Final thoughts on battery pack, before welding?
- Thread starter hypertoric_amplituhedron
- Start date
Is there enough room left for wiring, padding and support around the pack, between it and the casing? This includes on either side of the pack at the cell ends as well as entirely around it to the part of the casing shown in the pic.
(Other threads about various battery builds have a number of good suggestions for materials to use. Insufficient protection can result in the pack vibrating/bouncing around and damaging welds, cans, wires, etc. Wires can also be crushed and shorted.)
Is there enough room left for insulating between rows of cells?
(any kind of vibration could eventually cause cell casings to wear thru, allowing a short between adjacent groups of cells at different voltage potentials; it's been a suspected cause of fires posted on ES but the intensity of the fires and discouraged owners prevented this from being verified).
Will you have something solid to support the pack above the BMS? (otherwise the pack weight focused down onto that small area, especially under road impacts, could cause flexure and damage to the PCBs of the BMS).
(Other threads about various battery builds have a number of good suggestions for materials to use. Insufficient protection can result in the pack vibrating/bouncing around and damaging welds, cans, wires, etc. Wires can also be crushed and shorted.)
Is there enough room left for insulating between rows of cells?
(any kind of vibration could eventually cause cell casings to wear thru, allowing a short between adjacent groups of cells at different voltage potentials; it's been a suspected cause of fires posted on ES but the intensity of the fires and discouraged owners prevented this from being verified).
Will you have something solid to support the pack above the BMS? (otherwise the pack weight focused down onto that small area, especially under road impacts, could cause flexure and damage to the PCBs of the BMS).
I would suggest additional insulation between groups of cells. If a cell gets hot for any reason, the heat shrink wrapper will split and allow for a major short circuit. Between cells in the same group, there is no potential, so less of a problem.
If any cell decides to "vent with flame" or otherwise overheat and catch fire, you can be pretty much assured it will propagate to the other cells since there is no thermal barrier between cells. It will propagate until every cell goes off.
Don't charge indoors or near anything combustible.
If any cell decides to "vent with flame" or otherwise overheat and catch fire, you can be pretty much assured it will propagate to the other cells since there is no thermal barrier between cells. It will propagate until every cell goes off.
Don't charge indoors or near anything combustible.
How are the groups supposed to be connected together? The most likely-looking way is one long skinny grup end-to-end with another, which is no good because just a couple of strips will need to carry the entire current from one group to the next. Cell groups should face each other along their widest dimension to allow for lots of strips between their positives and negatives.
liveforphysics
100 TW
fechter said:
+1
Shrink can't be trusted to do more than split or chafe through.
hypertoric_amplituhedron
100 W
amberwolf said:
Aha, I didn't clarify that. The pack will be well wrapped, and protected with foam padding all around the perimeter, and sides. We will use dummy cells (an 18650-shaped object of some material) to smooth out the perimeter, to help the lone straggler cells stay in place.
amberwolf said:
No, they will be hot-glued in place as you see them. The idea is to jam the pack within dense rubberized foam all around, to eliminate any such vibration. Hopefully, it should have enough passive suspension within the box on all sides.
A loose fitting pack is what I'm trying to eliminate. I really wanted to do staggered cell holders, but only one manufacturer made them, and they didn't have nearly enough for 264 cells. I did quite a bit of searching for something similar. No such luck.
amberwolf said:
It depends on how much room is left, after all this padding goes in. May have to do external BMS, if so. I certainly don't want to crush the lovely D131. But, of course, should something happen, I will benefit from the 2 MOQ from bestech.
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fechter said:
Very good points. I'm guessing you mean insulating between parallel groups. I do live in FL, and it gets to be 100F in the sun, at the usual times I ride on my off days. Not so much at night, when I ride most of the time. Heat is a concern. It's one of the reasons I opted for as many amp-hours in parallel as I could fit, to keep things cool under 30a continuous.
But, extra insulation around parallel groups sounds like a great idea, and should be achievable without sacrificing much room or cells. Dually noted.
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GalFisk said:
h82w8v6 explained it. This is more technical than I can answer confidently. We will use larger pieces of cut-out nickel, not linear strips. I can't find a pic of what I'm talking about on google image searches.
hypertoric_amplituhedron
100 W
redilast said:
I bought 1,000 of those. We will be using them for sure!
I like the plastic cell holders that maintain space between the cells but those take up considerable space. For tightly packed cells, Nomex paper is good. It withstands high temps and adds abrasion resistance.
hypertoric_amplituhedron
100 W
fechter said:
Like this Nomex 410 stuff, here? What thickness would you recommend? Do you know a better supplier?
hypertoric_amplituhedron said:
The stuff I got looks like 20mil thick. 15mil is probably thick enough. I got mine many years ago and don't even remember where it came from. Nomex is probably the best, but seems pretty spendy. There are some other less expensive alternatives. Try a search for "Fish Paper" and you'll see all kinds. I see most of the fish papers are 10mil thick.
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