Parallel and series charge and discharge controllers

Parallel and series charge and discharge controllers

Parallel type charge and discharge controller

The basic circuit principle of the parallel type (also called bypass type) charge and discharge controller is shown in Figure 1.

Parallel and series charge and discharge controllers
Figure 1 – The basic circuit principle of the parallel charge-discharge controller

The switching device T1 in the charging circuit of the parallel charge and discharge controller is connected in parallel to the output end of the solar cell array. When the battery voltage is greater than the full cut-off voltage, the switching device T1 is turned on, and the diode D1 is turned off at the same time, the output current of the solar cell array is directly discharged through the short circuit of T1, and the battery is no longer charged, so as to ensure that the battery will not be overcharged and play an overcharge protection role.

D1 is an anti-reverse charging diode. Only when the output voltage of the solar cell array is greater than the battery voltage, D1 can be turned on, otherwise D1 is turned off, so as to ensure that the battery will not be reversely discharged to the solar cell array at night or in rainy weather, which plays a protective role against reverse charging.

The switching device T2 is a battery discharge control switch. When the negative storage current is greater than the rated current and the overload occurs or the load is short-circuited, T2 is turned off, which plays the role of output overload protection and output short-circuit protection. At the same time, when the battery voltage is less than the over-discharge voltage, T2 is also turned off to protect the battery from over-discharge.

D2 is an anti-reverse-connection diode. When the battery polarity is reversed, D2 is turned on to cause the battery to short-circuit and discharge through D2, and a large current is generated to quickly blow the fuse Bx, which plays a protective role against reverse battery polarity.

The detection control circuit detects the battery voltage at any time, generally using a Schmitt hysteresis circuit. When the voltage is higher than the full cut-off voltage, T1 is turned on for overcharge protection. When the voltage falls back to a certain value, T1 is disconnected and charging is resumed. The discharge control is also similar. When the voltage is lower than the over-discharge voltage, T2 is turned off, the load is cut off, and over-discharge protection is performed, and when the voltage rises to a certain value, T2 is turned on again to resume discharge.

Series type charge and discharge controller

The basic circuit principle of the Shenlian type charge and discharge controller is shown in Figure 2.

Parallel and series charge and discharge controllers
Figure 2 – Basic circuit principle of series-type charge-discharge controller

The circuit structure of the series charge and discharge controller is similar to that of the parallel charge and discharge controller. The only difference is that the connection method of the switching device T1 is different. The parallel type T1 is connected in parallel to the output end of the solar cell array, while the series type T1 is connected in series in the charging circuit. When the battery voltage is greater than the full cut-off voltage, T1 is turned off, so that the solar cell array will no longer charge the battery and play an overcharge protection role.

The functions of other components are the same as those of the series-type charge-discharge controller, and are also simple on/off-type controllers with hysteresis voltage, which will not be repeated here.

The composition and working principle of the above-mentioned two kinds of controller detection control circuits are shown in Figure 3.

Parallel and series charge and discharge controllers
Figure 3 – Over-voltage detection and under-voltage detection circuit of the controller

The detection control circuit includes two parts: over-voltage detection control and under-voltage detection control.

The detection control circuit is composed of an operational amplifier with hysteresis control. A1 is an overvoltage detection control circuit, the non-inverting input terminal of A1 provides the reference voltage corresponding to “overvoltage cut-off” by W1, and the inverting input terminal is connected to the battery under test. When the battery voltage is greater than the “overvoltage cut-off voltage”, the output terminal G1 of A1 is at a low level, and the switching device T1 is turned off to cut off the charging circuit, which plays an overvoltage protection role. When the battery voltage drops to less than the “overvoltage recovery voltage” after the overvoltage protection, the inverting input potential of A1 is less than the non-inverting input potential, and its output terminal G1 jumps from low level to high level. The switching device T1 is switched from off to on, and the charging circuit is reconnected. The “overvoltage cut-off threshold” and “overvoltage recovery threshold” are adjusted by W1 and R1.

A2 is the under-voltage detection control circuit, its reverse phase terminal is connected to the under-voltage reference voltage provided by W2, and the non-phase terminal is connected to the battery voltage (opposite to the over-voltage detection control circuit). When the battery voltage is lower than the “under-voltage threshold level”, the output terminal G2 of A2 is low level, the switching device T2 is turned off, and the output circuit of the controller is cut off to realize “under-voltage protection”. After under-voltage protection, as the battery voltage increases, when the voltage is higher than the “under-voltage recovery threshold”, the switching device T2 is turned on again to restore power to the load. “Under voltage protection threshold” and “under voltage recovery threshold” are adjusted by W2 and R2.