MPPT Solar LIPO Battery Charger

I was just charging my Li-ion battery manually with my IP2312 charger, the high current version I have made previously. Then the idea of charging batteries with solar with an automatic cut off option comes to my mind. What I can do is simply hook this IP2312 charging module with solar with a diode in series for reverse voltage protection. But this seems a very unprofessional and inefficient idea. And I found CN3165, a solar powered MPPT based single cell battery charging IC with protection features. I searched for some web documents and found this amazing DFRobot Solar Power Manager board based on the same IC.

The module comes with integrated MPPT (Maximum Power Point Tracking) to maximize solar energy conversion efficiency under various sunlight. Onboard integrated circuit based battery and power protection features which provide reliable power management for different types of solar projects.

I have designed a custom solution based on the IC which have same IC but in the same form factor of other boards, I think it will be better solution to other available battery chargers. PCBWay is the best solution out there I found for PCB fabrication. They offer a low-cost, highly reliable, and foolproof process from prototype to full-scale product manufacturing. With quick turnaround times, extensive material options, and exceptional customer support.

What is Maximum Power Point Tracking (MPPT):

Maximum Power Point Tracking (MPPT) is crucial in solar charging as it enables solar panels to operate at their peak power output, even with changing sunlight and load conditions. Solar panels produce varying amounts of current and voltage depending upon the light intensity. The MPPT system actively tracks these variations, adjusting to maintain maximum power output. The maximum threshold of a solar panel is defined on the basis of short circuit current (ISC) and open circuit voltage(VOC). MPPT identifies and locks in the optimal voltage at which the panel generates the max power, even as sunlight shifts throughout the day.

This locking point is known as max power point at which the voltage equals VMAX and current equals IMAX. A product of VMAX and IMAX gives PMAX (max power point of solar panel). This means the system can convert available sunlight more efficiently, increasing the energy captured by up to 30% compared to systems without MPPT. The CN3165 solar power management IC used in this module is designed based on these principles, maximizing power output by maintaining the output voltage near VMP through a constant-voltage MPPT algorithm.

DFRobot Solar Power Manager:

Solar Power Manager 5V is a small power and high-efficiency solar power management module designed for 5V solar panels. It features as MPPT (Maximum Power Point Tracking) function, maximizing the efficiency of the solar panel. The module can provide up to 900mA charging current to 3.7V Li battery with USB charger or solar panel. The ON/OFF controllable DC-DC converters with 5V 1A output satisfies the needs of various solar power projects and low-power applications.

Specifications

• Solar Power Management IC: CN3165
• Solar Input Voltage (SOLAR IN): 4.5V~6V
• Battery Input (BAT IN): 3.7V Li-Polymer/Li-ion Battery
• Charge Current (USB/SOLAR IN): 900mA Max Trickle Charging, Constant Current, Constant Voltage Three Phases Charging
• Charge Cutoff Voltage (USB/SOLAR IN): 4.2V±1%
• USB IN Voltage: 5V
• Regulated Power Supply: 5V 1A
• Regulated Power Supply Efficiency (3.7V Battery IN)
• 5V/USB OUT: 89%@10%Load, 86%@50%Load, 83%@90%Load
• USB/Solar Charge Efficiency: 73%@3.7V 900mA BAT IN
• Maximum Quiescent Current: <1 mA

How the Whole System Works:

The schematics has 5 sections,

First section is based on the DW06D IC, which protects the battery from overcharging and over discharging; the same protection feature can be found in typical TP4056 Li-Po charger boards.

Second section is based on CN3065, the main hero of this board. It comes in many variants, having the same pinout (CN3065/CN3165). This thing gets the input either from solar or from on board micro-USB seen in the last section of the schema. Some input output decoupling capacitor, led indicators, and current setting resistor completes the section.

Third section is a standard solar interface that comes with an indicator, which helps to find out if there is any power available or not from solar input.

Fourth section is a typical booster section containing an MT3068 booster with SY6280 current protection unit. This thing boosts up the 3.7V battery to 5V, to power up an output USB port and some onboard headers.

Fifth section contains input/outputs USB and power headers.

Starting the Solar Powered System:

• Connect the Li battery to BAT IN.
• Connect the solar panel to SOLAR IN.
• Insert the jumper on the ON of the blue header to enable battery.

Note: After inserting the battery jumper in the correct position, the module USB OUT/5V pin header (red) does not output any voltage immediately due to the protection function. To enable this function, either turn on battery charging or press the onboard boot button which can be seen in section one of the schema.

Cooling Fin Add-On:

If a 5W (or above) solar panel or USB charger is used, the CN3165 may run in full load, trying to charge the battery at maximum 900mA.

The chip has an over-temperature protection function, which will automatically limit the charge current, trying to protect the chip. To improve cooling and maximize charge current, which results in longer life-span and better performance, it is highly recommended to stick the Aluminum cooling fin with the blue thermal conductive silica pad to the bottom of the module.

Charging Cycle of CN3165 IC:

The module safely and quickly charges lithium batteries through three phases: trickle charge, constant current charge and constant voltage charge.

Trickle charge: When the battery is heavily discharged and voltage of a lithium battery is low, its internal resistance becomes high, so charging it with a large current initially is not advisable. Doing so can increase the battery temperature and shorten its lifespan. Trickle phase ends when the voltage across a battery reaches 80%, during this mode the charge current is limited up to a max limit of 10%.

Constant current charge: Once the battery voltage rises above 80% threshold, the module switches to the constant current charging, working at full potential and delivering a steady current of up to 900mA.

Constant voltage charge: As the battery voltage nears the charge cut-off level of 95%, the module shifts to the constant voltage charging phase. In this phase, it supplies a steady voltage while the charging current gradually decreases. Charging is considered complete when the current falls to 10% of the maximum. At this point, the red charging LED turns off, and the green done charging LED lights up.

Automatic recharge: If the battery is fully charged (DONE LED is ON) and the module input source (SOLAR IN) remains on, the battery voltage may gradually decrease due to self-discharge or load. When the voltage falls below 90%, a new charging cycle will automatically start.

USB/SOLAR IN Automatic Switching

Both the micro-USB and solar inputs are capable of delivering 900mA max charge current. To prevent charge conflict caused by using both inputs, the USB charge has a higher priority. When the USB input is powered on, the solar input will be automatically cut off and resumes charging on solar when USB input is powered down.

Regulated Power Supply

The module provides a ON/OFF controllable 5V 1A regulated output. The 5V outputs of the header and USB output share the same output voltage and maximum current, however, USB output can not be shutdown. The USB OUT employs the low quiescent power DC-DC boost converter and always remains ON to provide continuous power to the low power controller. The onboard headers power supply can be turned off by moving the blue jumper to GND-EN connection. This function is extremely useful in low power applications.

Note: Turning off 5V header output power will not turn off USB output 5V output. The total output power of USB output and 5V header should not exceed 5V*1.5A=7.5W.

On board LED Indicators on DFRobot Solar Power Manager

There are three types of LED indicators indicating the operation status of different parts of the module:

Reverse connection LED indicators: When the battery or solar panel are reverse connected the onboard orange is turned ON, informing the user of a reverse connection error.

Charge LED indicators: Charging RED LED is turned on by the function of charging with a micro-USB input or solar. Green LED is the signal of done charging.

Regulated output LED indicator: The ON LED(green) indicates the ON/OFF status of the 5V regulated output. Once one of the micro-USB, battery or solar inputs are available, the USB OUT outputs a 5V.

Protection Functions

Reverse connection protection: On the BAT IN and SOLAR IN, the reverse connection protection circuit prevents the reverse voltage from damaging the module and the corresponding LED will light up to inform the user. These can be seen in section 2 of schema as MOSFET M1 and Diode D1.

Regulated output protection: When the output is accidentally shorted or output current beyond 1A (overload), the output will be completely shut down to protect the output regulator. This is controlled by Section 1 DW06D and Section 4 SY6280.

Li-battery protection: The module employs a dedicated Li-battery protection chip to improve the life-span and safety of the battery. Based on Section 1 DW06D IC. When the battery voltage exceeds 4.3V, the chip shut down the charge path to prevent it from further being charged (but still allow discharging). When the battery voltage drops below 2.4V, the output of the battery is shut down to prevent it from further being discharged.

Final Testing:

Current Ratings from Solar:

Voltage from Solar:

The same thing I designed keeping the form factor very small, I usually preferred to go with custom aluminium PCB. But this thing only has battery charging capabilities which I think is a good to go with. You can find all the project details with, Gerber files and actual schematics are already uploaded on the PCBWAY hub. In addition you can participate in ongoing contest and win exciting rewards at PCBWAY.

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