[chbot] Battery Pack - the 27 chocolate fish challenge

[Mark Atherton]

Thanks Wes.

It turned out that the pack was not glued to the former, it was just 
the spot welded copper plates (not stainless) that held the pack together.

I ended up drawing a line down the middle of the pack, then running 
an abrasive, non-conductive Dremel cutting disk along the line.

3 cells will give me 11 volts, which is OK for the quadrocopter - 
weight is the issue why I don't want to short out the dead ones.

The battery spec states charging to 4.20V, so I set my PSU to 3 * 4.2 
= 12.60V (current limited to 500mA) then left the pack to charge.

I have been keeping a regular eye to make sure that each cell charges 
evenly, and they are all tracking very well so far at 3.80V each.

Of the remaining 7 cells, two are dead, and the remaining are 
all-over-the-place in terms of open circuit voltage, so I don't feel 
comfortable charging them in series at the moment. I may have to 
charge them individually, but I am more inclined to throw them out.

Regards,

Mark

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Is this link of any use?  It deals with the same 18650 Li-Ion cell.

http://www.wired.com/geekdad/2011/09/18650-things-to-do-with-an-old-laptop-battery/

=================

Hi All,

Last night Paul L was kind enough to give me a busted battery pack 
from an electric drill - www.idesignz.org/BP/battery_pack.jpg.

The pack contains 10 x 
<http://www.idesignz.org/BP/DM_IMR18650E.pdfLithium Ion cells.

Two cells are busted, hence the reason for the unit being thrown out, 
and of course they are in the middle.

The cells are capable of 20A discharge each, and two cells are in 
parallel. Short circuit current is likely in the order of 100A per 
cell given internal resistance of 35m ohms and 3.7V terminal voltage.

The connecting tabs are copper sheet that have been sport welded onto 
the end of the cells.

There is a black plastic saddle that the cells are attached (glued 
?), with about 0.5mm clearance between cells. Max working temp is 65C.

So the puzzle of the day is how to disassemble the pack safely.

My inclination is to start by cutting vertically with an abrasive 
non-metallic dremel disk - at least the neighbours will be isolated then.

Might then be tempted to soak in white spirit to dissolve the 
adhesive to the black saddle, but that may do nasty things to the 
green cell insulation.

If you short adjacent cells you **will* start a very nasty fire.

Any other thoughts ?

-Mark