The simplest case is shown in Figure 1. If the voltage at the B + terminal is 9V, only the green LED will be on, since the voltage at the base of Q1 is 1.58V, while the voltage at the emitter is equal to the voltage drop across the LED D1, in a typical case is 1.8V and Q1 is held closed. As the battery charge decreases, the voltage across LED D2 remains virtually unchanged, while the voltage across the base decreases, and at some point in time, Q1 will begin to conduct current. As a result, some of the current will branch off into the red LED D1, and this fraction will increase until all the current flows into the red LED.

Picture 1.	Basic circuit of a battery voltage monitor.

For typical elements of a two-color LED, the difference in forward voltages is 0.25 V. It is this value that determines the transition region from green to red. A complete change in the color of the glow, set by the ratio of the resistances of the divider resistors R1 and R2, occurs in the voltage range

The middle of the transition from one color to another is determined by the voltage difference between the LED and the base-emitter junction of the transistor and is equal to approximately 1.2 V. Thus, changing B + from 7.1 V to 5.8 V will change the green light to red.

Differences in voltage will depend on specific LED combinations and may not be sufficient to fully switch colors. However, the proposed circuit can still be used by connecting a diode in series with D2.

In Figure 2, R1 has been replaced with a Zener diode, resulting in a much narrower junction region. The divider no longer affects the circuit, and a complete change in the color of the glow occurs when the voltage B + changes by only 0.25 V. The voltage of the transition point will be equal to 1.2 V + V Z. (Here V Z is the voltage across the zener diode, in our case equal to about 7.2 V).

The disadvantage of such a circuit is its binding to a limited voltage scale of zener diodes. Further complicating the situation is the fact that low-voltage zener diodes have a too smooth bend in the characteristic, which does not allow you to accurately determine what the voltage V Z will be at low currents in the circuit. One solution to this problem might be to use a resistor in series with the zener diode to be able to make a small adjustment by slightly increasing the junction voltage.

With the shown resistances of the resistors, the circuit consumes a current of the order of 1 mA. With high brightness LEDs, this is sufficient for indoor use. But even this small current is significant for a 9-volt battery, so you have to choose between drawing extra current and the risk of leaving the power on when you don't need it. You will most likely feel the benefits of this monitor after the first unscheduled battery change.

The circuit can be converted so that the transition from green to red occurs when the input voltage rises. To do this, transistor Q1 must be replaced with NPN and the emitter and collector must be swapped. And with a pair of NPN and PNP transistors, you can make a window comparator.

Given the fairly large junction width, the circuit in Figure 1 is best suited for 9V batteries, while the circuit in Figure 2 can be adapted for other voltages.

What are the indicators of the charge of a car battery

The battery plays a key role in starting a car's engine. And how successful this launch will be depends largely on the state of charge. battery... Do many of us control the battery charge level? It is called, answer yourself this question. Therefore, it is highly likely 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 battery charge status. These indicators will be discussed in this article.

Technology does not stand still, and automotive manufacturers are struggling to make car travel and service as comfortable as possible. Therefore, on modern cars in the on-board computer, among other functions, you can find data on the battery voltage. But such opportunities are not available on all cars. Old cars may have an analog voltmeter, by which it is quite difficult to understand the state of the battery. For those new to the automotive business, we recommend that you familiarize yourself with the material about.

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

These 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 diagrams for making charge indicators with your own hands.

Built-in battery 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 how it looks if you take it out of the battery.

The device of the built-in battery indicator can be schematically represented as follows.

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

• As the battery is charged, the density of the electrolyte increases. In this case, the green ball-shaped float rises up the tube and becomes visible through the light guide into the indicator peephole. Typically, a green ball pops up when the battery is 65 percent charged or more;
• 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 "eye" 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 in the "eye" of the indicator there will be a red color;
• And another option is to lower the electrolyte level. Then the surface of the electrolyte will be visible through the "peephole" of the indicator. This will indicate the need to top up with distilled water. True, in the case of a maintenance-free battery, this will be problematic.

This built-in indicator allows for a preliminary assessment of the state of charge of the battery. Do not rely fully on the readings of the hydrometer. 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 only have one bank of data on density and state of charge. Since there is no message between them, one can only guess about the situation in other banks. For example, in this cell 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 intensive);
• The indicator is made of glass and plastic. Heat or cool plastic parts can warp. As a result, you will see garbled data;
• The density of the 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 charge indicators

Today, quite interesting devices can be found on sale for monitoring the battery charge level by its voltage. Let's take a look at some of them.

DC-12V battery charge level indicator

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

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

Main characteristics of the DC-12V indicator:

• Voltage range: 2.5-18 volts;
• Maximum current consumption: up to 20 mA;
• Dimensions of the printed circuit board: 43 by 20 millimeters.

Battery charge indicator circuit on LEDs. 12 volt battery charge control circuit

Making a battery charging control circuit for a car

In this article I want to tell you how to make automatic control over the charger, that is, so that the charger turns off itself upon completion of charging, and when the voltage on the battery drops, the charger turns on again.

I was asked by my father to make this device, since the garage is located far from home and running around to check how the charging is feeling there, it is not very convenient to charge the battery. Of course, it was possible to buy this device on Ali, but after the introduction of payment for delivery, the fee increased in price and therefore it was decided to make a homemade product with our own hands. If anyone wants to buy a ready-made board, then here is the link..http: //ali.pub/1pdfut

I looked for a board on an Internet in the .lay format, and I could not find it. I decided to do everything myself. And the program Sprint Layout'I met for the first time. therefore, I simply did not know about many functions (for example, a template), I drew everything by hand. It's good that the board is not that big, everything turned out fine. Then hydrogen peroxide with citric acid and etching. I drilled all the tracks and drilled holes. Further soldering of parts, Well, here's the finished module

Scheme for repetition;

Board in .lay format download ...

All the best…

xn - 100 - j4dau4ec0ao.xn - p1ai

Simple battery charge and discharge indicator

This battery indicator is based on an adjustable Zener diode TL431. With two resistors, the breakdown voltage can be set between 2.5 V and 36 V.

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

The only difference is adding n-p-n a transistor that will turn on any signaling device, for example, an LED or a buzzer. Below is a method for calculating the resistance R1 and examples for some voltages.

Battery discharge indicator circuit

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 a voltage divider across resistors R1 and R2. In the case of a discharge indicator, the LED should be on when the battery voltage is less than necessary. Therefore, an n-p-n transistor is added to the circuit.

As you can see, the regulated zener diode regulates the negative potential, so a resistor R3 is added to the circuit, the task of which is to turn on the transistor when the TL431 is 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 Ohm's law.

Of course, you can do without a transistor, but then the LED will go out when the voltage drops below the set level - the circuit is lower. 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 scheme has one drawback, which is constant current consumption, in the region of 10 mA.

Battery charge indicator circuit

V in this case the charge indicator will be on constantly when the voltage is greater than that which we determined using R1 and R2. Resistor R3 serves to limit the current to the diode.

It's time for what everyone loves the most - mathematicians.

I already said at the beginning that the breakdown voltage can be changed from 2.5V to 36V through the "Ref" input. And so, let's try to calculate something. Suppose that the indicator should light up when the battery voltage drops below 12 volts.

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

Resistor R1 is calculated 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 the 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 is as follows:

And here is a small list for the lazy. For a resistor R2 = 1k, the 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 low voltage, for example, 3.6V, the resistor R2 should have a higher resistance, for example, 10k, since the current consumption of the circuit will be less in this case.

A source

www.joyta.ru

The simplest battery level indicator

The most surprising thing is that the battery charge level indicator circuit does not contain any transistors, no microcircuits, no zener diodes. Only LEDs and resistors connected in such a way that an indication of the applied voltage level is provided.

Indicator circuit

The operation of the device is based on the starting voltage of the LED. Any LED is a semiconductor device that has a voltage limit point, only exceeding which it starts to work (light). Unlike an incandescent lamp, which has almost linear volt-ampere characteristics, the characteristic of a zener diode is very close to the LED, with a sharp current steepness with increasing voltage. in the chain for each segment of the chain separately. The voltage threshold for opening or starting an LED can range from 1.8 V to 2.6 V. It depends on the specific brand. As a result, each LED lights up only after the previous one is lit.

Assembling the battery level indicator

I assembled the circuit on a universal circuit board by soldering the output of the elements together. For a better perception, I took LEDs of different colors. Such an indicator can be made not only for six LEDs, but for example, for four. You can use the indicator not only for the battery, but to create a level indication on the music speakers. By connecting the device to the output of the power amplifier, parallel to the speaker. This allows you to monitor the critical levels for your loudspeaker, and you can find other uses for this truly very simple circuit.

sdelaysam-svoimirukami.ru

Battery end-of-charge indicator on LEDs

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 it 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

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 portable model can be assembled “on the knee” in a few minutes.

D809 - a 9V zener diode limits the voltage on the LEDs, and the differentiator itself is assembled on three resistors. Such an LED indicator is triggered by the current in the circuit. At a voltage of 14V and above, the current strength is sufficient for all LEDs to glow, at a voltage of 12-13.5V VD2 and VD3 glow, below 12V - VD1.

A more advanced version with a minimum of parts can be assembled on a budget voltage indicator - the AN6884 (KA2284) microcircuit.

Scheme led indicator battery charge level on the voltage comparator

The circuit works on the principle of a comparator. VD1 is a 7.6V zener diode, it serves as a reference voltage source. R1 is a voltage divider. At 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 during operation charger, making 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.

svetodiodinfo.ru

How to make a battery charge indicator on LEDs?

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 indicator You can do it yourself, 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: UOP1 + = UCT VD2 - UR8, UCT VD2 = UR8 + UR9 + UR10 + UR11 + UR12 = I * (R8 + R9 + R10 + R11 + R12) I = UCT VD2 / (R8 + R9 + R10 + R11 + R12) = 6.2 / (5100 + 1000 + 1000 + 1000 + 10000) = 0.34 mA, UR8 = I * R8 = 0.34 mA * 5.1 kΩ = 1.7V UOP1 + = 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 at its output will appear low level voltage, 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: UOP1- = I * R5 = UBAT - I * R6.

PCB and assembly parts

Printed circuit board made of one-sided foil-clad PCB, 40 x 37 mm, which can be downloaded here. 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 AL307 of any glow color.

This circuit can be used not only to monitor the voltage on 12 volt batteries. Having recalculated the values ​​of the resistors located in the input circuits, we get an LED indicator for any desired voltage. To do this, you should set the threshold voltages at which the LEDs will turn on, and then use the formulas for recalculating the resistances given above.

Read the same

ledjournal.info

Li-ion battery discharge indicator circuits to determine the charge level of a lithium battery (for example, 18650)

What could be sadder than a suddenly dead battery in a quadcopter during a flight or a turned off metal detector in a promising meadow? Now, if only it would be possible to know in advance how strongly the battery is charged! Then we could plug in the charger or put in a new set of batteries without waiting for the sad consequences.

And just here 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 were puffing over the implementation of this task, and today there is a whole carriage and a small cart of various circuitry solutions - from circuits on one transistor to sophisticated devices on microcontrollers.

Attention! The circuits given in the article only signal a low voltage on the battery. To prevent deep discharge, you must manually disconnect the load or use discharge controllers.

Option number 1

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

Let's see how it works.

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

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

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

Thus, in spite of its simplicity, the circuit allows you to know in advance that the battery has started to run out. While the battery voltage is 3.25V or more, the green LED is on. Between 3.00 and 3.25V, red begins to mix with green - the closer to 3.00 Volts, the more red. Finally, at 3V, only pure red is lit.

The disadvantage of the circuit is the complexity of the selection of zener diodes to obtain the required operation threshold, as well as the constant current consumption of the order of 1 mA. Well, it is possible that color blind people will not appreciate this idea with changing colors.

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

Option number 2

The following circuit uses the TL431, 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 voltage on the battery drops to this value, the microcircuit stops shunting the LED and it lights up. This will be a signal that the full discharge of the battery is very close (the minimum allowable voltage on one li-ion bank is 3.0 V).

If the device is powered by a battery from several cells connected in series lithium ion battery, then the above circuit must be connected to each bank separately. In this way:

To set up the circuit, we connect instead of batteries adjustable block power supply and selection of the resistor R2 (R4), we achieve the ignition of the LED at the moment we need.

Option number 3

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

Option number 4

A circuit based on two field-effect transistors, which literally consumes microcurrents in standby mode.

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

At a certain moment, as the battery is discharged, the voltage taken from the divider becomes insufficient to unlock VT1 and it closes. Consequently, a voltage appears at the gate of the second field worker, which is close to the supply voltage. It opens and lights up the LED. The glow of the LED signals us about the need to recharge the battery.

Transistors will do any n-channel with low cutoff voltage (the less the better). The performance of the 2N7000 has not been tested in this circuit.

Option number 5

On three transistors:

I think the diagram is self-explanatory. Thanks to the large coeff. amplification of three transistor stages, the circuit works very clearly - a difference of 1 hundredth of a volt is enough between a lit and unlit LED. The current consumption with the indication on is 3 mA, with the LED off - 0.3 mA.

Despite the bulky appearance of the circuit, the finished board has a rather modest size:

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

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

Option number 6

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

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

In this case, the green LED acts as a reference voltage source, consuming a current of about 15-20 mA. To get rid of such a voracious element, instead of an exemplary voltage source, you can use the same TL431, turning it on according to the following scheme *:

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

Option number 7

A circuit using so-called voltage monitors. They are also called supervisors and voltage detectors (voltdetectors) and are specialized microcircuits designed specifically for voltage monitoring.

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

Agree, it couldn't be easier! The BD47xx has an open collector output and also self-limits the output current to 12 mA. This allows you to connect an LED directly to it, 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;
• series MN1380 (or 1381, 1382 - they differ only in the case). 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 pick-up voltage is determined letter index: MN13811-L is just 3.0 Volts.

You can also take the Soviet counterpart - 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 think it's not worth completely discarding this microcircuit.

The undeniable advantages of circuits on voltage monitors are extremely low power consumption in the off state (units and even fractions of microamperes), as well as its extreme simplicity. Often, the entire circuit fits right on the LED pins:

To make the discharge indication even more visible, the voltage detector output can be loaded with a flashing LED (eg L-314 series). Or assemble the simplest "blinker" yourself for two bipolar transistors.

An example of a ready-made circuit that notifies of a dead battery using a flashing LED is shown below:

Another circuit with a blinking LED will be discussed below.

Option number 8

A cool circuit that triggers the blinking of the LED if the voltage is on lithium battery drops to 3.0 Volts:

This circuit causes a super-bright LED with a 2.5% duty cycle to flash (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? Unlikely.

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

Usually, 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 a lithium battery.

But there is also another solution. Logic elements - inverters can be used as an amplifier. Yes, this is a non-standard use of logic, but it works. A similar scheme is shown in the following version.

Option number 9

74HC04 circuit.

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

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

Option number 10

It's not even a discharge indicator, but rather a whole LED voltmeter! A linear scale of 10 LEDs provides a clear indication of the battery status. All functionality is implemented on just one single LM3914 microcircuit:

The divider R3-R4-R5 sets the lower (DIV_LO) and upper (DIV_HI) threshold voltages. At 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 the "point" mode. In this mode, only one LED is always lit, corresponding to the supply voltage. If you leave it as in the diagram, then a whole scale of LEDs will glow, which is irrational from the point of view of efficiency.

Only red LEDs should be taken as LEDs, because they have the lowest forward voltage during operation. If, for example, you take the blue LEDs, then when the battery runs down to 3 volts, they most likely will not light up at all.

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

The disadvantage of the circuit can be considered the impossibility of individual adjustment of the ignition threshold for each LED. You can set only the initial and final value, and the divider built into the microcircuit will divide this interval into equal 9 segments. But, as you know, closer to 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, and if you compare the same batteries, only discharged by 90% and 100%, you can see a difference of a whole volt!

The typical discharge graph of a Li-ion battery, shown below, clearly demonstrates this circumstance:

Thus, the use of a linear scale to indicate the degree of battery discharge does not seem to be very appropriate. We need a circuit that allows you to set the exact voltage values ​​at which this or that LED will light up.

Full control over the moments when the LEDs are turned on is given by the diagram below.

Option number 11

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

The circuit is operational up to a voltage of 2 Volts, consumes less than a milliampere (excluding the LED).

Of course, in order to reflect the real value of the consumed 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 the exact voltage values ​​corresponding to, for example, 5% -25% -50% -100% of the residual capacity.

Option number 12

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

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

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

The LED is taken in tricolor (from the LED strip), but only red and green are involved.

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

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

A freshly charged battery gives out about 4.1V - it is on green indicator... During charging, a voltage of 4.2V is present on the battery, while 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 number 13

Well, for a snack, I propose the option of reworking the standard protection board (they are also called charge-discharge controllers), which turns it into an indicator of a dead battery.

These boards (PCB modules) are mined from old batteries mobile phones almost on an industrial scale. Just pick up a discarded battery from a mobile phone on the street, gut it and the board is in your hands. Dispose of the rest properly.

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

Most often, a PCB board is like this:

Micro-assembly 8205 is two milliohm field pickups assembled in one case.

Having made some changes to the circuit (shown in red), we get an excellent indicator of the discharge of a li-ion battery, which practically does not consume current when it is off.

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

Resistor R3 limits the current through the LED. Its resistance must be selected in such a way that the LED glow is already noticeable, but the current consumption is not 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 disconnection of the battery at the time of discharge.

Instead of the 2N3906, any low-power available at hand will do. pnp transistor... It is not possible to simply solder the LED directly. the output current of the microcircuit that controls the keys is too small and requires amplification.

Please consider the fact that discharge indicator circuits themselves consume battery power! To avoid inadmissible discharge, connect indicator circuits after the power switch or use protection circuits to prevent deep discharge.

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

electro-shema.ru

Indicator for checking and monitoring the battery charge level

How can you make a simple voltage indicator for a 12V battery, which is used in cars, scooters, and other equipment? Having understood the principle of operation of the indicator circuit and the purpose of its parts, the circuit can be adjusted to almost any type of rechargeable batteries, changing the ratings of the corresponding electronic components.

It is no secret that it is necessary to control the discharge of batteries, since they have a threshold voltage. When the battery is discharged below the threshold voltage, a significant part of its capacity will be lost, as a result, it will not be able to deliver the declared current, and buying a new one is not a cheap pleasure.

A schematic diagram with the ratings that are indicated in it will give approximate information about the voltage at the battery terminals using three LEDs. LEDs can be of any color, but it is recommended to use such as shown in the photo, they will give a clearer associated idea of ​​the state of the battery (photo 3).

If the green LED is on, the battery voltage is within the normal range (from 11.6 to 13 Volts). White is on - voltage is 13 volts or more. When the red LED is on, it is necessary to disconnect the load, the battery needs to be recharged with a current of 0.1 A., since the battery voltage is below 11.5 V., the battery is more than 80% discharged.

Attention, these are approximate values, there may be differences, it all depends on the characteristics of the components used in the circuit.

The LEDs used in the circuit have very low current consumption, less than 15 (mA). Those who do not like this can put the tact button in the gap, in this case, the battery will be checked by turning on the button, and analyzing the color of the illuminated LED. The board must be protected from water and secured to the battery. It turned out a primitive voltmeter with constant source energy, the state of the battery can be checked at any time.

The board is very small - 2.2 cm. An Im358 microcircuit in a DIP-8 package is used, the precision of precision resistors is 1%, excluding current limiters. You can install any LEDs (3 mm, 5 mm) with a current of 20 mA.

The control was carried out using a laboratory power supply unit based on a linear LM 317 stabilizer, the device's response is clear, two LEDs may glow simultaneously. For fine tuning, it is recommended to use adjustment resistors (photo 2), with their help you can most accurately adjust the voltages at which the LEDs light up. The main part is the LM393 or LM358 microcircuit (analogs of KR1401CA3 / KF1401CA3), in which there are two comparators (photo 5).

As you can see from (photo 5) there are eight legs, four and eight are power, the rest are the inputs and outputs of the comparator. Let's analyze the principle of operation of one of them, there are three pins, two inputs (direct (non-inverting) "+" and inverting "-"), one output. The reference voltage is supplied to the inverting "+" (the voltage supplied to the inverting "-" input is compared with it). than direct) at the (+) power output.

The zener diode is connected in the opposite way (anode to (-), cathode to (+)), it has, as they say, a working current, with it it will stabilize well, look at the graph (photo 7).

Depending on the voltage and power of the zener diodes, the current differs, the documentation indicates the minimum current (Iz) and the maximum current (Izm) stabilization. It is necessary to select the desired one in the specified interval, although the minimum will be sufficient, the resistor makes it possible to achieve the required current value.

Let's get acquainted with the calculation: the total voltage is 10 V., the zener diode is designed for 5.6 V., we have 10-5.6 = 4.4 V. According to the documentation, min Ist = 5 mA. As a result, we have R = 4.4 V. / 0.005 A. = 880 Ohm. Small deviations in the resistance of the resistor are possible, this is not essential, the main condition is a current not less than Iz.

The voltage splitter includes three resistors 100 kΩ, 10 kΩ, 82 kΩ. A certain voltage "settles" on these passive components, then it is fed to the inverting input.

The voltage depends on the battery charge level. The circuit works as follows, a ZD1 5V6 zener diode that supplies a voltage of 5.6 V. to the direct inputs (the reference voltage is compared with the voltage at the non-direct inputs).

In case of a strong battery discharge, less voltage will be applied to the indirect input of the first comparator than to the direct input. A higher voltage will also be supplied to the input of the second comparator.

As a result, the first will give “-” at the output, the second will give “+”, the red LED will light up.

The green LED will shine if the first comparator gives "+", and the second "-". The white LED will light up if two comparators apply a “+” to the output; for the same reason, the green and white LEDs can light up simultaneously.

The most surprising thing is that the battery charge level indicator circuit does not contain any transistors, no microcircuits, no zener diodes. Only LEDs and resistors connected in such a way that an indication of the applied voltage level is provided.

Indicator circuit

The operation of the device is based on the starting voltage of the LED. Any LED is a semiconductor device that has a voltage limit point, only exceeding which it starts to work (light). Unlike an incandescent lamp, which has almost linear volt-ampere characteristics, the characteristic of a zener diode is very close to the LED, with a sharp current steepness with increasing voltage.
If you connect the LEDs in series with the resistors in the circuit, 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 the LED lighting can range from 1.8 V to 2.6 V. It all depends on the specific brand.
As a result, each LED only lights up after the previous one has lit up.

I assembled the circuit on a universal circuit board, soldering the output of the elements together. For a better perception, I took LEDs of different colors.
Such an indicator can be made not only for six LEDs, but, for example, for four.
You can use the indicator not only for the battery, but to create a level indication on the music speakers. By connecting the device to the output of the power amplifier, parallel to the speaker. This allows you to monitor the critical levels for your speaker system.
It is possible to find other applications of this, in truth, a very simple scheme.
nik34 sent:

Charge indicator based on old Li-Ion battery protection board.

An easy solution for indicating the end of a LiIon or LiPo battery charge from a solar battery can be made from ... any dead LiIon or LiPo battery :)

They use a six-legged charge controller on a specialized mikruh DW01 (JW01, JW11, K091, G2J, G3J, S8261, NE57600, etc. analogs). The task of this controller is to disconnect the battery from the load when the battery is fully discharged and disconnect the battery from charging when it reaches 4.25V.

Here is the last effect you can use. For my purposes, an LED is quite suitable, which will light up when the charge ends.

Here is a typical circuit for switching on this mikruhi and a circuit in which it needs to be redone. The whole alteration consists in soldering the mosfets and soldering the LED.

Take the red LED, it has a lower ignition voltage than other colors.

Now you need to connect this circuit after the traditional diode, which also traditionally steals from 0.2V (Schottky) to 0.6V from the solar battery, but it does not allow the battery to discharge on solar panel after dark. So, if you connect the circuit to the diode, then we get an indication of an undercharge of the battery at 0.6V, which is quite a lot.

Thus, the algorithm of work will be as follows: our SB, when illuminated, gives a spill on the lipolka and until the native charge controller on the battery works at a voltage of about 4.3V. As soon as the cut-off is triggered and the battery is turned off, the voltage on the diode jumps above 4.3V and our circuit, in turn, tries to protect its battery, which is no longer there, and by giving a command to a non-existent mosfet, the LED lights up.

After removing the SB light from the light, the voltage on it will drop and the LED will turn off, stopping eating precious milliamperes. The same solution can be used with other chargers, it is not necessary to focus on solar battery:)
You can arrange it as you like, since the controller's scarf is miniature, no more than 3-4 mm wide, here is an example:

Our magic mikruha on the left, two mosfets in one case on the right, they must be removed and soldered to the board in accordance with the LED circuit.

That's all, use it, it's easy.