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jmjones2000(at)mindspring
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 Posted: Sat Jan 31, 2015 1:20 pm Post subject: Internal Shunt in Alternator? |
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A friend of mine has a maule m4 with a Franklin 220. He is restoring the plane. The ammeter has never worked and when he removed the gauge, he traced one wire to the alternator. It was about 22 or 20 ga.
Are there aviation alternators out there with an internal shunt? I haven't heard of it but if not, this would be the cause of the ammeter not working.
Thanks
Justin
On Jan 31, 2015, at 08:04, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote] At 12:05 2015-01-30, you wrote:
--> AeroElectric-List message posted by: "ChrisM" <mullincl(at)gmail.com (mullincl(at)gmail.com)>
Bob,
Thanks to you and other participants for help with my questions.
Interesting that you are feeling so confident in the application of Li batteries. This is really a significant step forward in technology for small aircraft.
I have not said that it's a "step forward" . . . in fact,
I have raised questions as to the economics for the transition
to lithium. I will assert that lithium is an alternative
ingredient that may well be an appealing recipe for success.
I don't yet see a concise definition of 'success'.
There are three separate lines of inquiry that influence the
choice to incorporate lithium batteries into your personal
elegant solution.
Integration: It's no different than the study of how
transistors evolved with significant milestones marked
by the relative fragility of the PNP germanium
transistors that first flew in airplanes. Devices later
displaced with more robust NPN silicon. More recently,
the power mosfet is King Silicon. EVERY evolutionary
plateau was an improvement in performance, robustness
and service life. However, EVERY step up required major
changes to the circuitry and design philosophy to fully
exploit what the new device had to offer. One could not
simply pull out the old and plug in the new. This is
the foundation for my distaste of popular marketing
hype citing "lead-acid equivalency".
Lithium is equivalent to nothing . . . its greatest
advantages cannot be fully exploited without careful
attention to just how this ingredient 'fits' into
the recipe for success.
Cost of Ownership: When Burt Rutan was putting the sharp
pencil to the design of Voyager, weight was a critical
consideration.
He told us that it takes 5 pounds of fuel to carry
one pound of airplane around the world. Every pound
removed from empty weight removes 6 pounds from gross
weight at takeoff. Nearly one gallon more fuel. One gallon
at end of mission would carry Voyager another hundred
miles or so. But there were prices to pay. The materials
to build such a 'featherweight' airplane with any structural
integrity were very expensive. Further, fuel unique mission
requirement multiplies the weight of the airplane by 6 times
called for a fuel tank with wings having very attractive
l/d ratios . . . at the sacrifice of handling qualities.
Dick Rutan confessed that the airplane scared the hell
out of him . . . he had nightmares of dying in that
airplane. Without the fine support of King Radio for
an autopilot that would handle this winged beast,
the around-the-world mission would have humanly
impossible. Without pedantic attention to weight,
sometimes a great cost, the mission might not have been
possible.
Risk: Properly conducted FMEA seek to study, discover,
classify, understand and ultimately mitigate all the
ways that the product can first, cease to preform
intended duties as one of many players in the orchestra.
Then, mitigate failures that put the entire system at risk for
catastrophic collapse. It's one thing for the cello
player to break a string . . . quite another for
to be sneezing H1N1 into the surrounding environment.
You emphasized to "operate (Lithium battery) within well established limits and preventative maintenance to verify integrity." Will you elaborate regarding how this looks with Li? You have mentioned in the past about the lack of data from many manufacturers, and the lack of lead acid equivalency. Do you feel the BMS used by EarthX is a final equilibrator here?
The purveyors of lithium are the first folks to assert
that battery management systems are always a 'good'
idea. What ever form they take, the BMS mitigates risk
for catastrophic failure. Just how the BMS is configured
and applied in practice a big factor in performance, risk
and cost of ownership. It's unreasonable and added risk
to expect the consumer (OBAM aircraft builder) to take
on yet another task that amounts to micro-managing the
lithium physics. Especially when compared to the mature,
relatively docile qualities of lead-acid. BMS may not
be the 'final' answer to the svla vs. lithium decision
but certainly a major consideration.
An this still leaves the question I've asked and
nobody has come forward to answer, "What are the
numbers . . . how will the smaller weight and volume
numbers manifest in the performance and utility of
say, an RV7 presently fitted wity a PC680? Shorter
takeoffs? Higher mountains to challenge, cleared
out space to store your sandwiches?
Boeing's considerations for battery weight were but one
component in a HUGE model of cost/benefit ratios. The numbers
they considered enticed them to spend $millions$ in making
the switch to lithium. What are YOUR numbers?
The advanced EFII system I have been evaluating may be a bit too far up the ladder for my project, as you pointed out. The 10 ampere requirement quoted was per email from manufacturer and is for both the fuel and ignition systems. Majority apparently consumed by the fuel pump - one of two runs at a time to pressurize a fuel rail.
Yes . . . and I've heard 'up and running' numbers on
that system 'quoted' from 6 to 10 amps . . . but I have
yet to discover published data that speaks to the real
energy requirements for this system.
People may snicker at my insistence that the purveyors of
lithium come forth with "all the numbers" . . . like
Hawker/Enersys and virtually all contemporaries. But as
Lord Kelvin often opined, "without the numbers you have
barely scratched the surface of the science." I will build
on that sentiment by suggesting that the decision should not
devolve to preferring Big Macs just because they taste good
without knowing how they integrate into the energy
conversion/management system of a very complex machine.
Questions that remain undiscovered, unasked, unanswered
and/or ill-considered may bring the system down no matter
how good the product tasted.
EFII "owes" you the same quality of numbers that we expect
from Rotax, AeroVoltz, Icom, Smiley Jack's Prop Shop
. . . or anybody else that wants to play honorably and capably
in this sandbox.
Anyway, I am currently favoring a pullback to a set of P Mags, mechanical fuel injection, a single Li battery with a small detached back up, and a single alternator. This set up should perform similarly in practical terms, and be very reliable and light.
Sounds like a considered move . . . what now are your
electrical system numbers insuring comfortable termination
of flight limited only by fuel aboard?
Are you going to have a vacuum pump? Why waste a
perfectly good energy source by covering the pump
pad with a plate of aluminum? After nearly 20 years
of sifting the numbers, FMEA scenarios, costs of
ownership and performance, I suggest that Figure Z-13/8
is as near 'perfection' for flight system reliability
. . . assuming of course that you don't burden it with
an 120 watt engine support demands.
You speak of two batteries . . . why? One or both lithium?
Can you share your FMEA and cost of ownership reasoning?
Exactly how will that savings of wight manifest in performance
or utility of your airplane . . . and at what cost of
hours to integrate and maintain performance at minimum
levels throughout the service life of the battery?
Z-13/8 will keep your panel lit and allow you to
run any battery until it won't crank the engine any
more. The cost of ownership for the 4 pound wight
penalty of an SD-8 is far, Far, FAR lower than
that of any second battery you might choose to
lug around ESPECIALLY lithium.
Bob . . .
[b]
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jan 31, 2015 4:43 pm Post subject: Internal Shunt in Alternator? |
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At 15:16 2015-01-31, you wrote:
| Quote: | A friend of mine has a maule m4 with a Franklin 220. He is restoring the plane. The ammeter has never worked and when he removed the gauge, he traced one wire to the alternator. It was about 22 or 20 ga.
Are there aviation alternators out there with an internal shunt? I haven't heard of it but if not, this would be the cause of the ammeter not working.
Thanks
Justin
|
There were a few, less than elegant ammeter
installations that relied on copper wiring
resistance to stand-in for a real shunt.
The fact that one wire did go to the alternator
(I guessing b-lead terminal) I suspect the
other end is tied to the alternator-side of
the b-lead breaker. Hence, voltage drop more
or less proportional to b-lead current could
be impressed on an instrument for display.
Is he interested in getting the ammeter to
work? He might send it to me and I'll test
and quantify the instrument itself . . . we
could go from there to determine the most
practical way to get it up and running again.
Baring that, encourage him to install active
notification of low voltage . . . a flashing
light thingy. That's about 10x more useful than
any ammeter.
Bob . . . [quote][b]
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