CRF #2 - 250R - LGX P41A 20s1p - EM200

[amberwolf]

BTW, this is one of the strapping clips I was talking about; they call them buckles.


Metal Buckles for Poly Strapping - 1/2

The page also shows tools for doing the work. and they have a guide

Strapping Guide

Choose the best Strapping for your application. Read our guide to learn about types and materials, strapping tools and other helpful hints.

www.uline.com

They're available cheaper elsewhere, but I will say that in my many years working in retail unpacking things, there are some of these clips that come all bent up with loose straps, and I can bend them by hand (with a screwdriver for leverage), and some of them that I can't bend at all and have very tight straps. The better oens are usually darker grey in color, rather than shiny metallic, and they look in shape like these, rather than the cheap ones I see on amazon, etc., lke these
but they do have a useful picture of how the straps go thru it


They also make crappy plastic ones that look like a square "ring" with two "bones" loosely attached to it; these are not sufficient for something liek the forces needed on a battery compression rig.


I have a number of kinds of straps and clips I've saved from packing crates and pallets over the years, for use in projects at home. I even carry a few on whatever I'm riding at the time to strap things down to it if they wont' fit in the cargo areas built into my ride.

 

[j bjork]

Interesting to really calculate this, when I have done it on prismatics I have used 10mm alu endplates and just put as much pressure on it as I could with a clamp. How are you going to measure?

 

[bananu7]

How are you going to measure?

My initial idea was to set the tightening torque for the 4 bolts in the corners, but that comes out to like 1Nm or less... Turns out threaded bolts are pretty powerful. Not sure what advantages bands or straps would have over that approach.

 

[bananu7]

Going to earn the 'doin' science' reactions:



From 10.1007/s00158-023-03662-1.

Seems that between 30 and 60kPa would yield good results indeed.

 

[bananu7]

I don't know how I missed this post... VFR400 20kw Build

I'm now pretty sure that my ideas about v-clamps were overengineered. I'm going to simply use 10x4mm stainless steel bars, punch holes in the electrodes and bolt to the 4mm epoxy carrier directly. For the busbars, I'll get a section of 10x5mm copper bar and also screw everything together.

For the compression sides, the options I'm currently considering, but I don't think it will matter very much in the end anyway, are, in the order of most likely to least likely.

- 8mm epoxy fiberglass board (can be CNC'd to shape)
- 6mm aluminium sheet (can be laser cut to shape)
- 12-15mm plywood (I can cut it reasonably easily myself and is more pleasant to work with)
- 3D printed ribbed PLA board (unlikely as I don't have a printer big enough)
- flat composite laminate (DIY)
- composite laminate in a ribbed form (DIY)
- custom forged carbon ribbed form

That post also has a brilliant idea to enclose the bolts in PVC pipe - which I'm shamelessly going to steal. This should prevent chaffing if any of the cells come in contact with the clamping bolts. For the bolt diameter, it really seems that going past M5 is largely pointless, except perhaps for shear/bending loads - but I don't think the battery will see a lot of those. The idea is for the cells to be mostly held in place with the compression force, and the outer compression plates to extend around them in such a way there's no contact with the enclosure walls. If the whole structure rests in the outer shell evenly, the bolts should only ever see tension loads from the cells, which is what we want and comparatively tiny for what an M5 bolt can carry.

 

[jkrienert]

...That post also has a brilliant idea to enclose the bolts in PVC pipe ...

I'd suggest an alternative tube or pipe material since PVC's structural integrity is shortened in thermally cycled environments <0*C - >60*C, and is also highly toxic if inhaled in the worst case scenario, a battery fire. Maybe there are some alternative materials, like HDPE or LPDE tube, especially if you're working with M5 diam.

 

[bananu7]

I'd suggest an alternative tube or pipe material since PVC's structural integrity is shortened in thermally cycled environments <0*C - >60*C, and is also highly toxic if inhaled in the worst case scenario, a battery fire. Maybe there are some alternative materials, like HDPE or LPDE tube, especially if you're working with M5 diam.

Yeah, good point, I could use PE, PA or maybe even Teflon. I didn't really think much when I said PVC, but you're right it should be something durable.

Also perhaps a reason against plywood, then.