Charging current indicator for car batteries. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells
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If the charger (charger) for car batteries does not have an ammeter, it is difficult to guarantee their reliable charging. Possible deterioration (disappearance) of the contact at the battery terminals, which is quite difficult to detect. Instead of an ammeter, I offer a simple indicator of literally a few parts. It is included in the break of the "positive" wire from the charger to the battery.
Rice. 1. Charging current indicator
The scheme in fig. 1 is a transistor switch VT1 that turns on the LED HL1 when a given current flows through R1. In this case, the voltage drop across the resistor R1 (more than 0,6 V) is sufficient to open the transistor VT1 and ignite HL1. For a particular battery, the value of R1 is selected so that the LED lights up at the required charging current. By the brightness of its glow, you can approximately estimate the charging current. Resistor R1 - wire, made of 6 ... 12 turns of winding wire with a diameter of 1 mm. You can use a wire with high resistivity (nichrome) or an industrial-made resistor, for example, PEVR-10.
Rice. 1. Charging current indicator
On fig. 2 shows a similar circuit, but using the KR293KP4 optoelectronic switch. Such optocouplers are popular today among radio amateurs, they allow you to design electronic devices with a minimum number of elements. A resistor that limits the current in the optocoupler LED circuit is not needed, since for reliable operation of the key, a voltage on contacts 3,4 of the order of 1,1 ... 1,5 V is required. The current in this circuit is 10 ... 15 mA. The peculiarity of the circuit is in the connection of the actuating device on the optocoupler key. As can be seen from the figure, the input of the optocoupler (LED) is turned on at the "+" terminal of the memory on one side, and at the corresponding "+" terminal of the battery - on the other. The resistor on which the voltage drops, in this case, is the connecting wire itself between the charger and the battery, having a length of 0,8 ... 1,5 m. With reliable contact in the terminals, the voltage drop is not enough to operate the optocoupler. Contacts 5, 6 of VU1 are closed, current flows in the HL1 circuit, and the LED is on.
When using this indicator in devices with a high supply voltage, for example, for charging the battery of trucks with an on-board network voltage of 24 V, it is necessary to select the value of R1 so that the current through the LED does not exceed the maximum allowable.
Such current indicators can also be used in other designs where it is necessary to control the load current. They are switched on in a similar way - between the load and the power source.
Author: A. Kashkarov, St. Petersburg; Publication: cxem.net
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