Ianhill said:
I see alot of auctions in the UK on used laptop cells they seem to be getting around per 50units in unknown state and they are non returnable, I like the warnings its like tom hanks in turner and hooch this is not your room
I think these ebay listings for such price is not that great! All you might get ''extra'' is the work to tear apart the casing and have tabs and probably balance wires already on the cells.
Other than that, at least for EU, folks, there is a site https://eu.nkon.nl
There you can get cells for close to 2 eur a piece (new and also possibly with higher discharge!) The only ''con'' might be the fact that there's still a shipping cost and that tabbing each cell (by their company) costs extra 0.4 eur, so okay, 3 eur a piece or so, depending on pack size for already tabbed, new, known cells.
These are 2 examples:
https://eu.nkon.nl/rechargeable/18650-size/gp-imr18650-ch.html (+10 piecies for €2.18,
+50 piecies for €2.05) - Though, brand is unknown to me and im not that ready to search up any tests
https://eu.nkon.nl/rechargeable/18650-size/samsung-icr18650-26f.html (+10 piecies for €2.65,
+50 piecies for €2.55) - about the same specs but Samsung cell.
With shipping included for these samsung, I got a figure of 3.19 eur a piece (with tabs already spot-welded)=50 cells,
if it goes without a tabs (like for a sleds), then the final price is 2.79 eur a piece (when buying 50)
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So yeah, paying close to 2 eur is a bit risky.. I think, especially considering someone has used these cells for a while..+ all the extra work tearing them apart, especially, if you plan to use sleds anyways)
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@ElectricGod
Woah lots of great info to process and to reply to, I will try to do this shortly now, as Im not having enough time now to craft each of the reply to each of the segment
I've also thought / got the idea that it is somewhat stupid laptop battery manufacturers have not decided to use 3500mah cells instead of 2600mah ones.
As for the calibration, I think some laptops have built in this function in the bios or even on the OS level, to calibrate the battery pack.. you just have to fully charge it and then completely deplete it..
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The charging / discharging part of used laptop batteries
@ElectricGod So in which part do you actually measure the capacity the pack can output?
Somehow in my mind it seems ideal, if it were possible to determine each cell's capacity in the early run,. Though, from what you said, it now looks like a better option (more practical) is just to make the pack with the ''strong'' cells and then you measure the capacity of the whole pack the way it is, when you have ''rejected'' the weak cells.
It seems, that with ''fiddling with'' and replacing parallel pack batteries, till they reach optimium charge for all groups, also sorts them out and makes the pack of consistent cells in each group. After that it is possible to measure the capacity of the whole pack (when charging it), althrough you still dont know the capacity of each of the group's pack, so I assume they just need to balance each other out.
So okay, I think I actually answered to my own question. That the capacity can be tested at the end and not at the beginning of the ''trials''.
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About the temp sensor thing. Yes, the arduino way + thermal probe is probably the most sophisticated way. This way you can select different temp range and decide what action is done at each ''step''.
Op-amps might also work though I would personally go with arduino as for it might be bit easier than to build an ''old-school'' circuit out of simple components.