Spacer or no Spacer!

[Mrdanielmh]

What's the general feeling on the best approach to construct our cells together?

- tape cells together, and strap them back to back with no space
- add a spacer and tape and strap

I have done a fair bit of research and the opinion seems divided!

 

[FilterGuy]

I have done a fair bit of research and the opinion seems divided!

That should tell you: There is no perfect answer.

Here are my thoughts: For most of what we are doing with the cells, the charge and discharge rate is low enough that we don't need the spacers for cooling. So, for plastic cells, I just line them up and bind them together. However, Aluminum cells tend to have a bulge in their face so they don't fit flat against each other. For these cells I use thin plastic spacers so they stay flat to each other.

 

[Mrdanielmh]

Thanks @FilterGuy it is a minefield

 

[Dzl]

I agree with filterguy, no clear consensus. I've seen no data to suggest spacing or other passive or active cooling is necessary or advantageous at continuous low C-rates (less than roughly 0.5C, 0.25C if you want to be safe), heat is barely above ambient. That said, it shouldn't hurt in most applications.

Personally, I feel that for an application like marine or overland use, where jostling and vibration are unavoidable, securing the cells is a top priority, however you can best achieve this seems like the way to go. And personally I feel its easier to secure them as one big pack, but I think that they could be adequately secured in a number of ways with or without space between cells.

Long story short, in my opinion, either can be done right, neither will be catastrophically bad, one might win out over the other depending on your application and your priorities.

 

[sharpey]

VHB tape seems to be achieving both right? A bit of space between, and very secure. Would you guys agree? They have a version that is 3mm thick. (VHB 4959 )

 

[Mrdanielmh]

I think it'd help around the whole of the battery pack! I've read some people put popsicle sticks innbetween cells

 

[mapguy525]

plastic horseshoe shaped builder shims has been posted, as a spacer method on the forum. Use the ones that are not tapered. This way you don't have to deal with VHB mess if disassembly is required.

 

[John Frum]

A spacer probably won't hurt and might help.
Ideally it would be thermally and not electrically conductive.
Also if you use busbars, they should account for the spacers and have some tolerance.
Elongated holes are probably best.

 

[mapguy525]

Some cells have more cycle life if restrained. Example Eve LF280. From the documentation, LF280-72174 Version E, posted here:
https://diysolarforum.com/resources...-product-specification-version-e-2019-7-5.15/

On page 7 of the document -it describes life cycles; with fixture and without fixture. Fixture per the document is applying 300 kgf of force to the cells prior to charging.
"With Fixture" cells are specified to have 3500 cycle. "Without Fixture are specified to have 2500 cycle.

EVE per the documentation expect the cells to expand and contract with charge/discharge cycles.

At 30% SOC cell thickness spec is 71.5 +/- 1.0mm.
At 100% SOC cell thickness spec is 72.0 +/- 1.0mm

 

[Mrdanielmh]

Im thinking of using some plastic cornee protectors and some metal hose clamps to keep everything together

 

[FilterGuy]

Im thinking of using some plastic cornee protectors and some metal hose clamps to keep everything together

I did a build a while back exactly like that. I had to cut the tops of the corner protectors to make room for the terminals.