Dylan Smith wrote:
On 2013-02-04, wrote:
To be precise for an interconnect of 10m, two cables of 30mm diameter
would suffice. It would give the line boy a bit of a work out but isn't
impossible. Size-wise it's a bit like two fuel hoses but *considerably*
heavier.

I think you dropped a decimal point there.

4/0 AWG wire is about 12mm in diameter and rated for about 300 A.

No decimal point dropped.

Don't forget the DC current carrying capacity is not determined by
the radius, but the cross section area of the cable. So you wouldn't need
120mm dia. cable. A 12mm dia cable has an area of 113mm^2. Multiplying
by 10 we have a cable with a 1130mm^2 cross section, or a radius of
sqrt(1130/pi), or a 38mm diameter by just making it ten times larger
than a 300A cable (and not far off my initial guesstimate of 30mm dia).

Sounds about right.

That wire has about 1.5e-5 ohm resistance per meter (or 1.5e-4 ohm
for 10 meters). Applying V=IR to find the voltage drop, we have
V=3000*0.00015, or a 0.45v drop over this cable. So we'd have to
dissipate about 1.4kW of heat over this 10 meter length during the
charge. So yes, pretty toasty but it wouldn't melt the insulation.
It's the poor line boy who gets a bit of a work out though, he'd
have to drag about 200kg of cable out to the plane. Even lifting
the last 2m up off the ground to connect to the aircraft would be lifting
40kg of copper. The health and safety police certainly would frown on
that.

Minor nit:

There are two wires so shouldn't that be 2.8kW and 400 kg of cable?

Note I'm not saying it's *practical*, where I live the final distribution
circuits are only 180kW or so, which is less than the power that this
thing would need to transfer, so the FBO which probably have just a pretty
standard commercial office type electricity supply would need upgrading
to something that could power a factory (in other words, eyewateringly
expensive given that most GA FBOs are marginally profitable and live
hand-to-mouth). I also suspect that 10m of 38mm dia cable will be a bit
expensive too and a prime target for copper thieves. So even before
we get as far as thinking "will a 38mm dia cable with a suitable
protection device meet regulations?" the whole thing would be stymied
by the astronomical cost of supplying such a large amount of power to
an operation that at the best of times can just about cover the wage bill.

Totally agree here.

This is why no electric vehicle of any kind is ever going to "refuel" as
quickly as a gasoline vehicle no matter what the storage device other
than a fuel cell and for most people a refuel time of hours is not
acceptable.

One would think the research money for big electrical sources would be
better spent on fuel cells (not that they don't have problems of their
own like generating a lot of heat) than on batteries and capacitors.