On 6/14/2013 9:57 PM, Al wrote:
That doesn't sound right.
Wouldn't the cell with the higer resistance lose some of the Ah as heat?
It doesn't lose amphours directly. Look at it this way. Suppose you have
two identical cells; same amphour capacity, same internal resistance,
everything. They are identical twins.
Now put a resistor in series with one of the cells. Charge and discharge
the cells in series. The resistor affects the voltage; it lowers the
pack voltage during discharge, and raises it during charging. But it
does not affect the amphours going in/out of each cell. Put 10 amphours
into the string, and each cell gets exactly 10 amphours.
However, suppose that resistor is put *inside* one of the cells. The
heat produced by that extra resistor during charging and discharging
causes that cell to run hotter. The extra heat increases its
self-discharge rate, and changes its coulombmetric efficiency (the ratio
of how many electrons get stored compared to how many you ran through it).
For example, suppose it stores 99 out of 100 electrons at 70 deg.F, and
98 out of 100 electrons at 80 deg.F. Then the hotter cell stores 1% less
charge than the cooler cell on each charge cycle.
--
Failure is only the opportunity to begin again more intelligently.
-- Henry Ford
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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