Today I finished version 2 of my battery light circuit:
Here is the schema:
The SEPIC charging the battery works pretty nice now. First the controller was running very short time and making long breaks. The output voltage went up to 14V and then slowly down below 13V.
I was too lazy to calculate anything, I just thought I need more AC feedback. So I added CPOL2 between the output of the converter and its feedback input. It’s still not perfect, but it is much better than before. The output voltage ripple is now just about 0.2V.
Now the only problem remaining is that this indian aluminum rubbish wire loses 2.5V between the power supply and the circuit. The power supply is in the kitchen and this circuit in the living room. The wire is about 8 meter long. I assume the SEPIC draws 1A from the power supply, I didn’t measure it yet. So the resistance of this wire must be 2.5 ohms, which makes 0.15 ohms per meter. Rubbish. So tomorrow I’ll do some adjustments to the circuit and hope it will work…