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nuckolls.bob(at)aeroelect
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 Posted: Wed Mar 26, 2014 5:53 am Post subject: The lithium saga slogs onward . . . |
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In my quest to identify suppliers of lithium
batteries who will share operational details of
their BMS (battery management system) AND useful
contained energy plots, few suppliers have demonstrated
an interest in satisfying the unique curiosity of
those who build and fly airplanes.
So far, EarthX is the only one who has responded
positively. I have documentation that describes
their BMS operating philosophy. No family of
discharge curves yet . . . but them, most of their
customers are narrowly focused on engine cranking
cupcakes with a frosting of weight reduction.
I need to wrap of installment IV of the battery
series for Kitplanes . . . as of this moment, I'm
still short the necessary information to beat the
drums in favor of ANY commercial off the shelf
lithium product for OBAM aircraft.
My misgivings are NOT rooted in either disappointment
for weight savings or ability to get the engine started.
The problem is centered on knowing what we don't know . . .
exactly what size battery is needed to replace the
legacy SVLA products in which we have considerable
confidence.
Watch this space . . .
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Wed Mar 26, 2014 11:43 am Post subject: The lithium saga slogs onward . . . |
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FIY . . . got a peek inside this battery
from True Blue Power . . . who
has achieved the first TSO'd offering for
GA aircraft.
http://tinyurl.com/lxh6wqm
The battery is 17Ah (in AIRCRAFT Ah at
1-hour - not a 20 hour rate) and 24V. Weighs
about 16 pounds. So a 12v, 17Ah battery
would be about half that weight.
This battery is an array of 56 cylindrical
cells not unlike these 26650 cells available
from a variety of sources.
In rough numbers, this cell is a 10Wh storage
medium. 56 cells x 10Wh suggests you can expect about
560Wh from the array. This is consistent with
nameplate energy rating for the battery at 430Wh.
Being one of the few batteries where detailed
system integration data are available, we
can begin to size the task for incorporation of
this or similar products into airplanes.
A 12V version of the battery would be 215Wh
so if you have an electrically dependent engine
with a 100W service load, you could expect about
2 hours endurance for just an engine. Peel off
50-73 watts for electro-whizzies, your battery
only endurance expectations are just over 1
hour for new battery, just under 1 hour for
end-of-life battery.
Now for the sobering facts. There are two
circuit boards in the battery management system
(BMS). One is just under the heat-sink fins on
top of the battery. It's populated with a goodly
number of FAT transistors, probably N-MOS FETs
in TO-247 plastic packages.
The other board occupies a whole side of the battery
and is covered with perhaps 2-3 dozen surface mount
ic's and lots of jelly-bean parts. There's probably
more silicon in this battery than in your ICOM comm
transceiver, gps and transponder combined.
Further, I believe this battery will sell for about
$3200; so one might ball-park a 12v battery at $1600.
Of course, that's 'airplane' pricing that carries
the burden of TSO certification.
This product is the leading edge example of what it
takes to get approval for TC aviation. Other
product MIGHT offer similar capabilities for $less$
if they've not run the TSO gauntlet.
Just giving you guys a heads-up on what I'm discovering
as that battery articles move forward . . .
The REAL significance of this discovery exercise
is that to get 1-hour of battery only endurance in
a 200W airplane will take an array of 28 lithium
cells of the size cited above. This means that batteries
like this
[img]http://i.ebayimg.com/00/s/NTU0WDYwMA==/z/wsMAAOxyu1FRkXAX/,zQE9s3sqIw0BRkR,-Q60_3.JPG[/img]
http://tinyurl.com/k8yhurl
which are 4 x 4 arrays of similar cells probably
fall short of the 1-hour endurance hypothetical
half-a-True-Blue endurance cited above.
Further, this pretty little red thing cannot feature
the same degree of battery management that's built
into the True Blue product.
Tying this back to the venerable PC680 . . .
[img]cid:.0[/img]
We see that teh PC680 at the 1-hour rate is a 12.3Ah battery
when new. A 175W airplane will say lit up for about 45 minutes on
a new battery.
Bob . . .
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