Hi I have made this setup, with a 5v solar cell a Tp4056 charger, and an 18650 battery.The input voltage is about 5v from the solar cell, but the output voltage is only about 2.97v, it is the same as above the battery.
My wemos d1 min must have about 5v to work properly, it can not work with about 2.97v? What should I do??
Yours sincerely
Henrik
Get a bigger solar cell. 
Henrik_t7:
My wemos d1 min must have about 5v to work properly
So how do you expect a 4.1v battery to supply the 5v needed ?
A WeMOS D1 Mini will work just fine on 2.97 V connected to the 3.3 V pin. The problem is that a fully charged LiPo battery will be at 4.2 V which is excessive.
I am not sure what the dropout voltage of the regulator in the WeMOS D1 Mini is, if it is a LDO type and drops only 150 mV, then powering it via the 5 V pin from the LiPo would be just fine also. The problem is that the USB interface chip is wasting current.
A 5V solar cell might get 4.7 volts, the diode will want some volts and the TP4056 will want 5 to 8 volts. You'll have to call down to Scotty and let him know you need more power.
You'll want 12V, loaded, solar cells. Drop the 12V down to 6 and feed to the TP4056.
What you should consider the TP4056 will not manage power. The TP4056 will do quick charge discharge cycles during sunlight hours. This cycling will destroy the LiPo in about 4 months.
To lengthen the battery life use 3.3V instead of 5V. A 3.3VLDO (MCP1700) between the TP4056 and the MCU.
After 6 months or so of giving the whole TP4056 a go, I switched to using a 12V LiFePo4 16aH battery and a PWM charge controller. Works real well.
As a note the BME680 operates in sleep mode till woken, warms up, takes a reading, and goes back to sleep. Power savings.
If the battery is deeply discharged, the TP4056 will limit charging current to 1/10 of the normal full charging current until battery voltage goes above 3V. If the load current is higher than that 1/10 value, the battery will never charge. This is all described in the TP4056 datasheet.
If you really need 5V for the D1 Mini, I think you will need to add a boost converter. Otherwise, the D1 Mini's 3.3V regulator might be good enough. But you would need to monitor battery voltage, and shut everything down if it goes below about 3.5V.
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