Electrically Powered Ultralight Aircraft

On Sat, 11 Aug 2007 15:35:25 GMT, Larry Dighera
wrote:

I would assume that the source of these Li-ion Polymer battery fires
is excessive electrical current flowing through the battery either
from too high a charging rate, too high a discharge rate, or a short
internal (as in the case of the Sony laptop cells) or external, or
being over charged. Perhaps it would be prudent to install a circuit
breaker of fuse to prevent too high a current and a timer to
disconnect a forgotten charger.

I imagine the root of the problem is very low internal resistance
which, while making them very efficient, also allows the current to
"run away". Good circuit design can alleviate many of the issues, but
safety if the batteries are damaged in a crash is still an issue.

-Dana
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"Dana M. Hague" d(dash)m(dash)hague(at)comcast(dot)net wrote in message
...
On Sat, 11 Aug 2007 15:35:25 GMT, Larry Dighera
wrote:

I would assume that the source of these Li-ion Polymer battery fires
is excessive electrical current flowing through the battery either
from too high a charging rate, too high a discharge rate, or a short
internal (as in the case of the Sony laptop cells) or external, or
being over charged. Perhaps it would be prudent to install a circuit
breaker of fuse to prevent too high a current and a timer to
disconnect a forgotten charger.

I imagine the root of the problem is very low internal resistance
which, while making them very efficient, also allows the current to
"run away". Good circuit design can alleviate many of the issues, but
safety if the batteries are damaged in a crash is still an issue.

-Dana
--

Any battery chemistry, including lead-acid, can overheat with excess
charging current - usually to the detriment of the battery and whatever it
is in at the time. All can do damage if they are shorted. The problem with
the first generation lithium cells was the chemistry released oxygen when
overheated which combined with the flammable lithium made an incendiary
bomb.

The newest lithium-nanophosphate cells do not release oxygen and thus do not
burn or explode although they can be damaged by overcharging. Cells made by
A123 Systems, Saft, Valence and others are more than safe enough for use in
aircraft or cars. They have a little less energy capacity than the old
chemistry but they make up for it with fast charging and long life. They
can typically manage a 20C discharge rate without harm - that's 200 amps for
a 10 AH battery. Admittedly, you don't want to short that.

Bill Daniels

On Mon, 13 Aug 2007 17:39:44 -0400, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote in
:

safety if the batteries are damaged in a crash is still an issue.

I would think the hazard somewhat less than gasoline.

Larry Dighera wrote:
On Mon, 13 Aug 2007 17:39:44 -0400, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote in
:

safety if the batteries are damaged in a crash is still an issue.

I would think the hazard somewhat less than gasoline.

The battery can produce it's own ignition source.

On Tue, 14 Aug 2007 08:40:29 -0500, "Gig 601XL Builder"
wrDOTgiaconaATsuddenlink.net wrote in
:

Larry Dighera wrote:
On Mon, 13 Aug 2007 17:39:44 -0400, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote in
:

safety if the batteries are damaged in a crash is still an issue.

I would think the hazard somewhat less than gasoline.

The battery can produce it's own ignition source.


You have a point. While a source of ignition (sparking wires, hot
muffler?) is required to ignite post-crash gasoline fumes, it would
take an un-fused short circuit or significant deformation of a battery
to potentially ignite a lithium battery. Granted, if the crash occurs
as a result of fuel exhaustion, there is little fire hazard, while the
lithium would always be aboard.

Larry Dighera wrote:
On Tue, 14 Aug 2007 08:40:29 -0500, "Gig 601XL Builder"
wrDOTgiaconaATsuddenlink.net wrote in
:

Larry Dighera wrote:
On Mon, 13 Aug 2007 17:39:44 -0400, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote in
:

safety if the batteries are damaged in a crash is still an issue.
I would think the hazard somewhat less than gasoline.
The battery can produce it's own ignition source.


You have a point. While a source of ignition (sparking wires, hot
muffler?) is required to ignite post-crash gasoline fumes, it would
take an un-fused short circuit or significant deformation of a battery
to potentially ignite a lithium battery. Granted, if the crash occurs
as a result of fuel exhaustion, there is little fire hazard, while the
lithium would always be aboard.


How much of a fire hazard would a paper battery be?

http://www.energy-daily.com/reports/...per _999.html

On Wed, 15 Aug 2007 12:23:00 GMT, CanalBuilder
wrote in
:

How much of a fire hazard would a paper battery be?

http://www.energy-daily.com/reports/...per _999.html

That is an interesting device indeed. Given these quotes from the
article:

Rensselaer researchers infused this paper with aligned carbon
nanotubes, which give the device its black color. The nanotubes
act as electrodes and allow the storage devices to conduct
electricity. The device, engineered to function as both a
lithium-ion battery and a supercapacitor, can provide the long,
steady power output comparable to a conventional battery, as well
as a supercapacitor's quick burst of high energy. ...

Along with use in small handheld electronics, the paper batteries'
light weight could make them ideal for use in automobiles,
aircraft, and even boats. The paper also could be molded into
different shapes, such as a car door, which would enable important
new engineering innovations.

"Plus, because of the high paper content and lack of toxic
chemicals, it's environmentally safe," Shaijumon said. ...

"Plus, because of the high paper content and lack of toxic
chemicals, it's environmentally safe," Shaijumon said.

"It's a way to power a small device such as a pacemaker without
introducing any harsh chemicals - such as the kind that are
typically found in batteries - into the body," Pushparaj said.

I find the article to be somewhat contradictory in its characterizing
a lithium-ion battery as containing no harsh chemicals. And its claim
of using carbon electrodes in a supercapacitor seem very
counterintuitive for a low impedance device. It reads like an April
Fools Day hoax.

On Aug 15, 8:18 am, Larry Dighera wrote:
On Wed, 15 Aug 2007 12:23:00 GMT, CanalBuilder
wrote in
:

How much of a fire hazard would a paper battery be?

http://www.energy-daily.com/reports/...oring_Power_In...

That is an interesting device indeed. Given these quotes from the
article:

Rensselaer researchers infused this paper with aligned carbon
nanotubes, which give the device its black color. The nanotubes
act as electrodes and allow the storage devices to conduct
electricity. The device, engineered to function as both a
lithium-ion battery and a supercapacitor, can provide the long,
steady power output comparable to a conventional battery, as well
as a supercapacitor's quick burst of high energy. ...

Along with use in small handheld electronics, the paper batteries'
light weight could make them ideal for use in automobiles,
aircraft, and even boats. The paper also could be molded into
different shapes, such as a car door, which would enable important
new engineering innovations.


IF these can be made practical, they sound ideal for use in an
airplane. They are light, and they can be shaped in just about any
way to fit inside the airframe. Suppose they were integrated into the
airframe and wings such that a large percentage of the airplane
consisted of battery. It might be possible to get enough capacity
there for a practical general aviation electric plane.