Hello everyone, I have ordered 120 Molicel p42a 21700 cells for my battery build. I have not decided yet wether to go with 12s10p or the 14s8p. I plan to not use a BMS and instead balance charge with a hobby charger and use cell monitors to alarm me when the pack voltage has dropped too low. Some advice would be greatly appreciated!
Both work, with 14S you can reach a higher maximum speed. If you split it up in two packs, 6S might be easier to build, as you have both terminals (plus and minus) on the same side (top). With 7S you have to route one terminal up inside the pack, if you want both to exit on top. Good choice of cells.
I do plan to split the pack in two and then wire them in series in the board. Would the 12s10p give me more ride time?
Which hobby charger?
I’ve always run at 12S but am starting to think I’d rather move to 14S. Fliteboards new Nano battery is a 14S4P with the molicell P42A giving 16.8Ah and 45 min ride time.
If you configure your cells like that then you can always run half the battery when you want a lighter setup.
Yes, as there would be 8 cells more, the capacity would be bigger which should give you more riding time.
14s8p for sure if you can charge it easily.
Probably don’t need cell monitors if you have a vesc.
Just have the vesc start to cut power at ~46V (3.3V a cell) and shut down completely at 42V (3V a cell)
I hardly balance charge my 14s10p pack with the the same cells. They stay surprisingly really well balanced.
I am going to use the Icharger x8.
How much ride time does the 14s10p give you?
Here was the last long run I did. Pretty much non-stop 15-18mph with a little while over 20mph. Was fairly close to dead battery when I got back. So a little over an hour. Varies wildly depending on the foil I’m using and the speed I’m going.
I wish I could get watt-hour consumption, but the ilogger I had doesn’t support that 
If I am cruising around a lake trying to catch boat wakes I still have plenty of battery left after an hour, but I’m moving slower.
Hi
I was wondering the pros and cons of the different stacking methods eg shorter bridging tabs vs bigger air gap between cells ?
I have batteries in both configurations and can honestly say I have never noticed a difference in temp. Their may be a minimal one, but I haven’t noticed it.
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What thickness and width nickel tabs are recommended for this kind of setup?
Gareth
“Noticed” means that you have a sensor for temp measurement or is it you “feeling”
If we looking at 8P (for a 21700 cell size), then to play on the safe side I would use nickel that’s capable of carrying a total of around 200A. so each strip should be able to carry around 25A. I’m not sure who guys are buying their 21700 nickel strip from though so not too sure of the exact sizes.
The eskate community has some really decent nickel strip but it is slightly more expensive.
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Used these 0.2mm strips from ali: US $7.78 13％ Off | High purity 21700 Pure Nickel Strip 2P 0.15/0.2*27.5mm for battery spot welding ,21700 Li battery nickel tape spot welder
https://a.aliexpress.com/_mOmlGHY
Built 2 6S8P packs with Molicel P42A. No problems up to 100A battery current.
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I took this 0.15mm nickel strips and doubled it before welding on the batterie to a 0.3mm strip.
Welding this 0.3mm to the batterie needs some higher energy (105J), which was no problem for the kWelder
I made some testing before to find the optimum.
I am using .2mm x 30mm wide nickel. If you’re in the US I can recommend these guys.[https://higherwire.com/products/pure-nickel-strip-0-2mm-thick-x-30mm-for-spot-welding-5-or-10-cut-to-length10-feet])
I also am using the Malectrics spot welder and it works very well.
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Do you use a relay as a safety switch? Either for anti spark or with a magnetic kill switch.