Today's Message Index:
----------------------
1. 08:18 AM - Re: Diode from the Main Bus to the Endurance Bus (Robert L. Nuckolls, III)
2. 08:44 AM - Re: Diodes versus switches 101 ? (Robert L. Nuckolls, III)
3. 08:44 AM - Re: ANL/ANN current limiter (Robert L. Nuckolls, III)
4. 09:25 AM - Re: "Coat Hanger" antenna (Robert L. Nuckolls, III)
5. 09:49 PM - Plane Power's Friendly Warning Light (Dave Saylor)
Message 1
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| Subject: | Re: Diode from the Main Bus to the Endurance Bus |
At 10:59 PM 3/9/2008 -0400, you wrote:
>
>Hi Folks
>
>I have already one airplane flying using Bob's Z-11 architecture with
>absolutely no issues. It has been great & really appreciated all the info
>provided by Bob & the forum.
>
>I do have one question. I am not questioning the wisdom of the design but
>merely wondering why a diode is placed between the main bus & the
>endurance bus. I realize that it is there to prevent backfeeding from the
>E bus to the main bus when the master is turned off in the case of an
>alternator failure etc.
>
>However, you can easily install a 2-10 switch that could be used to set to
>1/ Both buses off
>2/ E bus only on, master off & all other buses turned off
>3/ Main bus & E bus on with the E bus being fed through the main bus & master
>
>Is the considered opinion of the group that a diode is more reliable than
>a switch & therefore used, or, to simplify the whole design or what?
>
>Just curious as there is a slight power loss across the diode of course
>which is the only negative and think of at this point.
The design goal is to have TWO INDEPENDENT paths of
power to the e-bus, ONE of which is battery direct so
that one can operate e-bus loads with the battery
master switch off.
If you use a single switch in the mode you've described,
there is a single point of failure in the switch.
Voltage drop in the diode is not significant. Consider
the fact that when power is expected to come through the
diode, the alternator is operating. This raises the main
bus to 14.2 to 14.6 volts. A typical 0.7 volt drop in the
diode offers an e-bus supply of 13.5 to 13.9 volts . . .
entirely satisfactory supply levels.
Contrast normal operating conditions with battery-only
operations where the e-bus will start out at 12.5 and
drop to 11.0 by the time the battery is used up.
Bob . . .
Message 2
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| Subject: | Re: Diodes versus switches 101 ? |
At 09:21 PM 3/9/2008 +0100, you wrote:
>
>
>I think it's important to take into account what the purpose of the switch
>and/or diode is, and more important, what the failure modes of the
>circuits around it is. A diode may be much more reliable when used within
>it's designed specs, but if you overload it, it will fail much quicker
>than a switch. Compare a diode and a switch, both rated at 25A. A
>short-circuit current of 100A through the diode for a few seconds will
>make it fail, most likely open circuit. The same current through a switch
>may heat it up and damage the contacts, even cause some sparks, but it may
>still limp along.
I've never replaced a diode that failed open. I don't
mean to imply that they NEVER fail open but in what must
be dozens of personal observations, I've never seen one
open. Oh yeah, take that back. I did have a plastic 1A
device that blew up such that the stuff between the wires
just disappeared. I guess that could be classified as
an "open".
Diodes are generally pretty robust. Exemplar devices
might include the diminutive 1A, plastic 1N4001 described
here . . .
http://www.aeroelectric.com/Mfgr_Data/Semiconductors/1N4001.pdf
and his big brother 25A bridge rectifier . . .
http://www.aeroelectric.com/Mfgr_Data/Semiconductors/gbpc12.pdf
Note that the single cycle surge (approx 8 milliseconds) for
the 1A device is 30A. The 25A device will stand off 300A
for 8 mS.
Power diodes for steering energy amongst the busses in
the heavy iron birds have been used for 50+ years. Their
failure rates have been exceedingly low.
Diodes also have an exceedingly long service life. I've
never seen one 'wear out'. On the other hand, switches do
have a service life . . . one that is profoundly affected
by numbers of operations per year and under what electrical
load and environmental conditions. I've seen switches open
up with very few cycles on them after ten+ years of sitting
in an airplane.
99.9% of observed diode failures in light aircraft were
in alternators where the designers of the installation
did not exercise due diligence with respect to cooling.
Concerns for a 25A diode used as the e-bus normal feedpath
management are not well founded.
Bob . . .
Message 3
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| Subject: | Re: ANL/ANN current limiter |
At 01:35 PM 3/9/2008 -0700, you wrote:
>
>Hello
>
> I have a relatively long run (10+ ft) of 1/0 CCA main battery power
> wire in my -8 I am building from the rear baggage all the way to the
> front firewall. I would like to install an current limiter on the output
> of the battery as an added layer of protection for my long wire run. I
> know Mr. Nuckolls has not advocated that on small aircraft, but I want to
> do it anyway as peace of mind since the wire passes thru quite few
> bulkheads and want to have something which will trip alot faster than I
> can act. So, which is the better choice, ANN or ANL and what current
> rating would be best, I have a 200 hp angle valve to start?
An ANL200 will carry 300A continuously. See:
http://www.aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf
This device can practically be expected to carry
worst case cranking currents without nuisance tripping.
At the same time, if you did fault that cable to
the edge of a lightening hole, the same ANL will
probably not trip while the wire burns its way
clear at the edge of the hole.
This is why these circuits have not been "protected"
in TC aircraft. Protection robust enough to stay
connected for worst case cranking will also carry
more than enough current in a 'soft fault' condition
to burn away the offending aluminum with little or
no damage to the copper.
Bob . . .
Message 4
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| Subject: | Re: "Coat Hanger" antenna |
At 07:59 AM 3/8/2008 -0800, you wrote:
>No offense to Ernest or Bob, the old coat hanger
>antennas that you terminated the coax with crimp on
>lugs has not been used in production airplanes since
>the 50's or early 60's.
>
>Coat hanger antenna
><http://www.aircraftspruce.com/catalog/avpages/av534.php>http://www.aircraftspruce.com/catalog/avpages/av534.php
>
>What Eric says about "EM field energy", which I recall
>bits from physics and armature radio, the coax,
>BNC connector is way more efficient. That inch of
>exposed shield/core & important lost insulation does
>count. The "coat hanger antenna connections are
>subject to corrosion and fatigue way more than a BNC
>connector. Just my opinion.
But without quantification. The advantages of the
modern antennas are mainly mechanical. They don't
twist in the insulator. In high-dollar models there
are p-static immunities due to the DC grounded
fabrication . . . and they look sexier and have lower
maintenance costs.
>
>No one is seriously using the coat hanger wire antenna
>on new OEM aircraft any more.
. . . for the reasons stated plus some others but
none related to observable performance.
>"Testimonials" that they work in the plane or bench are
>great, but unless you do a test on the airframe in an
>antenna test chamber (EMF / RF anechoic chamber),
>we are guessing. Besides performance there is the
>reliability of the installation.
>
>Just from an installation standpoint, spend the $124
>for the real antenna and leave the $50 coat hanger
>antenna for the closet. Antenna energy, non-ionizing
>radiation is EMF energy at high frequencies. It needs
>"ducting" to be most effective.
???? don't know what this "ducting" stuff is.
>
>Does the "strip-it crimp-it" antenna connection work?
>Yes it "works", but gosh ughaaa, ugly.
>
>We're talking about 5-8 watts of energy and communications
>of 5 to 50 mile, line of sight, listening for even more powerful
>transmitters, usually without obstacles. We can get away
>with a weak antenna.
"Weak" is un-quantified. However, just like concerns about
"iron poor blood" it may help sell alternative antennas.
>
>The coat hanger works, but its not ideal. We have better
>ways. If I was restoring a classic Beech or something, yea
>I'd keep the coat hanger antenna. Other wise coat hangers
>are for the closet (pun intended).
>
>$110-$150 for newer antenna design
>
><http://www.aircraftspruce.com/catalog/avpages/av17.php>http://www.aircraftspruce.com/catalog/avpages/av17.php
>
>PS: Some have experienced RFI with unshielded antenna
>connections thru gauges and avionics.
Now this IS a potential effect because the little
chunk of antenna inside the aircraft is indeed a
radiator.
However, in the age of plastic airplanes (both experimental
and T/C) and reasonable adherence to DO-160 radiated
and conducted susceptibility issues, potential victims
are not going to go T/U due to the small increase in
energy at the panel due to errant radiation. Field
strengths for your VHF comm while transmitting are really
strong in the cockpit (tens of volts per meter) even
with idealized antenna installations.
Bottom line is that we're fabricating OBAM aircraft.
Yes, there are sexier, more convenient and probably
more 'efficient' antennas to be considered over the
stone-simple, rod and feed-thru insulator antennas
that were quite popular 40 years ago. It all comes
down to the builder's preferences for trading his/her
personal expenditure of $time$ versus purchasing
the product of someone else's $time$ for a more
sophisticated design.
Performance risks for going the low-dollar, DIY
route are low and easily managed.
Bob . . .
Message 5
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| Subject: | Plane Power's Friendly Warning Light |
B&C's flashing warning light is pretty annoying, so I was glad to see Plane
Power's light is a steady, happy glow.
Trouble is, it turns out, that the annoying flash is pretty handy when you
really need to see it...no equipment failures to report, just didn't use the
checklist...twice >:-(
So, does anyone have a suggestion as to how to wire a flasher into the PP
light? Can I just use a simple automotive flasher, or do I need something
designed for less current? I want a fairly high (annoying) flash rate.
Hope I don't need a horn.
Thanks,
Dave Saylor
AirCrafters LLC
140 Aviation Way
Watsonville, CA
831-722-9141
831-750-0284 CL
www.AirCraftersLLC.com
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