Long time reader first time poster I'm currently in the process of doing a conversion of a van into a campervan (rv) I have 330ah of lesuire batteries that are currently connected via a battery guard system to the vehicles charging circuit.

I recently found the batteries are permanently connected to the vehicle batteries even when not charging which isn't ideal so I'm looking to build a dc dc charger after much reading up on the subject I'm looking at using UC3906 as the brains behind the operation via a boost converter to step the charging voltage upto 18v to supply the circuit. I seem to be unable to find a circuit design which will allow me to have a max charging current over 8a so I'm wondering if anyone may know more about it than me and point me in the correct direction

Attached is a circuit design which I have found which I'd like to use

If anyone could help i would be grateful

 

I have forgotten to add I'd want to aim for approximately 15-20a charging current and have it also able to be charged via a power supply from the 230v via a relay to disconnect the boost converter system