Charging 2 battery banks with different voltages with one solar array.
Our bus has 3 battery banks. 12v starting, 24v main storage, and 12v secondary storage for backup power. The two different storage banks are the result of an upgrade to a 24v system that left us with 6 Wal mart RV batteries that still had Lisa life, as well as a 12v 2500w inverter.
For some time we maintained the secondary system with an a.c. powered multi bank charger that got its power from the inverter connected to the solar array. We put it on a timer so that it wouldn't be charging when the sun was down. Not very efficient.
Recently I had an epiphany. I could place a second solar controller in the system on the output side of the main solar controller. The second controller would drop the 24 volts to 12 and charge the secondary bank. It is set to go into evening mode from 6pm to 8 am to prevent drawing on the main storage bank.