Go for it! The bolts work well but I would try to find a way to non-permanently get the locknuts secured in the deck. Might be better to have the locknuts inside the battery harness even. It’s just that the locknuts will eventually wear out so it would be nice to be able to replace them.
Anyway, I look forward to seeing what you do with it. Good luck man.
So a bit of an update. Had my first fall yesterday and I found a weakness in the design. Was riding on uneven grass and tried to jump up this big curb onto the road. Had both batteries and I was on my way back from the pump track so the board was heavy with both batteries. I hit the curb with the back wheels and landed sideways with my front sliding on the pavement. Caught myself with my hands and was unhurt other than a scraped up knee. One battery took the most of the damage.
So basically the XT90 loop key is too close to the edge and the edge is what hit the ground so it bent the connector on top of the battery. Repairable for sure and actually not too bad. I already made a fix for this. I added a big ol sacrificial forehead to the forward access panel. Now if I fall the access panel should get shredded, which is replaceable so no real worry.
I made it stick out and also added more area where it mates to the rest of the battery so when it hits the ground it will distribute the force more across the sides of the front instead of right where the charge port and connector are. I hope this works.
Another update. I am building a swappable setup for my buddies MTB. He will just have a single battery harness but the battery will be 12S4P instead of 2x 12S3P. I’ll be adding the forehead fix to that as well. Literally the only changes I made were extending both sides out by like 20 mm on each side.
Also, I’m building a 12S5P variant. Thing will be pretty heavy and I worry about the torque on the bolts when breaking hard since they will be so close to the center. I extended the battery harness along with the battery to fix this hopefully. I think 12S5P is the limit to this design since I’m only using an XT90 for power. If I go higher than this I may use an AS8 connector or have two XT90s side by side.
Loctite works really well for that, even after multiple uses, just add an additional drop after a few uses
I had a similar accident with my 3D printed enclosure where I fell and stepped in the loopkey
Just put a bunch of epoxy all over the loop key ports lol. It will be the last resort if the forehead fails me.
And yeah loctite will work but I don’t want to have to apply it everytime I take the battery on and off. I usually take a battery off once per ride so would be kind of a pain.
Did the same here, a bit of thin superglue so it penetrates and hold it in place and sealed with epoxy
On the loctite, once it builds up a bit, it acts as a Nyloc nut, kinda, you can put and remove a bunch of times without applying more and it still holds
Oh sweet that puts me at ease then. That will be the last ditch effort then if the locknuts wear out.
12S4P is done. I originally put the text and graphics on as a joke in the renderings but he loved them so they stuck. I think it’s my best work yet lmao.
Could you post the stl’s to thingiverse or another platform like that? Would love to take a look at them
github better XD
Steel helicals:
Bought a set a couple days ago 
They look so sick I can’t wait to receive em.
Btw I’m working on this. Trying to make it pretty comprehensive. I’ll update when done.
Update time!
I had so much fun with this board last year.
I installed BN geardrives:
I then thrashed the board hard at the pump track and on some very rooty mountainbike trails. I definitely don’t baby it…
Now it’s winter and snow is on the ground so that means it’s time to build! For this board I wanted to reduce the weight, because the geardrives are crazy heavy compared to my old belt drive setup. To do this I decided to lose some weight in the battery. I opted not to move to LiPos because I’ve had some not-so-fond experiences with them in the past. I settled on a 12S2P 18650 pack made up of Samsung 20S cells, which I determined to be the most power-dense cell available, according to its ratings anyway.
I finally found a few spare days, so I redesigned the enclosure and just finished putting it all together!
Here’s the new smaller pack compared to the older 12S3P 21700 P42A pack:
I’ll be building two of these packs. They should do great as backup ones I can keep in my bag during longer rides. My only concern is the regen current though. The Samsung 20S datasheet mentions the max is 4A, meaning I have -8A as a rated maximum total regen current. Obviously this is not enough braking power so I’ll be doubling it or even tripling it if I think I need to. I’ll be trading cycle life by doing this, but I think my life is worth more than a few extra cycles. I’ll need to be cautious about my braking though, that’s for sure, because the pack SOC will increase rapidly whenever I brake even slightly. To compensate I have the BMS charge cut-off voltage set to 4.1V per cell to minimize the risk of braking too hard for too long and going overvoltage. I’m not too worried though, because this pack will only really ever be used at the pump track, and I tend not to brake too often there.
You should avoid welding to the center of the negative side of the cell. There’s an internal connection there that can break if you weld on it.
Hmm okay, noted. Thanks! I’ll keep that in mind for the next pack.
Great design @BrassMittens but I don’t understand how you connect the two packs in parallel, when they are already set of parallel cells connected in series you then connect them in parallel again?? Isn’t this against rules on how battery packs works??? Sorry I’m not an expert on this field but I’ve never seen anything like this. Maybe you use each pack separately?
Do they discharge and recharge uniformly?
Can you provide a wiring diagram in case of the two battery packs?
it’s fine to put a set of, parallel cells in seires, in parallel
it’s like getting a say 12s2p and connecting it in parallel with another 12s2p
long as they are close in overall voltage when connected, it’ll work fine
as long as you don’t do both at the same time like this example:
It works. It’s the same as connecting multiple lipos in parallel and/or series. You’re just playing with total voltage and current depending on where the connections are made.
I’ve got 1x 12s2p and 1x 12s3p i run in parallel (or individually) - NESE modular jumper - 🐉 Dragon MTB build - #93 by sleepless
The major issue is you must only parallel packs with the same voltage. In practice that means fully charged and same 10s / 12s. I charge my packs individually for safety.
Thanks!
As poast and sleepless said, there’s no real magic to using packs in parallel. You can do it almost the same as you can parallel two cells together.
Yes, and this is important. I made the packs identical, so they both share half of the charge and discharge current and I don’t have to worry about one pack supplying more current than the other. They also have smart BMSs so I can make sure they are balanced and healthy. If they weren’t balanced I would NEVER charge them in parallel. I also would never connect my 12S2P and 12S3P on the same board together or attempt to charge them in parallel.
Not sure if this helps but here you go.
Honestly, I take a lot of risk putting the packs in parallel, and I don’t recommend doing it. If I mess up and connect them at different voltages I risk a battery fire from the huge balancing current from pack to pack. Or if I connect an unbalanced battery to a balanced battery and try to charge them together, I risk a battery fire from overcharging some of the cells in the unbalanced battery.
thanks @BrassMittens to clarify. I’ve asked the same question on stackexchange and now I understand the risk and limitation, but hey this is very cool idea and well made!
I’ll probably do the same as @sleepless using NESE modules, but I’ll seriously consider also your design, I really like the idea to size the battery based on different needs.
Thanks also to @poastoast (but from those pics it seems not a polarity mistake but more the issue with different voltage connction)
Speaking about voltage difference what is an acceptable value? 0,1 Volt difference is still ok?
