I rarely use my car. In essence, it’s not clear why I need it. Well, as a result, the battery always runs out. And every time I have to connect a spare battery, and put the dead one on charge. It is always a painful problem - not to let the battery on your car discharge below normal.
Therefore, I put together this “Car Battery Voltage Indicator” circuit, which I found on the Internet a long time ago and kept with me.
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 components:
1.tuning resistor 5k – 2 pcs.
2.chip LM3914
3.10 segment LED light bar (I used Kingbight DC-763HWA)
4.resistor R1 4.7k
5. resistor R2 1.2 k
6.For setup 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 from the right tuning resistor.
After installing the parts on the board, the device needs to be configured. Apply a voltage of 10.5 Volts and adjust the right trimmer so that the first bar on the 10-segment indicator lights up.
Apply 15 volts and adjust until the last bar on the 10-segment indicator lights up. And remember, only one strip should always light up. Secure the device in a convenient place.
Now you have a 10-segment indicator showing battery voltage in 0.5 Volt increments.
Vehicle on-board voltage indicator, given in this article, is intended for visual monitoring of the voltage of the on-board network of a passenger car. Everyone knows that the normal voltage value available in the vehicle’s on-board network has a positive effect on the service life of the battery, especially in winter. Therefore, in severe frosts, it is advisable to use it to start a car engine.
It should be such that with the engine running well, the generator would be enough for all energy consumers. And at the same time, there should not be too much of it, as this can lead to overcharging the battery.
Description of the vehicle voltage indicator
Optimal voltage of the vehicle's on-board network with a 12V battery, the range is considered to be from 11.7V to 14V. Going beyond these limits is extremely undesirable, since when it drops below 11.7V, the battery suddenly discharges, and when it exceeds 14V, it begins to recharge. You can monitor the vehicle’s on-board network using a simple indicator consisting of two comparators and three LEDs, the diagram of which is given below.
Indicator circuit very simple, the essence of its work is that the current voltage taken from the divider, built on resistors R2, R3, R4, is compared with the reference, built on the zener diode VD1 (5.6V). The optimal voltage is shown by a green LED, a state above 14V is indicated by a red LED, and accordingly a yellow LED indicates a state below 11.7V. The op-amp used in this circuit
In fact, all previous domestic cars have dial voltage indicators. on the battery. The indicators are simple, operating in a limited voltage range, and help the car owner promptly detect generator overload, contact loss, or problems with the relay-regulator.
In current domestic cars and in fact in all modern “foreign cars” there is no voltmeter. There is only an indicator lamp, which must light up when the voltage on the battery decreases significantly.
But, firstly, not only a significant decrease in voltage is scary for the battery, but also overcharging.
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 only discover it when you try to start the engine.
Description of the operation of the voltmeter-indicator of the vehicle's on-board network
Figure 1 shows the electrical circuit of a car voltmeter operating on an analogue principle, but providing information to a two-digit digital indicator.
The measurement interval is from 10 to 17 volts. The electrical circuit contains a meter on the LM3914 comparator chip and an electrical indication circuit on a diode decimal-binary converter, a binary-seven-segment decoder and two seven-segment indicators.
Microcircuit A2, using trimmer resistances R4 and R5, is set to measure the input voltage going to the divider R1-R3 in the range from 10 to 17 V. In this case, A2 actually indicates from 0 to 7, that is, a voltage of 10 V is taken as zero. The display at output A2 operates as a moving point.
That is, at any moment only one of its output keys is open. Instead of indicator LEDs, the inputs of the decoder D1, pulled to one, are connected to the outputs of A2, but through an electrical circuit on diodes VD2-VD12, 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 terminals of the D1 decoder, designed to work together with a seven-segment LED indicator.
Capacitance C3 is necessary to ensure that the voltage is measured smoothly, with a slight delay. This prevents 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 replaced with KR142EN5A. Diode 1N4007 is an arbitrary rectifier diode of low or medium power, for example, KD105. Diodes 1N4148 can be replaced with KD522, KD521. Capacitance C1 must be for a voltage of more than 20 V.
It is easier to set up a voltmeter using an regulated laboratory power supply. Apply a voltage of 17 V and rotate potentiometer R4 to get the reading “17”. Next, apply 10 V and rotate potentiometer R5 to get a reading of “10”. Then check whether the indication corresponds to the actual voltage within the entire range (10-17 V). If necessary, adjust using R4 and R5 several more times.
The device connects to the vehicle’s on-board network and is designed to quickly determine its status using four LEDs. Which indicate the following voltages:
If two adjacent LEDs blink, then the voltage is at the boundaries of the indicated intervals. Let's take a look at the diagram of the device, which is assembled on just one chip:
Before us are four operational amplifiers D1.1 - D1.4, connected according to the comparator circuit. Each of them, using resistive dividers, is tuned to its own range and controls its own LED. The controlled voltage is supplied to the inverse inputs of the amplifiers, and to the direct inputs - a reference voltage obtained using a simple stabilizer (VD1, R7, C1) and resistive dividers R1 - R6. Thanks to diodes VD2 - VD4, lighting each next LED (from bottom to top) turns off the previous one. Thus, at any given time, only one LED is lit or none is lit (voltage below 11.7 V). Inductor T1 and capacitors C2, C3 form a filter that eliminates impulse noise in the power supply circuits of the device.
The device can use any fixed resistors, which it is advisable to select as accurately as possible. Since there is no 500 Ohm rating in the standard series, resistor R4 is assembled from two 1 kOhm resistors connected in parallel. Trimmer resistor R5 is multi-turn, 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 ones are those with the letters E, D and G. Any indicator LEDs with the lowest possible glow current can be used as LEDs (ideally a series of instrumentation devices). Diodes VD2 - VD4 - any pulse.
The choke is made on a K10x6x3 ferrite ring made of 2000NM1 ferrite and contains two windings of 30 turns each, made with PELSHO-0.12 wire. When turning on the choke, it is very important to turn on the windings in concert (the beginning of the windings is indicated by dots), otherwise it will be of no use as a filter. Setting up the device comes down to adjusting resistor R5, which sets the lower indication threshold (below 11.7 V, HL4 has just gone out) and, if necessary, selecting R1 according to the upper threshold (above 14.8 V, HL1 has just lit up). All intermediate ranges will be set automatically. The current consumption of the device should be within 20 - 25 mA.
P. Alekseev
Monitoring the voltage of the car's on-board electrical network can be done by installing a voltmeter in the car to assess the charge of the battery, the operation of the generator and the voltage relay regulator. Moreover, its significance in cars with an ammeter (Moskvich of all types) is no 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 battery, but it does not allow one to clearly 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 (the relay-regulator needs to be adjusted), etc. Thus, a voltmeter, without reducing the advantages of the ammeter, separately, or better in combination with it, will allow you 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 controlled voltage of the on-board network can be within 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 low . In addition, you need to take into account the complexity of placing (or embedding into a panel) this device in the car.
As experience shows, a voltmeter-indicator made on the basis of miniature (signal) incandescent lamps covered with color filters has quite sufficient information content.
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 a controlled voltage range of 12 V and higher (almost up to 15...16 V), dividing it into sections, as shown in Fig. 2.
Rice. 2. Diagram of 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 overlap zones “Low charging current” and “High charging current”, two lamps each light up, indicating that the voltage in the car’s network is in one or another extreme value relative to normal. Lamp HL1 has an orange filter, HL2 - green, HL3 - red. They are located on the front panel of the device from left to right, making it easy to monitor the 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 circuits (the rightmost one for the “14.2 V and more” section is not complete) and differ only in the threshold operating voltages.
The device works as follows. When the ignition switch is turned on, the on-board power supply 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 transistor VT1. In this case, lamp HL1, connected to the collector circuit of this transistor, will receive power and glow. If the battery voltage is below 12 V (discharged), the HL1 lamp will not light. It will also go out when starting the car engine if the battery voltage drops below 12 V when the starter is running (usually this happens). 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 increases to 13.2 B, the second measuring stage on the zener diode VD3 and transistor VT3 is triggered and the HL2 lamp lights up (the HL1 lamp continues to light). 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 the extinguishing of the HL1 lamp. At this time, only the HL2 lamp is lit on the front panel of the voltmeter-indicator.
At a voltage of 14.2 V, the zener diodes VD5, VD6 and transistor VT5 of the third measuring stage will open. Lamp HL3 will now light up (lamp HL2 remains lit). 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 extinguishing of the HL2 lamp. Only the HL3 lamp remains lit on the instrument panel, which will remain lit with a further increase in voltage.
When the on-board network voltage decreases, for example from 15 to 12 V, the order of switching the warning lights will be reversed.
Resistors Rl, R7 and R13 protect KT608B transistors from collector current overload when lamps HL1 - HL3 are turned on, when the resistance of their cold filaments is 10...20 Ohms. Resistors R2, R8 and R14 bypass transistors VT1, VT3 and VT5, reducing the current flowing through them at switching moments when maximum power is dissipated on them. 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.
If it is not possible to select zener diodes, the required response thresholds of the measuring cascades can be obtained by changing the values of resistors R3, R5, R11, R15 or R4, R6, R10, R12, R16, as well as by selecting both at the same time. To reduce the operating threshold of transistors, you need to reduce the resistance of resistors R3, R5, R9, Rll, R15 or increase - R4, R6, R10, R12, R16 and vice versa. In practice, even with small changes in the resistance 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 KT608 transistors (VT1, VT3, VT5) must be at least 200. With a lower coefficient h21e, the process of opening and closing these transistors will be delayed to 0.3...0.4 V change in input voltage, which is undesirable in terms of clarity (“sluggish” switching of lamps) and accuracy of on-board voltage measurement.
The same results are achieved by connecting diodes in the forward direction in series with zener diodes (to facilitate the selection of the response voltage of the measuring cascades). This is explained by the fact that at low base currents of transistors, diodes (silicon and germanium) operate on the smoothly bending initial section of the straight branch of the current-voltage characteristic, where the increase in current with increasing voltage is relatively small.
The h21e coefficient of KT312B transistors (VT2, VT4) or KT315 transistors replacing them 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 cascades, an oscillatory process may occur in which lamps HL1 or HL2 will blink at a frequency of 3...5 Hz. This phenomenon can be eliminated by connecting a capacitor with a capacity of 0.01 μF between the base and collector of transistors VT2, VT4. With capacitors of the same capacities you can bypass the emitter-collector sections of transistors VT1, VT3, VT5. But it is not necessary to do this (it’s 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 network voltage is at the border , transition from one measuring section to another.
The performance of the indicator voltmeter and the accuracy of measuring interval boundaries are checked according to the diagram in Fig. 3, using an adjustable constant voltage source (10 to 16 V) with a permissible load current of 300 mA and a voltmeter.
Slowly increasing the voltage from 10 to 15...16 V and watching the lamps light up and go out, check the boundaries of the indicator operation areas. In case of discrepancy between these boundaries (see Fig. 2), which can be within 0.2...0.5 V due to the spread of parameters of zener diodes and transistors, or if these boundaries are desired to change, the zener diodes are replaced with others that have the appropriate stabilization voltage.
The design of the device is arbitrary. The author, for example, mounted it in a plastic box measuring 35x75x90 mm. On the front wall (35X75 mm) there are three lights (with orange, green and red filters). The box is installed (preliminarily adjusted to its location) 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 with a decorative frame. Flat color filters and indicator lamps HL1 - HL3 are installed under the glass. To eliminate the illumination of “not your own” color filters by lamps, the partitions should be strengthened in the corresponding places of the gap.
An indicator voltmeter can be used with equal success on all types of trucks and buses. If the vehicle's on-board voltage is 24 V, the following changes must be made to the device:
as indicators HL1 - HL3, install lamps MH26-0.12 (26 V X 0.12 A) or MH36-0.12 (36 V X 0.12 A);
Zener diodes of the D814 series should be replaced with zener diodes KS524G and KS527A (it is possible to connect other zener diodes in series);
increase the resistance of resistors Rl, R7 and R13 to 100... 120 Ohms, 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 source of regulated voltage (see Fig. 3) must have regulation limits of 20...30 V. The breakdown of the voltage control range (see Fig. 2) is made on the basis of the technical conditions for operating batteries and electrical equipment of cars.
