Composition of model aircraft lithium-ion battery charger
A typical model aircraft lithium-ion battery charger consists of: a power supply; a charger; a parallel charging board; and other accessories. A model aircraft lithium-ion battery balance charger generally only needs a power supply and a charger to charge the lithium-ion batteries, while the parallel charging board and other accessories are for making the charging process safer and faster.
A lithium-ion battery charger is a charger specifically designed to charge lithium-ion batteries. Lithium-ion batteries place high demands on chargers, requiring protection circuits. Therefore, lithium-ion battery chargers typically have high control precision and are capable of constant current and constant voltage charging of lithium-ion batteries.
Model aircraft lithium-ion battery charging method
Most dedicated model aircraft lithium-ion battery charging ICs charge batteries in this way. Model aircraft lithium-ion batteries have three charging methods: pre-charging, fast charging constant current (CC), and constant voltage (CV). During the pre-charging step, when the battery cell voltage is 3.0V or lower, the battery charges at a low rate. This restores the passivation layer, which can be fully discharged during long-term storage. It also prevents overheating at the 1C charging rate when partial copper breakdown occurs at the anode of the battery due to over-discharge short circuit.
1. When the lithium-ion battery voltage reaches 3.0V, the charger enters the CC step.
Fast charging current is typically limited to 0.5C to 1C to prevent overheating and subsequent degradation. When the model aircraft's lithium-ion battery is fully charged, the charger begins to control the battery voltage, and the charging current drops sharply to a predetermined end level when the CV stage is reached. To prevent prolonged charging of dead batteries, a fast charging safety timer is usually used. Even if the battery has not reached the shutdown current, the battery charger must be turned off after the safety time has elapsed.
2. Battery capacity is a function of battery voltage.
Generally, the higher the voltage of a lithium-ion battery for a model aircraft, the greater its capacity. However, a higher charging voltage also leads to a shorter battery life. At higher voltages, the positive electrode material reacts more rapidly with the electrolyte, and cobalt is permanently lost during the chemical reaction. This reduces the available energy storage material, resulting in a loss of chemical capacity. Therefore, the accuracy of the battery charging voltage is crucial.
3. Time is an important factor in battery charging.
Under constant current conditions, it takes approximately 30% of the charging time to reach 70% of the battery's total capacity, while under constant voltage conditions, the charging time is only about 70% of the total charging time. This is because there is internal resistance within the battery. The lower the internal resistance of the battery, the shorter the charging time.
4. The charging current must not exceed the maximum charging current specified in the datasheet. Using a current higher than the recommended current may cause problems with the battery's charge/discharge performance, mechanical properties, and safety, and may lead to overheating or leakage. For model aircraft lithium-ion batteries currently on the market that require 5C charging, it is recommended to avoid frequent 5C charging to prevent affecting battery life.
5. Charging voltage: The charging voltage shall not exceed the specified limit voltage (4.2V/cell), and 4.25V is the maximum limit for the charging voltage of each cell.
