Pulse charger with simple charge current display. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Pulse charger with simple charge current display. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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The universal circuit of the pulse charger is designed to charge small-sized batteries of all types (Ni-Cd & Ni-Mh). The distinctive features of this scheme are: simplicity, compliance with the rules and technology of charging batteries required by product manufacturers, versatility, which makes it possible to manufacture only one type of printed circuit board and by selecting elements to achieve different values of output voltage and current, high stability of output parameters, reduction of charge time according to Compared with conventional standard chargers, the original economical charge current indication circuit.

(click to enlarge)

An important advantage of switching power supplies is the lower heat generation on the elements, compared with standard non-pulse charge circuits similar in parameters. When charging with a pulsed charge current, the battery cells heat up much less.

Before starting the manufacture of the device, it is necessary to calculate the voltage at the end of the charge and the charge current. The value of the output voltage in idle mode is calculated according to the principle of 1.45 V times the number of battery cells. The amount of charge current is determined by the device itself, depending on the condition of the batteries. At the beginning of the charge cycle, the current is higher, as the battery charges, the current decreases and at the end of the charge does not exceed 1/10 of the battery capacity in Ah. Such parameters are considered optimal, do not harm the battery, make it possible to carry out up to 700 charge-discharge cycles while maintaining their battery parameters in the norms declared by the manufacturers. Charging time at these values is 4-8 hours. If it is planned to charge the battery at a temperature above 25 C, it is recommended to introduce into the circuit the control of the charge current from the temperature on the battery case, or limit the charge time, eliminating overheating of the battery at the end of the charge cycle.

The ratings of the elements given in the diagram are designed to charge a battery consisting of 8 - 12 cells, with a capacity of up to 7-8 Ampere / hour. If you plan to charge a battery with a smaller number of cells, then it is advisable to reduce the supply voltage. The value of the required charge voltage is set by selecting a tuning resistor R4. If the charging current does not exceed 300 mA, there is no need to install the transistor Q1 on the heatsink. LED D7 indicates the presence of charge voltage.

LED D6 indicates the presence of the charge current. When powered from the AC mains, the power of the mains transformer must be at least 25 W, the output effective voltage under load is 20-25% higher than the calculated voltage on the battery at the end of the charge cycle. (For example, if it is assumed that the output voltage will not exceed 9V, it is enough to set the transformer to a voltage of 12V.) At the existing ratings, a 24 Volt transformer is used in the circuit. As an option, it is recommended to install devices on the front panel of the device: an ammeter and a voltmeter, put resistance R4 in this case of a variable type and also bring it to the front panel of the device. Get a universal charger compact device.

As an additional application, this device can be recommended as a DC-DC converter, for example from 24-28V to 12V. This device can operate at high charge currents, while it is necessary to provide a radiator with an area of \u1b\u300babout 500 - 2 cmXNUMX for the transistor QXNUMX.

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