The device is connected to the vehicle's on-board network and is designed to quickly determine its state by four LEDs. Which indicate the following voltages:
If two adjacent LEDs are blinking, then the voltage is at the boundaries of the specified intervals. Let's take a look at the diagram of the device, which is assembled on just one microcircuit:
Before us are four operational amplifiers D1.1 - D1.4, connected according to the comparator circuit. Each of them is tuned to its own range using resistive dividers and controls its own LED. The monitored voltage is applied to the inverse inputs of the amplifiers, on the straight lines - the exemplary voltage obtained using the simplest stabilizer (VD1, R7, C1) and resistive dividers R1 - R6. Thanks to the VD2 - VD4 diodes, the ignition of each next LED (from bottom to top) turns off the previous one. Thus, at any given time, only one LED is on or not a single one is on (voltage is below 11.7 V). Choke T1 and capacitors C2, C3 form a filter that eliminates impulse noise through the power supply circuits of the device.
Any fixed resistors can be used in the device, which it is desirable to select as accurately as possible. Since there is no 500 Ohm nominal in the standard row, resistor R4 is assembled from two 1 kOhm resistors connected in parallel. Trimmer resistor R5 is multiturn, for example SP3-19a. Capacitors C2, C3 - K73-9 for an operating voltage of 250 V, C1 - type K10-17. In place of VD1, any Zener diode of type D818 can work, but the most thermally stable with the letters E, D and G. As LEDs, you can use any indicator diodes with the lowest possible glow current (ideally, a series of instrumentation). Diodes VD2 - VD4 - any pulse.
The choke is made on a K10x6x3 ferrite ring of 2000NM1 ferrite and contains two windings of 30 turns each, made with a PELSHO-0.12 wire. When you turn on the choke, it is very important to turn on the windings in concert (the beginning of the windings is indicated by dots), otherwise there will be no sense from it as a filter. Establishing the device comes down to adjusting the resistor R5, which is set to the lower indication threshold (below 11.7 V, HL4 has just gone out) and, if necessary, selecting R1 at the upper threshold (above 14.8 V, HL1 has just turned on). All intermediate ranges will be set automatically. The current consumption of the device must be within 20 - 25 mA.
For the first time, I was offered to write a review on a product by representatives of the store, my choice fell on a car USB charger under the iMars brand with two ports and an indicator of voltage and current. The ultimate goal was to replace two devices in my father's car - a voltmeter in the cigarette lighter, with which my father monitors the battery voltage in winter and the need to charge it, as well as a simple noname charger for the phone with a maximum current of 500mA.
Manufacturer promises maximum charging current 4.8A (2.4A + 2.4A), measuring the voltage of the vehicle's on-board network and the charging current of the connected devices. Let's see if we can replace two devices with one and whether the manufacturer's promises are confirmed further ...
The charger was packed in a cardboard box, inside which was the charger itself. No instructions or anything like that. All inscriptions on the box are in English.
Unpacking
Immediately after receiving the parcel, I decided to test the charger in my father's car (VAZ 2111) to check if it works. And then the first problem awaited me - the charger did not reach the length of the central contact of the cigarette lighter in this car ... I tested it in my Skoda Fabia - charging worked, but it is somehow not very convenient to carry out tests in the car, so I decided to power the charger at home from the power supply on 12V through the cigarette lighter socket to a cable that was bought sometime on aliexpress. And then the second problem awaited me - in this connector the charger also did not reach the central contact. The depth of the charger of 39 mm turned out to be too large ... So even without starting testing, we can say that the charger is not suitable for all cars and connectors, the maximum depth at which it will work is about 37 mm.
Something like using wires and blue electrical tape, I connected the charger to the power supply from the laptop, the charger displayed a value of 16.8U. 
Ok, the first simple test - connected to the charger iPad mini, charging is in progress. The indication, voltage and charging current change approximately every 2 seconds. Shows 2.15A current.
Next, you need to check the manufacturer's statement about the maximum current of 4.8A, but unfortunately I do not have a USB load, which many here use to test chargers, so I came up with the use of car incandescent lamps as a load (warm lamp load, in the literal sense of the word ).
I connected one lamp to the 12V H4 autolamp via a USB tester - the charger displays a current of 2.32A, the tester shows a little less, 2.14A
Let's continue testing, I'll try to connect the phone to another port together with the lamp. Since I don't have a second USB tester, I use a multimeter to measure the lamp current, and a tester for the phone. And then a surprise, the phone shows that it is charging, but the tester displays a very small current, only 0.09A.
Let's try to load the charger more. I connect the H4 light bulb to one port, the same as in the first experiment, and to the second - a 24V autolamp - its resistance is higher, the current will be less.
Result - 3.03A is displayed on the charger, 2.1A on the first lamp (the 5A limit is selected on the multimeter, look at the lower black scale), on the second lamp, the current is 0.66A. The total comes out 2.76A, the difference with the charging readings is 0.27A. The voltage dropped to unacceptable 4.42V.
Well, let's try all the same to squeeze the maximum out of this charge - I connect the same 12V H4 lamp, as in the first experiment, only with a much shorter USB cable. If you connect it to a working charger, then the protection is triggered and the charging is turned off, but if you first connect the load and then apply power to the charger, the lamp lights up:
The charger shows us a current of 3.28A, while the screen flickers noticeably more. The multimeter shows the current through the 2.9A lamp. Unfortunately, it was not possible to measure the voltage, since the USB tester was wildly sausage, all the segments glowed on the screen, the lamp connected through it did not glow. We can conclude that the maximum current that these charges can give is about 3A, but due to the voltage drop and ripple, no phone will charge.
You can easily disassemble the charger by picking up the silver display frame with something sharp. The detail covering the display is held on latches on the sides. Removing it - we open the inner world of the charger:
The protective film has not been removed on the screen, if you remove it, the numbers on the indicator will be clearer.
If you pull on the USB connectors, you can get the charger board. It consists of two parts connected at right angles - on the larger board there is an impulse voltage regulator, on the smaller one - USB ports, a display and a circuit for measuring and displaying voltage and current.
Summing up, I want to note that the manufacturer, as always, indicated overestimated current characteristics, the charger will not be able to issue 4.8A, the maximum that can be counted on is about 2.4A for both ports. Also, the shape of the charger will not allow it to be used in some cars with a deep cigarette lighter socket. In general, I liked the device, it is convenient that it combines the functions of a charger and a voltmeter, the current measurement function seems to me not so useful. After the review, I still plan to give the charger to my father, but for this I will replace the cigarette lighter socket with another, more standard one (since the VAZ 211x has problems with many charges in the cigarette lighter).
Finally, I want to note that banggood has sales, recently there was a discount on this charger and it cost $ 3.69
The product was provided for writing a review by the store. The review is published in accordance with clause 18 of the Site Rules.
I plan to buy +10 Add to favourites Review liked +10 +19I rarely use my car. In fact, it is not clear why he is to me. Well, as a result, the battery always "sits down". And every time I have to attach a spare battery, and put the hooked one on charge. It is an ever-painful problem to prevent the battery on a car from being discharged below normal.
Therefore, I put together this "Car battery voltage indicator" circuit, which I found on the Internet long ago and kept it.
But I changed it a little, and instead of 10 separate LEDs that were in the original circuit, I used a 10-segment LED indicator, because it takes up less space.
Required radio parts:
1. trimmer resistor 5k - 2 pcs.
2.chip LM3914
3.10 segment LED strip (I used Kingbight DC-763HWA)
4.R1 4.7k resistor
5.R2 1.2K resistor
6. For adjustment, you will need a voltmeter and an adjustable power supply from 10 to 15 volts.
Here is the circuit board of the device.
As you can see in the photo, I cut off one lead at the right trimmer.
After mounting the parts on the board, device configuration is required. Apply 10.5 volts and adjust the right trimmer so that the first strip on the 10-segment display lights up.
Apply 15 Volts and adjust so that the last strip on the 10-segment indicator lights up. And remember only one strip should always be lit. Secure your device to a convenient location.
You now have a 10-segment meter showing the battery voltage in 0.5 volt increments.
P. Alekseev
The voltage control of the on-board electrical network of the car can be carried out by installing a voltmeter in the car to assess the charge of the battery, the operation of the generator and the voltage regulator relay. At the same time, its significance in cars with an ammeter ("Moskvich" of all types) is not lower than in cars without an ammeter ("Zhiguli" of all models). This is explained by the fact that the ammeter shows whether the battery is charging or not, whether energy is being consumed from the generator or the battery, but it does not allow us to unambiguously judge the state of the battery: it is fully charged (therefore, there is no charging current), discharged, but charging no due to the low voltage of the generator (adjustment of the relay-regulator is needed), etc. Thus, the voltmeter, without diminishing the merits of the ammeter, separately, and better in combination with it, will allow to gradually monitor the state of the vehicle's on-board network before starting the engine, during operation at idle, medium or high speed.
Since the monitored voltage of the on-board network can be in the range of 12 ... 15 V (or 10 ... 15 V, depending on the required control limits), the dial voltmeter scale for better clarity should be stretched within these limits, otherwise the information content of the device will be small ... In addition, it is necessary to take into account the complexity of placing (or embedding into the panel) of this device in the passenger compartment.
As experience shows, a voltmeter-indicator, made on the basis of miniature (signal) incandescent lamps, covered with color filters, is quite informative.
A schematic diagram of such a device is shown in Fig. 1.
The choice of the controlled voltage range and its division into sections depends on the desire of the designer. The author adopted the range of controlled voltage 12 V and higher (practically up to 15 ... 16 V), with its breakdown into sections, as shown in Fig. 2.
Figure: 2. Diagram of the sections of the controlled voltage range
The sections "No charging", "Normal, charging current" and "Very high charging current" correspond to the burning of incandescent lamps HL1, HL2 and HL3. These lamps glow at voltages in the vehicle's on-board network of 12 ... 13.7 V, 13.2 ... 14.6 V, 14.2 V and higher. In the "Low charging current" and "High charging current" overlap zones, two lamps light each, indicating that the voltage in the vehicle's network is at one or another extreme value relative to normal. Lamp HL1 has an orange filter, HL2 is green, and HL3 is red. They are located on the front panel of the device from left to right, providing easy monitoring of voltage and its changes.
The voltmeter-indicator consists of three measuring stages, each of which corresponds to one of the voltage sections and controls "its own" lamp. The measuring stages are assembled according to identical schemes (the rightmost one for the "14.2 V and more" section is not complete) and differ only in the threshold voltages of operation.
The device works as follows. When the ignition switch is turned on, the on-board network power is supplied to the +12 V bus, and if the battery voltage is 12 V or higher, then the current flowing through the opened Zener diode VD1 and resistors R3 and R4 will open the transistor VT1. In this case, the HL1 lamp, included in the collector circuit of this transistor, will receive power and will glow. If the battery voltage is below 12 V (it is discharged), the HL1 lamp will not light up. It will also go out when the car engine is started, if the battery voltage drops below 12 V during the operation of the starter (this usually happens). At the same time, the other lamps of the voltmeter-indicator do not light up because the opening voltage of the remaining zener diodes is greater than the opening voltage of the zener diode VD1.
When the voltage of the on-board network rises to 13.2 B, the second measuring stage is triggered on the Zener diode VD3 and the transistor VT3 and the HL2 lamp lights up (the HL1 lamp continues to burn). A further increase in voltage to 13.7 V leads to the opening of the Zener diode VD2 and the transistor VT2 of the first stage, which bypasses the emitter junction of the transistor VT1, ensuring its closing and extinguishing of the HL1 lamp. At this time, only the HL2 lamp is on on the front panel of the voltmeter-indicator.
At a voltage of 14.2 V, the Zener diodes VD5, VD6 and the VT5 transistor of the third measuring stage will open. The HL3 lamp will now light up (the HL2 lamp remains on). If the voltage of the on-board network reaches 14.6 V, the Zener diode VD4 and the transistor VT4 of the second measuring stage will open, which will lead to the closing of the transistor VT3 and the extinction of the HL2 lamp. Only the HL3 lamp remains illuminated on the panel of the device, which will continue to burn with a further increase in voltage.
When the voltage of the on-board network decreases, for example, from 15 to 12 V, the switching order of the warning lamps will be reversed.
Resistors Rl, R7 and R13 protect the KT608B transistors from collector current overload when the HL1 - HL3 lamps are turned on, when the resistance of their cold filaments is 10 ... 20 Ohm. Resistors R2, R8 and R14 shunt transistors VT1, VT3 and VT5, reducing the current flowing through them at the moments of switching, when they dissipate maximum power. Shunt resistors allow KT608B transistors to operate without heat sinks, while the initial lamp current (40 ... 50 mA) heats up the filament very weakly and does not interfere with observation.
As indicators HL1 - HL3 in the device, you can use incandescent lamps MH13-0.18 (13.5 Vx0.18 A) or automobile 12 B X 1 Sv, the brightness of which is sufficient for observation in any conditions.
The stabilization voltage of the Zener diode VD1 should be 11.2 V, VD2 - 11.5 V, VD3 - 12.2 V, VD4 - 12.5 V. The total stabilization voltage of the Zener diodes VD5 and VD6 must be selected equal to 13.2 V.
In the absence of the possibility of selecting zener diodes, the required operating thresholds of the measuring stages can be obtained by changing the values \u200b\u200bof the resistors R3, R5, R11, R15 or R4, R6, R10, R12, R16, as well as by selecting both at the same time. To reduce the operation threshold of transistors, you need to reduce the resistances of the resistors R3, R5, R9, Rll, R15 or increase - R4, R6, R10, R12, R16 and vice versa. Practically, even with small changes in the resistances of these resistors, it is possible to change the response thresholds of the cascades by 0.2 ... 0.8 V.
The static current transfer coefficient h21e of transistors KT608 (VT1, VT3, VT5) must be at least 200. With a smaller coefficient h21e, the process of opening and closing these transistors will be delayed up to 0.3 ... 0.4 V change in the input voltage, which is undesirable with the point of view of clarity ("sluggish" switching lamps) and the accuracy of measuring the on-board voltage.
The same results are obtained by switching on diodes in the forward direction in series with zener diodes (to facilitate the selection of the operating voltage of the measuring stages). This is due to the fact that at low base currents of transistors, diodes (silicon and germanium) operate on a smoothly bending initial section of the direct branch of the current-voltage characteristic, where the increase in current with increasing voltage is relatively small.
The coefficient h21e of transistors KT312B (VT2, VT4) or replacing them KT315 transistors can be 50 ... 80. In the case of using transistors of the KT312 series with an h21e coefficient of more than 100 ... 150 at the moments of switching the measuring stages, an oscillatory process may occur, in which the HL1 or HL2 lamps will flash with a frequency of 3 ... 5 Hz. This phenomenon can be eliminated by connecting a 0.01 μF capacitor between the base and the collector of transistors VT2, VT4. Capacitors of the same capacities can shunt the emitter-collector sections of transistors VT1, VT3, VT5. But it is not necessary to do this (it is even better not to do it), since self-excitation occurs with a slight change in the voltage of the on-board network (0.03 ... 0.05 V) and, in addition, it very well informs that the mains voltage is at the border , transition from one measuring section to another.
The performance of the voltmeter-indicator and the accuracy of measuring the boundaries of the intervals are checked according to the diagram in Fig. 3, using a regulated DC voltage source (10 to 16 V) with an allowable load current of 300 mA and a voltmeter.
Slowly increasing the voltage from 10 to 15 ... 16 V and observing the lighting and extinguishing of the lamps, they check the boundaries of the areas of operation of the indicators. In the event of a discrepancy between these boundaries (see Fig. 2), which can be in the range of 0.2 ... 0.5 V due to the spread of the parameters of the zener diodes and transistors, or if you want to change these boundaries, the zener diodes are replaced with others that have the corresponding stabilization voltage.
The design of the device is arbitrary. The author, for example, mounted it in a plastic box with dimensions 35x75x90 mm. On the front wall (35X75 mm) there are three lanterns (with orange, green and red filters). The box is installed (pre-fitted in place) under the dashboard (to the left of the steering column) of the Moskvich-408 car.
The design looks good if you cut a slot (6x50 mm) on the front wall of the box and cover it with a strip of frosted glass framed by a decorative frame. Flat color filters and indicator lamps HL1 - HL3 are installed under the glass. To eliminate illumination by lamps of "not their" color filters, partitions should be strengthened in the corresponding places of the gap.
The voltmeter-indicator can be used with equal success on all types of trucks and buses. When the vehicle's on-board network voltage is 24 V, the following changes must be made to the device:
set the lamps MH26-0.12 (26 V X 0.12 A) or MH36-0.12 (36 V X 0.12 A) as indicators HL1 - HL3;
replace the D814 zener diodes with the KS524G and KS527A zener diodes (possibly sequential switching on of other zener diodes)
increase the resistance of resistors Rl, R7 and R13 to 100 ... 120 Ohm, and exclude resistors R2, R8 and R14.
In a 24-volt voltmeter-indicator, transistors KT608B and KT312B (KT315G, E, V, D) can be used.
The regulated voltage source (see Fig. 3) must have adjustment limits of 20 ... 30 V. The voltage control range (see Fig. 2) is broken down on the basis of the technical operating conditions of batteries and electrical equipment of cars.
In fact, all previous domestic cars have arrow voltage indicators. on the battery. Simple indicators, functioning in a limited voltage range, help the car owner to timely detect an overload of the generator, the disappearance of a contact or a malfunction in the relay-regulator.
There is no voltmeter in the current domestic cars and practically in all modern "foreign cars". There is only an indicator lamp, which must glow with a significant decrease in the voltage on the battery.
But, firstly, not only a significant decrease in voltage is scary for the battery, but also an overcharge.
Secondly, as practice shows, the standard indicator does not actually respond to turning off the battery while the engine is running. That is, if, for example, a terminal is disconnected, you will find it only when you try to start the engine.
Description of the work of the voltmeter-indicator of the vehicle on-board network
Figure 1 shows the electrical circuit of a car voltmeter operating on an analog principle, but giving information on a two-digit digital indicator.
The sampling interval is 10 to 17 volts. The electrical circuit contains a meter on a comparator microcircuit LM3914 and an electrical indication circuit on a diode decimal-to-binary converter, a binary-seven-segment decoder and two seven-segment indicators.
The A2 microcircuit with the help of trimming resistors R4 and R5 is set to measure the input voltage going to the divider R1-R3 in the range from 10 to 17 V. At the same time, A2 indicates actually from 0 to 7, that is, the voltage of 10 V is taken as zero. The display at output A2 functions as a moving point.
That is, at an arbitrary moment only one of its output keys is open. Instead of indicator LEDs, the inputs of the decoder D1, pulled up to unity, are connected to the outputs of A2, but through the circuit on the VD2-VD12 diodes, which, together with R7-R8, is a decimal-binary converter that converts decimal numbers from 0 to 7 into a three-digit binary code. This code goes to the outputs of the D1 decoder, designed to work together with a seven-segment LED indicator.
Capacitance C3 is necessary so that the voltage measurement is performed smoothly, with a slight delay. This allows you to prevent the appearance of erratic unreadable readings due to impulse noise in the vehicle's on-board circuit and excessively rapid voltage changes.
Stabilizer 7805 can be exchanged for KR142EN5A. Diode 1N4007 - an arbitrary rectifier diode of low or medium power, for example, KD105. Diodes 1N4148 can be changed to KD522, KD521. Capacitance C1 must be for a voltage of more than 20 V.
Setting up the voltmeter is easier with an adjustable laboratory power supply. Apply voltage 17 V and by turning potentiometer R4 get the reading "17". Next, apply 10 V and turn the potentiometer R5 to get the reading "10". Then check the compliance of the indication with the actual voltage within the entire range (10-17 V). If it is necessary to adjust with R4 and R5 several more times.