cycleops612
10 kW
Tats said:
a bit of a rant am afraid
for noobs, mainly am on about voltage droop in limn 18650S. They claim a voltage which is unreal. it sags rapidly and loses power. the rated 3.3v of lifepo4 is ~real. its ~constant til 97%~ discharged (if bms allows it, & some i see, do).
12 x 10 ah pouch cell =36v=360wh=3kg at 250gm ea
2500mah(and rapidly decreasing with age) (@4.2v=10wh) & 50gm ea, therefore, 360wh =36x50gm=1.8kg
So yeah it wins on weight, apart from needing more cells to achieve the same effect. For starters, the bottom 20% is just dead weight. Your 28ah would equal a 20ah lifepo4 in functionality in an ev app.
Last I checked, there were only a few 18650s over 3000 ma (when new), and only a few with C_rates above one, & they are `2350mah, not one and the same as 18650 supportets would have u believe i.e. that u can get 3000+mah AND hi c-rates.
The reality is folks, if u think a 10ah 18650 limn battery will yield 360 watts for an hour, u will be sadly and expensively disappointed. Half discharged, i would guess you would be getting well under 300w. Whats the point of a car whose power depends on how full the gas tank is? (admittedly, the c-rates disadvatage can be negated a bit by hi volts like 48v)
I doubt very much you need 28ah. You have solved the problem with a bigger gas tank. okaay?
Assuming the above numbers & say 36v. u have 28ax36v=1008wh, which at 10wh ea cell is 100 cells, each i think w/ 4 soldered connections.
Good luck finding the bad apple among them thats dragging the whole pack down. Just the labour cost makes it irreparable, or to the average joe who places the slightest value on his time. I imagine each cell in a faulty group of cellsmust be desoldered to test if faulty?
A 36v 30ah lifepo4 would consist of a mere 12 30ah pouch cells at 3.3v cells, each individually balanced & easily fault found. I seriously think a 20ah lifepo4 would suit you fine and last a lifetime, and would happily provide 1kw (1.5c) if needed, probably more for such a big battery in standard form, and 3c if the pak is designed for it (eg, ping batts).
A little bonus is that lifepo4S tend to understate their voltages. a 36v pak is really (12x3.3v=39.6v), ie, lighter and better than ratings suggest. lipo e.g pouch paks are exactly 37v and 10 cells. They have similar voltage droop to limn, but compensate with hi c-rates (more than needed for ebikes, which need the range of a more powerful battery anyhoo. 1.5c is usually fine for an ebike - steady use with bursts of acceleration).
Could someone please explain to me how a bms is supposed to do a proper job on balancing each cell, when i doubt many BMSs have much more than 16 monitoring ports?
I am pretty sure they cant and they dont. Its yet another 18650 lie. They manage groups of cells only, not individual cells.
I could be wrong. nobody knows what they dont know, but no one has sensibly refuted my oft stated views.
The paradigm we are being sold is, thats its ok to power a forklift with zillions of torch size batteries. It hasnt been best practice historically with previous tech, & it aint now either. Pouch cells are to new tech, what plate cells are to lead acid. i.e. A far better format for bigger apps.
I concede lifepo4 paks come in awkward regular shapes at times, but thats easily soluble.
Seems to me, watt hour for watt hour, the 18650 argument is, well yeah, its a crap, perishable, battery when u analyse the numbers right, but its 20% lighter. I know which i would choose - the proper battery i can simply forget and use for the life of the bike and beyond.
