TC4056 1 cell LiIon charger module

I have a lot of those little boards made around a TP4056 IC.

According to the datasheet:

The TP4056 is a complete constant-current/constant-voltage linear charger for single cell
lithium-ion batteries. Its SOP package and low external component count make the TP4056
ideally suited for portable applications. Furthermore, the TP4056 can work within USB and wall
adapter.
No blocking diode is required due to the internal PMOSFET architecture and have prevent to
negative Charge Current Circuit. Thermal feedback regulates the charge current to limit the die
temperature during high power operation or high ambient temperature. The charge voltage is
fixed at 4.2V, and the charge current can be programmed externally with a single resistor. The
TP4056 automatically terminates the charge cycle when the charge current drops to 1/10th the
programmed value after the final float voltage is reached.
TP4056 Other features include current monitor, under voltage lockout, automatic recharge and
two status pin to indicate charge termination and the presence of an input voltage.

This might be a problem with low capacity cells because to keep the charging in the safe area, the charging current must not exceed 1C (C=designed capacity).

Charging above this might give a temperature rise and this is not good for Li based cells. Of course, there are specific cells that accept charging currents above this safety limit but those are special ones thus not taking risks is a good approach.

Going to the datasheet of the TP4056 give us some interesting informations.

We can conclude that we can use this circuit directly connected to a small Solar panel able to output 6V.

But what about the current? 

Well, the charging current is set by the value of a resistor, Rprog in the test circuit below:

 The value of this resistor determine the charging current as per the table below:

On some modules, the resistor is marked "R3" but anyway, you can easily found it by tracing the circuit from the pin#2 of the IC; in the photo is the one below the little capacitor on the left side of the circuit:

From the factory it came with a 1K resistor which, according to the datasheet, correspond to a 1000mA (1A) charging current.

I changed it with a 2.2 KOhm one and the charging current dropped, as expected, around 500mA.

For final, here is what this module wants to tell us, based on the LED status: