I recently came across prismatic li-ion cells. I bought 150 of them for 1Eur/piece (untested, as the recycle company selling them’s core business were 18650’s).
My plan is to select the 78 best cells and place them in a 13x6 configuration.
I dont have to much information about the cells but they are rated at 3.7v 10A max 3c.
I have a question about testing:
-I try to charge them to 4.2V (most of the time I can only charge them to 4.05v)
Then I connect the battery to a user at 10A.
I set an alarm when below 2.6V, then I write down the amount of Wh.
My question: Discharging at 10A seems to me realistic (avarage 60A usage on my foil), but the amount of wh seems low(best so far 25wh per cell). But when I discharge at only 1A, the voltage takes a lot longer before it drops to below 2.6V, so delivering more Wh.
Another question:
Normally I run my ESC at 12s lipo (max 12x4.2=50.4V).
I now have a 60A13S li-ion BMS. With my prismatic cells(typically 4.05V max) I will generate 13x4.05=52.65V. Would this be a problem for my BMS?
I am very open for suggestions and (honest;)) opinions.
The effect, that (rechargeable) batteries provide less energy if discharged by a higher current (and vice versa), is common to all batteries because the velocity (density) of the chemical processes influences the physical build up of the electrode surface.
You have to find out the optimum range for the practical use of the batteries.
Most 12s esc can run up de 57-60v so 13s at 4,05v will not be problem and if the bms is for 13s it will be ok for discharge but for charging i think you need one that you can set to stop at 4,05v
As far as capacity , yes the higher the discharge rate is , the lower the capacity will be got the L-ion , not the same for lipo, they give almost full capacity if they don’t heat to much
I don’t know very well pismatic cell , but for the 18650 : you will get about 1/2 of the total capacity when discharging at max C rating
If you know you want 60a , test at 2-5-10A discharge , see where the capacity drop to much and built the battery with the number of cell needed to minimize capacity lost
Thanks Alexandre!
the cells weigh about 300grams, so at 13x6 (60A nominal discharge) It will weigh 23kgs… I have a big board, but I dont want it heavier. I will select all the cells with 25wh and above, which will give me minimal 1950wh. This should should be enough for 1 hour foiling.
Thanks, ill keep u updated!
So You are loosing about 1/3 of capacity at 10a ?
That is not bad , it gives you 45min of playing for 23kg … Heavy but safe … 14kg with 18650… For the next one
I have tested a couple now, I discharge from 4.1->2.6V @ 10A
Some cells are bad, and only give 7wh, but some also give me 27wh. I dont know the inititial capacity, so why 1/3?
I dont mind the extra 10kg, I dont go to mcdonald so often
This is especially very cheap. the cells are only 1eur/piece. 18650 is much more expensive.
The swell should not be a good sign indeed. Although I dont see a difference in performance of the swollen ones, they perform pretty good. However, I measured the bad cells, they tend to be around 350Grams instead of ±305 grams. Im starting to believe this could be an indication of bad cells… but why?
