Mr. Sharkey via EV wrote:
Beware! Copper water pipe is not pure copper, but is composed of alloy,
you won't be getting the conductivity of 99% copper. Also, crushing and
drilling pipe is time consuming and messy, the drilled holes can't be
properly deburred, and the possibility of corrosion/tarnish in the
sandwiched interior surfaces is real.
Good points. Also, copper work-hardens easily, which makes it stiffer
but a worse conductor. Coppper water pipe is hardened. As I recall,
rigid copper water pipe is about 30% less conductive than soft copper
sheet or wire with the same cross-section.
The only purpose for the stock Leaf busbars was to tie the middle
terminals of the paralleled modules together.
Why would you bother doing that?
These are used modules with a somewhat variable capacity remaining. I
was able to test that capacity and pair weaker modules with stronger
ones, creating a more robust pack assembly. Also, paralleling at the
cell level means half as many BMS channels. You see this as a bug, I see
it as a feature.
I think this is exactly why it is done. Saves money on the BMS, and lets
the manufacturer use mismatched cells to produce a matched pair.
Maybe tying the center terminals together with a fuse is a more cautious
approach. Using thin-ish wire would be a similar current-limiting
technique.
This has been done. It does reduce the risk of a meltdown or fire in
case one of the paralleled cells fails shorted. But the BMS needs to
*know* that it has happened, to prevent overloaded the remaining cell
and causing further damage.
Lee Hart
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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