I did not find a thread which properly answers this question so I hope by asking this here I can gain some understanding and it would be here for later use,
From what I understand, Constant current charging is when you fix the current supplied to a battery and the voltage would vary depending on the battery. Constant Voltage charging is when you connect a certain Voltage across the terminals of a battery, the OCV (open circuit voltage).
My Question lies in trying to use a combination of the two to try to fully charge a battery. Let me explain.
Constant Current Charging
I have been able to replicate constant current charging by connecting a 5V usb cable as the input into an SMPS. The SMPS is connected to an arduino which controls the current going into the battery. This is done by setting a reference current and then a PID controller keep the current around this reference current.
This was for a LiFePO4 battery which was charged at a constant current.
The charge cycle was controlled by the following states: Charge until 3.6V, rest for some seconds, discharge until 2.5 V, rest for some seconds and then repeat the cycle.
If you notice from the graph, after the battery is charged to 3.6V and enters a stage of rest where it is neither charge or discharging, it immediately falls to around 3.4V ( this can be seen around 3900 seconds). I have contributed this to ESR and parasitic capacitance in the battery.
I have read previously that it is possible to fully charge a battery to 3.6V by switching to constant voltage charging after 3.4V and just watching it until the battery draws very small amounts of current which would mean it is fully charged. Is this true?
The reason I have not tried this is because I do not have a constant voltage charging source. If I was somehow able to implement this, what constant voltage should be chosen?
Additionally, is the reason this drop occurs due to ESR and capacitance and if this is the case wouldn't this also happen with constant voltage charging?
Battery that I am charging: https://www.ampsplus.co.uk/ampsplus-14500-3-2v-500mah-battery-button