• DO NOT ATTEMPT THIS PROJECT IF YOU DO NOT HAVE ANY ELECTRICAL EXPERIENCE. LITHIUM-ION CELLS CAN BE EXTREMELY DANGEROUS WHEN MISHANDLED AND WILL LEAD TO FIRE IF DONE INCORRECTLY. TAKE ON THIS PROJECT AT YOUR OWN RISK!

• READ THE INSTRUCTIONS COMPLETELY BEFORE ATTEMPTING TO MAKE SURE YOU'RE COMFORTABLE WITH THE PLANS LAID OUT

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This project also assumes you've already done a VnR mod to the board so you can connect the battery to your Onewheel XR/Pint. If not please do that first. Check out https://sonnywheels.com/ for kits and tutorials.

My Onewheel XR's range just doesn't cut it for me anymore. A maximum range of 29KM in perfect conditions just isn't enough. Thankfully the community has found ways to boost the range in various ways depending on your model and hardware revision. These mods consisting of CnR, VnR and RnR.

However finding a 63V battery in the UK with a decent capacity isn't easy. Finding a cheap one is next to impossible!

So I made one myself, I originally wanted to make it weld-less however the contact resistance was ridiculous and caused undesirable losses and heat. This pack weighs around 4KG with an overall size of 145mm x 95mm x 235mm.

With this battery I have managed a 100KM ride on the single charge (With my XR) with a little over 10% battery remaining. This was on mixed terrain with some paved and some offroad with plenty of uphill and downhill stretches. The whole trip was a loop so the net vertical change ended up being only -5m so there was no cheating with regen for this test. See images of the route in the images for this print.

This design uses Sanyo 20700b rather than the usual 18650 cells, why? Because the slightly larger form factor gives a huge boost in capacity. Samsung 30Q's are pretty much the go to cell for these situation but are only 3000mAh. The Sanyo 20700b cells are 4000mAh with only an increase in 2mm in diameter and 5mm in length.

If you'd like to build one be aware you'll need to own a battery welding kit (avoid the Sunko ones, they are terrible). Kweld is by far the superior welder however you can DIY a spot welder with simply a high current car battery, starter relay and a handful of other parts.

One thing to note is you should never connect the battery to the Onewheel if they are not at the same charge level. As long as the voltages are close you can connect them up. The Onewheel will need to be powered on before connecting the battery otherwise the board will throw up an error.

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~ TOOLS: ~
- 3D printer (of course)
- Battery Spot Welder
- Tin Snips (or something durable enough to cut the nickel strips)
- Soldering Iron (and solder)
- Pozidriv Screwdriver (or if you prefer a different driver type use that with the appropriate bolts from the BOM below)
- Hairdryer (or another means of delivering heat via moving air)

~ BOM: ~
- 60 Sanyo 20700B cells https://www.fogstar-wholesale.co.uk/product/sanyo-20700b/
- 15s BMS https://www.ebay.co.uk/itm/123608817156
- 5m Pure Nickel Strip https://www.ebay.co.uk/itm/263068537518
- 8x M4 90mm Countersunk Screws https://www.ebay.co.uk/itm/263786061317
- 8x M4 Nuts https://www.ebay.co.uk/itm/181135033330
- 12AWG (or lower) Insulated Copper Wire https://www.amazon.co.uk/dp/B07CZ8V8F9
- XT90 Connector Pair https://www.amazon.co.uk/gp/product/B07S2ZW1R4
- 300mm x 1m Heat Shrink https://www.ebay.co.uk/itm/323865636500
- Kapton tape
- Zip ties
- Wire Heat shrink

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~ Instructions ~

• DO NOT ATTEMPT THIS PROJECT IF YOU DO NOT HAVE ANY ELECTRICAL EXPERIENCE. LITHIUM-ION CELLS CAN BE EXTREMELY DANGEROUS WHEN MISHANDLED AND WILL LEAD TO FIRE IF DONE INCORRECTLY. TAKE ON THIS PROJECT AT YOUR OWN RISK!

• READ THE INSTRUCTIONS COMPLETELY BEFORE ATTEMPTING TO MAKE SURE YOU'RE COMFORTABLE WITH THE PLANS LAID OUT

I would recommend researching battery building and cell welding before doing this project first. https://www.youtube.com/watch?v=JldTYkcFDM8 would be a start.

1. Print all 5 pieces.
2. Make sure the cells are all the same voltage before using. If not try to pair sets of 4 cells with similar voltages to avoid them instantaneously trying to level out the voltages when connected in parallel. Ideally there shouldn't be a huge difference between the highest charged cell and the lowest, if there is the first charge may take a while to completely balance charge for maximum performance. All the cells should be between 3v and 4.2v if you plan to use them, ideally having them all at their nominal voltage (3.7v) would be best but not required. New cells typically come at a good voltage for storing and welding.
3. Place the 15 sets of 4 cells into the halves of the 2 "20700 15s4p side"s with the start and end 2x2 sections being on opposing corners. Those end sections will be the corners of the models that have a section of 4 cells (2x2) walled off to prevent nickel strips being connected incorrectly.
4. Make sure the cells are in the correct orientation, you should have a tiled pattern of 2x2 cells facing up, then the next 2x2 set facing down. Please check the images to see examples of the pattern of cells as a single one facing the wrong way will cause a short circuit and risk a fire!!!
5. To hold the sides together you can use the 90mm bolts and nuts to temporarily clamp them together via the many holes through the prints.
6. When complete check which of the 2x2 corner slot will be your positive or negative terminal. On the BMS you will have 2 wires, blue and black. Black is the cell side negative before the BMS, blue is the battery negative after the BMS that will later connect to the Onewheel. Ideally you'll want the negative black wire to reach the negative 2x2 corner with ease.
6. Attach the BMS to the BMS plate with zip ties so that the Blue wire comes off where the holes in the BMS plate are. Then clip the BMS plate over one side of the battery cells so that the black wire reaches the negative 2x2 corner with ease.
7. Cut some lengths of Nickel strip, 75mm and 30mm lengths, you'll need a few but cut them as you continue through the instructions.
9. Begin welding the 75mm along the 1x4 slots on one side.Upon welding the cells treat this battery as if it is live, do not bridge any of the cell banks across the printed walls as this could cause a short circuit and then fire!! Make sure these welds are good, you shouldn't be able to tear the nickel off the cell with ease and I would recommend at least 4 welds per cell.
10. Once all the 1x4 slots are populated and welded do all the perpendicular 1x2 slots with the 30mm strips. Make sure to leave 1 empty slot per group as we'll need to add that last one when attaching the BMS balance leads. When leaving a blank slot try to not have them all on the same row so the leads can be separated later.
11. Once that side is complete begin work on the other side. To prevent shorting the welded side of the battery place one of the printed end caps onto that side, the cutout corner should line up with the 2x2 corner.
12. Flip the battery over and begin welding more of the 75mm strips along all the 1x4 slots followed by the 1x2 slots again leaving at least 1 per group empty for the balance lead later.
13. With both sides welded take the balance connector (15 red wires and 1 black) and plug that into the BMS if not already. The black wire will go to the negative 2x2 terminal on the battery as will the large black from the BMS. Then on the opposite side of the cells where the first positive terminal is the first red wire (next to the black wire) is going to go. Follow the nickel strip on that group down to the negative terminal of the second cell group, opposite that where the positive end is will be where the second red wire will go from the balance lead. The leads should essentially alternate between sides till you get to the end with each red wire corresponding to the next positive set of terminals in the circuit. Please see the below image of an example wiring diagram for the cell layout if you're unsure.
https://cdn.shopify.com/s/files/1/0018/3323/8583/products/15S_30A_55V_BMS_Li-ion_Battery3_400x.jpg?v=1571718002
14. Cut the BMS wires to size so that the wire can reach the corresponding 1x2 slot you left blank with a bit of slack so that the wire can run down the side of the battery, then wrap over the edge printed side piece along the batteries over to the missing 1x2 slot. The printed caps have channels where the leads will go and come out at some notched sections on 1 side of the battery. Be sure that they will come out the right side by looking at the cap before making the cut. A dry fit might be ideal to understand how the balance leads need to exit the battery over to the BMS.
15. Strip back some of the wire and solder the ends of the 16 wires to a 30mm strip of nickel of their own. For the black balance wire also solder the large black BMS wire to that nickel strip and for the 15th red wire solder some red 12AWG wire to that strip too as this will become the batteries positive lead to the onewheel. Leave the 12AWG wire uncut for now.
16. With the BMS balance leads soldered to the nickel strips begin welding them to the empty 1x2 slots in the correct order as before. Connecting these wrong will prevent the BMS doing it's job and can lead to a fire risk. Please refer to the earlier example BMS wiring image again if you're unsure.
17. When complete put your multimeter into volt mode and measure between the large blue wire and the large red wire. If you've got a voltage between 45v and 63v then that's a good start.
18. Now measure the cell groups. Unplug the BMS balance connector; then on the battery side measure between the negative connector and the first of 15 positive connector next to it. The voltage should be between 3v and 4.2v. Lower and your cell is too depleted, higher and your cell is overcharged. Move your probes so you now measure between the first and second positive terminals. Those should also read between 3v and 4.2v too. Move along until you've measured 15 readings and finished measuring between positive pins 14 and 15. If all is good we can continue, if not something is wrong and you'll need to check your welds, soldering and if it's all connected up properly.
19. Take the large blue wire and cable tie it via the holes in the one end of the BMS plate so that it sticks out the battery. Do the same with the red 12AWG wire you soldered earlier. This will at as a strain relief.
20. Begin taping the exposed nickel strips with kapton tape. Each BMS wire should lead out towards 1 side of the battery so that when the cap is placed on top the wires follow the channels in the print to the notched holes. Ideally only one lead should come out 1 notch so if they become worn they won't short together.
21. Once both sides are taped remove the bolts from earlier then place the printed caps onto each side so that the BMS leads come out of the notches and the missing corner on the caps are on the 2x2 section allowing the large cables to come out unobstructed. Be sure to have the balance leads follow the channels in the cap so they do not get pinched. Ifnot the cap will not sit firmly within the printed sides.
22. With the caps in place thread 4x 90mm bolts down each of the 4 corners of one cap through to the other side then pressfit the corresponding nuts on the other side. If you can't get them to fit remove the cap with the hexagonal holes and use a bolt to tighten them in or use a soldering iron to push them in. The soldering iron will heat the nut to melt its way into the hole but don't go too far and don't do this with the cap on the battery.
23. Tighten down the bolts so they grab the nuts but don't go too hard, these bolts are more to give the battery rigidity. If you tighten them too much you risk snapping a weld which is a nightmare to find and re-weld.
24. Add the rest of the bolts and nuts if you wish in whatever configuration you want. I went for a cross pattern with a bolt being every second hole diagonally for uniform coverage.
25. Take the red 12AWG wire you soldered earlier to the positive terminal on the 2x2 positive corner and without touching the bare parts of the cable with anything bring it up to the end of the blue wire so they are equal length coming off the BMS plate. Cut the red wire and make sure neither it and the blue wire touch as it will short. You may want to tape the exposed end of one.
26. With a female XT90 connector slide the XT90 terminal cover down the red wire then some heat shrink. Solder the red wire to the positive terminal on the XT90. Then slide the heatshrink over the exposed solder, wire and terminal so it's insulated completely.
27. Take the blue wire and slide it through the other side of the XT90 terminal cover, then slide some heat shrink down it too. Solder the blue lead to the negative terminal on the XT90 then slide the heat shrink over it so no exposed solder, wire of terminal is exposed. Finally slide the XT90 terminal cover up to the XT90 and clip it in place.
28. Grab your multimeter once again and measure the voltage coming out the XT90, you should have the correct polarity coming out the XT90 with the voltage again matching what you measured earlier between 45v and 63v.
29. Take some kapton tape and wrap around the battery so that the balance leads are securely held in place as well as the BMS connector and the exposed 2x2 slots are covered leaving nothing loose and no exposed metal.
30. With the 300mm heat shrink in hand slide it over the 2 shortest sides so that the longest edge has the heat shrink going along it. Leave some excess either side for it to slight wrap over the edges when it shrinks then cut the heat shrink.
31. Take you hair dryer (or other hot air device) and on low heat begin heating the wrap so that it begins to shrink. You don't want to be too hot else you might melt the printed parts and heat up the cells too much.
32. Once that is securely shrunk around the battery take the 300mm heat shrink and measure up some so that you can fit over the battery fits it's 2 longest sides which should leave no part of the battery exposed. Cut it leaving some excess over each end for it to slight wrap over the edges when it shrinks and once again shrink this layer.
33. For the last time check the voltage, if it's all good still you're done!