That is perfect! You don’t have to work about the nickel rating too much as the current will be spreaded between all cables you solder to it!
This setup it’s risky because of the flex of the pack, as it puts the force of the pack bending (even if it is just a little in the welds, which are not designed to take any force) but current ways it will be alright, as all the current will be distributed on 8 points throughout the nickel as opposed to just one.
If you don’t understand correctly i can make a quick sketch!
My idea is to glue together 24 cells in a honeycomb pattern (with fishpaper around the P groups of course, taking inspiration from How To Build a Compact 10s4p 18650 Electric Skateboard Battery (DIY Tutorial) - YouTube but 12S) The way he soldered the wire connecting the two 6S4P packs seems a little sketchy to my untrained eye so I think I’ll be running the wire on the outside. Hopefully by using a similar 3D printed frame the flex will be minimized. I think I see what you mean, but of course, if it wouldn’t be too much trouble, I think me and future readers would appreciate confirmation with a sketch!
Lol it was sketchy (very hard to solder, not dangerous) to my trained eye too. I wouldn’t do it again, I just needed to due to space constraints in the enclosure it was going into (that channel is me btw)
I was just about to post the video here, in response to:
I too think it will be okay, but I do recommend the extra strengthening bits on the outside or middle, as they will help alleviate extra stresses, oh, and heatshrink too. That clear stuff I used stiffens the pack even more
Only applicable to a non-flexible deck, of course. There will be a minute bit of flex in almost every deck but if it’s small enough, and you pad the battery on installation you should be fine.
Oh my what an honor! Keep it up, that video helped a ton!
I have made some quick CAD designs that I was planning on uploading when/if this is successful resembling those that you used (with a channel for the wire that would go along the rear instead of inbetween, along with other support features that I think would be beneficial). And am I correct in assuming you used 0.2mm thick nickel that is essentially 25mm wide (you didn’t seem to mention it in the video)? Also, after being questioned for choice of cell by tech.shit I too am curious why you’d go with the Samsung 30Q instead of the Molicell P26A, or was it simply because you were recycling them?
Hihi, one or two things to consider but this doesn’t majorly contradict anything said above I just think it’s useful background info
On the flex vs non-flex point:
People referred to brick packs, and if you’re not familiar with them they are often vertical arrangements (cells stand on the narrow circular end rather than lie on the long cylindrical side), and almost always packed in a pelican case style box. This has a couple of notable effect, firstly the longest dimension of the pack is significantly reduced and geometric rigidity (ie natural stiffness from the shape of the pack, disregarding construction methods) is increased quite a lot. Secondly it’s encased in a fairly stiff material but more importantly in a body that’s not subject to much load at all. As compared to a long(er) under board pack, where having one dimension much longer gives less rigidity and (IMO more importantly) having the enclosing material subject to very high loads.
The way that humans notice or experience flex in a board is mostly the slow or sustained bending, ie you jump on a board and it bows for half a second and springs back. What we don’t notice or think of the same are the really fast vibrations because if something moves half a millisecond instead of half a second you’re not gonna feel it, but there’s a lot of energy in a fast movement like that. So in short: vibrating is very similar to flexing, lots of stuff vibrates, under board batteries are a flexible shape enclosed in material that both vibrates and flexes (vibrates on uneven surfaces, flexes when you step on or drop a 3cm curb or whatever), and nickel welds should not be a big structural component of anything if you want it to last. IMO then you’re better off making P groups and wiring them together because wire can flex, but it’s not the end of the world. Plenty of packs have been made that lasted a goodly long time with nickel series connection, but it gives me the heeby jeebies. I’m open to being corrected on how relevant all of this is by a mechanical engineer, I’m outside of my electrical comfort zone here, also here’s some fun videos that extract data on otherwise-invisible vibrations from video. It takes short contrast patterns and blur artefacts and uses them to pull out information on very quick deflections that would just look like vibrations
On the battery current:
Bunch of good answers above about batteries only drawing what you ask, also consider this to get a reference point for how much current you need. I was answering someone asking about using high battery current and linked them to the ride logs of a biiiig fuck off board, where you can see both the maximum current ever used and importantly, the normal currents. It barely ever passed 60A, ie less than 3kW, and never in the life of the board passed 3.5kW as far as I can tell.
And this
To be extra clear: this should be a bit comforting that you can have a truly exceptionally high performance build without ever worrying about that 85A battery current range
Cell selection:
Discussion has already been mentioned but I’m gonna leave this link here
As well as mention that it’s not a huuge difference tbh. Definitely seems like a better pick, and P28A cells from a batch in the last 12-18 months perform a little better again, but it’s not going to be the difference between a usable board and an unusable one, 30Q has been a decent choice for a long time because it’s pretty decent.
It depends on rider. Ive easily pulled nearly of 6kw on my Evo. (120 batt amps @12s). It’s hard on bad roads, and it hits top speed pretty damn quick.
3kw is plenty. I’m running 4kw and 3kw on my current boards.
Ah fair fair, I was being a bit selective with my examples just because it seems like a first build for a not super demanding use case and it’s the info I wish I heard at the start instead of going nuts while I didn’t have a hope of using it. But yeah you can pull big power if you’re a lunatic or you’re racing or whatever
First of all, thank you for such an extensive answer! Very organized and easy to follow and has exactly the reassurance I was looking for, splendid! I’m coming from an ownboard w2 that has a blown BMS (2x600W motors) so I’m certain this will blow my socks off at 1/4 throttle.
I’m a fan of the clean, natural way of using nickel strips for parallel and series connections (especially since I have a lovely video guide that shows exactly how to do it). Though, it seems like the general consensus is wire for series connections is king (unless one’s got a good reason not to use it) so I’m starting to lean quite heavily towards that option.
I think I got exactly the answers I was looking for, thank you everyone! Hopefully my next post consists of my dream board in all its glory!
Conclusion: Use wires for series connections, 0.2x25mm nickel plates for parallel connections, add as much structural support as possible (along with the “obvious” stuff: fish paper, shrinkwrap, healthy dose of caution, etc), switch to Molicel P26A cells
Yeah that’s the conclusion I’d go with too, but as you said the nickel combo is potentially clean and easy. That NKON listing looks good if you’re in the EU, the only thing to keep in mind is that 0.2mm is the upper end of what spot welders outside of industrial environments can do. It’s very doable with a good welder like a kweld or SQ1 (not an expert here, battery builders thread is your friend) but requires a good bit of practice and messing around. As I understand, best practice is to get some cells to learn with, discharge them very low, and work by trial and error with feedback by posting pictures before moving to the main build.
You mentioned equipment at the university, do you know what spot welding gear they have? If you’ve got to buy your own it can get very expensive very quickly and buying a battery from a decent builder can be easier
I’m not entirely certain what welder they have, my plan was to test on the 2 extra cells I’d order and get some interal and external opinions. If push comes to shove I’ll have to mow some more lawns and dish out for a kWelder. This entire project is as much an excuse to learn as it is having a killer board to ride!
The thing we need to keep in mind is that we are taking about peak values. 12s 100A is insane and you will go very fast in seconds. The sustained current will be much lower.
I have a very similar setup that you are planning (12s4p brick battery in exactly your configuration with only nickel) on a loaded vanguard flex 4 and it’s doing great after 2 years.
To me it’s kind of strange that many people use the peak values as their basis for calculating the wire size.
For me as a battery builder it’s important to always size them to overcompensate for the highest possible. Can’t hurt to have extra current carrying capability, just makes everything cooler
Where I draw the line is using more than 10awg cable or xt-90 for the discharge lol
It makes sense to build for the worst case scenario instead of the common one, at least that’s my logic, that’s also why I now feel like wires might be the better option since if the pack were to shift out of alignment a wire could handle it while the strips might not? If you were to build that pack again would you go the same “nickel only” route?
Yea I would use the nickel only route again since it’s also smaller and I had very tight tolerances. If you are very paranoid you could also use 50mm nickel and fold it over the cells so you have more cross-section. My motors and ESC would overheat quicker than the battery so there really is no physical way I can draw that much for such a long time.
Even going 70km/h on flat ground only takes me around 2000w to sustain so unless You are doing uphill races you really don’t pull That much.
It builds in a cooling and reliability safety margin and takes into account the full voltage sag you would see. This is critical for max performance. It also builds in the ability to possibly run at higher current levels in the future if desired.
There are real benefits to using peak values. Just as there are real benefits to using average values. Which we choose to use is up to us based on our build strategy and personal preferences and priorities. Neither way is inherently the best way.
