Design Thought of Lithium Battery Solar Charger

Lithium-ion battery charging problem has been plagued by lithium battery users. How the charging can be convenient for people to use is also a headache for lithium battery manufacturers. Don't worry about it today, because we 've found a way to charge the solar energy that is both environmentally friendly and convenient. Today, lithium battery manufacturers share the design ideas for lithium battery solar chargers:

Maximum power point tracking

The maximum power point(MPP) is the solar cell working area that can obtain the maximum power[ 1] .. The graph in Figure 1 shows the area. The graph shows the relationship between the typical output current and output power and the voltage curve of the MPP dual solar panel. The MPP on the curve is obvious because it corresponds to the voltage and current of the maximum power output of the solar panel. MPP is related to ambient temperature and light, so it changes over time. This shows that chargers using solar power sources must have appropriate circuits to continuously track MPP. MPPT solutions as the environmental conditions change. Including simple open-loop technology(panel voltage maintained at fixed circuit voltage) and complex microcontroller technology(measuring input and output power, and then correctly adjusting panel voltage).

Reverse leakage protection

Reverse leakage is a phenomenon in which the charge stored in the battery is lost and returned to the power supply. When the battery voltage is higher than the power supply, reverse leakage occurs. When this happens, the power supply becomes the load of the battery and no longer charges the battery. This state does not appear when using wall power adapters or USB power supplies because the voltage output of these two power supplies always stays above the lithium ion power supply voltage. When using solar panels, the voltage of the solar panels will be reduced to below the battery voltage in the absence of light. Figure 2A shows a schematic diagram of a USB power charger connected to a battery. When the switch S1 is turned off, the power is disconnected from the battery and the battery has no current. When solar panels are used, if the same layout is used, the switch diode is turned on if the solar panel voltage falls below the battery voltage. A common way to solve this problem is to use a back-to-back switch

Charge termination

In the pre-steady pressure phase, the battery is charged with a constant current of 0.1 C(usually) to slowly increase the battery voltage to about 2.5 V. This phase is only used for deep discharge batteries. Once the battery voltage rises to ~ 2.5 V or more, a constant current is used to charge the battery. During the constant current charging phase, the battery is charged with a constant current of 1C(usually) until the battery voltage reaches ~ 4.2 V. Once the battery voltage reaches ~ 4.2 V, the battery is charged with a 4.2 V constant voltage. At this stage, the current entering the battery needs to be monitored. When the battery current drops to 0.1 C, the charge terminates. During the constant voltage charging phase, the current entering the battery will decrease because the battery impedance increases when the battery is full. Once the current is reduced below 0.1 C, the charging power must be completely disconnected from the power supply. If it is not completely disconnected, lithium plating will occur, making the battery unstable and dangerous. We must stop the lithium ion battery charging according to the current entering the power supply to ensure that the battery is just filled to its maximum power.

Solar panel crash protection

In some traditional chargers, we know in advance the current and voltage of the power supply. Therefore, the charger circuit is specially designed for operation within the specified range of power supply. When using solar panels, the current size and open-circuit voltage are dynamic, depending on the surrounding environment. Therefore, designing a control loop for a solar charger is more challenging than a power adapter on the wall.

Systems that use solar energy to charge lithium-ion batteries are trying to maintain the process of recharging lithium-ion batteries without accidentally causing solar panels to collapse. Because if the voltage of the solar panel falls sharply, it will not be able to obtain useful electricity from the solar panel. There is a greater chance of solar panels collapsing during the constant current charging phase. At this stage, solar panels may not provide the current needed to charge the battery. When this happens, the solar panel voltage begins to collapse rapidly. Therefore, the charger must be able to detect a rapid decline in the voltage of the solar panel and immediately reduce the current obtained from the solar panel to prevent the solar panel from collapsing.

Solar charger can provide a mobile, environmentally friendly charging method for lithium-ion batteries. When designing a solar charger, there are many problems that can not be encountered when designing a power adapter charger on the wall. If designers use their brains, they can design chargers that can use solar, USB, and wall power adapters to input the perfect charge for lithium-ion batteries.

Lithium battery manufacturers have been looking for a very convenient way for users of lithium batteries, but also hope that users to give us valuable advice!

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