The parallel controller is also called the bypass controller, which uses mechanical or electronic switching devices connected in parallel at both ends of the battery assembly to control the charging process. When the battery is fully charged, the output of the battery assembly is shunted to the bypass resistor or power module, and then consumed in the form of heat; when the battery voltage drops to a certain value, the bypass is disconnected to resume charging. Because this method consumes heat energy, it is generally used in small, low-power systems.
The circuit principle of the parallel controller is shown in Figure 1. The switching device K1 of the charging circuit in the parallel controller circuit is connected in parallel to the output terminal of the battery assembly, and the controller detection circuit monitors the terminal voltage of the battery. When the charging voltage exceeds the set full disconnect voltage value of the battery, the switching device K1 is turned on, and the anti-recharge diode D1 is turned off at the same time, so that the output current of the battery assembly is directly discharged through the K1 bypass, and the battery is no longer charged, so as to ensure that the battery is not overcharged, and play a protective role to prevent the battery from being overcharged.
The switch device K2 is a battery discharge control switch. When the battery’s power supply voltage is lower than the battery’s over-discharge protection voltage value, K2 is turned off to protect the battery from over-discharge. When the load is overloaded or short-circuited and the current is greater than the rated operating current, the control switch K2 will also be turned off to play the role of output overload or short-circuit protection.
The detection control circuit detects the battery voltage at any time. When the voltage is greater than the full protection voltage, K1 turns on and the circuit implements overcharge protection; when the voltage is less than the overdischarge voltage, K2 turns off, and the circuit implements overdischarge protection.
D2 in the circuit is a battery reverse connection protection diode. When the battery polarity is reversed, D2 is turned on, and the battery will be short-circuited through D2. The short-circuit current will blow the fuse, and the circuit plays a protective role against battery reverse connection.
Switching devices, D1, D2, and fuse BX are generally combined with the detection control circuit to form a controller circuit. The circuit has the characteristics of simple circuit, low price, low charging loop loss, and high control efficiency. When the overcharge protection circuit operates, the switching device has to withstand the maximum current output by the battery pack or the square array, so a switching device with a larger power should be used.
The series controller uses mechanical or electronic switching devices connected in series in the charging circuit to control the charging process. When the battery is fully charged, the switching device disconnects the charging circuit and stops charging the battery: when the battery voltage drops to a certain value, the charging circuit is turned on again to continue charging the battery. The switching device connected in series in the loop can also cut off the power supply of the battery assembly at night, replacing the anti-reverse charge diode. The series controller also has the characteristics of simple structure and low price, but because the control switch is connected in series in the charging loop, the voltage loss of the circuit is relatively large, which reduces the charging efficiency.
The circuit principle of the series controller is shown as in Figure 2. Its circuit structure is similar to that of the parallel controller, except that the switching device K1 is changed from being connected in parallel at the output of the battery assembly to being connected in series in the battery charging circuit. The detection circuit of the controller monitors the terminal voltage of the battery. When the charging voltage exceeds the set full and disconnected voltage value of the battery, K1 is turned off, so that the battery components are no longer charging the battery, so as to ensure that the battery is not overcharged, and play a protective role to prevent the battery from overcharging. The functions of other components are the same as those of the parallel controller and will not be repeated. Here is an introduction to the composition and working principle of the detection control circuit.
The detection control circuit of the series and parallel controllers is actually the detection control circuit of the battery over- or under-voltage. It is mainly to sample and detect the voltage of the battery at any time, and according to the detection result, send a control signal to turn on or turn off the overcharge and overdischarge switch devices. The principle of the detection control circuit is shown in Figure 3. This circuit includes two parts of circuits: over-voltage detection and control and under-voltage detection and control, composed of operational amplifiers with backlash control. Among them, IC1, etc. is an over-voltage detection control circuit. The non-inverting input terminal of IC1 inputs the reference voltage, and the inverting input terminal is connected to the battery under test. When the battery voltage is greater than the overcharge voltage value, IC1 output terminal G1 output is low level, so that the switching device K1 is turned on (parallel controller) or off (series controller), playing the role of overvoltage protection. When the battery voltage drops to less than the overcharge voltage value, the inverting input potential of IC1 is less than the non-inverting input potential, and its output terminal G1 changes from low level to high level again, and the battery returns to its normal charging state. The threshold reference voltage for overcharge protection and recovery is determined by the coordinated adjustment of W1 and RI. IC2, etc. constitute an under-voltage detection and control circuit, and its working principle is the same as that of the over-voltage detection and control circuit.