charging method

charging method

The charging method is the most critical. To charge the lithium battery, you need a charger that specifically supports the lithium battery charging mode.

Generally marked on the charger's packaging. Many chargers are compatible with two charging modes. When purchasing, pay attention to whether it is automatically recognized or manually set by the switch. If it is manually set, it must be set correctly according to the type of battery being charged. For nickel-cadmium/nickel-metal hydride batteries, the excellent charger uses a charging method with a pull-down negative pulse charge to reduce the polarization effect during charging. Normal low-cost chargers use constant current charging. The battery charging waveform depends on the oscilloscope for accurate observation.

The charger uses an RCC type switching power supply, that is, an oscillation suppression type converter, which is different from the PWM type switching power supply. The PWM type switching power supply consists of a separate sampling error amplifier and a DC amplifier to form a pulse width modulation system; and the RCC type switching power supply is only composed of a voltage regulator to form a level switch, and the control process is an oscillation state and a suppression state. Since the switching tube in the PWM type switching power supply is always on and off periodically, the system control only changes the pulse width of each cycle, and the control process of the RCC type switching power supply changes continuously nonlinearly. It has only two states: when the switching power supply When the output voltage exceeds the rated value, the pulse controller outputs a low level, and the switch tube is turned off; when the output voltage of the switching power supply is lower than the rated value, the pulse controller outputs a high level, and the switch tube is turned on. When the load current decreases, the discharge time of the filter capacitor is prolonged, the output voltage will not decrease quickly, and the switch tube is in the off state. Until the output voltage drops below the rated value, the switch tube will be turned on again. The cut-off time of the switch depends on the magnitude of the load current. The on/off of the switch is controlled by the level switch sampling from the output voltage. Therefore, this power source is also called a non-periodic switching power supply.

220V mains is rectified by VD1 ~ VD4 bridge to form a DC voltage of about 300V on the collector of V2. The intermittent oscillator is composed of V2 and a switching transformer. After power-on, 300V DC voltage is applied to the collector of V2 through the transformer primary, and the voltage is also supplied with a bias voltage through the base of the starting resistor R2 for V2. Due to the positive feedback, V2Ic rises rapidly and saturates. During the V2 entry cut-off period, the induced voltage generated by the secondary winding of the switching transformer turns VD7 on, and outputs a DC voltage of about 9V to the load. The induced pulse generated by the feedback winding of the switching transformer is rectified by VD5 and filtered by C1 to generate a DC voltage proportional to the number of oscillation pulses. If this voltage exceeds the regulation value of the voltage regulator VD17, VD17 will be turned on, and the negative rectifier voltage will be applied to the base of V2 to make it cut off quickly. The cutoff time of V2 is inversely proportional to its output voltage. The on/off of VD17 is directly affected by the grid voltage and load. The lower the grid voltage or the larger the load current, the shorter the on-time of VD17 and the longer the on-time of V2. Conversely, the higher the grid voltage or the smaller the load current, the higher the rectified voltage of VD5 and the on-time of VD17. The longer, the shorter the on-time of V2. V1 is an overcurrent protection tube and R5 is a sampling resistor of V2Ie. When V2Ie is too large, the voltage drop on R5 turns V1 on and V2 turns off, which can effectively eliminate the inrush current at the moment of starting, and also compensates for the control function of VD17. VD17 uses voltage sampling to control the oscillation time of V2, while V1 uses current sampling to control the V2 oscillation time.

If it is charging nickel-cadmium or nickel-hydrogen batteries, because of the memory effect of such batteries, it is necessary to discharge them from time to time. SW1 is a nickel-cadmium, nickel-hydrogen, lithium-ion battery charge transfer switch. The SW1 and precision reference power supply SL431 provide two different precision reference sources for the op amp LM3249, which are switched by SW1. When charging Ni-Cd and Ni-MH batteries, the reference voltage of the LM3249 pin is about 0.09V (no-load); when charging the Li-ion battery, the reference voltage of the LM3249 is about 0.08V (no-load). The design is determined by the chemical properties unique to both types of batteries. When SW2 is pressed, the base of V5 is turned to a low level for a moment, and the residual voltage on the rechargeable battery is discharged on R17 through the ec pole of V5, and the discharge indicator VD14 is lit. After pressing SW2, it will be released immediately. At this time, the residual voltage on the rechargeable battery is divided by R16 and R13. After C9 filtering, the base of V4 is provided with a high level, and V4 is turned on, which is equivalent to shorting SW2. As the discharge time is extended, the residual voltage on the rechargeable battery is also getting lower and lower. When the voltage on the base of V4 cannot maintain its continuous conduction, V4 is turned off, the discharge is terminated, and the charger is then transferred to the charging state.

Since the lithium battery does not have a memory effect, when the battery is lower than 3V, it cannot be turned on. The residual voltage is divided by the resistors R40 and R41 to obtain 2.53V, which is sent to the in-phase terminals 3, 5, and 10 of the operational amplifier, due to the voltage of the LM3249. Under the load is always 2.66V, so the 8 pin output low level, V3 is turned on, +9V voltage is charged to the rechargeable battery through V3ec pole and VD8. IC1d under the action of capacitor C6, the {14} pin outputs a pulse signal. Since IC18 pin is low level, VD12 is flashing to indicate that the battery is charging, and the corresponding capacity is 20%. As the charging time increases, the voltage on the rechargeable battery gradually rises. When the voltage division value of R40 and R41 is approximately equal to 2.58V, that is, IC13 pin is equal to 2.58V, IC12 pin is 2.57V after voltage divider, and its 1 pin outputs high level (since charging, IC19 The pin voltage is always 2.66V, V6 is on; otherwise, at no load, IC19 pin is 0.08V, V6 is off), VD10, VD11 are lit, the corresponding indication capacity is 40%, 60%. When the voltage divider value of R40 and R41 rises to 2.63V, the IC15 pin is equal to 2.63V, and the 6th pin is 2.63V after the resistor divider. The 7 pin outputs a high level, and the VD9 lights up, corresponding to the charging capacity. It is 80%. Only when the IC110 pin voltage is ≥2.66V, the 8 pin outputs a high level, and the VD13 lights up, corresponding to a charging capacity of 100%. Even if VD13 is lit, VD12 is still flashing, which means the battery is still not fully saturated. Only when the IC18 pin voltage is >6.5V, VD12 is gradually extinguished, indicating that the battery is fully charged to saturation.

VD16 acts as an overcharge and overcurrent protection in the circuit, and VD8 acts as a reverse protection to prevent reverse discharge of the battery after the charger is powered off.

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