The original pack has done well in excess of 100 cycles and it still runs great. It should continue to work great for another 300-400 cycles. The pack increases in temperature by only 10 degrees C after a 1 hour foiling session.
I have just built a new pack, for a new tow boogie, with more capacity at 13s8p. Towing into unbroken swell on the prone board and 999 foil with the tow boogie is by definitely my favourite form of foiling. The runtime with 13s6p is around 1 hr 15, and another 20-30 mins will be useful with this bigger pack.
After researching test results of cells, I decided on the Samsung 40T3, as it has a slight edge in capacity over the p42a after a few hundred cycles, with a longer cycle life The 40t3 has twice the cycle count of the older 40t. Around 600 cycles to 80% capacity. After 1000 cycles, around 77% capacity. Vast improvements over the cycle count of 18650 high discharge cells like the samsung 30q. 21700 is definitely the way to go for efoil/tow boogie.
I slimmed down the weight of the enclosure to try and regain some of the weight. Finished weight was 7.7kg for 13s8p in the polycarb case. The original 13s6p pack was 5.2kg. This new case itself weights 900g, by using 3mm polycarbonate throughout, which is about 400g lighter than my first case. I use 3mm triangle section strips liberally to stiffen the jointing surfaces, on both sides of all the top edges so it sitcks well to the lid with ISR 70-03.
I also saved a bit of weight and space with a smaller Heltech 40A / 20A BMS without bluetooth, charge only. I’m using a 12A charger to fill it up quickly. I plan to mount a small voltmeter on the pelican case, connected via the bms charge plug, so that if the bms trips during use then I’ll notice the voltmeter turns off.
I also optimized the size by using a much smaller Midi 150A fuse. This 13s8p pack still fits in the same pelican 1450.
I have built a bunch of other packs for various purposes using narrow strips of nickel, and it was so much cleaner and less fiddly to use the wide 30mm nickel strip again on this build. It goes together faster and safer, and handles lots of current. I’m using up to 90A to get onto the foil during waterstarts, which is 15A per cell on the original pack. 8mm 0.15mm nickel strip would waste about 30W as heat under this amount of load (1% wasted power, which isn’t actually too bad). This 30mm 0.2mm nickel has an effective width of approx 20mm per cell, so will have less than a third of the resistive heating compared to 8mm 0.15mm strips, so less than 10W of wasted heat at 90A in the original pack, and even less in this new 8p pack. Next time I might go thinner and use 30mm 0.15mm nickel.
