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18650 best soldering technique part2
#31
(08-14-2020, 08:34 AM)rev0 Wrote:
(08-14-2020, 08:07 AM)Redpacket Wrote: It's interesting that Tesla battery banks don't appear to have sleeves at all, they are all bare metal cans.
It seems they have deliberately done this for heat dissipation reasons?

I'm not as familiar with the way it was done on the Model S/X packs, I believe for those there was an electrically insulated aluminum "wavy" channel running through the cells to moderate temperature. For the newer Model 3 pack, the wavy aluminum channel is actually one of the electrical conductors (negative) while the other is the positive cap. Model 3 packs are potted also, making disassembly and harvesting of cells extremely difficult for most people. It seems the BatteryClearingHouse guy has been able to do it fairly well, and sells individual re-wrapped and laser welded (added button top, since the bare cell has an odd indented top) Model 3 cells.

Yeah I saw the wavy "heat pipe" too. But the heat pipe is passing otherwise bare cells in some right? Potting in some models so obviously not all bare metal.
Running off solar, DIY & electronics fan :-)
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#32
(08-14-2020, 08:34 AM)rev0 Wrote: I'm not as familiar with the way it was done on the Model S/X packs, I believe for those there was an electrically insulated aluminum "wavy" channel running through the cells to moderate temperature. [...]

Often you can find info about Tesla's designs in their patents. See also some of NASA's designs, e.g. from here.

NASA Wrote:The cells are coated with a thin paraxylene layer approximately 1 thousandth of an inch thick via chemical vapor deposition. This coating is abrasion resistant, inert, and electrically isolating, and is too thin to impact normal vent and burst operation of the cell.

In addition to the paraxylene, the cells are wrapped with a helical strip of mica paper. The mica is both electrically and thermally isolating, and retains its mechanical strength up to 900?C. The helical wrap serves a double function: it lightens the pack by using less material than a full sleeve, and serves to create a critical dead air gap in between the cells and the heat sink. As shown in Figure 5 the cell mica paper wrapping that ensures the air gap and is less likely to be damaged when inserting the cell assembly in the snug fitting bores of the heat sink.

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#33
OK, great, but being a NASA design & an exotic solution, this it not present on any of the cells sources that made it into the database so far?
Ie no practical help....
Agree mica is good electrically & thermally for sure. Doesn't heatshrink on though...
The air gap comments seem strange, that wrapping is obviously tight on the cell wall, "less material than a full wrap" & they say it help when there's a snug fit to the heatsink - so where's the air gap?
Running off solar, DIY & electronics fan :-)
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#34
^^ My post was a reply to your (and rev0's) posts in the same vein, so your critique is puzzling.

The air gap is presumably the helical strip between the mica wrapping.

Why should NASA care if mica doesn't "heatshrink on"?
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#35
The point of my reply is in line with this forum about DIY vs exotic NASA methods.
NASA's methods may not be achievable for DIY'ers - we need relevance to DIY here please.

Your post #26 earlier showed an air gap of 4mm wasn't enough & adjacent cells get cooked.
Most DIY builds seem to have a few mm between cells.
Now you're saying a cell in a snug fit hole has "air gaps"? Or the yellow band in post #32 is a gap in the protection?
Sorry, not looking like an air gap to me in #32.

If we want a method DIY folk can use it would need to be eg Kapton or "mica paper" material in tube form that could be easily cut to cell length & slipped onto a cell.
I'd suggest that spiral applied tape per post #32 would have inherent weakest along the tape edges negating much of what we would like to achieve.
Tape could be say 50% overlapped, getting better, but effort per cell climbing so less likely OK for DIY.
A pre-made tube format would seem to fit the DIY need best.
Running off solar, DIY & electronics fan :-)
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#36
^^^ I have no idea what you are talking about above. But it has nothing to do with anything I was "saying". Please try to read more carefully.
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#37
Your posts right here:-
(08-15-2020, 01:06 AM)gauss163 Wrote: The air gap is presumably the helical strip between the mica wrapping.
Why should NASA care if mica doesn't "heatshrink on"?
And
(08-14-2020, 03:51 PM)gauss163 Wrote:
NASA Wrote:The cells are coated with a thin paraxylene layer approximately 1 thousandth of an inch thick via chemical vapor deposition. This coating is abrasion resistant, inert, and electrically isolating, and is too thin to impact normal vent and burst operation of the cell.

In addition to the paraxylene, the cells are wrapped with a helical strip of mica paper. The mica is both electrically and thermally isolating, and retains its mechanical strength up to 900˚C. The helical wrap serves a double function: it lightens the pack by using less material than a full sleeve, and serves to create a critical dead air gap in between the cells and the heat sink. As shown in Figure 5 the cell mica paper wrapping that ensures the air gap and is less likely to be damaged when inserting the cell assembly in the snug fitting bores of the heat sink.
Air gap in a snug fit hole?
Find me mica tube for DIY'ers please.
No problem with NASA doing it, sound great, special paraxylene too, but how's a DIY'er going to do it?
Running off solar, DIY & electronics fan :-)
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#38
FYI - Here's a guy that soldered the heck out of an 18650 then took it apart and unrolled it looking for damage. Other than some superficial discoloration he didn't find anything or any voltage changes.

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#39
^^ You shouldn't expect to be able to see damage by naked eye (e.g. dendrites that can cause (micro) internal shorts may be much too small to be visible by eye).  The great difference in heat from soldering vs. spot welding has already been clearly demonstrated in this post in the original thread (unfortunately the original image was corrupted by a "moderator").
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#40
(09-25-2020, 01:06 AM)gauss163 Wrote: ^^ You shouldn't expect to be able to see damage by naked eye (e.g. dendrites that can cause (micro) internal shorts may be much too small to be visible by eye).  The great difference in heat from soldering vs. spot welding has already been clearly demonstrated in this post in the original thread (unfortunately the original image was corrupted by a "moderator").

"micro internal shorts" should be clearly evident by the cell turning into a self-discharging/heater cell, right? This has been demonstrated to not happen, or everyone's powerwall/pack would drain to 0 over time if left alone. I've got many soldered packs that do not self-drain even after months in storage untouched.
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