Guidance please on Battery setup

Hi good people!
I have two 12v 200Ah batteries + another two 12v 100Ah batteries, 3 solar panels each rated 24v @250w and a 50Amp MPPT controller. (Each of the larger capacity batteries came with a panel. The third panel is for the two smaller capacity batteries). The panels are currently wired in parallel.

Considering the Ah differences, can I utilize ALL the batteries in a parallel/series setup that gives me 24v?
If so, what configuration do you recommend that would ensure balanced charging?

Many thanks

Hi Swithin,
I don't have enough experience to guide you on the specifics of setting it up, but I would highly recommend a charge controller. They are designed to help charge a battery bank evenly and some other things to help prolong battery life.

Matt McSpadden wrote:Hi Swithin,
I don't have enough experience to guide you on the specifics of setting it up, but I would highly recommend a charge controller. They are designed to help charge a battery bank evenly and some other things to help prolong battery life.

.

Hi Matt,
Thank you for your response!
There's a 50Amp MPPT controller. The issue is: Is it okay to wire the 2 smaller batteries in parallel (to make 200Ah) and similarly the 2 big batteries (to make 400Ah) AND finally connect the two banks in series? Won't the capacity difference cause problems?

Swithin Serwadda wrote:Hi good people!
I have two 12v 200Ah batteries + another two 12v 100Ah batteries, 3 solar panels each rated 24v @250w and a 50Amp MPPT controller. (Each of the larger capacity batteries came with a panel. The third panel is for the two smaller capacity batteries). The panels are currently wired in parallel.

Considering the Ah differences, can I utilize ALL the batteries in a parallel/series setup that gives me 24v?
If so, what configuration do you recommend that would ensure balanced charging?

Many thanks

So the fact that it's a 24 volt panels tells me I would want to know the make and model of the charge controller before I offer any advice. Could you post a link to it please. I ask because many of the so called mppt chargers are not as advertised.

This article explains some reasons why it’s not generally good to mix batteries. In general uniformity is good with solar energy systems. You may get a little use out of mismatched battery but it’s life will be shortened.
https://gridsub.com/can-you-mix-different-ah-batteries/

Jeremy Baker wrote:This article explains some reasons why it’s not generally good to mix batteries. In general uniformity is good with solar energy systems. You may get a little use out of mismatched battery but it’s life will be shortened.
https://gridsub.com/can-you-mix-different-ah-batteries/

Many thanks Jeremy!

Total Battery Bank = 7,200W
Discharge Capacity = 3,600W/day with the recommended 50% discharge
Discharge Rate = 10% of Total Battery Bank = Charge Rate =  Solar Array Size = 720W or 750W
Recharge Capacity = 3,000W/day = 750W Solar Array x 4hr/day = 3panels x 250W/panel x 4hr/day

Now to answer your question. Technically you can combine the 200AH and 100AH batteries safely, but I don't recommend it due to significant losses.

S Bengi wrote:Total Battery Bank = 7,200W
Discharge Capacity = 3,600W/day with the recommended 50% discharge
Discharge Rate = 10% of Total Battery Bank = Charge Rate =  Solar Array Size = 720W or 750W
Recharge Capacity = 3,000W/day = 750W Solar Array x 4hr/day = 3panels x 250W/panel x 4hr/day

Now to answer your question. Technically you can combine the 200AH and 100AH batteries safely, but I don't recommend it due to significant losses.

Thank you. I hadn't mentioned that all the batteries are gel. Nonetheless I will go with the general recommendation not to combine them.

Let's do a bit of math.  A 200Ah battery will want to be charged at ~ 1/8th of capacity, which would be 200Ah/8 = 25A.  The battery will start charging at ~ 25-26V, not 24, so what you need is 25A X 25V = 625W.  I always include a derating factor because panels almost never put out their rated output.  I usually use 85%.

So, what you really need in the real-world is 625W/85% = 735W.

Looks like you really need all three of those panels to keep your main battery bank charged.  What is the Voc limit of your controller?  If it's 50A, I'll assume it's 150V.  At freezing, the Voc of each of your panels is likely to go up to 40Voc, so three in series would be just 120Voc, safe for that controller.

I'd suggest you get second panel and second controller for the smaller 100Ah bank which maybe needs 360W or so to stay totally charged.  What you can do in the short term until you get your final hookup is to use the first array to charge the second battery bank, but disconnect it once fully charged, and reconnect to the main bank.  The controller does not need to be as big.  Maybe a 30-40A Epever Tracer.  That has a lower Voc limit of 100V, but you will need no more than 2 large panels to keep it charged.

I don't think it is possible to do that, but I'm not an expert on panels