It is _very_ important that the inter-cell (or inter-battery) straps are
able to flex.
The flex is required because the cells/batteries will move or shift over
time, particularly in a moving vehicle. The straps must have some "give"
in them to allow relative movement between cells/batteries. If the
straps are rigid and have no ability to flex, that movement will indeed
occur regardless, and the terminals themselves will then move relative
to the cell itself. This will crack the cell enclosure, _greatly_
shortening the life of the cell.
Cells (or batteries) expand and contract as they are charged and
discharged, as much as 1% or 2%. Additionally, they slowly swell as they
age, as much as 7%. On top of that, they expand and contract when they
change temperature. In a moving vehicle, the entire battery pack will
flex as the vehicle goes over bumps and terrain. Nothing is completely
rigid. Every structure flexes to some degree or another.
The strap ends are typically bolted to the cells or battery terminals.
These bolted joints exert pressure on the strap connections. (Often,
they will include a spring washer (Belleville washer) to maintain the
clamping force.) This clamping force will also serve to clamp the
internal connection between the braid and the tube/crimp on the end of
the braid. If you use tinned braid, there is no need to do anything more
than to hammer it flat and adequately tighten the braid fastener.
What is particularly handy is that you can alter the number of braids
you stack up according to the current the strap must cope with.
I have used these fabricated braid straps for many years without failure
or incident in both home-built street EVs and a number of record holding
race EVs.
Bill D.
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