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In Reply to: RE: No, they don't... posted by PAR on March 22, 2017 at 00:23:37
in that how does a company that uses supposedly good quality cell manufacturers all of a sudden get a crappy batch of batteries/cells?
Some surmise that it wasn't the cell maker that was the problem, but that their fast charge BMS (battery management system) was the actual culprit. However, that doesn't make sense, since charging algorithms are pretty well established--being CC/CV--constant current/constant voltage and charging at X, Y or Z rates is withing parameters.
Others surmise that heat was the issue (cramped battery/cell,) but that should have all been known beforehand. Some believe that the internal spacing of the cell, to the phone, was too cramped and heat built up.
LiFePO4 chemistries are the safest, only because they have a higher thermal runaway point than traditional lithium-cobalt (260ish* F,) not seen any longer vs. lithium-manganese (290ish* F) vs. lithium-iron (300+* F), but we don't use the former two in these types of devices.
Don't know for sure, as there are more 'forgiving' chemistries that are typical, but good cells and good chargers go a long way in mitigating 'ka-booms'.
Chris
Follow Ups:
Most factories use very tight tolerances, checks and balances for mass produced products. Very good factories use Six Sigma which kicks it up another notch.
In almost every case of 'anything' you can follow the money to find the reason or cause for anything. Fear is a strong motivator and nothing like batteries blowing up to sway the Sheepish public away from Samsung.
LiFePO4 cells for phones/tablets are often in flexible foil packs, so they're easier to shoehorn into weirdly shaped places.
Cell expansion is well known and gets accounted for. Some surmise that it was the fast charging algorithm that put more stress on a cell, causing the electrolytes to heat up, vent some gas perhaps and expand the physical dimensions, not causing any shorts.
Problem is is that they'd have (and have) already tested this before and known that at a .5C (C=capacity of cell X) charge rate, the cell will be fine. At a 1C charge rate, mild heat and some expansion, at a 1.5C rate, expansion easy to detect and measure and finally, at a 2C rate, cell pouch ruptures due to heat/gas build up.
So...let's keep the charging rate down to a .75C rate as a fast charge option and be fine?
Anyhow...maybe there were some shenanigans?
Chris
If the algorithm changed it sure didn't affect other Android devices with Li batteries.
I would say beware of what the media wants you to believe.
These days most of what we see and hear is fake...you have to dig and use some amount of reasoning to learn the truth. Granted this world is full of Sheep so feeding them BS and having them swallow it is easy.
Last I read it was an engineering problem with the battery design in combination with cell phone design where the space for the battery was too confining.
Seem it only occurred when the battery expanded just a bit while charging causing a short inside the battery and BOOM!
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