# Possibilities for 24v Solar charging of 12v batteries in series and parallel with different Ah capacities

I have two 12 volt 200Ah lead acid batteries and two 12 volt 150 Ah lead-acid batteries. I have a 24 volt 50 Amp charge controller connected to a 150 watt PV panel (overkill for now, but ready for future expansion). Is it possible to connect the 200 Ah batteries in series (Bank A),and the 150 Ah batteries in series (Bank B) then connect Bank A and B in Parallel to connect to the 24 volt charge controller. I need to draw off 12v (80-120 watts) of LED lighting for our school classrooms.

Yes, that is perfectly reasonable, but also connect the 12V points across the two banks. So you have two banks connected in series, where each bank is a 200Ah and 150Ah in parallel. Also, if there is a chance things may get out of balance, you can put a protection circuit across each 12 bank (like ~16V zeners).

EDITED: Thought I better change the 15V suggestion to 16V. Just make sure a standard 14.4 volt charge (per 12V bank) doesn't cause notable zener current.

• Thanks for your prompt reply, Digiproc. Not sure if I can find an equalizer here in Madagascar, but will at least look. Thanks again! Mar 6, 2019 at 17:18
• Sorry, just re-read your comment and see you clearly indicated the zener diode was for a protection circuit, which I had assumed was a charging equalizer. Showing my ignorance! Sorry and thanks. I should be able to find that here. Mar 7, 2019 at 5:07

Mixing battery types in series is not a good idea for two reasons.

The series resistance of the two sets of batteries will not be the same, this will lead to them not being balanced.

The charging curves will most likely not be the same between cells of two different battery capacities so this will create problems for charging.

Yes you can put two different battery types in series, this is undesirable.

• Hi and thanks for your response! You said "Mixed battery types in series is not a good idea..." But if it is the two 200 Ah batteries connected in series (Bank A) and then the two 150Ah batteries connected in series (Bank B) is this still a problem? In my logic, if I then connect these two banks (A+B) in parallel, the voltages are the same on both banks (24v), so is this still a problem for charging or drawing off current? Mar 7, 2019 at 4:57