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  • MisterQED commented on Steve Willson Kujur's instructable Build a Power Bank in $23 months ago
    Build a Power Bank in $2

    I know about the Li charging as I just got delivery of my new SkyRC Imax B6, :-) and I was with you on charging but Jehu Garcia https://www.youtube.com/user/jehugarcia disagrees. He stated clearly that you can basically trickle charge Li-IOn batteries, as the current will drop to zero as the voltage matches the charging voltage and he has been doing it on his van for two years. I am not saying it is ideal, but it works. It is also probably crazy slow. I also agree that if one of the batteries is REALLY bad then a parallel setup can go south, but I will stand by my original claim, and double down due to the slow charging speed of the battery pack here, the parallel layout is generally safer. Even if we look at real lemon cells, they are much more likely to go south in series then para...

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    I know about the Li charging as I just got delivery of my new SkyRC Imax B6, :-) and I was with you on charging but Jehu Garcia https://www.youtube.com/user/jehugarcia disagrees. He stated clearly that you can basically trickle charge Li-IOn batteries, as the current will drop to zero as the voltage matches the charging voltage and he has been doing it on his van for two years. I am not saying it is ideal, but it works. It is also probably crazy slow. I also agree that if one of the batteries is REALLY bad then a parallel setup can go south, but I will stand by my original claim, and double down due to the slow charging speed of the battery pack here, the parallel layout is generally safer. Even if we look at real lemon cells, they are much more likely to go south in series then parallel as balancing circuits are not foolproof and can only handle minimal charging differentials between cells. If those limits are exceeded then the balancing circuits will fail and you may not even know that they have failed. This I got from one of the electric bike channels who came out as anti-BMS and pro active monitoring. In the end I think we can both agree the key thing is filter out the real lemons as they will get you in any configuration.

    The welding is also about not transferring heat into the cell. You are correct that a good solderer will "probably" not impart enough heat to damage a cell, but a rookie might. From what I have seen, lots of people solder their cells and they are fine, but the key is to cut down on the heat transfer. Sorry that people are crazy. I've just accepted that fact and move on. Good Instructable.

    You are correct on the soldering, but you are reversed on the parallel vs. series idea. The key with Li-Ion is to not let them get out of their voltage range which is 3.0 to 4.2V on the outside. They will last longer if you avoid those extremes. Running in parallel guarantees that all the batteries charge and discharge evenly as they are forced to balance one another. Running in 2S, this means 6-8.4V, but it allows the extreme possibility at full discharge 6V for one to still be at say 4V and the other to drop to 2V or anything else that adds to 6V. Obviously the more cells in series the more possibility for imbalance.

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