Charger attachment to protect the battery. Automatic charger disconnect
The article discusses the circuit of a simple device, by adding it to your charger (charger), the charging process can be automated. It will also help keep your battery charged during long-term storage, which will significantly increase its service life.
The device is an electronic relay that monitors the voltage of the connected battery. The relay has two response thresholds based on the highest and lowest voltage values, set during the commissioning process.
Contact group K1.1 is connected to the break in one of the wires going to the terminal block for connecting the battery. The device is also powered from this terminal block.
Device setup. To configure the node, you will need a power source with an adjustable voltage value. We supply power to input XS1 (Fig. 1). We install the slider of resistor R 2 in the upper position according to the diagram, and R3 in the lower position. We set the voltage value to 14.5 V. In this case, transistor VT 2 must be closed, and relay K1 must be de-energized. By adjusting R 3, we achieve the activation of relay K1. Now we set the voltage to 12.9 V, and by adjusting R 2 we turn off K1.
Since the contacts of relay K1.2, in the off state, bypass resistor R2, the activation and shutdown settings of K1 are independent of each other.
About the details of the device. Trimmer resistors R 2, R 3, type SP-5, precision zener diode D818 can be replaced with two back-to-back D814 with similar voltage stabilization values. Relay K1 with a supply voltage of 12 V, with two groups of normally closed contacts. Contact group K1.1 must be designed for the battery charging current.
Having supplemented the charger at your disposal for a car battery with the proposed automatic device, you can be calm about the battery charging mode - as soon as the voltage at its terminals reaches (14.5 ± 0.2) V, charging will stop. When the voltage drops to 12.8..13 V, charging will resume.
The attachment can be made as a separate unit or built into the charger. In any case, a necessary condition for its operation will be the presence of a pulsating voltage at the output of the charger. This voltage is obtained, say, when installing a full-wave rectifier in the device without a smoothing capacitor.
Scheme of the set-top box
It consists of a thyristor VS1, a control unit for thyristor A1, a circuit breaker SA1 and two indication circuits on LEDs HL1 and HL2. The first circuit indicates the charging mode, the second circuit controls the reliability of connecting the battery to the terminals of the machine.
If the charger has a dial indicator - an ammeter, the first indication circuit is not necessary.
The control unit contains a trigger on transistors VT2, VTZ and a current amplifier on transistor VT1. The base of the transistor VTZ is connected to the engine of the tuning resistor R9, which sets the switching threshold of the trigger, i.e. the switching voltage of the charging current. The switching “hysteresis” (the difference between the upper and lower switching thresholds) depends mainly on the resistor R7 and with the resistance indicated on the diagram it is about 1.5 V.
The trigger is connected to conductors connected to the terminals of the battery and switches depending on the voltage on them.
Rice. I. Schematic diagram of the machine attachment.
Transistor VT1 is connected by a base circuit to the trigger and operates in electronic key mode. The collector circuit of the transistor is connected through resistors R2, R3 and the control electrode section - the cathode of the SCR with the negative terminal of the charger. Thus, the base and collector circuits of transistor pa VT1 are powered from different sources: the base circuit from the battery, and the collector circuit from the charger.
SCR VS1 acts as a switching element. Using it instead of the contacts of an electromagnetic relay, which is sometimes used in these cases, provides a large number of switches on and off of the charging current necessary to recharge the cumulative battery during long-term storage.
As can be seen from the diagram, the SCR is connected by the cathode to the negative wire of the charger, and by the anode to the negative terminal of the battery. With this option, the control of the thyristor is simplified: when the instantaneous value of the pulsating Voltage at the output of the charger increases, current immediately begins to flow through the control electrode of the thyristor (if, of course, transistor VT1 is open).
And when a positive (relative to the cathode) voltage appears at the anode of the thyristor, the thyristor will be reliably open. In addition, “such inclusion is advantageous in that the thyristor can be attached directly to the metal body of the machine or the body of the charger (if the set-top box is placed inside it) as a heat sink.
You can turn off the set-top box using switch SA1 by placing it in the “Manual” position. Then the contacts of the switch will be closed, and through “resistor R2 the control electrode of the thyristor will be” connected directly to the terminals of the charger.” This mode is needed, for example, to quickly charge the battery before installing it in a car.
Details and design
Transistor VT1 can be the series indicated on the diagram with letter indices A - G; VG2 and VT3 - KT603A - KT603G; diode VD1 - any of the D219, D220 series or other silicon; Zener diode VD2 - D814A, D814B, D808, D809; SCR - KU202 series with letter indices G, E, I, L, N, as well as D238G, D238E; LEDs - any of the AL 102, AL307 series (limiting resistors R1 and R11 set the desired forward current of the LEDs used).
Fixed resistors - MLT-2 (R2), MLT-1 (R6), MLT-0.5 (Rl, R3, R8, R11), MLT-0.25 (others). Trimmer resistor R9 is SP5-16B, but another one with a resistance of 330 Ohm... 1.5 kOhm will do.
If the resistance of the resistor is greater than that indicated in the diagram, a constant resistor of such resistance is connected parallel to its terminals so that the total resistance is 330 Ohms.
The parts of the control unit are mounted on a board (Fig. 2) made of one-sided foil fiberglass laminate with a thickness of 1.5 mm. The tuning resistor is fixed in a hole with a diameter of 5.2 mm so that its axis protrudes from the printing side.
The board is mounted inside a case of suitable dimensions or, as mentioned above, inside the charger case, but always as far as possible from heating parts (rectifier diodes, transformer, SCR). In any case, a hole is drilled in the housing wall opposite the SS trimmer. LEDs and switch SA1 are mounted on the front wall of the case.
Rice. 2. Printed circuit board of the machine.
To install an SCR, you can make a heat sink with a total area of about 200 cm2. For example, a duralumin plate with a thickness of 3 mm and dimensions of 100X100 mm is suitable. The heat sink is attached to one of the walls of the case (say, the back) at a distance of about 10 mm - to ensure air convection.
It is also possible to attach the heat sink to the outside of the wall by cutting a hole in the housing for the thyristor.
Before attaching the control unit, you need to check it and determine the position of the trimmer resistor motor. A DC rectifier with an adjustable output voltage of up to 15 V is connected to points 1 and 2 of the board, and the indication circuit (resistor R1 and LED HL1) is connected to points 2 and 5. The trimmer resistor motor is set to the lowest position according to the diagram and voltage is supplied to the control unit about 13 V. The LED should light up. By moving the trimmer resistor slider up in the circuit, the LED goes out. Smoothly increasing the supply voltage of the control unit to 15 V and decreasing to 12 V, use a trimming resistor to ensure that the LED lights up at a voltage of 12.8...13 V and goes out at 14.2...14.7 V.
A. Korobkov.
Korobkov Alexander Vasilievich- leading specialist at one of the Moscow enterprises, born in 1986. He took up amateur radio at school, where he assembled a detector receiver as an eighth-grader. Two years later I mastered superheterodyne. In the 60s he developed and assembled a transistor tape recorder. The first publications in the magazine “Radio” date back to the same period. A little later he began to publish in the VRL collection. The main topic of publications in the last decade has been automotive electronics.
The article describes a set-top box designed to work together with a charger that does not have the function of disconnecting from the network after charging the battery. This set-top box should be of interest, first of all, to those car enthusiasts who, having a simple factory-made or home-made charger, would like to automate the charging process with minimal time and money.
It is known that the voltage at the terminals of a lead-acid battery charged with a stable current almost stops increasing as soon as it receives a full charge. From this moment on, almost all the energy supplied to the battery is spent only on electrolysis and heating of the electrolyte. Thus, at the moment the increase in charging voltage stops, it would be possible to disconnect the charger from the network. The operating instructions for car batteries recommend, however, that you continue charging in this mode for another two hours. This is exactly how the automatic charger I described earlier works. However, practice shows that this recharging is really only necessary when conducting an annual control and preventative charge-discharge cycle in order to determine the technical condition of the battery.
In everyday use, it is quite enough to keep the battery under constant voltage for 15...30 minutes. This approach makes it possible to significantly simplify the automatic charger without noticeably affecting the completeness of battery charging. If you charge the battery with an unstabilized current, then along with a gradual increase in the charging voltage (less pronounced than in the first case), the charging current decreases. Evidence of a fully charged battery is the cessation of changes in both voltage and current.
This principle forms the basis for the operation of the proposed set-top box. It contains a comparator, one of the inputs of which is supplied with a voltage that increases proportionally as the charging voltage on the battery increases (and decreases as it decreases) and at the same time proportionally decreases as the charging current increases (increases with decrease). The second input is supplied with the same voltage as the first, but with a significant time delay. In other words, as long as the voltage on the battery increases and (or) the charging current decreases, the voltage value at the second input of the comparator will be less than the voltage value at the first, and this difference is proportional to the rate of change of the charging voltage and current. When the voltage on the battery and the charging current stabilize (which will indicate that the battery is fully charged), the voltage values at the inputs of the comparator will be equal, it will switch and give a signal to turn off the charger. This idea is borrowed from .
The attachment is made using widely used elements. The maximum operating current is 6 A, but it can be easily increased if necessary.
The schematic diagram of the attachment is shown in Fig. 1.
The device consists of an input op-amp DA1, two voltage comparators at the op-amp DA2.1, DA2.2, a two-input electronic relay VT1 - VT3, K1 and a power supply consisting of a network transformer T1, diodes VD1-VD4, a smoothing capacitor C6 and a parametric voltage stabilizer VD5R19. The output of the charger is connected to terminals X1, X3, and the battery being charged is connected to terminals X2, X3. The mains plug of the charger is plugged into the X5 socket of the set-top box.
When you press the SB1 button, the mains voltage is supplied to the charger and to the mains winding I of transformer T1 of the set-top box. The unstabilized voltage from the diode bridge VD1-VD4 powers the electronic relay, and the output voltage of the parametric stabilizer powers the DA2 chip (DA1 is powered from the charger). Battery charging begins.
The voltage drop created by the charging current across resistor R1 is supplied to the input of op-amp DA1, connected according to the inverting amplifier circuit. The voltage at its output will increase as the charging current decreases. On the other hand, the output voltage of an op-amp is proportional to its supply voltage. And since the amplifier is powered directly from the battery being charged, the output voltage of the op-amp will be a function of both the voltage at the terminals of the battery being charged and the charging current. This design of the console made it possible to use it in conjunction with a wide variety of chargers, including the simplest ones.
A low-pass filter R4C2 is connected to the output of the op-amp, from which the voltage through the integrating circuits R7C3 and R5R6R8C4 is supplied to the inputs of the comparator made on the op-amp DA2.2. The R8C4 circuit has a time constant many times larger than the R7C3 circuit, so the voltage at the non-inverting input of this comparator will be less than at the inverting one, and the output will be set to a low level.
The comparator based on op-amp DA2.1 is a conventional threshold device, the inverting input of which is supplied with a reference voltage from the resistive divider R15R16, and the non-inverting input is supplied from the divider R11R12R13, connected to the battery being charged. The comparator switches when the battery voltage reaches 14.4 V and serves to eliminate the possibility of premature shutdown of the charger in conditions of insignificant changes in voltage changes on the battery.
As a result, until the voltage on the battery being charged reaches the specified value, the set-top box will not turn off the charger, even if the DA2.2 comparator has switched. This situation is possible when the charging current is set to a low value and, as a consequence, when the charging voltage and current change very slowly. Initially, the output of comparator DA2.1 also has a low voltage.
The outputs of both comparators are connected through resistive dividers R17R18 and R20R21 to the bases of transistors VT2 and VT1. Thus, when you press the SB1 button, these transistors remain closed, and VT3 opens. Relay K1 is activated and contacts K1.1 blocks the button contacts. The set-top box remains on after the button is released.
Since transistors VT1 and VT2 are connected in an AND logic circuit, they open only at a high voltage level simultaneously at the output of comparators DA2.1, DA2.2. This can only happen when the battery is fully charged. In this case, transistor VT3 closes and relay K1 releases the armature, opening the power circuit of the set-top box and charger.
In Fig. Figure 2 shows graphs of changes in voltage at the inputs of the DA2.2 comparator, as well as the charging current during the process of recharging the 6ST-60 battery using a simple charger with an unstabilized charging current. The initial state of charge of the battery is about 75%.
In the case when the set-top box will operate in conditions of strong interference, the power supply circuit of the op-amp DA2 should be bypassed with a ceramic capacitor with a capacity of 0.1 μF.
The set-top box is characterized by reduced sensitivity to mains voltage fluctuations. If, for example, it increases, then the voltage on the battery being charged also increases, but at the same time the charging current will also increase. As a result, the voltage at the output of op-amp DA1 will change slightly.
The attachment is mounted in a metal box measuring 140x100x70 mm. On its front panel there are clamps X1-X3, fuse FU1 and socket X5. Most of the parts of the console are placed on a printed circuit board measuring 76x60 mm, made of foil fiberglass 1.5 mm thick. The board drawing is shown in Fig. 3. Transformer T1 and relay K1 are mounted separately next to the board. Resistor R1 is soldered directly to terminals X1, X2.
Resistor R1 is made up of two parallel-connected resistors C5-16V with a resistance of 0.1 Ohm and a rated dissipation power of 1 W; the rest are constant - MLT. Trimmer resistors R9, R12 - SPZ-16v.
Capacitor C1 - KM5, the rest - K50-35. It is advisable to train capacitor C4 before installing it on the board by connecting it to a constant voltage source of 10...12 V for several hours.
Instead of KD105B, you can use KD106A diodes, and instead of KD522B, you can use any of the KD521 series. Zener diode VD5 - any low-power one with a stabilization voltage of 11... 13 V.
KT3102B transistors are replaceable with any low-power ones of the appropriate structure with a static base current transfer coefficient of at least 50, and when replacing the VT3 transistor, you should focus on the operating current of the existing K1 relay. When choosing a replacement op-amp K553UD2, it is necessary to take into account that not all operational amplifiers allow operation with an input voltage equal to the supply voltage.
The set-top box uses a ready-made low-power network transformer with an alternating voltage of the secondary winding of 14 V at a load current of up to 120 mA. Relay K1 - RMU, passport RS4.523.303, but any one with an operating voltage of 12...14 V, whose contacts are designed for switching an alternating voltage of 220 V at a current of 0.3...0.5 A, is suitable.
To set up the set-top box, you will need a stabilized voltage source, adjustable within 10... 15 V, and a digital voltmeter with a measurement limit of 20 V. First, the resistor slider R12 is set to the bottom, and R9 to the left position according to the diagram. A source is connected to terminals X1 and X3, the voltage at its output is set to 14.4 V and the set-top box is connected to the network.
Press the SB1 button, and relay K1 should operate. Make sure that there is a low voltage level (1.3... 1.5 V) at the outputs of the op-amp DA2.1 and DA2.2 (pins 10 and 12). Then measure the voltage at the output of op-amp DA1 (pin 10). It should be approximately equal to the voltage of the connected power source.
The terminals of resistor R8 are short-circuited for 30...40 s, ensuring fast charging of capacitor C4, and then after a ten-minute wait, the voltmeter is connected to the output of op-amp DA2.2 and the handle of resistor R9 is smoothly rotated until the comparator switches, i.e., the voltage increases abruptly its output to 11... 11.5 V. Then measure the voltage at the inverting input of the op-amp DA2.2 and use resistor R9 to reduce it by 15...20 mV.
It should be noted that the voltage in the input circuits of the comparator must be measured with a digital voltmeter with an input resistance of at least 5...10 MOhm in order to prevent capacitor C3 from discharging. Since the input resistance of many popular digital voltmeters does not exceed 1 MΩ, you can connect a ten-megaohm resistor at the input of the existing voltmeter, which, together with the input resistance of the device, forms a voltage divider with a ratio of 1:10.
Finally, rotate the knob of resistor R12 until the op amp DA2.1 switches. In this case, relay K1 should release the armature.
If a radio amateur does not have a digital voltmeter and does not have a power source, the set-top box can be adjusted directly during the actual process of charging the battery. To do this, connect the charger and battery to the set-top box, set the charger switch to the “On” position, and set the resistor sliders R9, R12 of the set-top box as indicated above. Press the SB1 button, make sure that relay K1 is activated and set the charging current in accordance with the operating instructions for the charger.
When the voltage stops increasing, continue charging in this mode for another 20...30 minutes and then smoothly rotate the knob of resistor R9 until op-amp DA2.2 is activated and the set-top box and charger are disconnected from the network. This concludes the adjustment.
In conclusion, it should be noted that to ensure that the battery is fully charged, it is advisable to set the maximum permissible values of the charging current in order to ensure good dynamics of voltage changes at the output of op-amp DA1. This is especially true for chargers with unstabilized output current and heavily discharged batteries.
Literature
This design is connected as an attachment to a charger, a variety of different circuits of which have already been described on the Internet. It displays on the liquid crystal display the input voltage value, the amount of battery charging current, charging time and charging current capacity (which can be either in Amp-hours or milliamp-hours - depends only on the controller firmware and the shunt used). (Cm. Fig.1 And Fig.2)
Fig.1
Fig.2
The output voltage of the charger should not be less than 7 volts, otherwise this set-top box will require a separate power source.
The device is based on a PIC16F676 microcontroller and a 2-line liquid crystal indicator SC 1602 ASLB-XH-HS-G.
The maximum charging capacity is 5500 mA/h and 95.0 A/h, respectively.
The schematic diagram is shown in Fig 3.
Fig.3. Schematic diagram of an attachment for measuring charging capacity
Connection to the charger - on Fig 4.
Fig.4 Connection diagram of the set-top box to the charger
When turned on, the microcontroller first requests the required charging capacity.
Set by button SB1. Reset - button SB2.
Pin 2 (RA5) goes high, which turns on relay P1, which in turn turns on the charger ( Fig.5).
If the button is not pressed for more than 5 seconds, the controller automatically switches to measurement mode.
The algorithm for calculating the capacity in this set-top box is as follows:
Once a second, the microcontroller measures the voltage at the input of the set-top box and the current, and if the current value is greater than the least significant digit, it increases the seconds counter by 1. Thus, the clock only shows the charging time.
Next, the microcontroller calculates the average current per minute. To do this, the charging current readings are divided by 60. The whole number is recorded in the meter, and the remainder of the division is then added to the next measured current value, and only then this sum is divided by 60. Having thus made 60 measurements in 1 minute, the number in the meter will be average current value per minute.
When the second reading passes through zero, the average current value is in turn divided by 60 (using the same algorithm). Thus, the capacity counter increases once per minute by one sixtieth of the average current per minute. After this, the average current counter is reset to zero and counting starts over. Each time, after calculating the charging capacity, a comparison is made between the measured capacity and the specified one, and if they are equal, the message “Charging complete” is displayed on the display, and in the second line - the value of this charging capacity and voltage. A low level appears at pin 2 of the microcontroller (RA5), which turns off the relay. The charger will disconnect from the network.
Fig.5
Setting up the device comes down only to setting the correct readings of the charging current (R1 R5) and input voltage (R4) using a reference ammeter and voltmeter.
Now about shunts.
For a charger with a current of up to 1000 mA, you can use a 15 V power supply, a 0.5-10 Ohm resistor with a power of 5 W as a shunt (a lower resistance value will introduce a smaller error in the measurement, but will make it difficult to accurately adjust the current when calibrating the device), and sequentially with a rechargeable battery, a variable resistance of 20-100 Ohms, which will set the value of the charging current.
For a charging current of up to 10A, you will need to make a shunt from high-resistance wire of a suitable cross-section with a resistance of 0.1 Ohm. The tests have shown that even with a signal from the current shunt equal to 0.1 volts, the tuning resistors R1 and R3 can easily set the current reading to 10 A.
Printed circuit board for this device was developed for the WH1602D indicator. But you can use any suitable indicator by resoldering the wires accordingly. The board is assembled in the same dimensions as the liquid crystal display and is fixed at the back. The microcontroller is installed on the socket and allows you to quickly change the firmware to switch to a different charger current.
Before turning on for the first time, set the trimming resistors to the middle position.
As a shunt for the firmware version for low currents, you can use 2 MLT-2 1 Ohm resistors connected in parallel.
You can use the WH1602D indicator in the set-top box, but you will have to swap pins 1 and 2. In general, it is better to check the documentation for the indicator.
MELT indicators will not work due to incompatibility with the 4-bit interface.
If desired, you can connect the indicator backlight via a 100 Ohm current limiting resistor
This attachment can be used to determine the capacity of a charged battery.
Fig.6.Determining the capacity of a charged battery
You can use any load as a load (Light bulb, resistor...), only when turning it on you need to set any obviously large battery capacity and at the same time monitor the battery voltage to prevent deep discharge.
(From the author) The set-top box was tested with a modern pulse charger for car batteries,
These devices provide stable voltage and current with minimal ripple.
When connecting the set-top box to an old charger (step-down transformer and diode rectifier), I was unable to adjust the charging current readings due to large ripples.
Therefore, it was decided to change the algorithm for measuring the charging current by the controller.
In the new edition, the controller makes 255 current measurements in 25 milliseconds (at 50Hz - the period is 20 milliseconds). And from the measurements taken, it selects the largest value.
The input voltage is also measured, but the lowest value is selected.
(At zero charging current, the voltage should be equal to the battery emf.)
However, with such a scheme, it is necessary to install a diode and a smoothing capacitor (>200 µF) in front of the 7805 stabilizer for a voltage not less than the output voltage of the charger
devices. A poorly smoothed microcontroller supply voltage led to malfunctions.
To accurately set the set-top box readings, it is recommended to use multi-turn trimmersor install additional resistors in series with trimmers (select experimentally).
As a shunt for a 10 A set-top box, I tried to use a piece of aluminum wire with a cross-section of 1.5 mmabout 20 cm long - works great.
This device is connected as a set-top box to a charger, a variety of schemes of which have already been described on the Internet. It displays on the liquid crystal display the input voltage value, the amount of battery charging current, charging time and charging current capacity (which can be either in Amp-hours or milliamp-hours - depends only on the controller firmware and the shunt used). The output voltage of the charger should not be less than 7 volts, otherwise this set-top box will require a separate power source. The device is based on a PIC16F676 microcontroller and a 2-line liquid crystal indicator SC 1602 ASLB-XH-HS-G. The maximum charging capacity is 5500 mA/h and 95.0 A/h respectively.
The schematic diagram is shown in Fig. 1.
Connection to the charger - see Fig. 2.
When turned on, the microcontroller first requests the required charging capacity. Set by button SB1. Reset - button SB2.
If the button is not pressed for more than 5 seconds, the controller automatically switches to measurement mode. Pin 2 (RA5) is set high.
The algorithm for calculating the capacity in this set-top box is as follows:
Once a second, the microcontroller measures the voltage at the input of the set-top box and the current, and if the current value is greater than the least significant digit, it increases the seconds counter by 1. Thus, the clock only shows the charging time.
Next, the microcontroller calculates the average current per minute. To do this, the readings of the charger are divided by 60. The whole number is recorded in the meter, and the remainder of the division is then added to the next measured current value, and only then this sum is divided by 60. Having thus made 60 measurements in the meter, the number of the average value will be current per minute.
Next, the average current value is in turn divided by 60 (using the same algorithm). Thus, the capacitance counter increases once per minute by one sixtieth of the average current per minute.
After this, the average current counter is reset to zero and counting starts over. Each time, after calculating the charging capacity, a comparison is made between the measured capacity and the specified one, and if they are equal, the message “Charging complete” is displayed on the display, and in the second line - the value of this charging capacity and voltage. A low level appears at pin 2 of the microcontroller (RA5), which leads to the LED extinguishing. This signal can be used to turn on a relay, which, for example, disconnects the charger from the network (see Fig. 3).
Setting up the device comes down to setting the correct readings of the charging current (R1 R3) and input voltage (R2) using a reference ammeter and voltmeter. To accurately set the set-top box readings, it is recommended to use multi-turn trimmer resistors or install additional resistors in series with the trimmers (select experimentally).
Now about shunts.
For a charger with a current of up to 1000 mA, you can use a 15 V power supply, a 5-10 Ohm resistor with a power of 5 W as a shunt, and in series with the battery being charged a variable resistance of 20-100 Ohms, which will set the charging current.
For a charging current of up to 10 A (max 25.5 A), you will need to make a shunt from high-resistance wire of a suitable cross-section with a resistance of 0.1 Ohm. Tests have shown that even with a signal from the current shunt equal to 0.1 volts, the tuning resistors R1 and R3 can easily set the current reading to 10 A. However, the larger the signal from the current sensor, the easier it is to set the correct readings.
As a shunt for a 10 A set-top box, I tried to use a piece of aluminum wire with a cross-section of 1.5 mm and a length of 30 cm - it works great.
Due to the simplicity of the circuit, a printed circuit board for this device was not developed; it is assembled on a breadboard of the same dimensions as the liquid crystal indicator and is fixed at the back. The microcontroller is installed on the socket and allows you to quickly change the firmware to switch to a different charger current.
