Today's Message Index:
----------------------
1. 12:21 AM - Re: EarthX lithium (Stuart Hutchison)
2. 11:57 AM - Re: EarthX lithium (Robert L. Nuckolls, III)
3. 12:14 PM - Re: Re: New Over-Voltage Protection Architecture (Robert L. Nuckolls, III)
4. 05:23 PM - Re: EarthX Batteries (speedy11@aol.com)
Message 1
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G'day Bob N.
Your comments in the PDF file about battery Ah rating under different
operating conditions reminded me of an interesting annecdote.
About 10 years ago, Energiser began marketing a series of cheap (approx $20)
AA battery powered chargers for cell phones. They are a simple plastic case
(inc circuit) for two primary AA cells, plus a short adaptor cord option for
the various cell phone models. Turns out they come fitted with lithium
cells for good reason.
>From spec data sheets at the time, the rating for a standard Energiser
alkaline AA cell was typically around 2700 mAh. The lithium cells were
about 3200 mAh, yet manufacturers quoted 5 to 7 times the endurance for
lithium cells in high power devices. This seemed counter-intuitive given a
similar mAh rating.
In practice, the lithium cells can deliver higher current without the
internal resistance soaring through the roof, so most of their energy is
delivered to the load rather than wasted as heat. It was easily proven by
replacing the AA lithium cells with alkaline cells. The alkaline cells
became too hot to touch and delivered about half a cell phone charge, while
the lithium cells delivered about 2.5 full charges. Conversely, using
lithium cells in a low power device such as a wall clock would offer a very
poor return on investment, given the lithium AA cells cost about 4 times the
price.
Cheers, Stu
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Tuesday, March 18, 2014 3:41 AM
Subject: AeroElectric-List: EarthX lithium
I just became aware of EarthX batteries based on comments here on the list.
I visited their website and studied a variety of assertions and comparisons
designed to promote sales. At first blush, these folks are hanging their
marketing hats on the same philosophy as other suppliers of lithium
technologies.
See attached document . . .
The DEARTH of good engineering data for these products makes it difficult if
not impossible to craft a well considered integration of the current COTS
(commericial off the shelf) offerings onto airplanes.
I had to delay submission of the last of four Kitplanes articles for a month
. . . not because theres a paucity of choices . . . but because the folks
selling them can't define performance in rational numbers. Still digging . .
.
Bob . . .
Message 2
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> . . . using lithium cells in a low power device such as a wall
> clock would offer a very
>poor return on investment, given the lithium AA cells cost about 4 times the
>price.
Yeah, your talking about these critters . . .
Emacs!
They're in the Size 91 package (AA) but offer a lithium-Iron
couple that's in the same ballpark as the carbon-zinc and
zinc-manganese flashlight cells (1.5 volts).
If you compare E91 alkaline cell data
Vhttp://tinyurl.com/nt2x8hd
with the L91 lithium-iron data
http://tinyurl.com/otkeubs
We see that both products are in the same ballpark
for contained energy but the L91 cell internal
resistance is about 1/2 that of the E91. So not
only do you get slightly more total energy, your
access to that energy at high discharge rates suffers
about 1/2 the losses in heat.
This 'lithium' product is a different animal from
the devices we're pondering as replacement for
engine-cranking/standby service. The boss-hogg
lithium cells are 3.3V couples and generally
much lower resistance still . . .
It's unfortunate that characteristic performance
of two cells are not presented in the same pews . . .
suffice it to say that the approx 1/2 internal
resistance will toss off less energy under high
demand loads.
On the Nickle-Metal Hydride side of the house
one may acquire 1.2V chemistry with very attractive
internal impedances . . .
http://tinyurl.com/nj5xx85
At 1.2V vs. 1.5 volts the contained energy
in watt-seconds suffers slightly but they'll
readily deliver their contents at high rates.
Down-side is that the self-discharge characteristics
of Ni-Mh compared to the Lithium-Iron or Zinc-Manganese
cells is pretty sad. Up-side is that you can readily
re-use these cells many times over and their
acquisition costs are nominal.
http://tinyurl.com/nklo97k
Your right, lithium-iron AA cells poor value compared
to other choices . . . unless your design goals
absolutely demand high rate discharge support
AND long shelf life.
Its all in the design goals . . .
Bob . . .
Message 3
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| Subject: | Re: New Over-Voltage Protection Architecture |
At 10:58 AM 3/19/2014, you wrote:
>You might be approaching a situation where "the cure is worse than
>the disease". You have to be careful when stacking widgets on top
>of gizmos in pursuit of greater reliability. That approach quite
>often leads to greater complexity & lower reliability.
Good put.
What is the line of thought that drives the
notion that simple removal of field voltage from
a runaway system is inconsistent with our
assessment of risk?
I'll have to ask around . . . I've been disconnected
from the field service loop in regulators for some
years . . . but I don't recall any controllers ever coming
back to B&C where a regulator fallen from grace
was blessed with salvation by the ov protection
system.
I'm not suggesting that such failure rates are zero but
they ARE quite small. Further the prudent response
to a competent FMEA dictates that we include such
protection in spite of those low failure rates.
It's been a long time since I've observed a car
approaching me at night with lights that were too
blue/bright demonstrating the fact that a poor
battery was doing its best to stand off a
runaway alternator.
I'm also reading anecdotal bits about stock,
automotive alternators being incorporated onto
aircraft sans ov protection. It MIGHT be that
contemporary regulators have achieved 10 to the
minus 9 or better failure rates that suggest
the ov protection is no longer necessary/useful.
If anyone runs across such an incident, I'd like
to hear about it.
Bob . . .
Message 4
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| Subject: | Re: EarthX Batteries |
I concur with Bob's comments. My dealings with the folks at EarthX has be
en professional and forthcoming.
It appears they are pushing hard to become the market leaders and their bat
tery monitoring system may be just the thing to get them there.
I have decided to distribute their batteries at my FBO operation and I will
be ordering two batteries soon to replace the PC680s in my RV-8A (Reno Rac
e 84). I will follow up with non-technical, but nonetheless interesting da
ta points on my experience using the lithium batteries.
Stan Sutterfield
Spruce Creek FBO
Daytona Beach
A heads-up to the List on my conversations with EarthX.
Of ALL the lithium wannabes I've approached for expanded
data on the operation and performance of their batteries,
EarthX has been the ONLY one to respond in any positive
and professional manner.
The e-mails I've forwarded to the List are conversations
with an individual in sales. I've received a data dump
from an applications person who promises to draw design
and performance talents into the conversation.
I'm not going to forward any more emails to the List
out of respect for their willingness to share what
may be considered proprietary data.
But I want to make the List aware of the fact that
EarthX seems interested in widening their customer
base on a foundation of well considered application
of their products.
I'm going to offer them assistance in crafting functional
specifications that speak purely to performance
in terms that would be appreciated by my colleagues
in TC aviation. At the same time, I will acquire
foundation for offering solid advice to the
OBAM aviation community as to suitability to
task for EarthX . . . or any other lithium
offering.
Watch this space.
Bob . . .
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