[time-nuts] Li-ion Battreries

[Didier Juges]

Well worth mentioning that you have found a reputable vendor. I may give
them a try.

A while back, I bought a dozen 18650 inexpensive(<$5 each) cells from 3
vendors picked at semi-random on eBay (4 from each) for evaluation and I
tested each one of them with a data logger.
The best one had about half the advertised capacity, the others went down
from there. Important to observe that none of the set I bought were even
remotely matched, a crucial consideration if you are going to put them in
series (a balancer will only ensure your pack is no better than the worst
cell in the pack).
Many of the 18650 cells you find on eBay (and maybe other places) are
actually coming from old laptop battery packs that normally should have
been discarded/recycled.

In my anticipated application, I only needed one cell (to be followed by a
small boost converter), so the issue of balance and matched set was not
important, but simply I needed the capacity and none were remotely
satisfactory. I ended up using cell phone booster packs, since I needed 5V
anyway.


On Sun, Jan 22, 2017 at 9:44 AM, Bert Kehren via time-nuts <
time-nuts at febo.com> wrote:

> I use 4 cell balancing and protection circuits, cost a couple of $ more but
>  well worth it, I use holders because of  limited availability of cells
> with  straps, but rest assured they are held down (discarded PCB)'s,
> I on purpose did not get into technical details I was only trying to share
> reliable sources, based on disappointing past experiences.
> Bert Kehren
>
>
> In a message dated 1/22/2017 10:00:45 A.M. Eastern Standard Time,
> attila at kinali.ch writes:
>
> Hoi  Bert,
>
> On Sat, 21 Jan 2017 08:08:22 -0500
> Bert Kehren via time-nuts  <time-nuts at febo.com> wrote:
>
> > purchased  _2x   Samsung 35E 3500mAh 10A 18650 High Drain Rechargeable
> Battery
> >  INR18650-35E_
> >
> (http://www.ebay.com/itm/112173495496?_trksid=p2060353.
> m2749.l2649&ssPageName=STRK:MEBIDX:IT)   for two reason 10 A load  and
> good price. These
> > cells have no  protection, which I want, since I will for  our
> applications
> > stack 4 with a 4  cell controller and in two application also  parallel
> cells
> > for a total of  8.  I have now completed my  tests  and concentrate my
> > battery work on using these   cells.
> > After having tested 26650 cells with disappointing   results my focus is
> on
> > 18650. I am sure there will be 26650 cells  available, but  right now our
> > focus is on 18650.
> > I have  no connection in any way with these two sources,  but think it
> may
> > be helpful for those that look for batteris and do not want to   go
> through
> > the process I went through.
>
>
> Some  small remarks: 18650 is by far the most common form factor
> of Li-Ion  batteries on the market. This is IMHO the better choice
> than the 26650 if  you want to be able to replace them in 10-20 years.
>
> If you stack Li-*  batteries, you will need to have a controller that
> monitors each cell  individually while charging or has some other means
> of ensuring that none  of the cells are overcharged (or rather that they
> are charged the same  amount). This kind of circuit is called balancer.
> A protection circuit does  _not_ replace a balancer. The protection circuit
> is only to protect against  catastrophic failure. Ie it is still possible
> to overcharge a battery even  if it has a protection circuit. You also do
> not know what the protection  circuit does to protect the cell. There are
> a lot of chips out there, that  simply open a switch and thus disconnect
> the cell. In this case, the  protection circuit of one cell will disconnect
> the whole stack and break  charging.
>
> A lot of the multi-cell Li-Ion charger chips have integrated  cell
> protection
> circuitry. Ie if you use one of them, you will not need an  additional
> protection circuit. But be aware, the regulation for battery  protection
> circuit states that the circuit has to be wired fix onto the  battery
> in a way that this connection cannot be broken (without breaking  the
> housing of the battery pack). The reason for this is, i think,  pretty
> obvious. I would recommend that you solder each cell  indidividually
> into your circuit instead of using some kind of holder. Or  if you are
> using a holder, make it such that there is no chance any of the  cells
> can be accidentally short circuited.
>
> Attila Kinali
> --
> Malek's Law:
> Any simple idea will be worded in the most complicated  way.
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