Continuing the discussion from Dogging, Wombling and free SOTA batteries. (Part 1) - #101 by K6EL.
Previous discussions:
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I managed to womble an old Tabacco tin. Thought this was highly appropriate and looks like it will fit perfectly for a 3 cell, 2 or 3 parallel battery using the largest vape batteries 21350, the 1500mAh ones. So a 4.5ah 12.8v battery.
Just waiting for JST and BMS to finish this.
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One annoyance with collecting these cells is the delay till you find the final one to make 3 the same. Currently I’ve got 2x 23350 1750mAh(6.48Wh) and 2x21350 1400mAh (5.18Wh) that are waiting for a matching one to come along. We should set up an exchange page so us Wombles can complete our packs!
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Yes! I have for months now, had 5 x 1400mAH, and 5 1500mAH. Not enough of either to make a 3s2p pack.
I have pondered whether it would be alright to parallel a 1500 with a 1400, and connect three such pairs in series.
I am tending towards doing so, although it doesn’t feel right, somehow!
I guess as long as the total current draw is well within the rating of both types, it should be OK?
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Adrian
I think different capacities in parallel should be OK - think of it as simply increasing the anode and cathode sizes so it’s like a single bigger cell …
Different capacities in series would be less good, as there is a risk of reverse-charging the lowest capacity cell (or parallel group) when discharging. But if you limit the discharge sensibly and rebalance when charging, even this may be acceptable.
Rick
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I think you can rely on Kirchoff’s laws to handle dissimilar capacities in parallel. So the voltages in parallel will stay the same. As you fully discharge one cell before the other, its voltage cannot drop below the cell which is not yet discharged though current may flow from the higher voltage cell to the load and to the other cell. BUT (in capitals) I would only use dissimilar capacity cells with a BMS to protect against over discharge etc.
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Well as of this month no more freebie batteries.
Selling vapes is banned in VK, except through pharmacies.
So the small vape shop where I got my cells from knew this was coming and closed a week before I went there with a bucket. Following that discovery I visited other outlets but they all said they had no discarded batteries.
I may try a couple of pharmacies but I doubt they will be taking back old vape power packs.
New 18650 cells are becoming cheaper so the gain for effort is diminishing.
73
Ron
VK3AFW
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