I want to run 20A constant current and 4.2V on a load using a variable DC power supply rated as 20A, 30V. But because my power supply is a switching CC, Cv type, and it kept switching to CV at only 1.2A. I really want to run it at 20A and 4.2V (CC, CV) on the same load despite the change of resistance of the load.
I will really appreciate step by step instruction on how to achieve that, if using resistors etc. In more details, the load is a 3.75V, 1000mAh battery and this battery is designed to take this much load for only 3 minutes to recharge. Currently the battery is on the nominal voltage checked using a multimeter.
I'd be charging that battery in a purpose built charging bag, and wearing Nomex overalls (you, not the battery) while doing so would probably do no harm.
You also want to be sure that the supply will genuinely deliver 20A at 4.2V.
the battery CAN tolerate the rate you say,
The supply is capable of safely delivering 4.2V at 20A for 3+ minutes.
The supply current limit can not be set when not loaded.
Disconnect any load.
Set supply to say 4.25V.
Set CC control to minimum.
Short supply output terminals
Adjust CC control until I = 20A
The supply is now ready. When loaded below 4.2V it will deliver 20A.
When Vload rises to 4.2V it will deliver 20A or less.
Connect supply to fully discharged battery with correct polarity.
After 3 minutes the battery WILL NOT be fully charged.
This is because when Vbattery rises to 4.2V the supply will go into CV mode ND current will be set by the battery. It will start to taper down.
CV to CC change over will probably happen in the 2 m to 2m 30s range.
This is a natural consequence of LiIon / LiPo chemistry.
IF you are sure that the batter will tolerate (for some values of tolerate) a constant 20A input then the charger should be set to 20A CC as above AND the supply voltage set "higher.
MAYBE 4.5V. Maybe 4.7 Maybe - flaming ruin .... .
This is not how the books ever say you can do it.
this violates the most fundamental principles of LiIon charging.
This sounds like fun :-)
If it works, more power to you, but battery life will be shortened so it will be less energy to you overall long term.