaker. This way you can monitor critical levels for the speaker system.
It is possible to find other applications of this truly very simple circuit.

Some batteries (usually above average quality) have a green indicator on the top (front), right, or left (some call it a light). This "eye" gives you an idea of ​​the charge or discharge of your battery. It has three main positions in total, and it does not always glow green. Today I will tell you in detail what it is and why it was created. We’ll also look at why it might not burn at all...

To be honest, this indicator was created only to signal you about your battery, because as a rule, their design is not collapsible, and therefore you cannot climb inside and see what is with the electrolyte - just look at its level or measure its density. Therefore, such a “light bulb” gives you a complete idea by which you can make this or that decision. However, the indicator may not always light green; as a rule, three modes are used here.

Indicator modes

The following combination is very common: green, white, black. However, some manufacturers use the following combination: green, white, red. But essentially it's the same thing. Let's go through these readings.

Green mode – fully charged battery, can be used in normal operating mode. That is, charging is not needed.

White indicator - he tells us about low electrolyte levels. This also happens in unattended ones; most likely, the battery was often recharged, and gaseous electrolyte was released through a special valve. You need to disassemble and add distilled water.

Black or red indicator - this tells us that our battery is discharged, and the indicator is critical; mandatory recharging is required! It is important! If the battery is left uncharged for a long time, it may fail.

As you can see, these colors give certain signals to the owner, look occasionally and then your battery will last a long time. I also want to note that this indicator does not have any light bulbs in its structure, the next point will change your understanding...

About a light bulb - not a light bulb

I wanted to write this information at the top, but it creates more intrigue. In the structure of this sensor, no light bulbs are used at all - neither ordinary incandescent (low-current) - as many people think, nor LED, nor anything else.

The structure is different here . In fact, this is an ordinary hydrometer, only built into the battery case. It automatically measures the density of the electrolyte, and at different values ​​it pops up - one or another ball, which is projected through a magnifying glass tube and a magnifying glass into a special window. It should be noted that the balls float up as if along special grooves, which are made in the shape of a pyramid - this is important! REMEMBER!

If the battery is charged, a green ball floats up and you see it in the window. If it is discharged, then either red or nothing at all floats in, so you see blackness. But if there is no electrolyte, then the end of the pyramid seems to be exposed - you see its end in the window, many people confuse it with white.

The use of electrics in a battery would not be justified - even if the light bulb were low-voltage, it would still suck some of the energy from the battery (and in winter this is oh so unnecessary). YES, and if it burns out, the owner will start to get nervous.

Now a detailed video, maybe someone didn’t understand about the pyramid...

Why doesn't it light up even after being fully charged?

A very common question, many still think that this is a light bulb and after charging it should light up! As we have already made clear, this is not at all true. And it is quite possible that when fully charged the green indicator will not come out! WHY?

YES it's simple:

• The green ball can simply “stick” on these “small runners”. Just shake the battery and it will take its place. This happens very often.
• Dirt from the plates gets in, over time the plates begin to crumble, the electrolyte becomes cloudy, it has particles of lead, so it prevents the indicator from transmitting information normally.
• The battery really failed, this also cannot be ruled out, even with long-term charging it does not gain density.

Is it possible to remove this indicator?

On most batteries, yes, this window can be unscrewed, similar to a cork - but it will have to be twisted with force, it can even be broken; my friends unscrewed it using pliers with thin ends, and small “holes” were made in the window for engagement. In general, it’s a “collective farm”, but theoretically it’s possible to remove it! It is also worth remembering that if you unscrew it, then the airless space inside has been violated, and it is quite possible that a gaseous composition will come out - “explosive gas” or “HHO”. Then you will need to add distilled water. So always think, do you need to disassemble the battery?

Actually, I’m finishing the article, the information is clear and to the point, I think it was useful to you, read our AUTOBLOG.

Using two resistors, you can set the breakdown voltage in the range from 2.5 V to 36 V.

I will give two schemes for using the TL431 as a battery charge/discharge indicator. The first circuit is intended for a discharge indicator, and the second for a charge level indicator.

The only difference is the addition of an npn transistor, which will turn on some kind of signaling device, such as an LED or a buzzer. Below I will give a method for calculating resistance R1 and examples for some voltages.

The zener diode works in such a way that it begins to conduct current when a certain voltage is exceeded on it, the threshold of which we can set using R1 and R2. In the case of a discharge indicator, the LED indicator should be illuminated when the battery voltage is less than required. Therefore, an n-p-n transistor is added to the circuit.

As you can see, the adjustable zener diode regulates the negative potential, so a resistor R3 is added to the circuit, whose task is to turn on the transistor when TL431 is turned off. This resistor is 11k, selected by trial and error. Resistor R4 serves to limit the current on the LED, it can be calculated using.

Of course, you can do without a transistor, but then the LED will go out when the voltage drops below the set level - the diagram is below. Of course, such a circuit will not work at low voltages due to the lack of sufficient voltage and/or current to power the LED. This circuit has one drawback, which is the constant current consumption, around 10 mA.

In this case, the charge indicator will be constantly on when the voltage is greater than what we defined with R1 and R2. Resistor R3 serves to limit the current to the diode.

It's time for what everyone likes best - math

I already said at the beginning that the breakdown voltage can be changed from 2.5V to 36V via the “Ref” input. So let's try to do some math. Let's assume that the indicator should light up when the battery voltage drops below 12 volts.

The resistance of resistor R2 can be of any value. However, it is best to use round numbers (to make counting easier), such as 1k (1000 ohms), 10k (10,000 ohms).

We calculate resistor R1 using the following formula:

R1=R2*(Vo/2.5V – 1)

Let's assume that our resistor R2 has a resistance of 1k (1000 Ohms).

Vo is the voltage at which breakdown should occur (in our case 12V).

R1=1000*((12/2.5) - 1)= 1000(4.8 - 1)= 1000*3.8=3.8k (3800 Ohm).

That is, the resistance of the resistors for 12V looks like this:

And here is a small list for the lazy. For resistor R2=1k, resistance R1 will be:

• 5V – 1k
• 7.2V – 1.88k
• 9V – 2.6k
• 12V – 3.8k
• 15V - 5k
• 18V – 6.2k
• 20V – 7k
• 24V – 8.6k

For a low voltage, for example, 3.6V, resistor R2 should have a higher resistance, for example, 10k, since the current consumption of the circuit will be less.

The quality of battery charging determines how successfully the car will start. Not many drivers monitor the battery charge level. The article discusses such a useful device as a car battery charge indicator: how it works, how it works, instructions and a video on how to make it yourself.

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Characteristics of the battery charge level indicator

On modern cars with an on-board computer, the driver has the opportunity to obtain information about the level. Older models are equipped with analog voltmeters, but they do not reflect the true picture of the battery's condition. Battery voltage indicator (VIN) is an option to have operational information about the battery voltage.

Purpose and device

The IN is assigned two functions - to show how the battery is charged from the generator, and to inform about the amount of charge of the car battery. The easiest way is to assemble such a device with your own hands. The circuit of the homemade device is simple. Having purchased the necessary parts, it is easy to assemble the indicator with your own hands. This way you can save money, since the cost of the device is low (the author of the video is AKA KASYAN).

Operating principle

The charge level indicator has three LED lights of different colors. Usually these are: red, green and blue. Each color has its own informative meaning. Red color means low charge, which is critical. Blue color corresponds to operating mode. Green color indicates the battery is fully charged.

Varieties

IN can be placed on batteries in the form of a hydrometer or in the form of separate devices with an information display. Built-in IDs are usually placed on. They are equipped with a float indicator (hydrometer). It has a simple design.

Factory identification numbers are available:

1. DC-12 V. The device is a construction set. With its help, you can monitor the charge of the battery and the performance of the relay regulator.
2. For those who have a car equipped with a second battery, a useful device will be a panel with an indicator from TMC. This is an aluminum panel with a voltmeter placed on it and a switch from one battery to another.
3. ID Signature Gold Style and Faria Euro Black Style - determine the battery charge level. But their cost is too high, so there is little demand for them.

Guide to making a device at home

The simplest and cheapest option is a self-made IN. Its purpose is to control how the battery operates when the voltage in the on-board network is within the range of 6-14V.

To prevent the device from working constantly, it should be connected through the ignition switch. In this case it will work when the key is inserted.

The following parts will be needed for the diagram:

• printed circuit board;
• resistors: 2 with a resistance of 1 kOhm, 1 with a resistance of 2 kOhm and 3 with a resistance of 220 Ohm;
• transistors: VS547 - 1 and VS557 - 1;
• Zener diodes: one for 9.1 V, one for 10 V;
• LED bulbs (RGB): red, blue, green.

For LEDs, using a tester, you need to determine and check the pins so that they match the color. The device is assembled according to the diagram.

The components are tried on the board and cut to the appropriate sizes. It is advisable to arrange the components so that they take up less space.

It is better to solder LEDs to wires rather than to a board, so that the indicators can be more conveniently placed on the dashboard.

Based on the manufactured device, it is impossible to determine specific battery voltage values; you can only navigate within what limits it is located:

• red lights up if the voltage is from 6 to 11 V;
• blue corresponds to voltage from 11 to 13 V;
• green means fully charged, meaning the voltage is greater than 13V.

The battery voltage indicator can be installed anywhere in the cabin. It is most convenient to place it at the bottom of the steering column: the LEDs will be clearly visible and will not interfere with control. In addition, the device can be easily connected to the ignition switch. After installation, the driver will always be able to know how charged his car’s battery is and charge his battery if necessary.