Quote:
Originally Posted by daddle
This link (from a CF post back around 1250) clearly shows that a LFP prismatic "cell" is actually a "battery" made from many flat pouch cells in parallel. However for a cruiser this does not result in increased reliability because defective cells cannot be easily removed.
Li-Ion BMS - Prismatic cells |
From the link:
“”Prismatic cells
Structure of a prismatic
battery cell: A prismatic Li-ion cell consists of multiple flat-wound, Li-Ion cells enclosed in a plastic case and connected to 2 large terminals.
Shandong HiPower cell
We cut open a Shandong HiPower, 160 Ah, Li-ion, prismatic
battery cell. (This cell is similar to a Thundersky / Winston / Sinipoly cell, and to a CALB / Sky Energy cell.)
(Cell courtesy of Peter Oliver of Make Mine
Electric.)
The cell consists of:
A plastic outer case (possibly PVC)
Two sets of flat-wound cells (similar to pouch cells, except not sealed in a bag)
Each set has about 24 foils coming out of it, for each of its 2 terminals
The negative terminal (shown) uses copper foils; the positive terminal (not shown) uses
aluminum foils
The foils are 0.05 mm thick (0.002 inches)
Two aluminum terminals (only the negative terminal is shown)
M8 bolt for terminal connection to the bus bar
A 20 mm nut to secure the terminal to the case
Internally, the foils are held against the terminal by two clamp pieces, and two sets of screws, washers and nuts
It appears that, in this particular cell, the clamp pieces on the negative terminal have dissolved, resulting in heat damage
Across the 51 mm thickness of the cell:
4 mm (8 %): air space for
cooling
6 mm (12 %): case
41 mm (80 %): cells””
Of no great importance but it can be assumed that each “set” contain 24 cells in a prismatic formation on an other hand, some one may see the “set” as a one cell concertina folded or whatever.
Of a greater importance is that as quoted “the negative terminal have dissolved”.
Fairly common in the
electrical industry copper to aluminium connections can cause problems. Any cruisers that own an aluminium boat may have an idea that leaving copper remnant in the
bilge is not a good idea. The problem is recognised.
Quote:
Originally Posted by T1 Terry
probably a bad contact where the tabs bolt to the terminal blocks.
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.
If that type of connection may last only few years and the connection is inaccessible and cannot be easily observed then the
reliability of such battery is in question.
It is easy to understand the consequence of
charging a battery in which a one cell capacity may have been halved due to one set in that cell being disconnected by a “dissolved connection”.
Proper monitoring of a battery should be able to detect a fault, raise an
alarm if required and prevent injury to people and damage to property by automatic isolation of the fault.
Quote:
Originally Posted by T1 Terry
We have had a few members put in side issues to create doubt in the safety of these cells for what ever reason they have, view them for just what they are, attempts to create doubt by mass hysteria, nothing more. If they can come up with verified instances where lithium ferrous cells have internally dead shorted and created a fire problem then it would be something to become concerned about, but that is not the case, so unless they can provide evidence of such cases, just put them down to troll posts and return to life as normal, ignore them |
So you reckon we should ignore among other, posts 2356, 2379, 2382.
On the same above link the following can be found:
“””Thundersky cell
Otmar Ebenhoech cut open a Thundersky cell (which apparently had bloated from being fully charged while not constrained).
Again, note that the positive terminal uses copper foils, and the negative uses aluminum.
(Picture courtesy of Otmar Ebenhoech of Cafe
Electric.)”””
Apparently the casing of that cell as not bulged because the cell was
Quote:
Originally Posted by T1 Terry
simply sitting on the shelf in warm to hot weather
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It easy to understand that trying to reshape a “bloated” cell and mostly one with a partial bulge due to inadequate “strapping” may cause some internal damage.
Quote:
Originally Posted by chala
Good luck but be careful
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The warning given is not there “to create doubt in the
safety of these cells” but to circumvent the possibility that the operator by is ignorance “create doubt in the safety of these cells” in fact most of the incidence that “create doubt in the safety of these cells” to the extent that some members are
Quote:
Originally Posted by daddle
reading CF with my goggles on  |
are due to some poor experimental practices.
“””come up with verified instances””” You and I do live in a regulated country where some prefer to remain discreet.
Quote:
Originally Posted by Zil
What exact reshaping is referred?
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The cell had been dropped; the operator used a large vise to reshape it. The fire that did occur did not happen during the reshaping of the cell but more than 7 days later.
Quote:
Originally Posted by roetter
Roetter,
This thread is great but hard to weed through a lot of the crap people want to stir up.
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I would not use that language but if you are referring to post 2490 you may be right.
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