Lead battery replacement option. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Lead battery replacement option. Encyclopedia of radio electronics and electrical engineering

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

A flashlight with a lead battery worked for me for two months, after which its battery began to discharge very quickly. On fig. 1 shows a diagram of this lantern, compiled according to the results of its disassembly and study. It was not possible to purchase a new lead battery to replace the faulty one. However, there were many lithium batteries from cell phones. The batteries were new, just the models of phones for which they were intended were outdated, there was no demand for spare batteries for them, so they were sold very cheaply.

It was decided to replace the failed lead battery with a 750 mAh lithium battery. Even if it has served its time in the phone, its capacity remains, as a rule, sufficient for a flashlight, where the current consumption is much less.

Since lithium batteries are very demanding on the modes of charging and discharging, they have a built-in charging controller that monitors the state of the battery, automatically stops charging at the right time and does not allow excessive discharge, turning off the load when the voltage is below the allowable one.

Lead battery replacement option
Fig. 1

In addition to replacing the GB1 battery with the G1 battery, a resistor R2 was added to the lantern, which limits the charging current pulse of the capacitor C1 when the lantern is turned on, the resistor R3, which ensures the discharge of the capacitor C1 after disconnection from the network, the capacitor C2. absorbing surges of charging current, leading to false operation of the battery charging controller. In addition, a 2 V VD5,6 zener diode is installed. After the controller automatically opens the charging circuit, it does not allow the voltage applied to the battery to increase to a dangerous value for it and other parts of the flashlight. The scheme of the lantern after its completion is shown in fig. 2.

Lead battery replacement option
Fig. 2

New elements (R1, R2, C2, VD2) were installed by surface mounting. The battery worked for me for two months, after which its battery began to discharge very quickly. On fig. 1 shows a diagram of this lantern, compiled according to the results of its disassembly and study. It was not possible to purchase a new lead battery to replace the faulty one. However, there were many lithium batteries from cell phones. The batteries were new, just the models of phones for which they were intended were outdated, there was no demand for spare batteries for them, so they were sold very cheaply.

Later, to speed up battery charging, capacitor C1 was replaced by another one with a capacity of 1 uF at 630 V DC. The capacitance of capacitor C1000 has been increased to 2 uF. In addition, the modifications shown in Fig. 3. A single zener diode VD2 is replaced by a more efficient voltage limiter on the same zener diode and transistor VT1. The voltage across the resistor R7 when the battery charging current flows through it is enough to open the transistor VT2. The HL2 LED included in the collector circuit of this transistor shines, signaling that charging is in progress, and goes out when the controller built into the lithium battery automatically stops it. Diode VD3 prevents the battery from discharging through the charger circuit after being disconnected from the mains.

Lead battery replacement option
Fig. 3

In a modified lamp, it is necessary, first of all, to check the operation of the voltage limiter. When the flashlight is connected to the mains, the voltage on the contacts intended for connecting the battery (in its absence) should not exceed 7 V. Having replaced the battery and observing the charging process, you should make sure that the controller built into the battery is working: when the nominal value for of this voltage accumulator, charging should stop, and the HL2 LED should go out.

Do not forget that the elements of the lamp, when it is connected to the network, are under its voltage. Therefore, be careful when making changes to the design of the lantern and taking measurements.

Author: B. Glebov

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