Charge and discharge protection of the solar charge controller
1. Direct charge protection point voltage: Direct charge is also called emergency charge. It belongs to fast charge. Generally, the battery is charged with high current and relatively high voltage when the battery voltage is low. However, there is a control point, also called protection. The point is the value in the above table. When the battery terminal voltage is higher than these protection values during charging, the direct charge should be stopped. The direct charge protection point voltage is also the "overcharge protection point" voltage. When charging, the battery terminal voltage cannot be higher than this protection point, otherwise it will cause overcharge and damage to the battery.
2. Equalization control point voltage: After the direct charge is finished, the battery will be statically set by the charge and discharge controller for a period of time, so that its voltage will fall naturally. When it falls to the “recovery voltage” value, it will enter the equalization state. Why design a charge? That is, when the direct charge is completed, there may be some batteries that are “backward” (the terminal voltage is relatively low). In order to pull these individual molecules back and make all the battery terminal voltages have uniform consistency, it is necessary to match the high voltage with moderate voltage. The current is recharged for a short while, so the so-called equalization, that is, "balanced charging" can be seen. The charging time should not be too long, usually from a few minutes to ten minutes. The time setting is too long and it is harmful. For small systems equipped with a two-cell battery, it does not make much sense. Therefore, the street light controller generally does not have an equal charge, only two stages.
3, floating charge control point voltage: Generally, after the charge is completed, the battery is also allowed to stand for a period of time, so that its terminal voltage naturally falls. When it falls to the "maintenance voltage" point, it enters the floating charge state, and currently adopts PWM. (Pulse-width modulation) mode, similar to "turbulent charging" (ie, small current charging), when the battery voltage is low, it will be charged a little. When it is low, it will be charged a little, and the battery will continue to rise. High, this is very good for the battery, because the internal temperature of the battery has a great influence on the charge and discharge. In fact, the PWM method is mainly designed to stabilize the battery terminal voltage, and the battery charging current is reduced by adjusting the pulse width. This is a very scientific charging management system. Specifically, at the end of charging, when the remaining capacity (SOC) of the battery is >80%, it is necessary to reduce the charging current to prevent excessive outgassing (oxygen, hydrogen, and acid gas) due to overcharging.
4, over discharge protection termination voltage: This is better understood. The battery discharge can not be lower than this value, which is the national standard. Although the battery manufacturers also have their own protection parameters (enterprise or line standard), but ultimately they must move closer to the national standard. It should be noted that, for safety reasons, the 12V battery over-discharge protection point voltage is artificially added with 0.3V as the zero-drift correction of the temperature compensation or control circuit, so that the over-discharge protection point voltage of the 12V battery is: 11.10v, then The over-discharge protection point voltage of the 24V system is 22.20V. At present, many manufacturers of charge and discharge controllers use the 22.2v (24v system) standard.