Battery over-discharge protection circuit

The lower limit of the battery voltage is the discharge end voltage. If the discharge continues below this voltage, the performance will be degraded or a fire may occur.

This over-discharge protection circuit does not require a male to connect the power supply. It is powered by a protected battery. Once the discharge end voltage is reached, the battery load and protection circuit are cut off.

The circuit is shown in Figure 1. Use 12V battery as the protection object. It can also be used for battery protection of other voltages. The non-inverting input terminal of comparator IC1 is connected to the 5V reference voltage. This voltage is provided by voltage regulator IC2. The inverting input terminal is connected to the protected battery terminal voltage through the potentiometer VR1. VR1 is used to adjust the protection voltage, here it is adjusted to the discharge termination voltage of the 12V battery, 10V.

When the inching switch SW1 is pressed, the battery supplies power to the protection circuit, the comparator output is "L", and the relay RL1 is powered on. While its contacts are self-protecting, the battery and load are also connected. After releasing SW1, the battery continues to provide power. At the same time, LED1 lights up, indicating that it is in a discharge state.

When the battery discharges to the set termination voltage (10V), the comparator flips over, the relay loses power, and the load and protector are disconnected from the battery to avoid over-discharge.

If the load of the battery is large and the contacts of the relay cannot pass a large current, a contactor can be added. Connect the relay contacts to the contactor coil power. Then use the contactor contacts to connect the load. The circuit is shown in Figure 2.

For example, when using a comparator with low driving capability (such as LM393 or operational amplifier LM358, etc.) that cannot directly drive the relay. A driver stage can be added after the comparator. The driver stage uses a high-power transistor RN2202 with built-in resistor. The circuit is shown in Figure 3. Figure 3 illustrates a 24V battery. At this time, the termination voltage value of VR1 adjustment should be 20V.

If the battery power leads are long, the line resistance will cause a voltage drop. This occurs when the battery voltage approaches the discharge end voltage. The output of the comparator keeps switching "L" and "H", causing the relay to chatter. For this reason, a hysteresis circuit consisting of R3 and R4 is added to the circuit. This malfunction can be avoided.

The above circuit. The coil voltage of the relay or contactor should be consistent with the battery voltage.