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*noob... capacity 12s8p vs 4s24?
#1
So im very new to the battery scene but been doing a lot of research. I just cant seem to figure out the capacity thing with different voltages. And what to use for my small pack

I have a pack that has 96 cells(life4po), its 12s8p, 39.6v and has 736 watt-hours(this is written on the pack) or (if i calculated right) 18.4 Amp-hours

but if I tear that pack apart and make it 4s24p, 13.2v  it looks like the same watt-hours, but it would have 55.2 amp-hours

(As i type im kind of figuring out more) ...  So the watt hours are the same, so the capacity is the same.  but the amp-hour rating is how long it can run something at that voltage? i guess that makes sense.

So then The plan is to hook it up to an inverter to run the laptop and things. 

what I dont get (even moreso)
My brain is thinking, 55.2amp hours at 13.2v would make it easy to connect a 12v inverter to power my stuff. but the inverter ramps up the voltage to 120 so the amp hour rating dosnt really matter anymore?

BUT if i do the 39.6v @ 18,4 amp hours i can use a 36v inverter to ramp up the voltage to 120 to power my stuff. but dont i have less amp hours if its wired like this? so LESS time to power something at a certain voltage?

Any help would be greatly appreciated.
Thanks!
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#2
Use watt hours instead.

Amphours is useless without having the voltage in the calculation.

Its easier to rum 12v IF you have alot of Gear at that voltage but its easier tonexpand running 48v (16s)
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#3
The devices use watts and will run about the same with either 4s or 12s. There are some loses when you use inverters.

If these are the recycle BAE 96 cell packs, I bought 2 packs and the cells individual capacity was between 1200 to 2100. I had 4 or 5 bad cells. I would say 96 cells will get you about 40 amp hours at 13.2 volts 4s24p, which is what i'm averaging.

If it was new cells you can keep it at 12s, but if its recycle cells you might want to get an accurate capacity test of all the cells. 4s would be more convenient for a small powerpack that will easily run a laptop with a small inverter.
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#4
with all calculations use the following formula

Power (watts) = Amp-hours x Voltage

So when the Voltage goes down the Amp hours have to go up. But yes Use What-hours and your power measure.
******Hi My name is Jason and I have SOCD (Solar Obsessive Compulsive Disorder)*******
Current Powerwall - 1400 Cells 7s200p (modular 40p packs) ~ 12kWh of storage     4x 315W Canadian Solar Panels

Working on the next 7s40p packs     ~2.5kWh

Waiting on 2000 Cells of unused Sony vt4 (2000mah 30A) ~ 15kWh      hehehehehe  More Power
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#5
(12-22-2019, 03:59 PM)jdeadman Wrote: Power (watts) =  Amp-hours x Voltage

Correct, with the addition that you want to use "Nominal" voltage. So, this is generally the middle point of the high/low range.
4.2 ➖ 3.2 = 1
1 ➗ 2 = .5
3.2 ➕ .5 = 3.7
So 3.7 would be Nominal voltage with this example. The Nominal voltage changes based on your particular application and voltage utilization ranges. For LiFePO4's this is lower Nominal range closer to 3.4V
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#6
You cant calculate nominal like that. Nominal have nothing todo with middle of voltage. Its based on the middle of the capacity.

3.65 on most liion and 3.2 on LiFePo4
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#7
Thank you guys, im a bit more enlightened now. the amp hour vs watt hour is weird

and yes JonyJoe this is the BAE used pack, i got 2 of them.
I was trying to figure out if it would better to keep them as the already assembled pack and use a 36v inverter (which would be substantially easier), or dismantle to make into 4s packs to use a 12v inverter.
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#8
And With nominal I've always had good luck with calc vs measured by using the Lowest Voltage I use and the Highest then dividing by 2

So for my powerwall I run the range of 3.6 to 4.1V so = 3.85 then multiply by your number of cells (*7 in my case) = 26.95 or for my rough calcs its 27V

But there is always errors and measuring built the way you want it and do a full discharge to actually see your Max usable capacity.
******Hi My name is Jason and I have SOCD (Solar Obsessive Compulsive Disorder)*******
Current Powerwall - 1400 Cells 7s200p (modular 40p packs) ~ 12kWh of storage     4x 315W Canadian Solar Panels

Working on the next 7s40p packs     ~2.5kWh

Waiting on 2000 Cells of unused Sony vt4 (2000mah 30A) ~ 15kWh      hehehehehe  More Power
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#9
(12-22-2019, 06:44 PM)daromer Wrote: You cant calculate nominal like that. Nominal have nothing todo with middle of voltage. Its based on the middle of the capacity.

3.65 on most liion and 3.2 on LiFePo4

Agreed, but mid-capacity is closer to 3.7 for normal current cells (like found in laptop batteries) and closer to 3.6 for high current cells (like found in power tool batteries).
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