More batteries with different Ah, same voltage?

[Jan Broz]

Hi,
simple question where I am unable to find the answer. I already have 52Ah 8 cells Lifepo4 to my solar off-grid system. Looking to buy more cells/batteries to my system, but I'd like to buy cells with higher Ah. Can I connect two or three batteries (8s lifepo4) with different Ah? For example, one 52Ah 8s Lifepo4 and one 100Ah 8s Lifepo4? Every battery will have its own BMS (Daly). I'd like to use as much capacity as I can.
Thanks for response

 

[rickst29]

Yes, that should work OK. I have 3 different sizes of "small" LFP batteries in my RV. They suck in charging power at different rates, and the biggest is still pulling in power while the small ones have been pretty much balanced (and quit) at full charging voltage. (When the current drops to near zero, I quit on the charger.) My batteries are only 4s, but nearly the same size yours (one at about 60Ah, another at 105Ah, and the biggest at 120Ah).

Yeah, if I knew where I'd end up - I'd have waited and done just one big battery (272/280 Ah). But I kinda grew into it, as prices kept falling.

 

[time2roll]

As long as the different sizes are in parallel you are fine. Series will give you trouble.

 

[Bud Martin]

I have been running my setup for about 3 months now, no issue so far.

Parallel LiFePO4 12V 90Ah pack with 12V 280Ah pack, any issue?

So if you truly stay between the knees, running from about 3.1 to 3.5 volts there should be no issues correct? I would like to parallel my 60ah DIY Fortune with my 100ah GYLL. I can set my Schneider CSW 4048 to step in and charge if the batteries drop below 49.6 v so no need for LVD unless...

diysolarforum.com

 

[Lt.Dan]

The thing about larger AH batteries in parallel is you will stress the larger battery more than the smaller one. If the battery is twice the capacity (ie 100ah vs 50ah), then when you pull 75 amps, that means roughly 50 amps will come from the large battery and roughly 25 amps will come from the small one, effectively working the larger battery twice as hard.

Just something to think about.

 

[Jan Broz]

ok, thank you very much. So both batteries with different Ah in parallel I will connect to the same connectors on inverter?

Or, probably not a good idea, if I have this parallel connection and I only connect the bigger battery to inverter and use it and the smaller battery I will use only for DC equipment (probably much smaller consumption). How MPPT reacts to different voltages when charging/discharging if I set cut off voltage to the same voltage as on both BMS?
Thanks

 

[Lt.Dan]

The best way to do it is to connect all the batteries to a bus bar, then connect the inverter to the same bus bar. This will better distribute loads.

 

[JoeHam]

The thing about larger AH batteries in parallel is you will stress the larger battery more than the smaller one. If the battery is twice the capacity (ie 100ah vs 50ah), then when you pull 75 amps, that means roughly 50 amps will come from the large battery and roughly 25 amps will come from the small one, effectively working the larger battery twice as hard.

Just something to think about.

But they’re each at 0.5c so isn’t that exactly how you would want it to work?

 

[Bud Martin]

But they’re each at 0.5c so isn’t that exactly how you would want it to work?

+1 That is what I was going to reply.

 

[Lt.Dan]

That does make sense, I was thinking with twice as much current, it would be twice a hard, but .5C is still .5C

Hmmm

 

[Jan Broz]

ok, thanks for all replies

 

[MrTrevino]

Hi Everyone, Extending on the combining of different Ah batteries... Would the below setup also work?