I have to admit I have no better reasoning than Samsung 30Q seemingly being very common (though I have seen some say 21700 is the new norm, nevertheless my enclosure is seemingly laser cut to fit specifically 18650 cells so it might be something I’ll consider next time). Those Molicell P26A look pretty nice on paper, even a little bit cheaper. How can that be (beyond the Min cap being 2600 vs 3000mAh)? If I were to switch to those what would the potential benefits be, more efficient?
Ok that makes sense and it sounds familiar, but how do I go about soldering these wires without simply shifting the strain to a parallel nickel connection? 4 seperate wires? Is there something I’m missing? I’ve usually seen this done with flexible packs where theres essentially a huge bracket covering the four cells so I’m trying to understand the implications from using strips instead.
they’re more available as samsung is trying not to let single cells into the wild anymore. and molicell is shipping them actively.
@Battery_Mooch has many threads describing why the cells we tend to prefer are better for our uses. I highly recommend reading through his posts. I can try to explain things but I’d just make a fool of myself.
again, read the battery builders thread. there are many tips discussing this in there. use the correct gauge of wire and the correct number to get an appropriate connection with a low profile.
Chill with the silicone wire is everything guys, context is key. This is essentially a brick pack, he will have to have solid connections.
This instance you’re really only left with this option. Silicone wire and such is the ideal way to do it, but this pack shouldn’t see flex. I’ve built quite a few of them solid, no problems.
See if you can locate some .2x25mm width nickel strip/sheet. One layer of that will be sufficient for the current requirements.
Yup.
At above about 5A or so (continuous or burst) per cell the higher efficiency of the P26A actually results in more running time (longer range). If you are at very low current levels then the higher capacity of the 30Q can take over and you’ll get more running time for them vs the P26A.
The P26A will also run a bit cooler (due to its efficiency) which helps to extend overall cell life.
On a less technical note…LG is actively trying to prevent the use of its cells outside of fully protected battery packs and seems to have sent not-so-pleasant letters to some vendors to help make this happen. Molicel on the other hand openly embraces end-users buying their cells and using them for vaping, DIY stuff, flashlights, etc.
Almost sounds too good to be true, but reasonable. Can’t believe I haven’t given these as much consideration as I should have. Going to try and switch to them instead.
But then I’d be back to the same dillemma again. Instead of having 60A to worry about I potentially got 140A to deal with (is it advisable to build to a limit set in the VESC like 100A or build to the max?). @A13XR3 would .2x25mm still be enough? What makes you say it is enough for 60A, is it from experience or something similar to this chart?
.2mm thick nickel seems to be hard enough weld, I can’t imagine needing to triple it to be within optimal range. Would that imply silicone wire is my only option when going over 60A?
I will proceed, taking into account all your guy’s feedback and post a final more formal battery plan before I start welding.
You’re not going to get 140A from that setup man, so you will not have to worry about that.
To clarify, your motors aren’t very big and your battery isn’t very big. If you pull 140 amps youre going to get crazy voltage sag (which would make your total output watts lower) and get your cells motors and Vesc very hot, which will end up with something damaged.
Also, you need some big hills and very high voltages to get to 140A, so you will only see that number momentarily, and not continuous.
Cells will try to deliver whatever you ask of them (with varying degrees of voltage sag or flames). You only have to deal with 140A if you draw 140A.
I recommend staying below 25A per cell for the Molicel P26A to minimize voltage sag but you can set your VESC settings at any level below that to better match other parts of your setup.
That’s right. Silicone wires don’t make a difference in this instance since the pack will be a brick. I would use wide nickel strips to handle the current.
For a commuter board you really don’t need something crazy like 140A. Just cruising in city trafic takes like 1-2kw maybe 4kw when accelerating. Setting the power to high only makes it more dangerous when commuting.
What great feedback! I feel like I’m actually learning something!
Yes, so it seems I’ll have to double down and just get the proper stuff: 0.2x30mm nickel (seems like it would work as opposed to the not as wide 25mm but I’ll have to do some more extensive measurements to be sure).
To make sure I interpreted you correctly, in practice it would look something like this (considering I go for the Molicel P26A and running them at 25A each, 100A total)? Note, the arrangement of the cells will not be the same but I’m focusing on the concept:
Transcript:
0.2x30mm nickel strips (for the cells in parallel, 56A optimal, 85A acceptable) and two AWG 12 wires (each optimal for 41A, 82A; each acceptable up to 61A, 122A total) connecting these “packs” in series.
So you are suggesting not going the silicon wire route and simply laying wide nickel strips across (and running the cells at 25A each). Would one layer of 0.2x30mm across be sufficient (and would any more even be possible)? Based on the table such strips would be “Acceptable” only up to 85A. Of course I would likely only pull around 50A most of the time (on a bad day) which is well within optimal for such a nickel strip. Though for times that I do pull closer to 4kW (almost 100A), won’t I get unsettlingly close to the “Poor/Hot” end of the spectrum (113A for such strips).
If I have presumed correctly: such a setup work, though be close to the risky side of things if I don’t double the layers [or is it not risky at all]? For the sake of clarity I’ve made a diagram of this scenario as well:
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
