A lead-acid battery charger with switchable safety life-extending mode and three-stage fast-charging mode

Abstract

A kind of switchable safe life-prolonging mode and three-stage lead-acid battery charger, by adding mode switching switch that can shield or release current to voltage pull-up signal in current threshold comparison and control unit of constant current charging mode, realize the conversion of two modes.When mode switching switch shields current to voltage pull-up signal, the highest output voltage of constant current stage and constant voltage stage is clamped at float voltage, enter safe life-prolonging charging mode, prevent overcharge, prolong battery life, ensure safe and stable charging of battery;When mode switching switch releases current to voltage pull-up signal, charger enters three-stage fast charging mode, voltage rises rapidly to standard voltage of conventional constant current, constant voltage stage, accelerates to complete charging.This charger improves simple structure, low cost, suitable for various specifications of lead-acid battery.

Description

Technical Field

[0001] This utility model relates to the field of battery charging technology, and in particular to a three-stage lead-acid battery charger with switchable safety and life-extending modes. Background Technology

[0002] The existing three-stage lead-acid battery charger completes charging in the sequence of constant current, constant voltage, and float charging stages. In the constant current stage, the output voltage gradually increases as the battery charge increases. As the battery voltage gradually increases, the charger's internal current threshold comparison and control unit automatically adjusts the output voltage to maintain a constant current. When the battery voltage reaches the preset constant current charging termination voltage, the voltage no longer increases but remains constant at this voltage, transitioning to the constant voltage stage. In the constant voltage charging stage, the charger continues to charge the battery at the constant current charging termination voltage. As the battery charge increases, the battery's electromotive force gradually increases, causing the charging current to naturally decrease. When the charging current drops to a certain set value, the charger automatically reduces the output voltage to the float charging voltage, transitioning to the float charging stage. The charger maintains the battery at a fully charged state with a very small current, preventing power loss due to battery self-discharge. The three-stage lead-acid battery charger has the advantages of fast charging speed and relatively full battery charging. However, in the constant current stage, the constant current charging termination voltage, raised by the current threshold comparison and control unit to maintain a constant current, continues until the end of the constant voltage stage. If the ambient temperature is high, the battery is aging, or the charging parameters are set improperly, this process can easily lead to overcharging, water loss, temperature rise, and plate corrosion, thereby shortening the battery life. Therefore, current technology lacks a simple, low-cost charger that allows users to actively switch between a safety-extending solution or a three-stage charger based on their charging speed requirements. Utility Model Content

[0003] This utility model discloses a lead-acid battery charger with a switchable safety-extended life mode and a three-stage fast charging mode. A mode switching switch is added to the voltage regulation signal circuit of its current threshold comparison and control unit. This switch can selectively shield or allow the current-voltage pull-up signal, realizing the switching between two modes: When the switch shields the pull-up signal, the signal circuit is locked in float charging mode, and the highest output voltage of the constant current and constant voltage stages is clamped at the float charging voltage, entering the safety-extended life charging mode. This prevents overcharging, ensures safe and stable charging, and significantly extends battery life. When the switch allows the current-voltage pull-up signal, the charger enters the three-stage fast charging mode, and the voltage returns to the standard voltage of the conventional constant current and constant voltage stages, accelerating the charging process. This improved charger design has a simple structure, low cost, and is suitable for various specifications of lead-acid batteries.

[0004] Technical solution

[0005] This invention provides a lead-acid battery charger with switchable safety-extended life mode and three-stage fast charging mode, comprising a rectifier and filter circuit, a control circuit (such as a PWM controller), a power switch, a transformer, an output rectifier and filter circuit, and, crucially, a voltage sampling circuit and a current threshold comparison and control unit. The output signals of the voltage sampling circuit and the current threshold comparison and control unit are fed back to the control circuit for adjusting the charging voltage and current.

[0006] The core improvement of this invention lies in the addition of a mode switching switch (K) to the feedback path where the pull-up signal output by the current threshold comparison and control unit affects the voltage reference or voltage feedback signal. This switch (K) is used to selectively control whether the pull-up signal affects the voltage reference or voltage feedback signal.

[0007] Specifically:

[0008] The mode switching switch is positioned between the output of the current threshold comparison and control unit (reflecting the pull-up signal after current threshold comparison) and the node that can affect the voltage feedback signal or voltage reference setting (usually connected to the voltage divider network of the voltage sampling circuit or the relevant pin of the control chip).

[0009] The two states of a switch:

[0010] Safety Extension Mode: When switch (K) is in the "Off" or "Shielded" position, it blocks the effect of the current threshold comparison and the pull-up signal output by the control unit on the voltage regulation signal. At this time, the pull-up signal cannot increase the voltage or decrease the voltage feedback signal, causing the effective voltage division ratio of the voltage sampling circuit to be locked at the state corresponding to the float charge voltage. The control circuit therefore clamps the charger's maximum output voltage to the float charge voltage level.

[0011] Features: The highest voltage in both the constant current and constant voltage stages is the float charge voltage, and the float charge stage maintains the float charge voltage;

[0012] Benefits: Prevents overcharging, provides a gentle charging process, and extends battery life.

[0013] Three-stage fast charging mode: When the switch (K) is in the "closed" or "released" position, its allowable current threshold comparison and the pull-up signal output by the control unit normally act on the voltage regulation signal. The pull-up signal can raise the voltage reference or reduce the voltage feedback signal, restoring the standard voltage division ratio of the voltage sampling circuit under normal three-stage charging. The control circuit therefore sets the charger output voltage to the standard three-stage charging voltage:

[0014] Features: During the constant current phase, the voltage rises to the normal constant voltage point; during the constant voltage phase, the voltage is maintained; and during the float charging phase, the voltage switches to the float charging voltage.

[0015] Effect: Fast charging, shortening charging time.

[0016] The mode switching switch (K) can be a mechanical switch (such as a toggle switch or a push-button switch) or an electronic switch (such as a MOSFET, a relay, or an analog switch chip), which can be manually operated by the user or automatically controlled according to external signals.

[0017] Beneficial effects

[0018] By adding a mode switching switch (K) and controlling its connection and disconnection of the current threshold comparison and the pull-up signal path output by the control unit, this invention achieves seamless switching between two charging modes:

[0019] Safety Life Extension Mode: Limits the maximum voltage to the float charge voltage throughout the entire process, completely eliminating the risk of overcharging, suitable for scenarios with high battery life requirements;

[0020] Three-stage fast charging mode: restores standard high-voltage fast charging to meet the need for rapid power replenishment.

[0021] Users can choose flexibly according to their actual needs, taking into account charging speed while ensuring battery safety and lifespan. Attached Figure Description

[0022] Figure 1 is a block diagram illustrating the principle of the 3842 chip charger circuit implementation example of this utility model.

[0023] Primary side (high voltage side): AC power is rectified and filtered, then passes through a starting resistor to power the 3842 chip. The 3842 chip (combined with an oscillator and a 5V reference) drives the MOSFET. The switching transformer converts the power into electricity. Current detection feedback on the primary side (high voltage side) limits the maximum output current of the MOSFET. Optocouplers transmit secondary side signals to regulate the primary side.

[0024] Secondary side (low voltage end): The electrical energy transmitted by the switching transformer is rectified and filtered before being output. The secondary side supplies power to the chips on the secondary side (low voltage end). The voltage detection circuit compares the sampled voltage with the standard voltage provided by the 431 microcontroller to limit the output voltage to a preset value. The current threshold comparison circuit compares the voltage obtained from the current sampling with the current reference to control the indicator light display status. A cooling fan ensures heat dissipation. The mode selection switch K determines whether the current threshold comparison and control unit output a high signal, which is then transmitted to the voltage sampling circuit for comparison with the standard voltage to raise the output voltage.

[0025] Figure 2 is a schematic diagram of the voltage / charging current waveforms of a lead-acid battery under three-stage charging mode. It illustrates the changes in voltage and current during the charging process. The charging process is divided into three stages: Constant current charging stage: The current remains constant at a constant value, and the voltage continuously rises along the voltage curve, rapidly replenishing the battery's charge. Constant voltage charging stage: The voltage remains constant at a constant value, and the current gradually decreases along the current curve until it reaches the float charging conversion current threshold. This stage allows the battery to approach full charge, preventing overcharging. Float charging stage: The voltage drops to the float charging voltage, and the current further decreases and stabilizes, used to compensate for battery self-discharge and maintain a fully charged state. This stage is commonly used in long-term online power supply scenarios.

[0026] Appendix Figure 3 This diagram illustrates the voltage / charging current waveforms of a lead-acid battery under extended lifespan mode. It shows the changes in voltage and current during charging, divided into two stages: Constant current charging stage: The current remains constant at a constant value, and the voltage rises along the voltage curve, rapidly replenishing the battery and increasing its capacity quickly. Float charging stage: The voltage stabilizes at the float charging voltage, and the current gradually decreases along the current curve to compensate for battery self-discharge and maintain its capacity.

[0027] Comparison Appendix Figure 2 and attached Figure 3 It will be observed that the "constant voltage" is higher than the "float charge voltage," resulting in a faster charging speed in the three-stage charging mode. However, this also causes faster corrosion of the battery's positive electrode grid and a higher rate of water electrolysis in the electrolyte. In the safety-extended life mode, the maximum charging voltage is only the float charge voltage. This results in less battery wear but a longer charging time. Integrating both charging modes into a single charger would obviously compensate for their respective shortcomings. It would significantly extend battery life without hindering users' emergency fast-charging needs.

[0028] Appendix Figure 4 Appendix Figure 5 Appendix Figure 6 These are three embodiments of this utility model, and the schematic diagram of a charger circuit designed with a 3842 chip. Detailed embodiments are described below. Detailed Implementation

[0029] Appendix Figure 4This is one specific embodiment of the present invention, a schematic diagram of a charger circuit designed with a 3842 chip. 220V AC power is filtered bidirectionally by LF1, rectified into a pulsating DC voltage by VD1-VD4, and then filtered again by C3 to form approximately 300V DC voltage. This 300V DC voltage provides a startup voltage to pin 7 of the pulse width modulation integrated circuit IC1 via the startup resistor R4. After receiving the startup voltage (when the voltage at pin 7 is higher than 14V, the integrated circuit starts working), pin 6 outputs a PWM pulse, driving the power switch transistor (MOSFET) VT1 to operate in a switching state. The current flows through the source (S) terminal, drain (D) terminal, R7, and ground terminal of VT1. At this time, the induced voltage generated by windings 8 and 9 of the switching transformer T1 provides a stable operating voltage to pin 7 of IC1 via VD6 and R2. The external oscillation resistor R10 and oscillation capacitor C7 connected to pin 4 determine the oscillation frequency of IC1. IC2 (TL431) is a precision reference voltage source. IC4 (optocoupler 4N35) is used to stabilize the charging voltage. Adjusting RP1 (510 ohm semi-adjustable potentiometer) allows for fine adjustment of the charger voltage. LED1 is the power indicator light. This indicator light will emit red light after the power is turned on. After VT1 starts working, the voltage output from the secondary winding 6-5 of the transformer is rectified by the fast recovery diode VD60 and filtered by C18 to obtain a stable voltage (approximately 53V). This voltage is used to charge the battery through diode VD70 (which prevents the battery current from flowing back to the charger), and through current-limiting resistor R38, Zener diode VZD1, and filter capacitor C60 to provide 12V operating power to comparator IC3 (LM358). VD12 provides a reference voltage for IC3, and after being divided by resistors R25, R26, and R27, the voltage is sent to pins 2 and 5 of IC3.

[0030] With mode switch K off, it operates in a three-stage charging mode. During charging, there is a voltage of 0.18-0.2V at the top of R33. This voltage is applied to pin 3 of IC3 via R10, and a high-level signal is output from pin 1. The high-level signal output from pin 1 is split into three paths: the first path drives VT2 to conduct, starting the cooling fan; the second path lights up the red LED through resistor R34; and the third path is current-limited and input to pin 6 of IC3 through resistor Rk. At this time, pin 7 outputs a low level, the green LED turns off, and the charger enters the constant-current charging stage.

[0031] When the battery voltage rises to the normal constant voltage point, the charger enters the constant voltage charging stage, and the current gradually decreases. When the charging current decreases to 200mA-300mA, the voltage at the upper end of R33 drops, the voltage at pin 3 of IC3 is lower than that at pin 2, pin 1 outputs a low level, the red LED turns off, transistor VT2 is cut off, the fan stops running, and the low level output from pin 1 is input to pin 6 through resistor Rk for current limiting, causing pin 7 of IC3 to output a high level. This high level goes through resistor R35 to light up the green LED (indicating that the battery is fully charged, but it is not truly fully charged at this point; it will actually take another one or two hours to fully charge), and through R52, VD18, R40, and RP2 to reach pin 1 of IC2, causing the output voltage to decrease, and the charger enters the trickle charging stage (float charging). Changing the resistance value of RP2 can adjust the voltage of the charger's float charging.

[0032] With mode switch K closed, it is in safety extended life mode. Pin 6 of IC3 is forcibly grounded by the switch. This causes pin 7 to output a high level regardless of the current detection comparison result. In addition to lighting up the green LED, another path leads to pin 1 of IC2 through R52, VD18, R40, and RP2, which reduces the output voltage and locks the charger in float charging mode. Changing the resistance value of RP2 can adjust the float charging voltage of the charger.

[0033] Appendix Figure 5 This is the second specific embodiment of the present utility model.

[0034] With mode switch K off, it operates in a three-stage charging mode. (Working principle and appendix are not included.) Figure 4 Exactly the same.

[0035] With mode switch K closed, it is in safety extended life mode. Switch K connects the 12V power supply to IC3 to resistor Rk, because R52 >> Rk. After current limiting through resistor Rk, the voltage of VRD2 is still forcibly pulled high, and then reaches pin 1 of IC2 through R52, VD18, R40, and RP2, causing the output voltage to decrease and the charger to lock in float charging mode. Changing the resistance value of RP2 can adjust the float charging voltage of the charger.

[0036] Appendix Figure 6 This is the third specific embodiment of the present utility model.

[0037] The schematic diagram of a charger circuit designed with a 3842 chip. 220V AC power is filtered bidirectionally by LF1, rectified into a pulsating DC voltage by VD1-VD4, and then filtered again by C3 to form approximately 300V DC voltage. This 300V DC voltage provides the startup voltage to pin 7 of the pulse width modulation integrated circuit IC1 through the startup resistor R4. After receiving the startup voltage (the integrated circuit starts working when the voltage at pin 7 is higher than 14V), pin 6 outputs a PWM pulse, driving the power switch (MOSFET) VT1 to operate in switching mode. The current flows through the source (S) terminal of VT1, the drain terminal, R7, and then to ground. At this time, the induced voltage generated by windings 8 and 9 of the switching transformer T1 provides a stable operating voltage to pin 7 of IC1 via VD6 and R2. The external oscillation resistor R10 and oscillation capacitor C7 connected to pin 4 determine the oscillation frequency of IC1. IC2 (TL431) is a precision reference voltage source. IC4 (optocoupler 4N35) is used to stabilize the charging voltage. Adjusting RP1 (510 ohm semi-adjustable potentiometer) allows for fine adjustment of the charger voltage. LED1 is the power indicator light. This indicator light will emit red light after the power is turned on. After VT1 starts working, the voltage output from the secondary winding 6-5 of the transformer is rectified by the fast recovery diode VD60 and filtered by C18 to obtain a stable voltage (approximately 53V). This voltage is used to charge the battery through diode VD70 (which prevents the battery current from flowing back to the charger), and through current-limiting resistor R38, Zener diode VZD1, and filter capacitor C60 to provide 12V operating power to comparator IC3 (LM358). VD12 provides a reference voltage for IC3, and after being divided by resistors R25, R26, and R27, the voltage is sent to pins 2 and 5 of IC3.

[0038] With mode switch K closed, it operates in a three-stage charging mode. During charging, there is a voltage of 0.18-0.2V at the top of R33. This voltage is applied to pin 3 of IC3 via R10, and a high-level signal is output from pin 1. The high-level signal output from pin 1 is split into three paths: the first path drives VT2 to conduct, starting the cooling fan; the second path illuminates the red LED through resistor R34; and the third path is input to pin 6 of IC3. At this time, pin 7 outputs a low level, and the green LED is off. Meanwhile, the low-level output from pin 7 of IC3 pulls down the voltage divider current through R52, mode switch K, VD18, and RP2, allowing the charger output voltage to rise to the constant voltage charging voltage, and the charger enters the constant current charging stage.

[0039] When the battery voltage rises to the normal constant voltage point, the charger enters the constant voltage charging stage, and the current gradually decreases. When the charging current decreases to 200mA-300mA, the voltage at the upper end of R33 drops, the voltage at pin 3 of IC3 is lower than that at pin 2, pin 1 outputs a low level, the red LED turns off, transistor VT2 is cut off, the fan stops running, and the low level output from pin 1 is input to pin 6, causing pin 7 of IC3 to output a high level. This high level passes through resistor R35 to light up the green LED (indicating that the battery is fully charged, but it is not truly fully charged at this point; it will actually take another one or two hours to fully charge). Another path passes through R52, mode switch K, VD18, RP2, and reaches pin 1 of IC2, causing the output voltage to decrease, and the charger enters the trickle charging stage (float charging). Changing the resistance value of RP2 can adjust the voltage of the charger's float charging.

[0040] With mode switch K off, it is in safety extended life mode. The output level of pin 7 of IC3 is isolated by switch K, and the feedback voltage signal can only be obtained according to the voltage divider network composed of R16, R19, R17, and RP1. This reduces the output voltage, locking the charger in float charging mode. Changing the resistance value of RP1 can adjust the float charging voltage of the charger.

Claims

1. A lead-acid battery charger with switchable safety-extended life mode and three-stage fast charging mode, comprising a rectifier and filter circuit, a control circuit, a power switch, a transformer, an output rectifier and filter circuit, a voltage sampling circuit, and a current threshold comparison and control unit, wherein the output signals of the voltage sampling circuit and the current threshold comparison and control unit are fed back to the control circuit to adjust the charging voltage and current, characterized in that: A mode switching switch (K) is added to the feedback path of the pull-up signal output by the current threshold comparison and control unit to the voltage reference or voltage feedback signal. This switch is connected between the output terminal of the current threshold comparison and control unit and the node that affects the voltage feedback signal or voltage reference setting, and is used to selectively control whether the pull-up signal has an effect on the voltage reference or voltage feedback signal.

2. The charger according to claim 1, characterized in that: When the mode switch (K) is in the off or shielded state, the pull-up signal is blocked, clamping the charger's maximum output voltage at the float charge voltage and entering the safety life extension mode.

3. The charger according to claim 1, characterized in that: When the mode switch (K) is in the closed or open state, the pull-up signal is allowed to function, causing the charger to output the standard three-stage charging voltage and enter the three-stage fast charging mode.

4. The charger according to claim 1, characterized in that: The mode switching switch (K) is a mechanical toggle switch or an electronic switch, and the electronic switch includes one or more of a relay and a MOSFET.

Images