TL431 12V Battery Charger Complete 

Cool application of the opto in the circuit. Simpler than designing a non isolated circuit. Saves on calculating many circuit interactions.

A most interesting battery charger video. Thank you.

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Please Sir what modifications could be made to charge 4 lithium ion battery (16.8V) in series?

What modifications can be done to get 20A out of the circuit to be able to charge 200AH lead acid battery