The new Electric Cessna 172

wrote:

snip old stuff


Most of what I was reading didn't seem to indicate that the goal is to
replace, but rather to compliment existing technologies, e.g. charging
applications.

http://phys.org/news/2012-10-sponge-...lectrodes.html
- Graphene

http://phys.org/news/2011-08-energy-...-electric.html
- SMC

Lot's of little techical problems in both of those articles.

The biggest is talking about recharging in minutes.

It is a rather simple calculation to calculate the current requirments
to recharge a device (doesn't matter battery or capacitor) to the full
energy level in a few minutes.

When you do that you discover that the size of the cable required so that
it will not vaporize due to the current density is as big around as your
leg with matching connectors.

Energy sources are rated in KWh and is equivalent to 1000 x V x A x h.

A typical electric car battery is around 30 KWh and 100 volts and 6 minutes
is 0.1 hours so:

30,000 / (100 x .1) = 3,000 Amps

To put the wire required in perspective, those big heavy cables on an
arc welder are good for a current of around 100 Amps so your charging
cable would have to be about 30 times bigger than arc welder cables.

I'm not saying it will (ever) power an airplane. Just looked
interesting and sometimes there are great discoveries that come out of
research, often in applications that were never part of the planned
research itself.

Yeah, that is usually the case.


Peace.

On 2013-02-01, wrote:
To put the wire required in perspective, those big heavy cables on an
arc welder are good for a current of around 100 Amps so your charging
cable would have to be about 30 times bigger than arc welder cables.

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.

However, the price and other installation details of getting the
300kW feed to the FBO is left as an exercise for the reader...

Dylan Smith wrote:
On 2013-02-01, wrote:
To put the wire required in perspective, those big heavy cables on an
arc welder are good for a current of around 100 Amps so your charging
cable would have to be about 30 times bigger than arc welder cables.

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.

Keep in mind any real world implementation would have to follow existing
regulations such as NEC and while a 30mm copper wire isn't going to
vaporize, it certainly isn't going to be cool.

Also there can be a great difference between "possible" and "practical".

However, the price and other installation details of getting the
300kW feed to the FBO is left as an exercise for the reader...

And that is if you only do one at a time.

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).

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.

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.

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.

On 2/5/2013 1:05 PM, wrote:


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.

Oh no! We can't have any machinery in a vehicle that generates lots of
heat!

I'm as discouraged about fuel cells as you are about batteries.

This fuel cell plane is distinctly unimpressive, I haven't heard any
recent news on it.
http://www.popularmechanics.com/tech...n/news/4257294

There's also not much recent news on the few fuel cell cars that Honda
was or is leasing in California. Plain Hydrogen has some real problems
as a mass fuel. I don't see fuel cells becoming popular until they
perfect reformers, which are the "Holy Grail" technology that will allow
them to use liquid fuels. So far, reformers work mostly only in the
lab, and are very sensitive to fuel impurities.

Vaughn wrote:
On 2/5/2013 1:05 PM, wrote:


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.

Oh no! We can't have any machinery in a vehicle that generates lots of
heat!

I'm as discouraged about fuel cells as you are about batteries.

This fuel cell plane is distinctly unimpressive, I haven't heard any
recent news on it.
http://www.popularmechanics.com/tech...n/news/4257294

There's also not much recent news on the few fuel cell cars that Honda
was or is leasing in California. Plain Hydrogen has some real problems
as a mass fuel. I don't see fuel cells becoming popular until they
perfect reformers, which are the "Holy Grail" technology that will allow
them to use liquid fuels. So far, reformers work mostly only in the
lab, and are very sensitive to fuel impurities.

Problem is current fuel cells generate a LOT of heat and there are limits
to how much you can easily dump, especially for a car at a stop light.

I don't see fuel cells as becoming a mass anything until they run on
something the average idiot can handle at least as safely as gasoline,
and hydrogen has far too many issues to qualify.

On 2013-02-05, wrote:
There are two wires so shouldn't that be 2.8kW and 400 kg of cable?

The calculation was for two wires (out and return), and to be pedantic
we're actually trying to dissipate 1.4kW of heat over 20m of cable, but
the assumption is that the two cables will be tied together thus reducing
the surface area enough that you can't really allow for the full 20m of
cable for heat sinking purposes.

On 2/4/2013 12:54 PM, wrote:
would have to follow existing
regulations such as NEC

You would be surprised at the places where the NEC doesn't apply, and I
wouldn't bet money that it would apply here. Still, the laws of physics
always apply and any such installation where people must handle
energized conductors would certainly need to be built to some stringent
safety standard.

Vaughn wrote:
On 2/4/2013 12:54 PM, wrote:
would have to follow existing
regulations such as NEC

You would be surprised at the places where the NEC doesn't apply, and I
wouldn't bet money that it would apply here. Still, the laws of physics
always apply and any such installation where people must handle
energized conductors would certainly need to be built to some stringent
safety standard.

As a general rule of thumb, the NEC applies to things connected to the
electrical grid, so my guess is that it would apply.

Not that it matters in the slightest as this will never become reality.