Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Sorry, got myself twisted around as I was writing my response. Yes, all the amps are going through all the cells, even though the cell voltages are fluctuating.
Help with 128 batteries each one is 280ah, and want to configure for 48v system.
- Thread starter kromc5
- Start date
Wow this thread went poorly.
I'm curious if people would use this, the 2a version did well for my test system.
I suspect a daly for cutoff and the 10a version of that balancer, each doing it's proper purpose, might make a reasonable and affordable system.
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I'm curious if people would use this, the 2a version did well for my test system.
I suspect a daly for cutoff and the 10a version of that balancer, each doing it's proper purpose, might make a reasonable and affordable system.
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Ohms_Cousin
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Ohms_Cousin
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So if i am understanding this correctly,
if a load on the battery bank draws 250 amps from a battery bank made up of 280Ah cells, then each cell is drawing 250amps, and thus almost at the 1C rate for the cells?
if a load on the battery bank draws 250 amps from a battery bank made up of 280Ah cells, then each cell is drawing 250amps, and thus almost at the 1C rate for the cells?
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
In a nutshell, YES. If two identical packs are in parallel then that load would be split between the two and they would discharge fairly evenly.
Ohms_Cousin
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Right. I understand that part then.
So if a total battery pack is setup as 1 x 16s 280Ah cells + another 1 x 16s 280 Ah cells (to be clear, so 2 x 16s of 280Ah cells -16s2p?) then a total of a 200 amp draw on that total combined battery would be 100 amps across each of the 16s sets in the total battery ? (wording it awkwardly but want to make sure its crystal clear what I am trying to get at)
So 100 amps of load is drawn from each 16s string to make up the total combined draw on the battery of 200amps overall ?
What I dont get is, (or want to be sure about) from that one 16s string of 280Ah cells that is contributing 100 amps to the total 200 amp load, how much is each 3.2v cell contributing to the 100 amps being drawn from the 16s string?
I think its really really important to understand this concept well - so I would like to make sure I am getting this 100% correctly. Its a steep curve to get on top of while trying to ingest all this information and understand battery packs well when you are a beginner. Thanks for any insights, its all good.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
You have a fairly good handle on it.... The "individual cell" question is another matter, KISS says divide 100A by 16 cells which comes back as 6.25A per cell but that isn't 100% either...
Ohms_Cousin
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You are right, but they do not with an active bms which is able to pass some amps to an other cell (1-2 A). And that's the advantage of an active balancer which will be able to suck a little more amp from one cell then the other when the voltage delta is out of the configuration profile (let's say 30mV, 50mV).
For this 128cells I would do 8 bank of 16 cells each bank, 8 bms then parallel all that... And I would constraint those cells in 8 boxes. A shunt per pack for capacity display and a circuit breaker to isolate pack(s) if needed.
And some warning stickers...do not short circuit one pack....cause that's a lot of energy in one place...
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I think the difference is “supplying” 100 amps vs supplying approximately 1/16 of 100 amps while the sum of the amps supplied by the other 15 cells still passes through.
Trying to parse supplying as an active action vs. passing through as a passive action.
In series, amps don't add/subtract each other - only volts. So each cell is supplying 100. A cell won't act as a passive conductor and pass 100 amps but "provide" less. The electrons must flow from one side to the other. IR will impede the ability to pull higher currents and differences in IR will cause differences in temperature and all kinds of other effects, but it only becomes really important in parallel setups.
I agree, an active BMS would transfer from one cell to an other but:
-average would still be 100 A (if 100A are drawn from the whole pack)
-in no case the 100A would be divided by the number of cells.
This is in my opinion the minimum basics one should know before "toying" with such huge cell capacity!
In serie:
-power is divided because voltage is divided between each cell, ampere are (without active BMS) the same across all cells
In parallel:
-power is divided because amps are divided between each cells, voltage is the same across each cell...
Yes I fully understand the difference between series and parallel.
Trying to define the meaning of “supply” is what I was trying to differentiate but it’s not important in the big picture.
Allow me to clarify what I am trying to point out.
We use our batteries to “supply” us with power. As an example let’s use a 48v battery, 16 cells at 3v each.
At 100 amps that “supplies” 4800 watts.
Each individual cell supplies 300 watts.
So each cell is responsible for 1/16 th of the power supplied.
We use our batteries to “supply” us with power. As an example let’s use a 48v battery, 16 cells at 3v each.
At 100 amps that “supplies” 4800 watts.
Each individual cell supplies 300 watts.
So each cell is responsible for 1/16 th of the power supplied.
Great way to think about it, and it works for both series and parallel discussions.
My post was just a précision, those 2A balancing are nothing in regard of a "high" discharge like 100A anyway.
I agree on what you said, those are not AA cells, there is lot energy in those, we got to be careful.
Went through all the information and yt videos and decided to place the order for 9 Chargery bms systems, wanted to have an extra on hand. After reading over them all Batrium still seems super nice but the chargery is much less overall and seems very easy to work with.REF: Li-Ion BMS - White Paper - Dissipative vs. nondissipative balancing (a.k.a.: Passive vs. Active balancing)
QNBBM's from DeliGreen (they own the QNBBM brand)
HelTec Smart BMS'
Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers
Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importerscncdheltec.en.alibaba.com
You may want this as well:
https://diysolarforum.com/resources/general-lifepo4-lfp-voltage-to-soc-charts-tables-12-24-48v.109/
For Quick Math Help (the darn formulas)
Amp-Hours (Ah) to Kilowatt-Hours (kWh) Conversion Calculator
Convert amp-hours to kilowatt-hours using this electrical conversion calculator. Learn the formulas to convert Ah to kWh with examples.www.inchcalculator.com
Hope it helps, Good Luck
Steve
Most of the time, energy independence come with an other way of consuming this energy.
Lean how to use less, 100kwh of batteries is a lot....
This is why I'm building my RV with propane stove/cooktop and water heater, a good residential fridge, a good dishwasher, and a heat pump clothes dryer (I would have gone propane, but none are available in compact sizes), and 240v mini-split. It does mean I'm burning fuel, but going "all electric" (e.g. induction cooktop or electric oven) just isn't a good option (yet) with these kinds of setups.
