APL's Pressure Contact Battery box

[stan.distortion]

They get used a lot and there's a lot of info on improving the quality but they're rarely much good, the overhangs just don't suit 3d printing. Running a tap and die through works well though, I'll often do smaller sizes to the tapping bore, never had any strip at a depth of around 2x the dia but it's usually easier to use self tappers, they work very well but I'll usually print a square hole, seems to help avoid splitting and can be printed at any angle.

Printing larger thread sizes with a lead to get the tap or die started can work ok too but in general large printed threads are a last resort imo, if it wont work with wood then it probably wont work all that well with 3d printing.

Automotive clips and fasteners can be a good source of ideas for alternative methods and ratchets can work surprisingly well if the layers can be lined up correctly, I'd done some recently with 10mm x 3mm strips, only spring loaded (split at the ends with the teeth on the narrow edges, not self tightening), didn't get a really good shape on the teeth but it still took something like 12kg to pull them apart.

 

[APL]

Thanks for the good information, really good to know. Sounds like printing smaller and tap + die is the way to go. Need to make the threads bigger too, your right. Shouldn't be very much screw pressure on them I think, 2 - 5 lbs, maybe? Overall pack stress may be different though. There's always twist-lock too, but that might be even more complicated.

I was thinking that if the strip was made in two halves, the threaded side can easily be hole tapped, and the other side can be the copper link cover with the plug/seats molded in. More pieces, but it could be glued or riveted together and sealed up tight.

Well, I don't know if it's a good idea yet, but It's starting to look a little better to me. Kind of like everything being sealed up inside. Needs parallels yet. It would be nice if it could be printed though, cause then anybody can make it at home from a simple e-mail STL.

Here's a simpler series link .. it has to hop over the ring part. A bit of a mess drawing it though.



Edit; I don't know too much about the fuse wires that Tesla has used, but something like that could take the place of the cross-over
part of the link, and then the copper could just be a washer and a disc to make sourcing simpler.

I'll have to do a major re- draw already I guess.

 

[APL]

OK, I was able to get a little farther on the drawing this weekend. The two piece idea works well, and for parallels I put in some small spade connectors with flat-pin connects.

Still just an idea in the raw, so lots of material could be trimmed off, and the size of things reduced. Just another way to do the compression thing.



4, 5, and 6 cell units would allow for all the series numbers from 13S to 20S. Bottom sockets would form the back plates and maybe
shrink wrap could finish it off. Cells are slightly spaced, so cooling is possible, but makes for a larger battery pack.



Parallel and series gangs all fit together. Maybe not water-proof, but certainly water-resistant.





Anyway, that's the gist of it, for what it's worth. I don't plan to take it any further, just saying that it's possible. If it's a good idea
maybe someone will run with their own version.

Lots of plastic, but self contained and could be sealed. Square packs are not always adaptable to bikes, but perfect for house, marine and other uses.

 

[john61ct]

Seems the other hardware's getting up to the same price per cell as the batteries themselves?

 

[stan.distortion]

Lol, it's finally dawned on me that you're taking power from the same end of the cell! Feeling stoopid now, I'd just assumed you where doing the same at both ends and couldn't work out why Cool idea Not sure if there's some reason it's not used, maybe steel cans can limit amps but I'm guessing it's just no-one has thought to try it, plenty of applications where the batteries internals would be more limiting than the case.

Do you need to encase every cell? Looks like it takes up a lot of space and limits cooling and I can't see any benefit. For the threads, I'd probably try something like the 1" airhose connectors, quarter turn lock. 3d printing can be really good for that kind of thing, might take a bit of tweaking to get the first one right but after that they'll all be pretty much bang on, good repeatability.

Nothing wrong with threads though, the tube will have very little tensional strength no matter what you do, certainly not enough to trust it entirely for the full cell terminal pressure. Annealing will probably help a lot if that's the plan but could cause a lot of irregularity from deformation, tensional loads through the layers are pretty much always a bad idea.

Would a tension spring through the middle of each 4 cells work, a cross piece on the bottom to spread the load? Assembly could be a pain in the butt but it might be as simple as pulling it apart and slipping in the cells, that would be a fairly long spring length, probably plenty for 1/2" extra spring travel.

 

[APL]

So true $$, lots of plastic, but still a concept, and don't forget that compression systems can be used over and over again, where as welded systems are for the most part discarded and re-purchased. That, and being able to check and maintain parallel health might
help justify some cost.

I had the thought of a trimmed down minimal-size injection molded version of this idea, but it would need an outer case no doubt.

Yea Stan, I just re-invented the flashlight! :lol: I'm just really not happy with the way 18650 cells need to have plastic and paper washers covering the neg shoulders. This concept takes advantage of that, uses less copper/nickel, and is unexposed.
It was really the shoulder thing that got me started on this.

No, the cells don't need to be enclosed,.. it was an idea to make assembly easy and sealed. Your quarter turn lock is a better idea than threads, for sure, and perfect for 3D. Another idea is a small plastic ring with the twist-lock could be bonded onto the cell end, ..but gluing is what the plastic outer-can avoids, with more expense.

The threaded idea insures that all the cells make contact, which is one of the big issues with compression packs. Otherwise, it could be a bit more traditional by using through bolts or tension springs like you suggested, and might be another way to go. The cell-cans could be exposed to the air, or just straight plastic tubes can be used to space and seal.

Well anyway, just another possible direction to meander with compression packs.