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More amp hours but how?

WorldwideDave

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I was looking at a he differences between 100 amp hour and larger 200 amp hour batteries. Will tire one open and it seems that a few things make a battery have more capacity:

The individual cells and
The number of cells.

For example one battery can have 4 cells, each 25 amp hours, for 100 amp hours wired in series, another battery can have larger cells for more amp hours, and I saw one with 8 cells inside hat was a 200 amp hour battery. I think when it’s a 200 amp hour battery it is 4 in series, 2 strings in parallel, keeping it 12.8v but doubling the 100amp hours by 2 is 200 amp hours.

The BMS most likely needs to support that I would think.

Reason I am asking and might be confused is because I want a huge 12v battery at a low cost. Like 400 amp hours for under 600 bucks. I can buy some of the 150 dollar 100amp hour batteries and wire them in parallel for under 600. Wondering of other options out there. Seems the 200 and 280 Ah batteries are abundant but not cheap.

Is doing two 200 ah batteries in parallel better than doing four 100 ah batteries in parallel?

Thanks. Just learning.
 
The 4 cells are 4x 3.2v 100ah cells which make a 12.8v 100ah when wired in series (4s). The 8 cells in a 200ah battery are 8x 3.2v 100ah cells connected in 2p4s (2 in parallel, 4 in series) for 12.8v 200ah.

You can put batteries in parallel, just fuse each one upon it's connection to the bussbar at max discharge current of the BMS and keep parallel cable lengths equal.
 
Paralleling smaller batteries might give you a battery bank with a higher current capacity (or might not, depends on the current rating of the larger pack you choose). Make sure you understand your maximum discharge current requirements for your system, and pay attention to the maximum discharge current of the individual batteries. Personally, I'd rather have a generous margin from spec'd current rather than planning to run the batteries near maximum discharge.
 
Let’s say that I wanted 100 amps continuous discharge for pool heater and circulation pump. I have a single 200 Ah battery. I would be discharging 100 from that single battery. If I put 4 100Ah batteries in parallel, would it be discharging just 25 amps across 4 batteries for 100amps total?
 
On the charge side I have a 250/70 SCC, 150/80 SCC, and 100/20 SCC. So at the most under best conditions I could charge at 170 amps but I restrict things to 50 amps max across 3 arrays right now.
 
Let’s say that I wanted 100 amps continuous discharge for pool heater and circulation pump. I have a single 200 Ah battery. I would be discharging 100 from that single battery. If I put 4 100Ah batteries in parallel, would it be discharging just 25 amps across 4 batteries for 100amps total?

Theorietically, yes.

In practice no.

That would require 4 batteries that are perfectly matched, which, due to manufacturing tolerances, likely won't happen.

I guess it somewhat depends on what your personal feeling is on what constitutes "perfectly matched". Within 500mA of each other? 200mA?
 
Whatever I’ve experienced so far is that often times the smaller batteries advertise 100 A BMS, but what they mean is they can surge up to 100 A for maybe 15 seconds, but if you run it continuously at 100 A you will overheat the conductors. The BMS might never shut it off either, so instead you would likely cause a fire. Or worse, a thermal runaway inside a battery. Therefore, if I could keep the constant current to be under 50 A on a battery, this is rated for 100 A I would feel better.
 
Let’s say that I wanted 100 amps continuous discharge for pool heater and circulation pump. I have a single 200 Ah battery. I would be discharging 100 from that single battery. If I put 4 100Ah batteries in parallel, would it be discharging just 25 amps across 4 batteries for 100amps total?
Yes, that's correct. A typical 200Ah package has a 200A max discharge, so you'd be running at 50% of spec. vs. a 4x100Ah parallel array with typical 100A BMS where you'd be running at 25% of spec. Since you're well within margin for either configuration, it comes down to decisions based on price, available space, wiring & fusing complexity, etc.
 
They’re probably aren’t a lot of hundred amp our 12 V batteries that can run continuous 100 A. Besides, if it was 100 amp power battery and it was in the middle of the night with no solar, the battery would be dead within an hour.
 

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