fred_dot_u Posted March 28, 2021 Posted March 28, 2021 As best as I can determine, the S8 battery is a 16s2p lithium ion pack, approximately 60volts. There's a watt-hour calculator that suggests the pack is 3.3 to 4.4 amp hour capacity based on a minimum voltage of 60 and a maximum of 60, more or less. The dimensions I've measured are 300 mm x 70 mm x 40 mm within a few mm. A quick check on the 'net shows a few 10 amp hour packs of similar dimensions and configuration. Is this higher figure a result of marketing exaggeration and/or more realistic calculations by Airwheel? I'm down to a max charge of 70 percent and that's rather foreboding. I've swapped out the battery with my busted S8 and have no better results. Both scooters are likely to be nearly the same age, which fits the current situation. I may Franken-mod my scooter to take an external battery, maybe standing on end behind the seat post. I'm open to opinions and suggestions. Quote
Chriull Posted March 28, 2021 Posted March 28, 2021 9 hours ago, fred_dot_u said: A quick check on the 'net shows a few 10 amp hour packs of similar dimensions and configuration. 10 Ah with a 16s2p pack can only be reached with 21700 cells (5Ah per cell). 18650 cells have a maximum capacity of 3500mAh - so 7 Ah maximum for such a pack. Which of of course does not hinder creative sellers to write any numbers on the packs, or as one can buy fake 18650 cells with about every capacity printed on it. PS: 16s2p have a nominal voltage of ~16*3.7~59V, a maximum voltage reached while fully charging of 17*4.2V=67.2V Quote
fred_dot_u Posted March 29, 2021 Author Posted March 29, 2021 (edited) Thanks for the clarification. I appreciate insight from those more experienced. I've dismantled my pack today, as it left me stranded for the very first time. The partially discharged voltage levels for the cells are scattered from 3.66 to 3.99, pretty much all over the place. There's what appears to be a full pack BMS, as each set of cells is soldered to the main board. After a charge, terminated by the external charger, the voltages run from 3.81 to 4.21, mostly matching the disparities on the low end measurements. I don't know what current max is expected for this scooter, so I've ordered 16850s with high current capability and 3.5 Ah per cell, figuring that I was happy with the range of the stock pack and that drawing lower than rating current may make the pack last longer than a year. Another item I've learned during my 'net travels is that these S8s weren't manufactured since 2019, so shelf life for the pack probably factors into this reduced life of use. I'm hopeful that the cells I've ordered will be fresher! Edited March 29, 2021 by fred_dot_u Quote
Chriull Posted March 29, 2021 Posted March 29, 2021 5 hours ago, fred_dot_u said: The partially discharged voltage levels for the cells are scattered from 3.66 to 3.99, pretty much all over the place. There's what appears to be a full pack BMS, as each set of cells is soldered to the main board. After a charge, terminated by the external charger, the voltages run from 3.81 to 4.21, mostly matching the disparities on the low end measurements. Since no cells are "stuck" below 2.5V there seem not to be "dead"! If they use some kind of bms similar as in eucs you could try charging them until the led becomes green, let it rest for 1-2 hours and repeat. Could balance your batteries again after some cycles. https://forum.electricunicycle.org/topic/22109-passive-balancing-a-simulation/?tab=comments#comment-359235 Quote
fred_dot_u Posted March 30, 2021 Author Posted March 30, 2021 Another clarification for which I thank you. I wasn't aware that the low end danger zone is 2.5v. That's much lower than I would have expected. I spent a good part of the day yesterday block charging the pack. I have an RC charger with balance and was able to bring a block of four cells right up to 4.20 v. The idea of doing this three more times was not attractive. I then realized I have a 12s charger and put it to good use. Today, the pack is reading 100% on the S8 app and got me through two grocery stores without incident. I won't be attempting to get to and from those stores until and unless the pack presents itself as reliable. Even then, it will have to be a weekend so I can have wifey-rescue capability! Quote
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