WiFi LoRa 32 V2 and solar panel management

[peroanjo]

Hello everyone, this is my first post here so I hope I am doing this correctly.
I’m trying to set up a weather monitoring station using a WiFi LoRa 32 V2 module. I want it to be powered with a 3.7V Lithium ion cell, and this cell would be recharged using a small 5 volt solar panel that would be constantly pluged in. I’ve seen that this board has a tp4054 battery charger regulator, can I connect the solar panel directly to the 5V input in the board? Do I need any additional hardware?

Furthermore, do you think that that leaving the solar panel constantly plugged will shorten the battery life? Maybe I should monitor the battery voltage and start charging when it reaches 3.8V and stop charging when it reaches 4.1V, this would be done using a mosfet transistor.

Any help will be kindly appreciated!

[jasonXu]

hi,

You can plug in solar energy to charge. But the charging voltage of the solar panel is best to be: 5.5V-7V.

Questions about battery life:
Normal charging cycle:
When the Vcc pin voltage rises above the UVLO threshold level and a setting resistor with an accuracy of 1% is connected between the PROG pin and ground or when a battery is connected to the charger output, a charging cycle starts . If the BAT pin level is lower than 2.9V, the charger enters trickle charge mode. In this mode, the TP4054 provides about 1/10 of the set charging current in order to raise the current and voltage to a safe level to achieve full current charging.

When the BAT pin voltage rises above 2.9V, the charger enters the constant current mode, and at this time provides a constant charging current to the battery. When the BAT pin voltage reaches the final float voltage (4.2V), the TP4054 enters the constant voltage mode, and the charging current begins to decrease. When the charging current drops to 1/10 of the set value, the charging cycle ends.

[UniquePete]

So this appears to be almost identical to the charging circuit on the Wireless Stick Lite (the Wireless Stick Lite circuit does not appear to include the Schottky diode). Am I then correct in assuming that I can simply connect an appropriate (5.5-7V) solar panel (with a Schottky diode) up to the 5V pin on the Wireless Stick Lite module and battery charging will be managed through this circuit?

[jasonXu]

Am I then correct in assuming that I can simply connect an appropriate (5.5-7V) solar panel (with a Schottky diode) up to the 5V pin on the Wireless Stick Lite module and battery charging will be managed through this circuit?

You need to add a diode.

[jeg]

Hello,

I would like to use the TP4054 with a small solar panel, one that only produces 30mA at 5V. According to the user manual, RPROG should be

RPROG = 1000/I_BAT = 1000/0.03A = 33kOhm.

But also according to the manual, “the charger is stable with program resistor values as high as 20k.” So maybe RPROG=33k is unstable.

So I see two possibilities:

1. Set RPROG to 33k. Will it be stable?
2. Set RPROG to 10k (I_BAT=100mA). But the solar panel will only supply 30mA. Will it work?

Thanks for any help.

JEG.

[UniquePete]

On the subject of solar panel sizing, in my own applications, I have found that I need a 50mA solar panel (40mA was too small) to maintain battery charge when using a CubeCell Dev-Board Plus, with a range of sensors, transmitting every 60 sec. [and sleeping in between]. This is a purely empirical observation, but there are still many [practical] factors that feed into this ‘equation’—battery capacity, sunlight hours per day, duration of overcast/low light conditions etc.

I don’t currently run any ESP32 configurations in [solar panel +] battery-only environments, because I have been unable to get their sleep power usage down as low as that of the CubeCell ASR6502, so I would be surprised if an ESP32 configuration used less power than the CubeCell ASR6502.

[jeg]

@UniquePete thanks for that information. However, your issue is evidently a matter of supply vs. demand. I’m more wondering if the charger chip will work if the VCC compliance is less than the programmed charging current. I probably either need to up my solar cell size or get a different charging solution. Thanks again!