[time-nuts] Li-ion Battreries
EWKehren at aol.com
EWKehren at aol.com
Sun Jan 22 10:44:17 EST 2017
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.
In a message dated 1/22/2017 10:00:45 A.M. Eastern Standard Time,
attila at kinali.ch writes:
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
(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
> stack 4 with a 4 cell controller and in two application also parallel
> 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
> 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
> be helpful for those that look for batteris and do not want to go
> 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
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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