20s2p VESC Onewheel Battery Build
This article details the build process I use for the battery pack being used in the 20S Ultimate DIY One Wheel Build project.
If you are interested in buying one of these batteries for your own DIY project, you can find it in the web shop:
https://www.mariocontino.com/store/p/20s2p-custom-battery-for-vesc-onewheel-builds-conversions
The BMS units that work with this pack in the intended space are:
The ZBMS from Z Battery Solutions (currently in first production)
The battery itself is not particularly complicated. There aren’t odd cells to place, and every parallel group of 2 cells sits together and connects in series in a fairly straightforward way. For anyone familiar with smaller electric skateboard batteries, this shape is similar to the brick shaped batteries used in split-enclosure eskates, where the battery is housed in the front, and the ESC is in a separate rear enclosure. Essentially, the cells sit side by side, in alternating directions, and form a common U loop. In this case, the cells fall to the left in a diagonal stagger, making it slightly wider, but less tall. And so, it fits easily in a stock Onewheel XR battery box.
Note the insulation between cells. Fish paper is one of the most common separators for DIY batteries, mainly because it’s both electrically and mechanically insulative, and it’s fairly cheap and easy to buy. You can order rolls of it on AliExpress, usually sized exactly to the cell height. This makes it easy to slice strips off that suit the purpose.
In the above picture, what I’ve done is placed it in such a way that it’s contacting the 3 surfaces that touch between alternating parallel groups. There is the side contact, and also the diagonal contact.
Each parallel group contains 2 cells, and so it’s important when I’m building to just make sure that I’m avoiding the risk that the cell wraps can deform under heat, compression, impact, vibration, etc. This pack isn’t such a tight fit in the enclosure that it’s likely to squish the wrap away, but this is one of the things that fall under “best practices” as the DIY and boutique battery building cohorts have come to understand.
Naturally, fish paper (or barley paper, as it’s sometimes called) isn’t the End All, Be All of cell insulation. The stock Onewheel battery packs use a plastic cell holder frame, similar to what you’d find in e-bike, scooter, and power wall batteries. What actually matters is insulation and separation. Separating cells in a frame adds insulation since the air gap is a great insulator. Fish paper is also a great insulator against electricity AND abrasion, which is why cells have those insulation rings. Those rings insulate against the nickel used to connect the cells, and the heat created during their assembly and their use.
Sitting below the cells, and around the sides, is the same paper. I put it around the sides, since there will be 4 nickel overhangs on this pack. On the right, will be the series jumper connection to the other half, and on the left side will be the positive and negative terminals.
The photos above show the fitment in the stock XR box (left) and the Fungineers’ Funwheel ST standard box (right). The pack fits them both nicely. The BMS shown is the ZBMS from Z Battery Solutions. It’s what I will be using in my personal build project, and will be offering these packs wired for that BMS. The ZBMS fits both boxes without modifications. The ENNOID XLITE 24s needs some modification on the stock XR box, specifically the removal of the separator wall. This allows it to slide down against the battery, and clear the lid properly. If doing so, I would personally cover the bottom surface with Kapton tape and some foam padding, and then secure it to the box with some hot melt glue, or VHB tape. In either case, I always secure the parts down inside enclosures however I can, to prevent their damage from inevitable impacts the board will endure.
I went ahead and laid down fish paper strips creased into V shapes between the cells, creating an insulated channel for the balance wiring to sit in, rather than sitting on the bare cells. While this area won’t see compression from the lid or the wrappings, it’s a decent measure, and doesn’t take much.
By the way, this is why I did not glue the tops of the cells there. It makes the halves less rigid during the build, but it gives great clearance when laying down the wiring. The structure is made up for after wiring, via strapping tape and the final heat shrink.
The choice of nickel here is kind of an artifact of building eskate batteries. Frankly, most of what I’ve been doing with this build is informed by my day-to-day activity working on electric skateboards, which see an insane amount of impact and vibration from the road. Especially in the cases of boards with urethane wheels.
Anyway, the nickel here is custom cut, by hand of course, since I don’t have much in the way of fancy machinery. I do have a lovely X-Acto guillotine slicer though, and have been using it for the last year with great success. It slices nickel very well, and has been useful for everything needing precise cutting in the shop. Below is an affiliate link if you’re interested in the model I use:
https://amzn.to/3DKVEqA
The nickel I’m using comes from my supply of 30mm wide, 0.15mm thick strip, which I then cut down to about 25mm wide. A 60 degree angle is cut to shape it into a trapezoid, and then 1/4” radius corner chompers take that sharp corner off. Affiliate link also below:
https://amzn.to/3Whz8Nh
What’s left are pieces that sit nicely across the series connections, and have enough material to more than handle the draw that these packs are likely to see. If you’re curious about current capabilities for different conductors from wire to nickel strips, here is a great resource:
https://forum.esk8.news/t/conductor-current-ratings-sro/7660?u=mariocontino
This is also why I prefer to use this kind of nickel. Obviously, it’s more work, but I believe it’s a much better end result in terms of current ceiling and structural rigidity than the commonly used “ladder” type of nickel. I have seen that used in some packs like this, but I personally don’t think it’s the best choice. Failing the glue and tape, nickel often ends up being a structural component as well in some cases, and having a bit more there, is a decent idea in my opinion.
Lastly, I used small nickel “balance tabs” that can be found on eBay or AliExpress. They’re essentially small die cut nickel shapes meant for creating tabs for a BMS’s wiring to solder to more easily. These are welded at an angle, to sit in between the cells and accomodate the wiring.
The image above should mostly be self-explanatory, but to walk through what I did briefly, I added Kapton tape on either end of the halves to help secure the fish paper trenches, as well as end-capped the halves with fish paper. The insulation between the halves is very important, since those are welded cell groups facing one another and will be under pressure. My habit is Kaptop tape right on the surfaces, and then fish paper on top of that. Kapton adheres a bit more easily to the metal surfaces, and adhesive fish paper really sticks to that. It keeps it on easily, so that’s what I do.
Jumping ahead a bit in order to address this, on the right side of the pack is the series jumper from one half to the other. I make these with 1/4” tinned copper braid, as it has roughly the same current ceiling as 12awg wire, but it’s flat and very workable with its length. Under it is fish paper from the side wrap, and in the center joint just in case. The copper braid is heat shrinked also, with the ends cut short for soldering it to the nickel pieces at those ends between the halves.
Since the solder joints are larger, I usually do the main pack terminal wiring first. After that, a smaller iron tip will do decently for both the charge circuit wiring and the balance wires.
Since both the ENNOID XLITE and the ZBMS use 2 separate JST connectors for the balance wiring, I elected to do it in two layers. This seemed reasonable, since that surface of the pack simply does not sit under compression in the enclosure. The stock XR box leaves a few millimeters of space, and the Funwheel ST box leaves that surface entirely open. Still, I oriented the wiring harness to avoid wiring overlaps (out of habit, mostly).
Following the wiring diagrams of your chosen BMS is important, and so is trying to figure out where twists and bends in wiring can be placed to have the least impact. No solution is ever perfect, but I believe this layout does it decently while reducing the most risk and setting up the battery for good longevity and durability in use.
Again, nothing and no one is perfect. So I prefer to manage imperfections rather than deny them.
The above photo shows the Tesa cloth harness tape that I place between the layers of the balance wiring. This harness tape is fantastic, and is usually used to wrap wire looms in auto applications. It’s surprisingly abrasion resistance, and quite insulative. It’s one of the tricks that I learned from Ted Christensen from Big Red’s Boards, who incidentally, is on my Trusted Battery Builder’s list. I’m sure he’d have no trouble making a pack like this easy-day.
If you’d like to check out the Tesa tape, affiliate link is below:
https://amzn.to/3SYyJN6
The second layer of balance wiring sits over the Tesa tape, and gets routed between the cells like before.
If you look closely at the left photo, you’ll see that I used heat shrink tubing going over the wires and their solder joints to the balance tabs. This helps insulate and separate them from adjacent wires that travel alongside them from the other half of the pack to the front face. Another point of note is that for ENNOID XLITE wiring on a 20s pack, the last few wires have to be connected to the positive of the last cell of that half. So for this 20s pack, the last few wires going to the positive of the 10th group just go straight across and get soldered to the joint where the series jumper goes from 10 to 11. I’ll show in the next photos where the last few wires go. This isn’t necessary for the ZBMS, as those extra wires are just left out at the end. It’s always good to really internalize the wiring diagrams before embarking.
The balance wiring gets held secure with strapping tape, as per usual. If you’re interested in the fiberglass strapping tape I use, see the affiliate link below:
https://amzn.to/3UdEO95
The second photo above shows the top of the pack covered over with a wide Kapton tape, which adheres nicely to all surfaces and keeps all the wiring secure in the channels between the cells. Wide Kapton take can be found, as per the usual, here:
https://amzn.to/3Nia2tL
Once everything is secure, I give each half a once over with the strapping tape for structural support. Before then, the back of the pack was secured with strapping tape in the rear, across the halves. Also, there were 3 pieces of narrow Kapton tape (affiliate link: https://amzn.to/3FwjxDM) that wrapped lengthwise around the halves to keep them together. This is fairly important to keep everything bundled while working. Forgive me for mentioning it so far down the article.
Once all that securement is done, the build is essentially finished.
Keep in mind, that before doing the balance wiring, I took time to place the connectors where they would need to go once installed in a box with the BMS unit being used. This is commonplace for custom eskate batteries, since sometimes the BMS ends up in an odd place, or at an angle somewhere. Then the wires have a certain path they need to take, and so they need to be secured that way before any fine work is done with cutting and soldering. Routing balance wires can be a bit of a hassle if it’s not prepared for.
Above are just some extra views of the pack in progress, and some configuring going on for the ENNOID XLITE V1.
As can be seen, the pack, once wrapped, fits nicely in the stock XR box with plenty of clearance for padding foam, and room for the harness wiring that enters the box.
I hope this guide was helpful in some way. Feel free to continue on with the rest of this project build at the main article: https://www.mariocontino.com/articles/ultimate-diy-one-wheel-build
