More grist for the battle of the battery

Bill Daniels wrote:
I'm not suggesting lash-ups. A discrete 'brick' or 'slab' battery pack with
matched charger is what I am talking about.

Well, that is what you would do, but you are more careful than most...

I've read the warnings from the model airplane sites. The warnings seem to
all be about charging. I never charge a battery in the glider.

Look more carefully, there are also warnings about explosions resulting
from short circuits. I've seen a similar video where they just shorted
the terminals together, and let the cell sit for a minute or two...

Marc

Bill Daniels wrote:

What would be the advantage of this battery over the 12 volt, 7 to 9
amphour SLA for your application? Neither size nor weight seem important
in a battery of only 8 amphours, whether SLA or Li-ion. That's a Nimbus
you fly, right?


It's about a 6 pound weight savings. (1 Lb vs 7 Lbs) for 7-8 AH. That
allows the battery to be behind the panel with short wires instead of behind
the seat with long wires. Total weight savings are not that important but
the battery's effect on balance and weight of the 'non-flying' parts is.
I've been running W&B's and 6 pounds is important.

This is an interesting idea. It might be an easy way to power a
transponder with a separate battery, without the hassle and expense of
mounting a 6 pound battery somewhere it won't become a projectile.

The Becker and Microair transponders have max input voltages of 30
volts, so no problem with 16.2 full charge voltage that's an issue for
you. Encoders, like the ACK 30 I use, have similar values. It would mean
using two different chargers, one for the Li-ion, one for the SLA, but
that seems like a minor inconvenience.

snip

As for safety, the motorglider guys are flying around with GASOLINE, right?
That burns too.

Surprisingly, fire fed by the gasoline is a rare event in motorgliders
(wire fires seem more common, along with burns from the canopy focusing
the sun), and we continue to hurt ourselves in the usual ways glider
pilots do.


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Eric Greenwell
Washington State
USA

A Lear Jet caught fire when a battery overheated and burned a hole in the
fuselage. This was caused because the new battery had such a tremendous
current capacity. No, it was not a lithium ion, it was a nicad. That was
about 35 years ago and the FAA issued cautions about the problems created by
nicad batteries.

I have also read about people being seriously burned when the nicad
batteries they were carrying in their pocket shorted out on their keys,
burning a hole in their pants and in one case leaving an imprint on the
thigh of the victim.

Any device that stores or creates energy is a potential hazard. What is
required is that the user understand the potential hazards and minimize the
risks.

We drive around in cars full of gasoline, which may burn or explode in an
accident, on tires that may suddenly deflate because of an object striking
them. And, we are 4 feet away from a vehicle coming the opposite direction
going 50 miles per hour. Sometimes where we draw the line between what is
safe and what is not is rather arbitrary.

Colin

At 02:12 15 November 2005, Marc Ramsey wrote:
Bill Daniels wrote:
I'm not suggesting lash-ups. A discrete 'brick' or
'slab' battery pack with
matched charger is what I am talking about.

Well, that is what you would do, but you are more careful
than most...

I've read the warnings from the model airplane sites.
The warnings seem to
all be about charging. I never charge a battery in
the glider.

Look more carefully, there are also warnings about
explosions resulting
from short circuits. I've seen a similar video where
they just shorted
the terminals together, and let the cell sit for a
minute or two...

There is a cure for that, a fuse. Regs in the UK require
a fuse within a very short distance from the batttery,
2.5 ins from memory and I use 3 amp. Not a lot of opportunity
for a short of any sustained time with that arrangement
if the terminals are insulated as they should be.
A standard lead acid battery will do very spectacular
things if shorted out as well, I remember (many many
years ago when young) trying to light a cigarette using
a strand of winch wire across the winch battery terminals,
worked fine until the top blew off the battery. It
would seem that even then smoking could damage your
health.

PS You needed a good pair of gloves :-). I think we
might have invented the automobile cigar lighter without
knowing it.

"Don Johnstone" wrote in
message ...
At 02:12 15 November 2005, Marc Ramsey wrote:

There is a cure for that, a fuse.

True, but there is no fuse that can protect from an internal short circuit.
Any type of battery can (at least rarely) do this. I have seen both lead acid
and NIMH batteries burn up this way. (It the case of the NIMH it was an irate
firefighter whose portable radio had nearly caught fire.) Naturally, the more
energy in the cell, the more heat, smoke, and (possibly) flames you can expect.
Lithium batteries have a very high energy density and the innards love to burn,
so internal shorts are a particular concern with them.

How great is the danger as a practical matter? That is the true question
here!

Vaughn

COLIN LAMB wrote:
.../..
I have also read about people being seriously burned when the nicad
batteries they were carrying in their pocket shorted out on their keys,
burning a hole in their pants and in one case leaving an imprint on the
thigh of the victim.

There was story in Model Aviation a few years ago about just that
happening to an RC model flier. He put his NiCd glow-starter in the same
pocket as his keys without capping it. Unfortunately his pocket also
held half a dozen .45 cartridges from the morning's target practice....

--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

"Eric Greenwell" wrote in message
...
Bill Daniels wrote:
Lithium Ion rechargeables seem to have recently seen a 50% or so price
drop.
A 4-cell, 14.8V, 8AH with charger and mounting plate can be had for
$169.99
(USD).

Can you supply a URL? While I strongly discourage people from making up
their own Li-ion battery packs for their glider due to potential safety
problems, a _production_ battery pack with it's dedicated charger would
likely alleviate most of the concerns I have about using a large Li-ion
battery in a glider. I don't worry about the little ones in my PDA, cell
phone, or camera.

Sometimes Froogle doesn't find the same things on successive searches. Here
is an example of what I'm talking about.

http://store.linkexpresspc.com/de16liprbafo.html

Specifications:
- Rating: 14.8V == DOUBLE CAPACITY 8800mAH (8.8AH)
- Capacity : 132 WHR 16CELL
$149.00 @ LinkExpressPC

As for the warning videos and scary stories in the press, most people know
these are merely efforts at proactive legal defense. (Lawyer for the
plaintiff: "You sold these CHEMICAL FIRE BOMBS for use in CHILDREN'S TOY
AIRPLANES?) (Lawyer for the defense: "Gee, yer honor, we warned 'em - see
our scary video on the web.) It's an effort to immunize the manufacturer
against 'frivolous' lawsuits.

In fact, most technically savvy users know Li-Ion batteries are plenty safe
if a few simple precautions are used. Mainly, use the correct charger in a
fire safe location. Once charged, don't damage the case or short them.
That's pretty good advice for any rechargeable battery no matter the
chemistry.

Bill Daniels

Vaughn wrote:

"Don Johnstone" wrote in
message ...


There is a cure for that, a fuse.

True, but there is no fuse that can protect from an internal short circuit.
Any type of battery can (at least rarely) do this. I have seen both lead acid
and NIMH batteries burn up this way. (It the case of the NIMH it was an irate
firefighter whose portable radio had nearly caught fire.) Naturally, the more
energy in the cell, the more heat, smoke, and (possibly) flames you can expect.
Lithium batteries have a very high energy density and the innards love to burn,
so internal shorts are a particular concern with them.

How great is the danger as a practical matter? That is the true question
here!

Indeed; however, there are a jillion laptop batteries in use, but very
few problems (I haven't heard of any, but there must be some). For
glider use, I'd want to know what the usable temperature range is (some
units specify only up to 95 deg. F), what altitude they can be used to
(haven't seen any specifications for that), and what safety features are
built into them (fuses, both for amps and overheating, might be
standard, and welcome, features, for example).


--
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Eric Greenwell
Washington State
USA

Bill Daniels wrote:

Can you supply a URL? While I strongly discourage people from making up
their own Li-ion battery packs for their glider due to potential safety
problems, a _production_ battery pack with it's dedicated charger would
likely alleviate most of the concerns I have about using a large Li-ion
battery in a glider. I don't worry about the little ones in my PDA, cell
phone, or camera.


Sometimes Froogle doesn't find the same things on successive searches. Here
is an example of what I'm talking about.

http://store.linkexpresspc.com/de16liprbafo.html

Specifications:
- Rating: 14.8V == DOUBLE CAPACITY 8800mAH (8.8AH)
- Capacity : 132 WHR 16CELL
$149.00 @ LinkExpressPC

I think this style would be much more suitable than a laptop battery:

http://tinyurl.com/8zl55

Essentially the same ratings and price ($169 with charger), it has a
standard output connector and a easier to mount shape. Google "external
laptop battery" without the quotes. There is a wide range of price and
power in this style. Something like this might be very practical for
gliders, though I still want to know more about maximum ambient
temperature and altitude allowed, and built-in safety features.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"Eric Greenwell" wrote in message
...
Bill Daniels wrote:

Can you supply a URL? While I strongly discourage people from making up
their own Li-ion battery packs for their glider due to potential safety
problems, a _production_ battery pack with it's dedicated charger would
likely alleviate most of the concerns I have about using a large Li-ion
battery in a glider. I don't worry about the little ones in my PDA, cell
phone, or camera.


Sometimes Froogle doesn't find the same things on successive searches.
Here
is an example of what I'm talking about.

http://store.linkexpresspc.com/de16liprbafo.html

Specifications:
- Rating: 14.8V == DOUBLE CAPACITY 8800mAH (8.8AH)
- Capacity : 132 WHR 16CELL
$149.00 @ LinkExpressPC

I think this style would be much more suitable than a laptop battery:

http://tinyurl.com/8zl55

Essentially the same ratings and price ($169 with charger), it has a
standard output connector and a easier to mount shape. Google "external
laptop battery" without the quotes. There is a wide range of price and
power in this style. Something like this might be very practical for
gliders, though I still want to know more about maximum ambient
temperature and altitude allowed, and built-in safety features.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Yep, that's a better example. I think I saw that one on my earlier search
but I couldn't find it the second time. There are quite a few of these on
the market from a variety of vendors. The price is falling as they become a
commodity. I think I could build a box for an internal laptop battery that
would have contacts and a restraining latch. Just push the battery in until
it clicks - no wires to futz with.

Many laptops and gadgets sit on car seats in the sun and then get turned on.
I have certainly done that but I don't know of any problems. I remember
trying to boot a laptop I left on a car seat in Phoenix. It was so hot I
couldn't hold it. After it booted, I couldn't read the LCD until the A/C
cooled it down. Generically, Li-ion polymer batteries are tolerant of
temperature extremes. The laptop batteries are regarded as 'smart'
batteries in that they have processor chips inside that manage them. I
think they may even limit the voltage to 14.8V.

Bill Daniels