Popular Post alcatraz Posted August 20, 2019 Popular Post Share Posted August 20, 2019 Hey fellow riders... I planned my 60 cell V8 battery build for a long time and only recently got around to finish it. I had worries of building an unbalanced pack as I planned building with used cells. The used cells also came partially from an old v8 pack which had damaged cells in it (corrosion damage) and partially from used cells ordered online (same model cell). The two cell kinds had different remaining capacity and slightly different internal resistance. To make things more unsettling to proceed, I had 30 good cells and 30 slightly more used cells. Avg 3200mAh capacity on the newer cells and avg 3020mAh capacity on the older. A 60 cell pack with 20 groups requires 3 cells in each group and with 30+30 it's impossible to balance the group capacity out. I did my best to keep the groups within 150mAh of eachother. Lower wasn't possible without throwing away "good" cells. My experience of building the pack is that it's very time consuming. It took me a lot of hours. Points I learned: 1. It's very useful to leave the cells fully charged for a long period of time. I didn't do so intentionally but because the project was delayed. My plan was to measure internal resistance (i can see it on my 18650 charger) and weed out bad cells that way. That never happened. The resistance readings were very hard to stabilize, even when measuring several times and calculating averages. In the end I ignored the internal resistance. Mistake? Seems no. The pack appears very nicely balanced after several rides. It appears that leaving cells fully charged is a good test in itself to see which cells have accelerated internal discharge. I rejected a few cells that didn't measure high internal resistance on the charger, by this measure alone. They had all a different voltage drop, some severely different and some were of the new cells with large measured capacity which surprised me. I'm happy they didn't end up in the pack because they would have been a pain to take out. I would maybe never have gotten to it and just discarded all the cells. 2. It's good to get it right the first time. When operating a spotweld machine it's not always easy to find the right settings. Too low and you got a crappy connection. Too high and you'll melt the cell casing. I couldn't risk having to take the pack apart again and tear casing off the cells, rendering them useless. 3. You can get shock from a battery. I put protective tape over the terminals after each one was finished welding. I still got a few jumps. Protect the terminals well. Conclusion: As long as the cells are the same model (lg mh1) in my case, it seems it is ok to mix old and new cells given they passed the long term discharge test. You can expect the cells to remain in very good balance arranging them by capacity alone. Even with group capacity differences of 1.5% it seems they don't deviate when discharging/charging (on a v8 bms). The v8 bms is not doing much, if anything. When I took the old original pack apart I had cell voltages all over the place (corrosion damage). If I had to build the battery pack again I would probably have spent a bit more money on getting cells that come from the same batch. It would simplify things. It saves a lot of time because the capacity arrangement takes just a few moments instead of days. Lg MH1 cells are really good. They are cheap and last a long time. I've heard sanyo/panasonic cells last even longer. Maybe next time I'll use those. In either case I'm very happy with the pack I built. 1 4 Quote Link to comment Share on other sites More sharing options...
Chronic Posted August 20, 2019 Share Posted August 20, 2019 (edited) You're did a good job. Your attempt to expand the battery pack was good, and your skills will improve. Edited August 20, 2019 by Chronic 1 Quote Link to comment Share on other sites More sharing options...
Sidewalk Enforcer Posted August 23, 2019 Share Posted August 23, 2019 Pics or it didn't happen. Maybe I missed the thread, but I'd love to see a pic of this DIY battery pack in your V8. Quote Link to comment Share on other sites More sharing options...
alcatraz Posted August 23, 2019 Author Share Posted August 23, 2019 3 hours ago, Sidewalk Enforcer said: Pics or it didn't happen. Maybe I missed the thread, but I'd love to see a pic of this DIY battery pack in your V8. Ha! I put some up in this thread. https://forum.electricunicycle.org/topic/14060-v8-2nd-battery-vs-upgrade/ 1 1 Quote Link to comment Share on other sites More sharing options...
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