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Re: [EVDL] "One mm per volt" Battery pack layout guidelines

>
>First, arcing is not a problem below about 30v.

But high-current arcing _is_ a problem below 30 volts in a powerful
battery pack. Especially a large one. You _might_ get away with 1/2
mm per volt separation below 30 volts, but it would depend on how
much current the cells are capable of delivering to a fault. That is
why the "normal" rules for conductor separation you would use for
electronics design do not apply in an EV-sized battery pack.

Once you strike the arc, and plasma is being fed by the vaporizing
adjacent conductors, you have started the cascade that with spread to
other adjacent conductors in the battery pack. The current is not
conducted by the air, but by the metal vapor, so it doe not take much
voltage to sustain an arc fed by currents high enough to vaporize the
conductors.

Arc welding is pretty much the same physics as a the arcing that
occurs in a battery pack across a fault. The typical arc welder is 17
to 40 volts. The voltage increases with arc length, and _decreases_
as current goes up. In welding, typical arc lengths are ~10 mm at ~25
volts at ~200 amps. The resistance of a given arc length goes _down_
in proportion to current. At 1000 amps, that same 10 mm arc will only
drop ~6 volts.

If you have a very powerful battery pack, it will feed more
current into any given fault arc, and you need more separation for
the arc to self-quench. Otherwise, it will sustain and .........

Bill D.

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