The battery builders club

What wiring diagram did you use ?

It might be 42v just sitting there, my concern would be how that pack deals with vibrations. And my guess would be probably not well.

Sharp edges of nickel sticking out from the pack are pretty concerning too.

The reason we use nickel is so we can weld it to the packs. If soldering, copper should have been used. Without roughing up first, solder doesn’t hold very well to nickel at all.

Edit: i’m not trying to be an arsehole here but even if this pack isn’t the worst we have seen, it’s far from suitable for it’s use case and needs work before it is safe

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So, I’ve been test riding my (mostly finished) ebike for a week or two now, and I am disappointed to say that my battery pack is by far the limiting factor :confused: I tried to save some money by going with cheaper, lower discharge cells (Nkon had NCR18650PFs for $2.00) since it was such a large pack (20s7p), but the voltage sag is unacceptable at the power levels I’m trying to achieve. I am now in the unenviable position of wanting a new pile of cells, and I figure this would be the thread to ask in, to see what the market looks like now that Nkon doesn’t ship to the US anymore.

Side note - Anyone interested in a ~1.4KWh 72v battery pack? I’ve got one, low cycles, probably good for 50-60A (Just not 120, like I wanted). It’s actually two packs - one 8s, one 12s, with a series link. I’ll find some pics later if anyone is interested. Full disclosure, it was soldered, not welded, but my technique is excellent, and very fast - low heat input.

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Check out this thread dude, a lot of discussion on US based battery suppliers.

Sorry to hear it didn’t work out!

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bummer about the pack. same thing happened to me in my first esk8 pack. The pack ended up getting paired with some hub motors and worked fine.

IMR has sales every now and again. very fast shipping, check out what’s on sale now. sure you can find them a little cheaper, but after all the time and effort of making a pack the difference seems negligible

30T’s 40t’s and 25s’s all on sale right now.

https://www.imrbatteries.com/sale/

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This approach might be worth a look

It’s not that clear from his posts, but he’s using a high capacity low discharge pack in parallel with a low capacity high discharge pack.

The high discharge pack deals with peak demand, and the high capacity pack charges the high discharge pack when demand lifts.

To be somewhat safe, would need to choose the lipos very carefully and understand what the limits are.

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8s6p flat six block layout, no folded nickel.

In my experience though folding nickel between p groups is more likely to cause broken welds than broken nickel, but it also depends greatly on the direction of the folds. If the board nose is north, east-west folds with the bend hump deck side are the least likely to have issues if any at all. north-south bends and north-south nickel group jumpers are the biggest problems.

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I have a pack that’s divided into two sides of about 80mm (max) in width, so a total width of about 160mm. I want to put shrink wrap (lay flat) around each side individually. The pack has a height of about 18mm.

What size flat heat shrink wrap do I use?

Thought about using this but don’t know what size.

You want about 10% to 50% extra material…(160mm + 20mm) * 1.1 = ~200mm

Ah thanks! I meant both sides individually so calculated it myself, (80 + 20) * 1.1 (and 1.5) = 110-150 mm so I will try to find a size somewhere near those numbers.

First Battery Build - 12S 7P Samsung 30Q - Cells ordered from Liion Wholsale and delivered in 2 days.
I assembled the p-groups with neutral cure silicone and welded the nickel strips with a K-Weld. I used a mix of either 3 12 AWG wires or 2 10 AWG wires on the series connections because I didn’t have enough of either wire to do them all the same, but I doubt the electrons will care. I didn’t get a photo of the balance leads before I secured everything down but I made sure to run them individually and not cross any wires. I am using the LLT smart BMS for charge only and a charger port capable of handling 45A although I have it installed on a 6 amp charger. Shrink wrap will be here Friday, but I still need to peel back some of the Gorilla Tape to install the battery temperature sensors. I learned 90% of what I know about battery building here and on the old forum. Thanks to everyone here for sharing the knowledge

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@ZachTetra This is the diameter, right?

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For wrapping a 80mmx20mm section, 120mm give or take. For 160mmx20mm section, 215mm give or take

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hey, looks awesome!

wait…gorila tape…?
:joy:

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I would keep the pack and convert it to a charge and ride backpack setup.

Built yourself a new pack with quality 21700s. If you can wait for a sale even better

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Nice one! I wrapped my first pack in tape too… i’ll never do that again :joy: would rather buy new cells than try and unwrap it :joy:

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Thanks for the advice. Unfortunately unless I significantly change either the pack layout or the enclosure, I’m limited to cells 65mm long - They’re assembled laterally, so any increase in cell length will result in a pack that doesn’t fit, unless I do a complete redesign.

Friendly reminder to buyers of batteries: seeing readouts of mains voltages, individual p-group voltages, a few of the packs spot-welds, and even a short video of Dremeling a small portion of the nickel for purity can save you a whole lot of pain.

I found out a certain reputable battery builder was using some steel infused nickel for some amount of time… hopefully it never ends up mattering 🤷

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Ordered kapton tape and it was terrible, wouldn’t stick to anything, not sure if the stuff I ordered was typical of kapton tape or just cheap junk. . I started using the gorilla tape to keep the balance wires neat and in place and the next thing I knew the whole front of the pack was covered. I learned a TON while building this pack and there are definitely a few things I will do differently on my next one, but I feel confident that this will be safe and reliable. I can say for sure I hugely underestimated the amount of labor that goes into building a battery of this size, when I was first looking at what quality battery builders charge for a pack the pricing seemed high to me. Now after making one for myself it seems like a bargain. I totally enjoyed the process though and look forward to the next one, I have a huge roll of guerilla tape!

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