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| Learning Path for buiding my own BMS |
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| Siwastaja:
--- Quote from: mc172 on July 25, 2019, 02:22:51 pm ---How about this? https://sound-au.com/articles/lithium-charging.htm --- End quote --- Complete bullshit, all myths, very few facts. They give a flashy start where they talk about the properties of metallic lithium, this discredits it all at once. There is no Li(0) in lithium ion batteries. The failure mechanisms are completely different. This is such a fundamental misconception that I'm amazed someone still makes it, in such a long analytical article. Then they have the very basic concepts all backwards. Other myths on the page: - lithium content myth - float charge myth - LiPo is different to li-ion myth - battery pack must be a separate module with its own protection electronics myth - "a battery balance system is absolutely essential" myth - "The balance circuits are responsible for ensuring that the voltage across any one cell never exceeds the maximum allowed". NO! NO! NO! NEVER! - wrong instructions for the conditioning cycle, with no safety instructions whatsoever for overdischarged cells Stopped reading half way through. Maybe the biggest issue is the total mixup between monitoring and balancing. Passive resistive dissipative balancer that work at 4.2V cannot guarantee that the pack is in balance, and cannot guarantee that cells are not overcharged; actually it's the opposite, it will increase the risk of dangerous imbalance in corner cases, because now there is a new source of quiescent currents, which may not be properly balanced. They will imbalance the pack during use and storage, yet the balancers are only active for a short time at the end of charge, so have limited time to do their work, sometimes nearly zero. (Think about the user who never fully charges the pack, because they have heard this will increase the battery life (rightfully so)!!) A proper BMS monitors and shuts down the charger if any cell hits the limit. Elliot's approach to the problem does not do that, but completely relies on the balancer's capability to keep the pack in balance. Which usually happens, but not always. In reality, cell-level HVC always comes first. Then, balancing is an optional extra, which has nothing to do with safety (the HVC cuts the charger, after all), but is installed to keep the pack energy storage from decreasing. A pack with self-contained balancers but no cell-level HVC is more dangerous than a pack with no cell-level electronics at all. The former is not used by the industry; the latter is. In reality, packs up to 6s (but more typically up to 2s) do exist without neither balancing nor cell-level monitoring, at all. Depending on case, this may or may not be acceptable. Following the advice on this page is more dangerous than flying without any BMS whatsoever. This is fairly typical case, in fact. BMS is non-trivial, but everybody knows how "important" it is "to have one". As a result, many have a cargo cult approach to it. This is extremely dangerous. |
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