Yeah that seems like the most economical way to do it safely. I was looking at the NESE system, and one of the promoted benefits is the ability to remove cells easily, so I wanted to see how that would actually be useful.
It makes the process faster and less annoying because you don’t have to redo all your spot welds. But you still have to shuffle the cells and make sure each p-group has the same number of new and old cells.
The other potential drawback is the increased size and decreased density of the pack, due to the NESE modules taking up space.
At the end of the process you’ll have a handful of old cells left over, and you can get yourself a power bank like this to stick them into!
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Yeah, but I was going to do a top mounted brick anyways so space is less of an issue, but it’s made it quite difficult to find prebuilts or used batteries, since they all tend to be flat packs.
Battery is definitely the most difficult part of my build so far. I originally wanted to go with LiPo packs because they’re affordable and familiar, but then I realized my charger (50W max) would take 48 hours to fully charge all four of them, and buying a quad charger is half the price of the batteries. Then I looked at some pack builders, but that’s way out of budget. Now I’m looking at the NESE system, which seems ok, but is neither particularly cheap nor simple. I could print all the stuff and do the soldering, but I don’t get the bulk discounts on cells and still need the NESE hardware with overseas shipping, which really eats into the budget.
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I feel ya. NKON was the best deal running for cells in the US while they were still shipping here. I’m just glad I got my ebike pack cells ordered before they stopped, that would have ben a lot of extra $$$. (150 cells)
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The manufacturers say a cell has reached the end of its life when, typically, it’s lost 20% - 40% of its capacity (depending on the cell). But that depends on how hard it’s been run, how it’s stored, and how it’s charged. And a cell doesn’t suddenly become unusable after losing 20% of its capacity. It might be frustrating to use but it’s not useless.
You might get 50 cycles or you might get 1,000 cycles. The “grade” of the cell and its manufacture date (how long it was stored before you bought it) can have an effect on its cycle life too but we typically won’t know the date and storage conditions.
It’s why we stress not mixing cells and matching cells where you can. It just makes things so much easier since there are so many unknowns.
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Cost reduction
You don’t need expensive high-side MOSFET drivers or expensive P-channel MOSFETs to switch lowside.
The half-decent BMS will switch highside.
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ALSO
DON’T WASTE YOUR TIME WITH “REFURBISHED” CELLS THEY ARE NOT WORTH THE TROUBLE
JUST PAY THE EXTRA TO GET FACTORY NEW.
HOLY SHIT FUCK REFURBISHED CELLS.
GIVES ME BAD MEMORIES OF THIS ONE CHEAPASS SOCIOPATH WHO WOULD GET REFURBISHED EVERYTHING AND FUCKING BACKSTABBED ME.
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A BMS is around $30 and a charger not much more.
Forget about the “hobby chargers” or “lipo chargers” just use a regular brick style charger with a BMS.
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My buddy who got really into eMTB after I showed him my build, ended up using laptop cells and a lot of parts from that sketchy esk8 site which I cant remember. It was a 10S12P 24Ah pack with each cell tested on a zanflare. The voltage sag is not bad until the battery is below 36v, granted the motors are running on a “55amp” esc.
As sketchy as that board is, that thing has held up pretty well, crushing small hills and even keeping up with 50 Mile journeys no charging. The cells were free, and the cost of buying real cells was a deal breaker for getting into it at the time.
Im just here to say that even with the fun voltage sag on 12P, that thing pushes itself pretty dang good despite the highly suspicious components. Don’t worry though, I finally got him in on a local group buy for p42a, and he’s going to be gutting it for some nice ~ESC’s based on vesc~ this winter. That is of course if it doesn’t ignite in the meantime!
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Oh yeah, I forgot to add, those cells were mixed like crazy, some from 2013, all the way up to 2018… The resistance was all over the place and the capacity was within a 10% margin.
The pack averaged 2000mAh per cell at 500mAh discharge, although their rated capacity was around 2200mAh
To be honest we didn’t think it would work and just wanted to see if it would save him the $300 battery. I think he’s racked up around 700+miles on that thing. It still amazes me.
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Would a BMS designed for Li-Ion batteries work with LiPo packs? I thought their nominal voltages were slightly different, although I’m not positive on the final voltage. If the balance leads are plug and play, I might just go that route then with a Daly or something.
The reason why this worked
Is because of this. If you test the internal resistance of each cell, then more doors are opened. But there is a very specific way this has to be built. You need to match the Ir per P-pack as close as possible.
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Yes. The chemistry is essentially the same (different cathode material for more energy density in li-ion and other tweaks), and the most important voltage (charge cutoff) is the same at 4.2v.
This is not the case with LFP or LTO cells, those are very different.
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OK DULY NOTED.
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Not a wheel issue, but split angle deck level issue with drop through trucks on a hummie…
Hope this helps somehow…?
I have a work in progress build, testing Sunmate 155s on BN270 on hummie drop through.
Rear Randall 35degree doesn’t work, because it ends up 10mm lower than front of deck (Which has a 50deg Randall) and when you lean hard the deck might hit the rear hanger (thiiick deck 
)
Planing to route top of the rear deck a little bit (maybe…) to give clearance for the hanger and even out deck heights with a small packer below front truck mounting (to lower front end maybe 5mm). Deck might be level that way also.
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Is there a way to take advantage of burst current max of a battery pack without running the risk of running continuously above the cont rating?
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Not that I know of.
Honestly if you’re running that close to your maximum already, it might be time to look into upgrading your pack, either in size, or with higher rated cells.
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These wackadoodle batteryhookup lifepo4 cells are rated at 3C cont and 10C for 10S bursts. Pretty huge difference. wondering if there’s any way to take advantage of it.
I guess it probably mostly depends on how usable it is (how much sag it produces) and how much heat is produced. There’s probably a happy medium a few A higher than 18.
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That is it exactly.
Any cell can be burst rated at almost any value. It all depends on the safety margins you set, voltage sag limit, temp limit, and cycle life you want. Any rating not from the manufacturer should be looked into thoroughly before using it. Depending on my requirements I could set a burst rating of 25A or 125A for a Molicel P42A .
The length of the burst and its duty cycle has a HUGE effect on what the rating would be. I could do 125A bursts for 1 sec every 60 seconds but could not do 10 sec bursts every 20 seconds and expect the cell to survive.
Just stating that a LiFePO4 cell has a 10S burst rating of 10C doesn’t help us. How often can we do that? Can I burst for 10 sec every 20 sec? What is its impact on cycle life? Why wasn’t it 9C or 11C?
I am completely ignoring performance here. Any burst rating essentially does that as the voltage sag will be huge.
Without knowing the burst length and duty cycle for the rating along with the other criteria for setting the burst rating (voltage sag, temperature, cycle life, etc.) the burst rating is useless. It’s set by the marketing team or it’s a just a capability of the cell (not a true rating) without regard for its long term effect on the cell.
Just my personal opinion…
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Haha feeling inspired are we? I think with a 4P at the bare minimum I’ll be alright for urethane cruiser builds since my average riding battery amps is around 35-45A combined and small bursts of current to accelerate up to riding speeds should fall within the 10C/10sec. Although let me get a couple cycles on this pack before I call it, havent seen anyone else making a pack out of them so it may not be as good as it sounds on paper.
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