On Dec 19, 2005, at 3:13 PM, Shawn Wilton wrote:

> I've been googling for how to detect the difference between a 3(series)
> cell lithium pack and a 9(3x3) cell lithium pack.

> I was thinking maybe create a dummy load, with a sense resistor and
> determine how much current the pack would kick out, but that doesn't
> seem to give a different value across the packs.
>
At any useful level, this would probably cause the pack's over-current
prediction to kick in.  Most Li-ion cells will provide way more current
than the over-current protection is designed to allow (it's probably not
good for the cells, but it will happen!)

You should be able to figure it out by seeing how much the cell voltage
changes when a known amount of power is put into or out of the pack, 
since
the Li-ion cell discharge curve is relatively linear.  Pump 5W into a
"uncharged" 1000mAH pack and it should move 3x further up the charge
curve than pumping the same energy into the 3000mAH pack..  But I'm not
sure how long it would take to get meaningful numbers out, and one
might get confused by partially charged packs and such...

BillW
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