12V27A battery

12V27A battery charging protection circuit and discharge protection circuit

12V27A battery charging protection circuit and discharge protection circuit requirements. The design of 12V27A battery charging circuit and discharge protection circuit is very important. Due to the high energy density of 12V27A battery, when overcharged, the battery temperature rises and the energy will be excessive, so the electrolyte decomposes and produces gas, which easily causes the internal pressure to rise and cause the risk of spontaneous combustion or rupture. Therefore, the protection of 12V27A battery is very important.

Principle of 12V27A battery protection circuit

The reason why 12V27A battery (rechargeable) needs protection is determined by its own characteristics. Since the material of 12V27A battery itself determines that it cannot be overcharged, over-discharged, over-current, short-circuited and charged and discharged at ultra-high temperature, 12V27A battery components always appear with a delicate protection board and a current fuse. The protection function of 12V27A battery is usually completed by the protection circuit board and current devices such as PTC. The protection board is composed of electronic circuits. It accurately monitors the voltage of the battery cell and the current of the charging and discharging circuit at all times in an environment of -40℃ to +85℃, and controls the on and off of the current circuit in time; PTC prevents the battery from being severely damaged in a high temperature environment.

Ordinary 12V27A battery protection boards usually include control IC, MOS switch, resistor, capacitor and auxiliary devices FUSE, PTC, NTC, ID, memory, etc. Among them, the control IC controls the MOS switch to turn on under normal circumstances, so that the battery cell is connected to the external circuit. When the battery cell voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off to protect the safety of the battery cell.

12V27A battery charging protection circuit and discharge protection circuit

1. Charging of lithium batteries

The maximum charging termination voltage of a single 12V27A battery is 4.2V. It cannot be overcharged, otherwise the battery will be scrapped due to too much loss of lithium ions at the positive electrode. When charging lithium batteries, a dedicated constant current and constant voltage charger should be used. First, constant current charging is performed until the voltage across the 12V27A battery is 4.2V, and then the constant voltage charging mode is switched on; when the constant voltage charging current drops to 100mA, charging should be stopped.

The charging current (mA) can be 0.1 to 1.5 times the battery capacity. For example, for a 1350mAh 12V27A battery, the charging current can be controlled between 135mA and 2025mA. The conventional charging current can be selected at about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours.

2. Discharge of lithium batteries

Due to the internal structure of lithium batteries, lithium ions cannot all move to the positive electrode during discharge, and a part of lithium ions must be retained at the negative electrode to ensure that the lithium ions can be smoothly embedded in the channel during the next charge. Otherwise, the battery life will be shortened. In order to ensure that some lithium ions remain in the graphite layer after discharge, the minimum discharge termination voltage must be strictly limited, that is, the 12V27A battery cannot be over-discharged.

The discharge termination voltage of a single 12V27A battery is usually 3.0V, and the minimum cannot be lower than 2.5V. The length of battery discharge time is related to the battery capacity and discharge current. Battery discharge time (hours) = battery capacity/discharge current, and the 12V27A battery discharge current (mA) should not exceed 3 times the battery capacity. For example: for a 1000mAh 12V27A battery, the discharge current should be strictly controlled within 3A, otherwise the battery will be damaged.

The design of the 12V27A battery protection circuit is very important. We require that the 12V27A battery power protection chip should be able to achieve the following basic functions: overcharge protection, over-discharge protection, overcurrent protection and short-circuit protection. From the above application requirements of lithium batteries, it can be seen that in order to improve the service life of lithium batteries and ensure the safe use of batteries.

The 12V27A battery protection circuit needs to have the following functions

(1) If the charging voltage exceeds the maximum value allowed by the battery, it can provide a battery discharge circuit.

(2) If the discharge voltage is lower than the minimum value allowed by the battery, it can provide a battery charging circuit. Then cut off the connection between the battery and the external circuit, and then cut off the connection between the battery and the external circuit.

(3) If the charging and discharging current of the 12V27A battery is greater than the limit value, the connection between the battery and the external circuit is cut off.

(4) When the 12V27A battery returns to normal state, the protection circuit should be able to release the protection state accordingly so that the battery can continue to work normally.

Overcharging and over-discharging of lithium batteries will affect the life of the battery. Usually we need to pay attention to the charging voltage and charging current of the 12V27A battery. Then select a suitable charging chip.

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