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zorro
Member
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# Posted: 8 Sep 2025 06:07pm - Edited by: zorro
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So I am having a discussion on some battery capacity/output and i seem to be going round in circles - i am likley incorrect, but wanted to confirm
If i have 4 x 12.8V/280ah batteries, what is the MAX voltage and WH that can be achieved?
Not saying the best set up, simply maximum
I "thought" it was as follows............
1 - wire 4 in series = 51.2V
2 - ah remains constant at 280ah
3 - total WH = 51.2V x 280ah
Total = 14336WH
Am I totally incorrect, like I am being told
I am not expert in this, so likely wrong!!
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gcrank1
Member
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# Posted: 8 Sep 2025 07:06pm
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Are these lead Acid bats?
If so, you will only have a MAX Usable ah/wh of half of the total or you dramatically reduce the battery bank life. My target when using LA was to on use 1/3 of the total and 50% only occasionally. If you consistently go deeper than 50% you will murder the bats.
1) 4 x '12v' (nominal voltage) in series is a 48v system
2) Yes, the ah's stay the same
3) Your math is correct for WH but I prefer to err on the conservative side by using the nominal 48v
So that makes a total of 13440wh, max drawdown of the top 50% is 6220, 33% is 4435
Then with an inverter hooked up to make 120vac (or?)you will have conversion losses and idle loss so you get even less of the calc.
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MtnDon
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# Posted: 8 Sep 2025 10:04pm
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Quoting: zorro Am I totally incorrect, like I am being told
As gcrank1 stated if you have 4 batteries that are nominally 12 volt batteries the System voltage would be 4x12 = 48 volts. They might be more than 12 volts per battery when freshly and fully charged, but 48 would be the voltage used for capacity calculations. So the Wh would be 12x280 = 13,440 Wh. How of that is practical to use in real life depends on battery type.
If you are sizing this for a real system you may want to check whether or not the batteries in question can supply the amp discharge rate for whatever inverter size you want to use.
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zorro
Member
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# Posted: 8 Sep 2025 10:05pm
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This was a discussion/argument on FB with someone who said that you could NEVER GET the 51.2v and 14336wh from 4 x LifePO batteries (12.8v/280ah)
I argued that you can by placing them in series
May not be the best option, but that it would be possible
Thanks for confirming i was not totall crazy
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gcrank1
Member
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# Posted: 8 Sep 2025 11:08pm - Edited by: gcrank1
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So its just another (too typical) FB argument that misses the point that no matter what top voltage you start at (my LFP settles nicely at 13.3) once you start using the bank it diminishes to something less.
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MtnDon
Member
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# Posted: 9 Sep 2025 10:45am - Edited by: MtnDon
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Oh crap; a FB argument! Everyone i
thinks they are an expert on FB. As Betty White is purported to have said a long timeago; "sounds like a huge waste of time"
Be selective and avoid all those rabbit holes.
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Steve_S
Member
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# Posted: 9 Sep 2025 11:45am
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For 48v you calculate using # of cell X nominal voltage of 3.2v per cell X cell amp rating.
16X3.2v = 51.2v X 280ah = 14336wh or 14.336kwh.
We always use the nominal voltage of 3.2v for LFP because it is the mid-point (50%) of the working voltage range (3.000-3.400). Should be noted that when fully charged and settled post charging, cells will typically settle between 3.380-3.400 pending on age/temp/load cycles.
Batteries in series is NOT optimal and there are some tradeoffs that will cost you a little of the top.
Hope it helps, good luck.
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zorro
Member
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# Posted: 9 Sep 2025 10:25pm
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Thanks guys
So i was pretty much correct
Yeah i have closed that discussion down and blocked the troll going forward
He was of the type that knows everything but in effect, knows even less than me…………and that is saying something!
Thanks again for the confirmation
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paulz
Member
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# Posted: 10 Sep 2025 01:53pm
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Thanks Steve. Volts Amps and Watts is easy enough for this dummy to understand but throwing in time, with varying battery lifespans always confuses me.
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gcrank1
Member
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# Posted: 10 Sep 2025 05:10pm
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I made it easy on myself. When charged up they are like a full tank of gas, somewhere around a quarter tank its close to time to think about getting a refill.
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