Battery over-discharge protection circuit

The lower limit of the battery voltage is the discharge termination voltage. If it is lower than this voltage and continues to discharge, the performance is degraded, and the fire is caused by the heavy.

This over-discharge protection circuit is powered by a protected battery without the need for an additional power supply. Once the discharge termination voltage is reached, the load and protection circuits of the battery are cut off.

The circuit is as shown in the middle picture. With 12V battery as protection object, it can also be used for battery protection of other voltages. The non-inverting input of comparator IC1 is connected to a 5v reference voltage, which is provided by regulator IC2. The inverting input is connected to the protected battery terminal voltage through the potentiometer VR1. VR1 is used to adjust the voltage regulation, here to 10V of the discharge termination voltage of the 12V battery.

When the jog switch SW1 is pressed, the battery supplies power to the protection circuit, the comparator output is "L", the relay RL1 is electrically connected, and the contacts are self-protected, and the battery and the load are also turned on. After SW1 is released, the battery continues to supply power. At the same time, LED1 emits light, indicating that it is in a discharged state.

When the battery is discharged to the set termination voltage (10V), the comparator is turned over, the relay is de-energized, and the load and protector are disconnected from the battery to avoid over-discharge.

If the load on the battery is large and the contact of the relay cannot pass a large current, a contactor can be added. Turn the relay contacts to the contactor coil power supply and use the contactor contacts to switch the load on. The circuit is as shown above.

If a comparator with low drive capability (such as LM393 or op amp LM358) 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 resistors. The circuit is shown below. The figure below shows a 24V battery. At this time, the termination voltage of VR1 adjustment should be 20V.

If the battery has a long power lead, the line resistance will cause a voltage drop.

This will cause the output of the comparator to continuously switch "L" and "H" as the battery voltage approaches the discharge termination voltage, causing the relay to vibrate. To this end, a hysteresis circuit consisting of R3 and R4 is added to the circuit to avoid such malfunction.

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

1. Take a triode, the base is connected to two voltage-dividing bias resistors, such as tentatively set to two 1K; 2. The collector string is a relay with a rated working voltage of 3V; 3. The normally-on switch is connected to the battery positive pole. The other end is connected with a bias resistor and a relay coil; 4. The lower bias resistor and the emitter are connected to the battery negative pole; 5. The two contact of the 3 and 4 steps supply power to the circuit; 6. The resistance of the bias resistor is adjusted. Make it open at 3.9V.

1. Take a triode, the base is connected to two voltage-dividing bias resistors, such as tentatively set to two 1K;

2. The collector string is a relay with a rated working voltage of 3V;

3. Connect the normally open switch to the positive pole of the battery and the other end to the bias resistor and relay coil;

4. The lower bias resistor and the emitter are connected to the battery negative pole;

5. Powering the circuit from the two contacts of steps 3 and 4;

6. Adjust the resistance of the bias resistor so that the relay is disconnected at 3.9V.

This solution uses only four components. To make the circuit more perfect, the emitter can be stringed with a low resistance resistor. If you don't have a basic circuit foundation, you can ask others for advice according to this plan. This is the most convenient, and it is easy for people to understand.

You can also change the upper bias resistor to an adjustable resistor of about 10 kΩ.

(1) The positive voltage output terminal of the power supply is connected in series with a MOS tube or a triode to realize the switching function.

(2) The output DC voltage of the battery is divided by the resistor (for example, at 3.9V, the midpoint voltage of the two resistors is Uo)

(3) The op amp is made into a comparator, the comparison voltage is equal to the resistor divider Uo (this voltage is obtained by the battery through the voltage regulator chip, connected to the inverter inverting terminal; the op amp is connected to the neutral point of the voltage divider resistor) Output output terminal MOS tube G class

When the output voltage drops below 3.9V, the comparator operates, and the output closes the MOS transistor, that is, the connection between the battery and the subsequent circuit is turned off.

Use op amps, such as lm318, 358, 324, etc.

As shown in the figure, adjust R3

VCC is connected to the battery + pole. When the battery is 11V, adjust R3 to make K1 pull in, and the contact disconnects the load.

Then use a ne5532 as a comparator.

The working voltage of the ne5532 is 3-22v, which is no problem for the 12v battery.

When the battery voltage is higher than 11v, the switch tube is turned on, and the inverter can be reversed; when the voltage is lower than 11v, the switch tube is turned off, and the inverter stops, which serves to protect the battery.

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