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What is the principle of smart charger

Release time:

2024-06-11

Rechargeable batteries have the characteristics of high performance-to-price ratio, large discharge current and long life, and are widely used in various communication equipment, instruments, and electrical measuring devices. However, different types of batteries such as nickel-cadmium batteries (Nicd), nickel-metal hydride batteries (NiMH), and lithium-ion batteries have different charging characteristics and processes.

Rechargeable batteries have the characteristics of high performance-to-price ratio, large discharge current and long life, and are widely used in various communication equipment, instruments, and electrical measuring devices. However, different types of batteries such as nickel-cadmium batteries (Nicd), nickel-metal hydride batteries (NiMH), and lithium-ion batteries have different charging characteristics and processes. Different charging control techniques should be used for different batteries. Commonly used control techniques are: voltage negative incremental control, time control, temperature control, very high voltage control technology. The voltage negative increment control is recognized as one of the more advanced control methods. While charging, it can be determined that the battery is fully charged when a negative increase in battery voltage is measured, thereby converting the charging to a trickle charge. Time control scheduled charging time, when the charging time is reached, the charger to stop charging or turn to trickle charging, this method is safer.

The temperature control method is that when the battery reaches a full state, the battery temperature rises rapidly, and the battery temperature or temperature change is measured to determine whether to stop charging the battery. The high voltage control is based on the high allowable voltage of the rechargeable battery to judge the charging state, which is more flexible. This paper introduces an intelligent charger, which can charge nickel-cadmium battery (Nicd), nickel-hydrogen battery (NiMH) and lithium-ion battery, and has the ability of automatic detection of rechargeable batteries.

Charger Design Ideas

When designing a universal smart charger. The charging characteristics of the three batteries need to be fully considered, and different charging modes and corresponding algorithms are given for the characteristics of each battery.

Ni-MH/Ni-Cd battery charging mode

The two nickel batteries have similar charging characteristics, so the same charging algorithm can be used. The main charge control parameters of these two batteries are-ΔV and temperature θ.

The criterion for the conversion of Ni-MH/Ni-Cd batteries from pre-charging to standard charging is as follows: ① The voltage level of a single cell is 0. 6~1V;② battery temperature -5 ~ 0C. The criteria for battery saturation charging are: ① battery voltage drop or close to low growth-ΔV = 6~15 mV/section; ② high battery temperature θmax>50 ℃;③ battery temperature rise rate dθ/dt ≥ 1. 0 C/min. Since the change of temperature is easily affected by the environment, the variables used to determine the charging stages are mainly-ΔV and θmax, in which the detection of-ΔV requires sufficient A/D resolution and high current stability. There is the following relationship between the measurement of-△V and A/D resolution, the stability of charging current and the internal resistance of the battery: when the internal resistance of the battery is equal to 50Ω (close to saturation charging), the charging current = 1200mA, the current drift is equal to 5%, and the very high charging voltage of a single battery is 1. 58V, then the current drift may cause the battery voltage change of 3 mV.

Lithium-ion battery charging mode

When charging and sampling a lithium-ion battery, the measured voltage is the online voltage of the battery, and the online voltage is generally higher than the static voltage (related to internal resistance). In the charger design, the measurement parameters of the lithium ion battery charging stage conversion judgment only online voltage, voltage sampling deviation is less than 0. 05V.

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