Opinions on cell to cell series connections

Is it beneficial?

  • Yes

    Votes: 1 100.0%
  • No

    Votes: 0 0.0%
  • Probably, but too it's much work

    Votes: 0 0.0%

  • Total voters
    1

Stephen Ryan

Member
Joined
Mar 17, 2018
Messages
30
As described here@2.05, the 'optimal' way to wire a battery pack is foreach cell to have its own direct connection to its series counterpart in the next parallel pack (pic below). "Ideallyyou want 1 series connection for every cell in a parallel group"

Ignoring the vast amount of work this would be, opinions on its effectiveness?

image_flankc.jpg
 
With cell level fusing this would complicate construction. Most large projects assemble packs of parallel cells, then hook them up in series.

It would only be possible if all series and parallel cells were in one pack.

For high drain projects, this would be effective. If I were building an e-bike pack, I would construct it as pictured above. Most high drain packs are constructed like so. (Power tool batteries - e-bike batteries and so on)
 
I didn't vote only because it depends on application and pack construction... but I very much agree with Geek said.
 
cell-level fusing is useful on an ebike pack because it might be involved in a crash. If one cell is dented, it might experience an internal short. Nothing will stop that one cell from going into a downward spiral, but a fuse can separate it from the rest of the paralleled string, which eliminates an overheating incident with the rest of the P-string (except maybe the risk of the actual heat from the erupting cell)

Obviously, a power wall will not have a crash, but...this is also where many builders use partially-used cells...which is actually a great use for their remaining life. Used cells will experience a wide variety of amounts of heat from the discharge peaks. If a sensitive cell gets a little too hot, it can go into a death spiral, even if the amp-draw isn't that high.

If you have an un-restricted dead-short on an entire P-string (because one cell develops an internal short, and the heat shrivels the internal separators), then...A large P-string has a huge amp difference between normal amp-draws from each cell, and the max full P-string short. If one cell has an internal short, it causes the entire P-string to react as if the bad cell is suddenly replaced with a fat copper wire.

This means that on an ebike pack (high-amp cells, maybe only 4P), the fuse selection is much more critical, but...on a large powerwall (low amp cells, 10P or more), there is a wide range of fuse materials that will work just fine.

If you are using individual cell fuses, you can put a fat copper wire between every two cells for the series connection...(of course, that would work best with an even number of cells in the P-groups)
 
When I first started building battery packs, since I wasn't going to be using any high drain devices, I never gave it much thought.I didnt use enough series connections, on a 3s30p battery pack I might have added only 3 series (nickel strip) connections, and those packs always went out of balance. It took me a while to figure out what the problem was, I thought since I was using recycled 18650 batteries, that was causing the problems.

Seeing pictures of other people battery packs, I did notice everyone was using series connection between every cells,I did go in and added more series connections and that fix my balancing problems. I think that would be the biggest reason to use as much series connections as you can fit. Its alot ofextra work up front, but it saves you from going back in later and adding more nickel strip.

This 3s90p 65ah battery pack was severely out of balance. But after I added more series connections its performing excellent.

image_bgahwg.jpg
 
I agree, as many series connections as practical. Owitte's setup is a great example of this. Lots of small packs, connected to big busbars.
 
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