Hey guys I have a somewhat serious question and I’m hoping some of the battery experts can weigh in for me. I recently purchased a used Stealth electric bike with no battery so I did some research on battery options. Not wanting to shell out for a $2k stock battery (and having some experience building smaller packs with BMS), I decided to go the DIY route. Now that the pack is built and ready to use, I’m having a “What was I thinking?” kind of moment. I have spent about $700 to build a 21s3p 30ah lipo pack with a bestech 100amp BMS. My question is this: Now that the pack is built, is it safe to use if I am cautious and take the necessary precautions? Or would I be better off safely discharging it, throwing it away, and building a smaller, more expensive one with 18650s or Lifepo?
I fully admit that I was stupid to not pose this question before spending all the time and money that I did. I accept that and now I just want to proceed in the most intelligent and safe way possible.
I also acknowledge $700 is a lot to throw down the drain, but I am more than willing to take the loss if it means saving the bike, my home, and most importantly, human life.
Here are the battery details:
To get my desired voltage and capacity to fit in the battery compartment (as well as my budget), I chose to permanently parallel individual 1s Lipo cells taken from new HK Multistar 10000mah batteries. I first assembled 21 packs of 3 paralleled cells. I connected them by running a nickel strip through the pouches’ tabs, bending the strip ends over one another on top of the tabs, spot welding it to form a compact loop, then adding solder to ensure each tab had a good connection to the others (I tried to keep heat buildup to a minimum, but of course the solder was very hot). I then connected the 3p packs in series using more nickel strips (enough to stay within conservative ampacity limits) to get 21s3p. I then wired up the BMS, and added a few JST-XH balance leads that run to the front of the pack to be able to check individual cell voltages at any time. After that I added charging and discharge plugs, a few protective plastic panels, and taped it all together. I wish I had taken pictures of the process, but here is the basic schematic for my design (BMS not shown):
Here are my main concerns:
1. I foolishly did not discharge test the 63 cells that went into this pack beforehand. I now realize that if there are any bad cells in the pack, they could at best drag down the other cells they are paralleled to, eventually killing them (best case scenario), or start a very nasty chemical fire with 30ah of lipo to feed it (worst case scenario).
2. The battery is a very tight fit in the bike’s battery compartment, leaving no room to add foam or any other shock absorbing material. I’m worried the first crash on the bike could damage or puncture the cells.
3. I’m currently storing it in a vented steel toolbox on the cement floor in my garage. I plan to do all my charging there as well with an 84.7v lithium charger . In the event of a charging failure, would the toolbox be enough to contain the fire? I’ve installed a fire alarm in the garage as well and plan to closely monitor the battery anytime I charge, but I don’t know if I’d be able to do much to extinguish the fire if the battery did go up in flames.
I'd greatly appreciate any advice, opinions, or past experiences that could help me gauge the danger level I’d be assuming if I decided to use the battery. If you do feel it's ok to use as long as it's with a wary eye, I'd appreciate any safety tips or items of concern specific to my design (I won't ask you to list off all the items of general lipo safety, unless there is one point you feel I should be particularly aware of). Or if you’d just like to comment about how big of an idiot I am, that’d be fine too. Don't hesitate to let me know if you really feel that my battery attempt belongs miles underground.Thanks in advance, I hope you’re all enjoying some good riding weather.
I fully admit that I was stupid to not pose this question before spending all the time and money that I did. I accept that and now I just want to proceed in the most intelligent and safe way possible.
I also acknowledge $700 is a lot to throw down the drain, but I am more than willing to take the loss if it means saving the bike, my home, and most importantly, human life.
Here are the battery details:
To get my desired voltage and capacity to fit in the battery compartment (as well as my budget), I chose to permanently parallel individual 1s Lipo cells taken from new HK Multistar 10000mah batteries. I first assembled 21 packs of 3 paralleled cells. I connected them by running a nickel strip through the pouches’ tabs, bending the strip ends over one another on top of the tabs, spot welding it to form a compact loop, then adding solder to ensure each tab had a good connection to the others (I tried to keep heat buildup to a minimum, but of course the solder was very hot). I then connected the 3p packs in series using more nickel strips (enough to stay within conservative ampacity limits) to get 21s3p. I then wired up the BMS, and added a few JST-XH balance leads that run to the front of the pack to be able to check individual cell voltages at any time. After that I added charging and discharge plugs, a few protective plastic panels, and taped it all together. I wish I had taken pictures of the process, but here is the basic schematic for my design (BMS not shown):
Here are my main concerns:
1. I foolishly did not discharge test the 63 cells that went into this pack beforehand. I now realize that if there are any bad cells in the pack, they could at best drag down the other cells they are paralleled to, eventually killing them (best case scenario), or start a very nasty chemical fire with 30ah of lipo to feed it (worst case scenario).
2. The battery is a very tight fit in the bike’s battery compartment, leaving no room to add foam or any other shock absorbing material. I’m worried the first crash on the bike could damage or puncture the cells.
3. I’m currently storing it in a vented steel toolbox on the cement floor in my garage. I plan to do all my charging there as well with an 84.7v lithium charger . In the event of a charging failure, would the toolbox be enough to contain the fire? I’ve installed a fire alarm in the garage as well and plan to closely monitor the battery anytime I charge, but I don’t know if I’d be able to do much to extinguish the fire if the battery did go up in flames.
I'd greatly appreciate any advice, opinions, or past experiences that could help me gauge the danger level I’d be assuming if I decided to use the battery. If you do feel it's ok to use as long as it's with a wary eye, I'd appreciate any safety tips or items of concern specific to my design (I won't ask you to list off all the items of general lipo safety, unless there is one point you feel I should be particularly aware of). Or if you’d just like to comment about how big of an idiot I am, that’d be fine too. Don't hesitate to let me know if you really feel that my battery attempt belongs miles underground.Thanks in advance, I hope you’re all enjoying some good riding weather.