[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.
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 
>  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 
> 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.

Attila Kinali
Malek's Law:
Any simple idea will be worded in the most complicated  way.
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