[time-nuts] Li-ion Battreries
attila at kinali.ch
Sun Jan 22 07:25:56 EST 2017
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
> (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.
Any simple idea will be worded in the most complicated way.
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