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Cell spacer issues
#1
Two things i noticed in a recent 7S36P build, with the common garden black cell spacers from ebay.

1. Using Panasonic cells with std green wrapping, theres a bunch of wiggle when the cell is fitted to the cell spacer. For stationary applications, this isnt an issue but the build was for a motorhome house pack, and the movement will put stress on both the welds and the cell level fuses. Ok i could have added some glue between the cell and spacer, but that seemed kind of drastic. I will probably run a bead of glue or mastic along the top surfaces of the cells. Any other ideas?

2. They seem to made of ABS or similar brittle, low melting point plastic. I was a bit surprised at how easily they break, and also melt. Are we doing ourselves any favors using this stuff just cause it was cheap on ebay? For the strength, my advice is dont go relying on the cell spacers, use a flat surface and plenty of additional mechanical support. For the heat issue, i guess hot cells are a big enough problem to address directly, but the cascade failure that could occur if one cell overheats and vents, melting the surrounding insulation, causing more to short, and overheat, might be worth adding some kind of additional insulation between the cells.
Jaycowley likes this post
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#2
1. If they dont fit properly was it really 18650 cells? In worst case another wrap on the cell sort it

2. Yes they are brittle. You need to fit them properly and when done it will work alot better.

With that said a motorhome or moving application should not have cells in a soft mount nor do i personally think cell level fuses on those black plastic holders are the best. It will not work long term in every case. The black holders with the cell level fuses are for static mounts. If you on other hand spot-weld them with nickel strips it will work better but then again it depends on cells you use and how you do it.
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#3
Its only a part of a mm, but enough to make them wobble. My guess is that they want the spacers to fit every possible 18650 cell so go with the largest common denominator.
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#4
18650 is One size.... You then have other sizes like 17670.. . Are you sure they are 18650?

The worst i have hade perhaps was 1/10th off and thats the size of the sleve. Most of they time they are dead tight
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#5
You are right, they make them big enough to fit all 18650s. If I remember correctly, the cell holders are 18.4mm in diameter and 18650s are usually 17.8 or so up to 18.4mm in diameter depending on manufacturer and cell. Plus the cell holder designer probably put a buffer in the size of the cast to accomadate for plastic shrinkage during cooling. As for the material, they were designed for ebikes to be as light as possible. If 1 cell catches fire, there is no stopping it, anyway.
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