19s2p VESC One Wheel Battery | Build Log
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WARNING:
Lithium-ion batteries are inherently dangerous. They can overheat, catch fire, explode, or leak hazardous chemicals if mishandled, damaged, overcharged, short-circuited, punctured, improperly stored, or exposed to extreme temperatures.
Projects involving lithium-ion batteries are dangerous by nature. Working with these cells carries risks of thermal runaway, burns, toxic fumes, fire spread, and property damage. Only qualified individuals should assemble, modify, or repair battery packs. Use proper protective equipment, properly specified chargers, battery management systems (BMS), fuses or protection circuits, appropriate insulation measures, and safe charging/discharging practices. Always follow applicable safety standards, and local regulations. If you are not experienced or trained, do not attempt battery pack assembly.
Part 1 - Design Thoughts, Desired Outcomes, Rationale
Why 19s2p? To explain that, I’ll give some context. This is a battery failure I experienced 2 years ago.
Back a few years, the original TORque Box from The Float Life and my accompanying 18s2p battery configuration were just about the best all around power option for a self-built, DIY style one wheeled board. Most people at this point call it a VESC one wheel, since it’s a one wheeled balance board that uses VESC based motor control. Since there is a good amount of information on that topic itself already out on YouTube and the social media groups for Onewheels, I’ll skip the lore of “VESC Onewheel” here. I bring this topic up here, because that old style 18s2p battery configuration was the most robust, reliable, and easy to install battery setup for these kinds of projects, and I’m proud of the “ME4T/MEAT Pack” and its history. There are many of them still running in boards, and they remain as having the lowest failure rate of all the third party battery options for VESC based one wheel builds.
The original MEAT Pack, now retired. Surrounded by the bones of its successor.
As time goes on though, things change, and so do expectations. In line with that, I wanted a little bit MORE. A bit more range, a bit more power, a bit more battery.
At first, my impulse was to take the existing 18s2p configuration and add more cells to the front enclosure of the board. Since Fungineers was working on new box designs at the time (this coincided with the Thor Box release, and Mo at Fungineers spoke with me about cell fitment in the front box), I was leaning in that direction. However, after having my own split pack installation in testing for months, I came across a critical issue. The long and short of it is, that installing a split battery pack (a modular one, since the front cells are a module on their own) with a non-modular BMS poses a dangerous risk of the ground location shifting when the series connection within the battery is broken. This is what happens when the front and rear modules of the pack are unplugged. The load (the VESC) remains connected, and so the ground location of the system changes, and the BMS sees voltages and polarities that it was not designed for.
What this results in, is BMS failure. Specifically, BMS failure that can lead to uncontrolled heating inside a sealed battery enclosure.
In my testing, this led to a fire. Not just a fire, though. A fire that consumed the board, burned my bench, and started while the board was OFF and UNPLUGGED. Which is the worst condition of a battery fire possible, since there was no outward cue of a failure, and I was not present. I returned to the garage at the moment that the board began erupting smoke and fire.
Here is what remained of my split pack:
Fast forward to 2025, and I was looking for options for a new battery design for my projects. While other battery builders were seemingly glad to lean into the 18s2p/2s2p split pack, I wanted nothing to do with it. Oddly enough, there were and still are builders who insist that split pack layout is fine, citing their own specific examples of “2000 miles with no issues”, even with monolithic (non-modular) BMS units. Despite my attempts to explain how risk of system failures work, it’s not my problem to solve and naturally, any project success is a good thing. No one wants anything to fail. And I would not wish my experience on anyone.
Either way, a different approach felt more prudent and so I reached out to an old friend and colleague of mine who had extensive experience with PEV battery design in general, and more specifically, PCB based battery packs. He and I have long shared outlooks on battery assembly, and also share a similar experience-based fear of lithium ion batteries. And because of that, I believe we have a more grounded and realistic respect for the technology.
Over the span of a few months, he and I arrived at the new pack shape. It takes the old 18s2p idea, shifts the layout, and adds one more group of cells to the empty “shoulder” in order to arrive at a similar pack design, but with just 2 more cells. Electrically speaking, it is literally the middle ground between the old 18s2p brick, and the larger 20s2p arrangements.
A perfect medium.
Part 2 - Parts & Manufacturing
This battery design has a few parts to it, and each part is made up of different parts. Parts on parts. I will do my best to lay out each part and its constituent parts. #parts
Fabrication Files
This ZIP archive contains the digital files used for making this battery pack. The files are separated into their respective folders are they apply to the assembly process.
19s2p Battery Assembly Files
