Charge meter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Charge meter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Batteries, chargers

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Car batteries are often charged with devices that do not have a current stabilizer. The device proposed in this article allows, in this case, to objectively determine the end of battery charging. Moreover, it will do this with arbitrary shape and average value of the charging current.

The end of charging the battery with a stable current is usually determined by the expiration of a known time period (the so-called charging by time). However, in reality, the charging current changes due to the action of various destabilizing factors. Since the internal resistance of batteries is very small, even a small change in the charging voltage can cause a significant change in current.

On the other hand, the introduction of a current stabilizer into the charger significantly complicates the design of the device and reduces the efficiency. One way or another, commercially manufactured car chargers, as a rule, do not provide stabilization of the charging current.

It is known that in order to fully charge the battery, it needs to be informed of a certain electric charge (amount of electricity) equal to the product of the charging time and the average current. In other words, the end of charging can be determined by the value of the charge reported to the battery. In this case, changes in current during the charging process will not affect the charge, but will only lead to an increase or decrease in the charging time.

The need to measure the charge also arises in other cases. For example, when carrying out training charging of a battery, it is always necessary to find out the capacity that will be given to them when discharging to the minimum allowable voltage. When performing various electrochemical processes (for example, electroplating), it is also useful to measure the amount of electricity that has passed through the solution.

To measure the charge passed through the measuring circuit under conditions of unstable current, the device described below was developed. Its schematic diagram is shown in fig. 1.

(click to enlarge)

The basis of the device is a voltage-to-frequency converter, made on the DA1 chip. The voltage at its input, proportional to the charging current, comes from the current-measuring resistors R1, R2 (either from one or both, depending on the measurement limit selected by the SA1 toggle switch). Since the conversion function is linear, the output frequency of the DA1 chip is directly proportional to the charging current. The operation of the integrated converter KR1008PP1 is described in detail in the literature [1,2]. therefore omitted here.

The output pulse voltage of the converter is fed to the input of the frequency divider DD1. It reduces the frequency of input pulses by 32768 60 = 1 966 080 times. The conversion factor and the frequency division factor are chosen such that when the voltage at the input of the converter is 1 V, the pulses at the output of the counter follow with an interval of 0.1 h (or 360 s). In other words, one pulse at the meter output corresponds to an electric charge of 0.1 A h passing through the measuring circuit. when the contacts of the toggle switch SA1 are open, or 1 Ah when they are closed.

A simple calculation allows you to determine the required conversion factor: 1966080/360=5461 Hz/V. Since this frequency is significantly (more than 50 times) higher than 100 Hz. the conversion error when measuring the charge carried by a pulsating (after full-wave rectification) current should be insignificant, which was confirmed experimentally.

Two-digit binary-decimal pulse counter, made on two counters modulo 10 DD2. DD3 with digital indicators HG1. HG2. counts the number of ampere-hours or their tenths. The decimal point of the HG1 indicator is on in the "10 Ah" mode, the decimal point of the HG2 indicator flashes when the charging current flows in the load circuit and the more often, the greater the current.

To set the moment of disconnection of the charging current source after the flow of a given charge, the device has an installation block consisting of two decimal counters-decoders DD4. DD5. switches SA3, SA4 and logical node on the elements DD6.1. DD6.2.

The change in the state of the counters DD2 - DD5 occurs by the decline of the input pulses, and setting to the initial state - by applying a high level voltage to the input R.

In the charge measurement mode, the required charge value is set with the SA3 and SA4 switches, the counter capacity "1 Ah" or "10 Ah" is selected with the SA100 toggle switch (the division value of the least significant digit of the counter is 0.1 or 1 Ah, respectively). The input of the device is connected to the break in the load circuit in accordance with the diagram shown in fig. 2, a, supply mains voltage to the device and close the contacts of the toggle switch SA2 "Start".

Charge meter

This figure shows a functional diagram of the installation for measuring the amount of electricity reported to the rechargeable battery GB1. According to the same scheme, an installation is assembled for carrying out an electrochemical process.

After a while, those outputs of counters DD4. DD5. which will be connected to the moving contact of the switches SA3, SA4. high voltage will appear. The same level will appear at the output of the element DD6.2. As a result, first. the generator, made on the elements of DD6.3, will start working. DD6.4, generating a pulse sequence with a frequency of about 2 kHz. and the buzzer BF1 will give a signal indicating that a predetermined amount of electricity has flowed through the battery being charged.

Secondly, the transistor VT1 will open and the electromagnetic relay K1 will operate, the contacts K 1.1 of which, having opened, will de-energize the load. In this state, the installation will be until then. until it is disconnected from the network.

The charge meter is powered by a bipolar voltage regulator 2x9 V. made on DA2, DA3 microcircuits. Step-down network transformer T1 - unified from the Chamber of Commerce and Industry series. Capacitors C6-C10. protecting device chips from interference, install one at a time near each of the chips DD1 - DD5.

At a voltage of 1 V at the input of the voltage-frequency converter, the decimal point of the indicator HG2 turns on with a period of approximately 3 s. indicating the flow of current through the load circuit. The more this current. the more often the inclusion of the point.

The cathode filaments of the HG1 and HG2 fluorescent indicators are powered by the negative arm of the stabilizer. This is done to increase the voltage difference between the anodes - elements and the indicator cathode, which makes it possible to increase the brightness of the display. Fluorescent indicators in the meter are powered by low voltage (nameplate voltage 20 ... 30 V), so their anodes - elements are connected directly to the outputs of the K176IE4 counters, without additional transistors.

Instead of IV-ZA, IV-b indicators are suitable, however, they are larger and consume more cathode heating current, so you will need to select resistors R7. R8. Transistor VT1 - any low-power silicon npn structure (for example, from the KT312, KT315, KT503, KT3117 series). Diode bridges VD1, VD2 - any of the KTs402-KTs405 series: diode VD3 - also any of the KD503 KD509, KD510, KD513, KD521, KD522 series.

Capacitors C4, C11 - oxide. K50-16 or K50-35; C3 - ceramic (KM-4. KM-5. K10-7V. K 10-47) or mica, and it must have a small TKE (MPO), since the stability of the conversion coefficient depends on this; the rest - of any type, Resistor R1 consists of two parallel-connected C5 - 16V with a nominal value of 0.2 ohms and a power of 5 watts. It can be made independently from a piece of thick high-resistance wire. Trimmer resistor R4 - multi-turn SP5-2; the rest are MLT, S2-23, S2-33, and R2 is made up of two resistors connected in parallel (for example, with ratings of 1 and 10 ohms).

Relay K1 used imported. Best BS902CS (its winding has a resistance of 500 Ohm. The contacts are designed for switching DC and AC current up to 10 A at a voltage of 220 V) It has dimensions of 20x15x15 mm. A suitable domestic relay for a charge meter can be selected from the automotive group [3].

The TPP232-127/220-50 transformer can be replaced by any of the TLL23 series) -127/220-50-TPP235-127/220-50. in this case, the secondary windings should be connected in such a way that a voltage of 1 ... 2 V is supplied to the diode bridges VD12 and VD15. The network transformer can also be made independently. It is wound on a tape magnetic circuit ShL16x20 Winding I contains 2400 turns of wire PEV-1 0.08. windings II and III - 140 turns of wire PEV-1 0.25 each.

Sound piezoelectric emitter BF1 - any of the ZP series. Toggle switch SA1 - P2T or another, designed for a current of at least 5 A; SA2 - any. Salt switches SA3 - MPN-1.

The charge meter is assembled in a plastic case with dimensions of 200x80x65 mm. The parts are placed on two boards made of textolite, the installation is made by hanging conductors. On one of them with dimensions of 190 130 mm, attached to the bottom of the case, T1 elements are installed. VD1. VD2. DA2. DA3, C4, C5, C11, C12, R1, R2, K1, BF1. The remaining parts are soldered on the second board (165x45 mm) screwed to the front panel of the DAI Voltage Stabilizers. DA2 are mounted on heat sinks with a cooling surface of 30...40 cm2 each.

Calibrate the device as follows. The input contacts of the meter are included in the open circuit of the load according to the scheme of fig. 2,a and set the operating current to 1 A. The contacts of the SA1 toggle switch should be in the open position, and the SA2 toggle switch should be closed. By repeatedly measuring the pulse repetition period at the output of the converter DA1 (pin 7). trimming resistor R4 set their six-second period. Then check the accuracy of the six-minute period of pulses at the output M (pin 10) of the counter DD1 and. if necessary, correct with the same resistor.

It should be noted that it is possible to objectively establish the charge that the battery must accept if its real capacity is known and it is discharged to the lower permissible limit.

To determine the battery capacity, a discharge unit is assembled according to the scheme in Fig. 2.6.

Maximum direct current. which can be passed through the input circuit in the "100A h" position of the SA1 switch - 10 A. and in the "10 A h" position. - 1A. If the measured current is in the form of pulses (for example, when charging a battery), then the average current value must be reduced to 6 ... 7 A. Otherwise, the resistor R1 will overheat. With open contacts of the toggle switch SA1, the current should not exceed 1 A.

Literature

Gutnikov V.S. Integrated electronics in measuring devices (ed. 2. Revised and added) - L. Emergoatomizdat. Leningrad branch. 1988. p. 269-273.
Yakubovsky S. V., Nisselson L. I., Kuleshova V. I. et al. Digital and analog integrated circuits. Handbook (under the editorship of Yakubovsky S.V.). - M. Radio and communication. 1990. p. 432-445.
Bannikov V. Small-sized automobile electromagnetic relays. - Radio. 1994. No. 9., p.42; No. 10. p. 41.

Author: A. Evseev, Tula

See other articles Section Automobile. Batteries, chargers.

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