bvgandhi via EV wrote:
Hi,
I have lately come across a lot of work done on reconfigurable battery packs
which uses the concept of scheduling of battery cells. Instead of oversizing
the battery pack with too many cells and adding additional failure modes,
reconfiguration works on the idea of using switches and scheduling cells as
per power requirement of the vehicle. Does anyone here have any opinion or
ideas about this this or has seen previous practical implementations ?
In general, if you have the cells, then *use* the cells. Otherwise, they
are just dead weight.
All types of batteries have internal resistance. This means they are
more efficient at lower currents (more amphours, less voltage drop).
Discharging them at higher currents increases the I^2R losses (i.e. less
range, more voltage drop). So it is better to always draw power from all
the cells, rather than first from some of the cells, then from different
cells, etc.
However, cells have different capacities. If you always draw the same
power from every cell, then some will go dead sooner than others. So it
makes sense to have some method to distribute the load between the cells
according to their ability.
Many old EVs had reconfigurable battery packs. Their controllers were
basically a set of switches that reconnected the pack in various
series/parallel combinations to adjust the voltage and thus speed.
During the times when cells are in parallel, they are forced to the same
voltage, which automatically balances the state of charge between them.
The ones at a lower state of charge naturally supplied less current. See
the Henney Kilowatt controller at
<http://sunrise-ev.com/controllers.htm> for an example.
--
Obsolete (Ob-so-LETE). Adjective. 1. Something that is simple,
reliable, straightforward, readily available, easy to use, and
affordable. 2. Not what the salesman wants you to buy.
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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