I want to put heatshrink on each 3S2P group separately since I think it would be somewhat difficult to put it on the whole pack due to the non-rectangular shape.
Now, I’m still deciding how to best do the series connections. My first idea was doing it with small pieces of 12 AWG wire as shown on the picture above. Or maybe with a slightly longer piece like this (might be easier to do and allow for more flexing):
Unfortunately, the enclosure is pretty low in the middle and I’m not sure if I can do it that way without having the deck press too hard on the wire. One other option I’m considering is using a bunch of 20 AWG wires like this:
One other option is to connect with nickel strips that I would solder on. That would likely be easiest to do and it would look clean. The downside is that there would be almost no flex at all but maybe it’s not a problem since the battery is pretty short?
Nice! It looks like you have room front to back. Have you considered doing it Deckoz style, with series wires in between the cells, not on top?
Also if you do the connections asymetrical, it’s possible/likely that due to the high resistance of nickel you get faster wear on the cell closer to the 12awg wire.
It’s hard to keep nice thick braided flat wire from being soaked in solder over such short runs. Even if not soaked, it definitely stiffens up. But it that enclosure I imagine flex is minimal?
I have, but I think it would be really hard to do with such a short piece of wire. Plus, I would have to solder pretty much on the cell.
Makes sense. I’ll go symmetrical then.
What do you think about just doing the series connections with a piece of nickel strip? It would be easy to do. Wouldn’t add much to the height. Nice and symmetric. It’s for a Tayto deck. It’s short and doesn’t flex much. Plus, I’ll be basically standing on the trucks => even less flex.
Or I could do the 20 AWG wire connections. That would be a bit fiddly but should work pretty well. Similar to the braided wire except it’s easier to avoid getting it soaked with solder too much. 20 AWG is rated 11A so if I put 6, that should be enough. Better than single 12 AWG.
Dumb question, but just want to double check. I have these nickel tabs that I will solder the balance wires onto all the positive terminals of the cell groups.
If I have the tab welded like this over the nickel strip that makes the series connection, will it work or will it in some way connect to the negative terminal of the cell group?
It will connect BETWEEN the positive terminal of one P-group and the negative terminal of another P-group. All the metal parts connected to the nickel tab are BETWEEN the positive and the negative. It doesn’t matter where exactly you solder the balance wire.
Especially for high powered cells I hate to use nickel for the power lines. Looking at the build, it’s probably around 30A/cell, right? All my A123 packs (2p) are all copper soldered to the cells. I always stare and stare at the piles of nickel strip (including .25 and .30 nickel) and spot welders, then I reach for copper braid instead… This is not as bad as you might think. I think in a lot of other RC hobbies, it’s typical to solder to cells for high power applications. But then again, with all the testimonials on the forums, I’m probably way overthinking/overbuilding things.
If you’re considering spanning groups with nickel, it’s actually quite similar to doing a fold-over, right?
The 20awg experiment looks interesting! Can’t think why this would be bad, except for the tedium of making 144 or so solder joints.
How much is acceptable cell voltage difference? I noticed some being 3.517 while others were more like 3.524. This is before charging and with 0 cycles.
I didnt think about it then, but I am a bit concearned now.
I think I’ll do that. It will be good for science.
It’s “only” 96 solder joins since I this would only be done for making the 3S2P packs, which I can then easily connect together with 10 AWG wires soldered between the cells at the front and back part of the battery pack.
