Charger for all types of batteries. Scheme, description

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Charger for all types of batteries. 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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Recently, many devices have appeared that promote accelerated charging of batteries, with currents often exceeding the rated capacity.

Without denying the possibility of using such modes in exceptional cases, we note that this possibility should be reflected in the technical documentation, and the characteristics of the mode are given - current, time, temperature of the electrolyte or battery case. If these data are not available, it is better to use the proven "old-fashioned" method that does not harm any type of battery - direct current charging (in other words, from a direct current source).

What it is?

We are accustomed to using sources of voltage, and the more constant it is, the better. For an ideal voltage source, its output voltage remains constant, independent of the load resistance, while the current supplied to the load changes (that is, its internal resistance is zero).

For an ideal current source, the output voltage changes with the load, while the current remains constant (internal resistance is infinity). The simplest way to turn a voltage source into a current source is to connect an additional resistor in series with the load, and we will get an internal resistance equal to this additional resistor. At Rint. For a 0,002 Ohm car acid battery, it is enough to include a 2 Ohm resistance in the charge circuit for good stabilization of the charging current. Those who know Ohm's law can practice calculating such a resistor with a battery voltage of 12,6 volts and Rint 2,5 ohms.

The use of modern integrated voltage stabilizers allows you to create very simple circuitry sources of stable current.

(click to enlarge)

Note that stability is observed when the load current changes, and will change slightly when the supply voltage changes. This circumstance is usually neglected, but if you want perfect stability, stabilize the power supply. The current calculation is very simple - the current in amps is 1,2 V divided by the resistance R1 in ohms. To indicate the current, a transistor was used (mandatory germanium due to the low opening voltage), which makes it possible to visually observe currents up to 50 mA.

Diode D1 and fuse F2 protect the charger from improperly turning on the battery. The capacitance C1 is selected from the ratio: 1 Ampere needs 2000 microfarads.

Advantages of the proposed device: not afraid of short circuits; no matter the number of cells in the rechargeable battery and their type - you can charge acid sealed 12,6V and lithium 3,6V and alkaline 7,2V. The current switch should be turned on exactly as shown in the diagram - so that resistor R1 remains during any manipulations. The use of a variable low-resistance resistor is undesirable due to the instability of the moving contact at load currents of more than 0.2 A.

Restrictions: the maximum voltage of the rechargeable battery must be less than the supply voltage by 4 volts; the 142EN12 chip is installed on a radiator that dissipates 20 W in the case of a single alkaline cell being charged with a maximum current of 1A.

Charging current 0,1 of the capacity is suitable for all types of batteries. To fully charge the battery, it must be given 120% of the nominal charge, but before that it must be completely discharged. Therefore, the charging time in the recommended mode is 12 hours.

Proposals to stop charging when a certain voltage is reached should be treated with some caution - as a rule, the voltage at the battery terminals after removing the charging current gradually drops, and this leads to the charging mode being switched on again if insufficient hysteresis is set in the comparator; in addition, the selection criteria for this voltage are different for different batteries. We remind you that the battery MUST BE DISCHARGED before charging. The "correct" branded chargers do just that - first, on their own initiative, they discharge the connected battery, and then they charge it.

Publication: radiokot.ru

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