charging multi li ion cells

[alpg88]

i'd like to install li ion cells in my current project.
i have a dozen of 18650 salvaged from laptop batteries, they seem to be working fine (for some reason half of cells in the original pack were dead, but other half like new, 3.7-4,2 charged, tested in my l900, and seem to be working fine)
so my plan is to have 2 or 3 cells in series, connected to a pcb, and to have 3-4 pairs or trios with separate pcb for each group.
that means i'll have 3-4 protected packs in parallel,
does presence of pcb means i don't need balance charger and can get away with constant current charger??? or not?
and how do i charge them?? connect all pack in series for charging, but run in parallel? or charge and run in parallel, cuz i can't run all cells\packs in series, too many volts, i wouldn't want another voltage regulator, extra part, extra heat, unless it is necessary
thanks.

 

[VidPro]

Re: charging multi li ion packs

packs protection can keep the batteries from being ruined quickly and permentally, but the protection is just that. Protection is supposed to be the last ditch effort to stop the worst things from happening to the cell items.
The charge itself still shouldnt go over 4.2 for each cell item, still, and it is helpfull if there is a discharge cutoff that sits a bit higher than the protection end.

then current charging, is supposed to be ok, IF you stop at 80% charged. (like who is gonna do that
WHY
because you can charge the first 80% at a constant rate then when most of the chemicals are converted over , the charger needs to slow down, that is the "purpose" of the shift to CV charging after the ~80% is reached. So purpose of either of the cute chosen alogrythms is just so the rate changes as the chemicals inside do.

Protection keeps the cells in the pack within the range of survivability, but "balancing" sets the cells all up to be fully charged at the end of the charge. without balancing, the state of charge of each cell item get OFF over time. Especially with older cell items pulled out of other devices.

so
if you want a good plan, make a mondo protected pack or 2 packs to stay within a lesser cell item limit. protection can be purchaced for huge voltage type packs with multiple series cell items galore, also can be high amperage possible protection.

match the cell items for capacity, and before assembly check for self-discharge , and not reaching full charge.

if your using old cells or even if your not, have the whole contraption be able to be dissasembled, it wont be too long before your going to have to work on it or check it out, so no use in making it impossibly locked down.

Parellel cells at will, prior to series the cells, that way (with voltage max alogrythms) the parelllel cell items will act like one big fat cell . Untill any ones of them are self-discharging, not charging fully, or anode disconnect to open.

connect the pack protection (obviously)

stuff balance connections on the pack (or off the protection). so the max voltage applied on each parellel set doesnt go over , and so the charge of each item can be set to fully charge, AND you can monitor the voltage of each parellel set. Balance connection wires now can be bought for neer nothing, they are finnaly easily available for making your own balanced pack.

if i was trying to get off really Cheap, in charging a mega series pack of over 8 cells in series, i would apply 2 balance chargers, but the chargers NOT connected to the same battery or ac source, so they would maintain isolation, otherwise the charger will have to be capable of balancing such a number of cells in series. I suppose that is redundant as a 8X li-ion should be sufficient for your crasy mods and they have reasonably priced 8X balance chargers now.

the reason the cells in a laptop pack can be dead, even though there are usable cell items inside, is because the cells probably safety disconnected , they were either bad or the balancing or protection sucked. Generally though i find that the "good" cells left from the bad pack, are short lived, and will over TIME have more problems then they are worth. BUT they can be great for learning, and setting up your own stuff without destroying good usable cells that will live long times.

oops correction added already

 

[alpg88]

Re: charging multi li ion packs

wow, thanks vidpro:twothumbs.
i didn't think it would be that comlicated, i think you convinced me to use nimh pack instead.

 

[VidPro]

Re: charging multi li ion packs

wow, thanks vidpro:twothumbs.
i didn't think it would be that comlicated, i think you convinced me to use nimh pack instead.

it not, it just sounds that way. 1/3rd as many cell items, and a wire between each cell item (or parellel set).
i dont want to discourage you, it is as fun as your awesome multi led mods. lightweight, and powerfull.
especially with the issues of parelleling ni-mhy or ni-cd and the v-drop charging.
Thanks to the LSD ni-mhy in large sizes like C&Ds though, that is a great option too.

 

[alpg88]

have a question again.
just got 32650 protected cells, from kd, ordered charger too, but they sent me wrong one, so i can't charge them now.
i'll exchange the charger, but anyway it only charges single cell.
so i was looking at battery space site, and saw some li ion pack chargers, i'd really like to charge all sells at once, don't really wanna wait 2 days to charge all cells one by one.
the cells are protected, so in my understanding if i charge them in series and one cell in the middle charges, its protection will kick in, and brake the circuit, thus not letting charge the rest of the cells.
in parallel, i get different story, if i send 4x the current (batts are 5mh, charge rate .2-.5c), so let say i charge each at 2 amps, i send 8 amps to 4 cells in parallel, they wont get exactly 2a each, and if one cells charges-shuts off, than i'll have 2 or 3 cells eat all 8 amps, that doesn't sound imo.
so is there a way to charge 4 protected cells, at once.
or buying 4 separate single cell chargers is my only option???

 

[SilverFox]

Hello Alpg88,

When charging Li-Ion cells in parallel, all the cells charge to the same voltage and maintain the same voltage during the charge, as long as the resistance in the hook up wiring is kept to a minimum. If you are charging in parallel and a protection circuit gets triped, get yourself a new charger. This indicates that the charger is exceeding 4.2 volts during the charge.

When charging Li-Ion cells in series, it is much better to incorporate a balancing circuit that keeps the cells in balance during the charge process.

Tom