Hello Pavel!I’m sorry to hear that the previous builds didn’t work out as expected.
Electronics can be tricky, and sometimes the smallest detail makes all the difference! Let’s try to figure this out together.
What input voltage are you using in your setup?Technically, this circuit has an internal voltage drop of approximately 2.5V to 3V due to the transistor configuration and the operational limits of the UA741.
If you are using a 12V source at the input, the battery will unfortunately never reach a full charge. To overcome this ‘barrier’, you really need at least 16V to 18V DC at the input (P1).
Also, please make sure your TIP35C is mounted on a large heatsink, as it can get quite hot during the process.If you could share the specs of your power supply or a photo of your build, I’d be happy to take a closer look for you.
We’ll get it working!
Best regards!

Hello Pavel!I’m sorry to hear that the previous builds didn’t work out as expected.
Electronics can be tricky, and sometimes the smallest detail makes all the difference! Let’s try to figure this out together.
What input voltage are you using in your setup?Technically, this circuit has an internal voltage drop of approximately 2.5V to 3V due to the transistor configuration and the operational limits of the UA741.
If you are using a 12V source at the input, the battery will unfortunately never reach a full charge. To overcome this ‘barrier’, you really need at least 16V to 18V DC at the input (P1).
Also, please make sure your TIP35C is mounted on a large heatsink, as it can get quite hot during the process.If you could share the specs of your power supply or a photo of your build, I’d be happy to take a closer look for you.
We’ll get it working!
Best regards!