# Battery Pack Configuration Questions



## Sunking (Aug 10, 2009)

MrZion said:


> My question starts off by looking at EVWEST, because they have modules listed in the link below that can be used in a 4p2s configuration with their AC-50 setup. Does 4p2s make sense, I thought each parallel string needs the same amount of batteries in series?


Typically the configuration is expressed as xSyP. They expressed it as yPxS

P = cells in Parallel 
S = cells in Series. 

Makes no real difference because because 4P2S = 2S4P. It means you have 4-cells n Parallel and another 4 cells in Parallel wired in Series with the other 4 cells. 8 total cells. 

The voltage would be the two cells in series voltage. Example say 2 x 3.7 volts = 7.4 volts. The capacity would be the 4 cells in parallel so if they were 20 AH cell is 4 x 20 AH = 80 AH. Together make a 7.4 volt 80 AH module.


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## MrZion (May 4, 2016)

Sunking said:


> Makes no real difference because because 4P2S = 2S4P. It means you have 4-cells n Parallel and another 4 cells in Parallel wired in Series with the other 4 cells. 8 total cells.
> .


Right, I new about p and s but I thought that meant there were 6 modules, not eight. Now that makes sense though, cheers!

Another question, what would you say are the do's and don'ts are about constructing battery pack boxes with let say LiFeO or Leaf modules or Tesla modules?


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## Sunking (Aug 10, 2009)

MrZion said:


> Right, I new about p and s but I thought that meant there were 6 modules, not eight. Now that makes sense though, cheers!


Not sure we are on the same page. It makes a single module of 8 cells. With 8 cells there are a few ways to configure them.

8s, or 8p, or 2s4p. Each cell is 3.7 volts @ 20 AH (68 watt hours per cell.) makes no difference how we configure them 

8S is 29.6 volts @ 20 AH = 592 watt hours.
8P is 3.7 volts @ 160 AH = 592 watt hours
2S4P is 7.4 volts @ 80 AH = 592 watt hours. 



MrZion said:


> Another question, what would you say are the do's and don'ts are about constructing battery pack boxes with let say LiFeO or Leaf modules or Tesla modules?


The numbers have to fit like above with like cells or modules


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## MrZion (May 4, 2016)

Sunking said:


> Not sure we are on the same page. It makes a single module of 8 cells. With 8 cells there are a few ways to configure them.
> 
> 8s, or 8p, or 2s4p. Each cell is 3.7 volts @ 20 AH (68 watt hours per cell.) makes no difference how we configure them
> 
> ...


My bad I miss used the term modules, we are on the same page. When I used the term modules I was referring to the link I provided, but what you said makes sense, and I already new that this is commutative.

Your answer to how to construct a battery box was not what I was going for, more like a deeper explanation into materials used, how snug should each module be based on the type of battery(prismatic, pouch etc.) as well as chemistry(LiMnO or LiFeO). I was hoping for advice based on past experience etc. 

Cheers!


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## Solarsail (Jul 22, 2017)

I believe nSmP is the inverse of mPnS. For example 3P2S would be first putting 2 cells in series and then putting three of these series pairs in parallel.


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## Solarsail (Jul 22, 2017)

MrZion said:


> Another question, what would you say are the do's and don'ts are about constructing battery pack boxes with let say LiFeO or Leaf modules or Tesla modules?


You may find it actually easier to buy the Panasonic 18650 cells and string them together. This way, you are not confined to what EVWest modules are configured. And it may be cheaper, and you get brand new batteries. The Tesla packs can only be at 70% usable capacity and who knows what kind of abuse they have seen. If they have been wholly discharged, they will still charge and look like a usable pack, except their capacity could be as little as 20% of new usable capacity.

A EVWest 3 kWh pack is $690.

Without the assembly and fusing and packaging the same amount of Panasonic cells would cost = $3.50*3000/(3.7*3.4) = $834. Quantity of cells needed = 3000/12.58 = 240.

You can then get any voltage that you want by putting them in P and S.

You will need a power supply, CCCV step-down charger, a balancer, a protector and a fuse, if you build from scratch.


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## e^2 (Jul 22, 2017)

I've been sitting on the battery packs topic for a month now. I was going to get 8kWhr of these hoverboard batteries with 1000 2200mah LG 18650 packs but I've had a couple of comments back from experienced members warning that if they aren't managed properly, they might blow. For the BMS setups, would you really need to manage every cell? Or just the level of each 32P1S? I think that is what Tesla does, they monitor each 1S pack of 18650 and rely on the voltage of the collective to prevent any problems(someone please tell me I'm wrong). Doing it this way would also just give you an average capacity instead of know set capacity.


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