The review will include a study of the few characteristics of this module, a slight modification to adjust the indication thresholds, and installation of a power bank with three lithium batteries (3S connection circuit) into the case. There was already a similar board for one lithium battery, but there the author boasted more about his “collective farm” and did not study the board itself. This review will contain a complete circuit diagram and modification of the board.
While ordering another electronic item from DX, I accidentally noticed this module and remembered that I had an ancient Power Bank lying around (hereinafter I will call it PB to avoid disputes about the correct spelling) in which there is not even an indication of the battery charge level. After some hesitation, I added it to my cart. I would not buy such a board separately. Laziness goes to the post office to buy hundred-ruble bags and my conscience does not allow me to bother sellers with such a trifle. By the way, I ask you in advance not to reveal to me the truth that in other stores these boards are several times cheaper. I took it here solely because of convenience (added to a large order). The difference of 100 rubles is insignificant for me.
The board arrived in a small antistatic bag. 
All elements are located on one side. Two contacts for connecting the battery for soldering. Indication by four LEDs, each of which turns on at a certain voltage value on the battery. The board is powered by the same voltage that it measures. The edges are not processed (textolite fibers were sticking out). The installation of the elements is neat, only the LEDs are sealed crookedly and filled with unwashed flux. I give the machine a five, the installer a two. 
The board seems completely microscopic. 
I started with the main thing - I measured the response thresholds of the LEDs. 
In a small voltage range (tens of millivolts), the LED blinks or lights dimly. After several repetitions I got the following threshold values:
- red LED: 11.7 V;
- 1st yellow LED: 12.1 V;
- 2nd yellow LED: 12.5 V;
- green LED: 12.9 V.
Consumption from 26 mA (11 V, LEDs are not lit) to 59 mA (14 V, all LEDs are lit).
It immediately became clear that the board was made for a lead-acid battery. It's a shame, I have lithium. At a voltage of 3.9 V per element (slightly discharged), even the red LED will go out. Of course, I didn’t expect the bells and whistles of the indicator. Was hoping for something like . No worries, I'll improve it. Before that I redrew the diagram. 
Nothing revolutionary. A parallel stabilizer (a stabilizer with parallel connection of a control element, in this case R14, R15), using a resistive divider R6...R11, generates a series of reference voltages that are supplied to the non-inverting inputs of four comparators (one microcircuit, open-collector transistor output). The inverting inputs are supplied with supply voltage after the divider R1, R12. When the voltage at the inverting input exceeds the voltage at the non-inverting input, the output transistor opens and turns on the corresponding LED. There are many varieties of such a scheme (,), but the principle of operation is the same for all. You can read in more detail. Sometimes another LED is added that operates continuously, which increases the number of indication levels to five.
Modification for lithium
The modification was reduced to changing the parameters of the divider R6...R11, taking into account the typical voltages of lithium batteries (3...4.2 V, three in series). The required indication range is 9…12.6 V. It turned out that I had very few resistors of this standard size, I was too lazy to take out a hairdryer and solder them out of the radio junk, so after a few experiments I managed to get by with adding two 10 kOhm resistors. While still working, I decided to align the LEDs. As a result, three out of four stopped working. After a little shock, I realized that the board is not very good with the metallization of the holes, and the soldering is only on one side. I tinned it again, sparing no rosin and solder. All LEDs worked except one yellow one. I applied a couple of volts directly to him and realized that he was a corpse. Saying: “It’s good that it’s not a comparator,” he rummaged through his reserves and put green instead (it seemed more logical). As a result, the circuit began to look like this (the added resistors are highlighted in red). 
As a result of the refinement, the following response thresholds were obtained:
- red LED: 10.0 V (3.33 V per element, charging required);
- yellow LED: 10.6 V (3.53 V per element, charging is desirable);
- 1st green LED: 11.3 V (3.77 V per element, charge more than 50%);
- 2nd green LED: 12.0 V (4 V per element, battery fully charged).
If desired, it would be possible to choose better thresholds, but I am happy with this option.
Intended use
The object of modification was supposed to be such a PB. 
It was purchased back in '11, when the term power bank did not yet exist. There were just mobile batteries. I liked this model because it had a multivolt output (5, 9 and 12 V), was purchased and subsequently modified several times. The internals are similar to (in the same review there is a similar modification, only with a homemade board). Three flat batteries, each with its own protection, are connected in series and connected directly to the 12 V output/input. 9 V is made by a linear stabilizer. To obtain 5 V, a step-down DC-DC converter board is used. Through it, the PB produces 3500 mAh, which corresponds to the capacity of each element of about 1800 mAh. To prevent batteries from discharging during storage, they are mechanically switched off using a key switch. The only indicator is a two-color LED connected to the converter. Normal operation and overcurrent are displayed. 
All electronics are located next to the batteries, the free space is filled with “branded” pieces of Chinese cardboard. I pulled out everything that could be pulled out, tried on the board and the button that would connect it (so that it wouldn’t light up all the time). 
I made holes in the designated places. The burnt out LED also came in handy as a button. 
I installed it and soldered it. Initially, all connectors to the PB housing were secured with some kind of sealant. I didn't change the technology. It would be better to fix the button with hot glue or polymorphus so that it would not spring back, but I didn’t bother and just poured more sealant. It will harden after drying. I did it late in the evening and left it open overnight. I collected it in the morning. 
Conclusions.
The board fully performs its functions. Lithium batteries require modification, but lead batteries can be used straight away. Another thing is that devices with such batteries (cars, UPS, solar battery controller) usually already have an indication. In short, the board is in the category of “buy to keep lying around in your desk just in case.” If you have time, you can make such a circuit yourself or simply install a voltmeter.
I'm planning to buy +29 Add to favorites I liked the review +33 +57Not all cars have an indicator that displays the battery charge level. The car owner must independently monitor this indicator, periodically checking it with a voltmeter, having previously disconnected the battery from the car's electrical network. However, a simple electronic device will allow you to get approximate indicators without leaving the salon.
Selection of circuit and components
Finished design
Structurally, a homemade battery charge monitoring 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 activating one of them, the information received is correctly interpreted.
Due to the small size of the device, you can use a regular breadboard. The optimal device circuit is pre-selected. 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 components, it is necessary to arrange them on the printed circuit board according to the diagram. Only after this can you cut it to the desired size. It is important that the indicator has minimal dimensions. If you plan to install it in a housing, you should take into account its internal dimensions.
This circuit is designed to monitor the operation of a car battery with a network 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.
Today we will make a simple design to help any car enthusiast. Every driver is familiar with the situation when car battery discharged at the most inconvenient moment and to guard against such cases, you need charge indicator and control car battery. Such a controller has Three built-in LED indicators - yellow, green and red.
Due to its compact size
circuit board, the controller circuit can be carefully adapted on the control panel or somewhere in the front board; in general, you need to act according to the circumstances, being guided by the features of the control panel of your car.The device is implemented on just one chip and is powered directly from the on-board 12 Volt network.
The device itself was assembled at the request of a friend who complained about the low battery level in winter. The entire process is monitored by a microcircuit that works very accurately.
Zener diode - any one will do, domestic or imported, for any power. The main thing is to choose a zener diode with a stabilization voltage of 5.6 Volts. Of the most common zener diodes, KS156A, BZX55C5V6, BZX79-C5V6, BZX88C5V6 and others are excellent.
As we know, tension in the on-board network when the car is running, it does not exceed 14.4 Volts, and the voltage of the battery itself is 12-13 Volts. When everything is normal, that is, the voltage is normal, the green LED of the controller lights up, when it is above the normal limits, the red one lights up, and when the voltage on the battery is below 12 Volts, the yellow LED lights up.
When the car is running very rarely the red LED may light up, don’t worry - this is normal! When the yellow LED is on, the battery needs to be charged, but for those who don’t have chargers, it doesn’t matter! On our website we have provided a huge number of charger circuits for every taste!
Regarding the housing for the indicator, I think that if you adapt the device, say, under a board, then there is no need for a housing, just fix the board with silicone or hot-melt adhesive and the device will serve you faithfully for a long time.
When the battery is discharged, starting the car is quite problematic. To avoid such an unpleasant “surprise”, it is enough to simply use a voltmeter from time to time. However, not all motorists and do not always do this, because it is much more convenient to have some kind of device that shows how much longer the battery charge will last.
What are the indicators?
The rechargeable battery (or battery) consists of six interconnected elements, the voltage in each should normally be about 2.15 volts, i.e. the total battery voltage approaches 13.5 volts. If the charge drops below critical values (approximately 9.5 volts), this can lead to deep discharge of the battery and, as a result, its complete failure.
Modern technologies “meet” motorists halfway and make their lives 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, it is necessary to use other types of indicators of this important indicator. So, you can find separate crystal displays on the dashboard, there are hygrometer indicators, and you can also (if you have the appropriate skills) make a battery charge indicator yourself. Many alarm 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 a hydrometer. It consists of an eye, a light guide, a leg and a float (that’s why 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 that shows the three main states of the battery:
- the green float ball shines through the viewing eye, which means that the battery is more than half charged;
- the eye remains black (this is visible through the indicator tube), 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 is visible 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 is “thirsty” - the electrolyte level is critical, it is urgently necessary to add distilled water (and this is quite difficult to do, since such batteries are maintenance-free).
Note! Although a built-in battery charge 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 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 cannot withstand the temperature conditions of the battery, so the data is received incorrectly;
- float indicators do not in any way determine the temperature of the electrolytic liquid, but the density also depends on it, so an electrolyte at a low 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 battery monitoring devices; each car owner can choose the design and functions to suit 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 of all devices is the same - to determine how charged the battery is and to signal about it.
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 control 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 dimensions of the indicator window are 4.3 by 2 cm.
If you install a second battery in a car, you can use an indicator from TMS - this is a small panel made of industrial aluminum with LEDs with a built-in voltmeter and a switch between adjacent batteries.
Among the expensive models (and unreasonably expensive, for the price of a new battery), we can highlight the voltage controllers of the American company “Faria Euro Black Style”. The body color is usually black, the diameter of the display window is 5.3 cm, and the screen is illuminated in white. 12 volts are required for power supply.
How to assemble a charge indicator yourself
If a car owner is comfortable with a soldering iron, he can assemble the analyzer with his own hands; you can find many assembly diagrams. Using one, the simplest, you can assemble a charge indicator reminiscent of the DC-12 V described above. It operates on 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 green LED each. After assembly, according to the diagram, the board is inserted onto the dashboard, and the ends of the LEDs are placed in a place convenient for viewing. In this case, a fully charged battery will be indicated in green, blue - when the charge is normal (from 11 to 13 volts), and if the battery is close to discharge, the red LED will light up.
It is unpleasant when a car cannot start simply because the battery is discharged at the most inopportune moment. A voltage indicator, purchased in a store or soldered yourself, will help avoid unpleasant “surprises” and warn in advance that the battery requires recharging.
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