Forgive my ignorance of electronics. I am looking for a very simple float charge circuit with a variable DC input.
The situation is as follows: I have a off grid solar system on a boat with 4x 6v deep cycle golf cart batteries in series-parallel, forming a 12v battery bank, charged by an mppt solar charge controller. I want to use this same charge controller to top off the starter battery (standard 12v lead acid) without making it part of the deep cycle bank. It only needs to run when there is sun and voltage is above 12.7 vdc.
The problem: almost all commercially available float chargers are for AC input and include a transformer. DC-DC chargers are quite expensive, and very overkill.
The goal is to make as simple a circuit as possible for $10 or less in parts. Over and under-voltage protection are already handled by the primary MPPT charge controller.
Solution? Can I simply put a current limiting resistor and a diode from the deep cycle battery bank that will allow 200ma of current flow into the starter battery when above 12.7 vdc? Something like this:
As you are rolling your eyes at this, remember how grateful you are to have a basic education in electronics so simple circuit do not baffle you!