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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Coulometer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells The device described in the article allows you to set and control the amount of electricity (charge) that you want to pass through the load, that is, the product of current and time (Ac). When the set value is reached, a signal is generated that can be used to turn off (block) the current source and (or) give any signal. There are industrial devices designed for such purposes, but they are very complex. Compared with them, the proposed device is much simpler, made of available parts and not difficult to set up. Such a device can be successfully used, for example, to limit the charge of car batteries, as well as in other cases when it is necessary to control the receipt of metered amounts of electricity by the load. The device was developed as an addition to the current stabilizer described in [1]. However, it can work in conjunction with any other current source, including unstabilized ones. The specified amount of electricity is set on a seven-digit indicator. The maximum value in this case is 9 As, i.e., for example. a current of 999 A can flow through the load for almost 999 hours (10 s). With a higher current, the maximum time of its flow decreases accordingly. The block diagram of the device is shown in fig. 1. As you can see, the load A1 of the current source G1 is connected to the common wire through the measuring resistor Ri.
The voltage drop created on it, which is directly proportional to the current through the load, is fed to the DC inverter amplifier A2. The voltage from its output is fed to the input of the voltage-to-frequency converter (VFC) U1. Its output signal, the frequency of which is directly proportional to the input voltage, enters the digital unit. The latter processes this signal and issues a command to turn off the current source. An inverter amplifier (Fig. 2) is necessary when using the current source described in [1], since in it the load is included in the break in the wire connecting the negative terminal of the rectifier bridge to the common wire. For this reason, the voltage taken from the measuring resistor Ri has a negative polarity, and for the VFC used, it must be positive. The use of an inverter amplifier made it possible to reduce the requirements for the accuracy of manufacturing the resistor R and (the deviation of its resistance from the calculated value is compensated by the corresponding change in the gain by the tuning resistor R3). The resistance of the resistor Ri is about 0,01 Ohm, which allows you to control the current up to 100 ... 150 A. It is made from a nichrome or constantan wire of the required diameter.
When using a current source that provides a positive polarity voltage across the measuring resistor, an inverter amplifier is not required and the VLF input can be directly connected to R. However, in this case, it is necessary to select its resistance very accurately in order to avoid a large measurement error. The device uses a somewhat modified VLF, described in [2]. The revision (Fig. 3) consisted in replacing the K155 series microcircuits with more economical KR1533 series, introducing a voltage regulator for their supply (due to this, the need to use an external source of a stabilized voltage of 5 V was eliminated). Instead of K544UD1A (DA1), the OS CA3140E was used. The resistance of the resistor R7 is reduced to 360 MΩ (in practice, this turned out to be quite enough for the device to work). To match the levels of the output signal of the VLF and the input signal of the digital block, a cascade on the transistor VT5 was introduced. The principle of VFC operation is described in detail in [2], therefore, this article is not considered.
The schematic diagram of the digital block is shown in fig. 4. It consists of a line of pre-set decimal counters, power-on reset counters, pre-set readings, and an output signal conditioner.
When the power is turned on, the DD3, DD4, DD6 microcircuits are set to the initial state by the pulse generated by the R6C3 circuit. The counters DD7-DD14 do not have an input for setting the zero state, therefore, a node is introduced on the element DD1.1 and the counter DD3. Pulses with a repetition rate of about 1 Hz coming from the generator (its circuit is shown in Fig. 5) to one of the DD1.1 inputs pass to the DD3 counter, since there is a zero level at the second input of the element. At the same time, these pulses are fed to the counter-decoder DD6. Its outputs are connected to the inputs for pre-setting counters DD7-DD14. As the pulses arrive, the counters are set to zero in turn. With the arrival of the eighth pulse on DD6, the HL1 LED lights up, signaling the device is ready for operation "At the same time, the DD1.1 element is blocked by a log. 1 signal coming from output 8 (pin 9) of the counter-decoder DD3.
When the power is turned on, the one-shot, made on the elements DD17.2, DD1.4, generates a short pulse, which sets the trigger on the elements DD17.3, DD17.4 to a single state. From the output of the element DD5.2, a signal with a log level is removed. 1, with which you can block the current source. At the same time, the HL2 LED lights up. On the elements of the DD2 chip, triggers are assembled that suppress the bounce of the contacts of the buttons SB1, SB2. With a single press of the SB2 button, the DD14 counter is switched on in the preset mode, while a comma lights up on the indicator of the corresponding digit, and the HL1 LED goes out. With subsequent presses of the SB2 button, the counters are transferred to the preset mode in turn. The desired number (from 0 to 9) on the corresponding indicator is set with the SB1 button. Thus, by manipulating the buttons SB1 and SB2, they type on the display the required number corresponding to the product of the current (in amperes) and the time (in seconds). The device is started by pressing the SB4 button. At the same time, the log level is set at the output of the DD17.3 element (and, accordingly, at the output of DD5.2). 0, allowing the operation of the current source, a current begins to flow through the resistor R and (see Fig. 1) and pulses appear at the output of the VFC with the corresponding repetition rate. Entering the inputs of the counters, they reduce the number previously set on the indicators until it becomes equal to 0. As soon as the log level appears at all outputs of the parallel transfer of the counters. 0, the one-shot on the elements DD17.2, DD1.4 generates a pulse that switches the trigger DD17.3DD17.4 to the initial state, and the count stops, and the current source is blocked again. The operation of the device can be stopped with the SB3 button, and after a while it can be resumed with the SB4 button, while the countdown will continue from the value at which the work was interrupted. Elements DD1.2, DD1.3 and DD16.1 - DD16.6 provide the ignition of commas on the indicators in the preset mode. The digital block output signal is used to control the current source. This can be done in various ways, for example, by applying this signal to the base of a transistor loaded with a powerful relay (Fig. 6), the contacts of which are included in the load circuit. In the current source [1], you can get by with a low-power relay by turning on its closing contacts between the variable resistor R3 engine and the common wire.
The schematic diagram of the display unit is shown in fig. 7. It contains seven decoders K176ID2 (DD1-DD7) and the same number of indicators ALC338A (HG1-HG7) with a common cathode. It is acceptable to use indicators with a common anode, but in this case, the outputs of 6 microcircuits DD1-DD7 and the common anodes of the indicators (through the appropriate resistors) must be supplied with a supply voltage of +9 V.
The device is powered by stabilized voltages of +12 and -12 V. To power the digital part and the display unit, either an external 9 V source is used, or the voltage obtained from the stabilizer on the KR142EN8A chip connected to the +12 V source. When assembling the VFC, the output of the collector of the transistor VT1 and output 2 of the DA1 microcircuit must be bent and, wrapped with a piece of tinned wire, soldered into the corresponding hole. When mounting the display unit board, it is convenient to use commercially available standard tires as jumpers on the parts side, but they can also be made from a mounting wire. In the inverter amplifier (see Fig. 2) and VLF (see Fig. 3), resistors C2-23 are used (R6 is composed of two with a resistance of 5,1 MΩ), in extreme cases, MLT can be used. Resistor R7 is made up of two 180 MΩ CMM resistors. In the remaining nodes of the device, it is permissible to use resistors of any type. Trimmer resistors - SP5-2, SP5-22. Oxide capacitors - K50-35 or similar small-sized ones, the rest - of any type, suitable in size. Instead of SA3140E (see Fig. 3) and KR140UD22 (see Fig. 2), it is permissible to use the KR544UD1 A op-amp, and instead of the KR1533 series microcircuits (see Fig. 3) - their counterparts from the K555 series. In the digital unit, you can use the K176 series microcircuits, as well as CD4029 (analogous to K561IE14), CD4011 (K561LA7), CD4001 (K561LE5), CD4002 (K561LE6), CD4017 (K561IE8), CD4022 (K561IE9), CD4050 (K561PU4). ALS338A indicators are replaceable by ALS324A, ALS3ZZA. To set up the device, a DC voltmeter and ammeter, as well as a frequency counter, are required. Temporarily disabling the blocking of the current source and turning on the ammeter in series with the load, turn on the current source and set the current to 10 A. Then connect a voltmeter to the output of the inverter amplifier (if used) and resistor R3 (see Fig. 2) set the voltage to 100 at the output of the amplifier mV. Next, a VLF is adjusted (the technique is described in detail in [2]). Here I would like to note that first you need to balance the op-amp DA1 using the resistor R12. Then, by connecting the VLF input to a common wire, try using resistor R5 to get the signal of the lowest possible frequency at the output (one pulse in 10 ... 30 s). After that, a voltage of 100 mV is applied to the input of the VLF from the output of the amplifier-inverter and, by controlling the pulses on the collector of the transistor VT5 (see Fig. 3) with a frequency meter, by moving the slider of the resistor R10, the frequency is set to 100 Hz. The digital block (see Fig. 4) does not need to be configured, you only need to check its operation. Immediately after turning on the power, the indicators can show any number. Then, within seven seconds, they should turn to zero in turn, while commas should also turn on in turn on each of the indicators. After that, the HL1 LED turns on (HL2 is also on). The device is ready to work. In conclusion, the blocking of the current source is again switched on by the output signal from the digital block. The device was designed to work with high currents. At lower currents, the number of digits of the indication and the counters corresponding to them can be reduced. If the device is supposed to be used in long-term modes, it is desirable to provide backup power in case of power failure. A backup battery (accumulators or galvanic cells) with a voltage of 5 ... 9 V is connected to the power bus of the digital unit through a diode. Of course, the display unit, as well as the HL2 LED of the digital unit, in this case must be powered bypassing this circuit, for example, from a separate stabilized source. After such refinement, the current consumption of the digital unit from the battery will be minimal. In the event of a mains voltage failure and its subsequent restoration, the counting process will not be interrupted and will continue without loss. Literature
Author: I.Korotkov, Bucha village, Kyiv region
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