Today's Message Index:
----------------------
1. 03:48 AM - Re: Battery or Contactor Issue? (Robert L. Nuckolls, III)
2. 04:33 AM - Re: Viking engine duel battery setup (Robert L. Nuckolls, III)
3. 04:53 AM - Re: Relays on Lear jets (Robert L. Nuckolls, III)
4. 05:02 AM - Re: RG400/RG142 BNC Male crimp connector (Peter Pengilly)
5. 05:15 AM - Re: Viking engine duel battery setup (Robert L. Nuckolls, III)
6. 06:10 AM - Re: Viking engine duel battery setup (Robert L. Nuckolls, III)
7. 08:15 AM - Re: Viking engine duel battery setup (Robert L. Nuckolls, III)
8. 09:46 AM - Solid state DC/DC relay follow-up. (Robert L. Nuckolls, III)
9. 10:20 AM - Re: Viking engine duel battery setup (Thomas E Blejwas)
10. 03:23 PM - Proposed new Z diagram? (Dj Merrill)
11. 03:28 PM - Re: Viking engine duel battery setup (Robert L. Nuckolls, III)
12. 04:03 PM - Re: Proposed new Z diagram? (Robert L. Nuckolls, III)
13. 05:49 PM - Re: Viking engine duel battery setup (Les Kearney)
14. 08:03 PM - Re: Proposed new Z diagram? (Dj Merrill)
Message 1
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| Subject: | Re: Battery or Contactor Issue? |
At 12:28 PM 1/3/2014, you wrote:
>RV-8A, Z-13/8 architecture with
>Off-Batt-Batt/Alt switch to get electrons
>flowing. 380 hours over 3 years, original Odyssey PC 680 battery.
>
>Flew for 1.3 hours 1 Jan with no problems. On 2
>Jan when I turned on Batt/Alt switch, nothing
>happened. Removed cowl and got out voltmeter
>12.8 volts to hot side of main contactor.
>
>Turned off switch, then back on same results nothing.
>
>A couple minutes later as I was digging out the
>electrical diagrams and references with Batt/Alt
>switch still on, contactor clicked and system
>operation was normal with 11.5 volts on the cockpit voltmeter.
>
>I am going to replace the battery, but wonder if
>there is an issue with the contactor. Tried to
>search Aeroelectric files for contactor
>troubleshooting, but couldnt get system to respond.
>
>Paul Valovich
Unfortunately, you didn't take enough voltage readings.
While the battery master was ON but with the contactor
NOT energized, you needed to know the voltage on the
ground-side terminal of the coil that goes off to the
battery switch.
Had this voltage ALSO been 12.8 volts, then you would
know that causation for failure to close was downstream
of the master switch control path either in wiring, the
switch or it's ground path.
Had the voltage been zero, then you would know that
either (1) the battery-master and associated wiring
was good and (a) the contactor coil had an intermittent
condition or (b) the contactor's moving parts were
'sticking'.
If you could get the problem to duplicate, having
the extra voltage reading would be helpful. A second
reading for contactor coil current would be definitive
too. Put your multimeter in the current mode and use
it to ground the master switch terminal of the contactor
with the master switch OFF. This will emulate the switch
path to ground and will either show about 1 amp of
contactor coil current (coil good, contactor not
closing, therefore sticking) or zero current which
says coil is open. If coil current is good, rap the
housing of the contactor with a screwdriver handle
and see if it drops closed with the aid of some
mechanical encouragement.
Before you replace the battery, it would be interesting
to do a load test on it. Do you have a Battery Minder
or a Schumacher 1562 charger? I would bench charge the
battery overnight and then load test it at 9 volts
to see what the engine cranking dump rate is. 200A
will get you started, 500-700A is what you expect
from a new battery.
This is a classic example of opportunity to make
measurements and KNOW what the problem is before
turning any wrenches. KNOWING the problem is
critical to fixing it with confidence. If you
cannot get it to duplicate for the purpose
of conducting a detail diagnostic, then there
are no concrete assurances that you've identified
and fixed the real problem.
Bob . . .
Message 2
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| Subject: | Re: Viking engine duel battery setup |
At 12:29 PM 1/3/2014, you wrote:
> Bob,
>
>You wrote:
> "There's a small risk
> for an overvoltage condition which is classically
> managed with a legacy o.v. sense and response system
> that has been part and parcel of aircraft alternator
> and generator systems for 60+ years."
>Yes, but the Viking has an auto-based system, with an integrated
>regulator. You make the comment:
>
> "In other words, there are no demonstrated alternator
> faults that go beyond simple failure to function . . .
> a condition that does not propagate damage or operational
> stress to other parts of the system. Hence, no additional
> form of 'isolation' is indicated."
>Is this true? Is there some recent information that suggests that
>the "runaway" auto regulator is too unlikely to be an issue. I've
>been planning for a "crowbar" and an expensive contactor for this
>potential event. Am I overreacting?
The statements I made were in the context
of the discussion for 'isolation diodes' in the b-lead.
The incorporation of diodes external to the
alternator for the purpose of 'isolation' has
no foundation in the physics.
OV conditions are another matter. There ARE
failure modes within built in regulators which
are not sufficiently detailed to allow
incorporation of STOCK internally regulated
alternators into aircraft under the LEGACY
design goals.
If one embraces those goals then some understanding
of the options for ADDING ov protection to the
system is necessary. See:
http://tinyurl.com/nexuekf
http://tinyurl.com/cx6426c
There have been some interesting discussions
about design goals for system robustness and
the implementation of failure tolerance in
OBAM aircraft over the years. Some positions
were adopted by individuals unable to demonstrate
an understanding of failure tolerant design goals
. . .
http://tinyurl.com/7lhbbah
http://tinyurl.com/nexuekf
http://tinyurl.com/omnuypr
My goals and those of my employers over
the years has been to first reduce
probability of malfunction with
robust designs backed up by further reduction
of risks with failure tolerant designs.
Alternators are but one of many components
with an ability to elevate your concerns
while airborne . . . but easily managed.
Bob . . .
Message 3
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| Subject: | Re: Relays on Lear jets |
At 12:55 PM 1/3/2014, you wrote:
Bob,
On an earlier post today, you mentioned a project where you energized
a relay before any current flowed thru it, and de-energized it after
current flow stopped.
Can you tell me how you did this and why. If the relay was not used
as a switch, then why was a relay used in this solution?
This was a design requirement unique to a system
that moves flight control surfaces with a motor.
This is common to trim systems, autopilots, flaps
and more recently fly-by-wire systems.
In the conduct of an analysis for failure mode
effects, any fault that causes anomalous or unintended
motion of a flight control surface needs to be
fitted with a means for rapid manual or perhaps
automatic shutdown.
In a flap system design for Eclipse some years
ago, we incorporated a crowbar system that opened
the motor supply breaker to effect a shutdown.
In the trim system for the Lear, a hard-contacts
relay was used in series with the motor power path
to the solid state electronics that controlled motor
speed and direction.
The fault monitoring system needed to watch
the both control and shut down components for
failure so it was necessary that the series relay
be exercised to demonstrate functionality. Obviously,
if the relay fails to close, the trim doesn't run.
But if it failed to open, then some means for
detecting and annunciating the event was called for.
The technique chosen in this application was to
have the disconnect relay operate every time the
pilot called for trim. But in the interest of
long relay life, it was advantageous to close
the relay milliseconds before the motor was
energized through solid state electronics. Similarly,
the motor was de-energized through solid state
switching milliseconds before the relay was
commanded open. Hence, the relay contacts were
preserved for carrying out a single, important
task . . . offer mechanical disconnect of trim
system power when commanded by the pilot's
Wheel Master Disconnect system.
By making the relay offer both closed and open
conditions for each trim event, the monitor system
could watch for and detect both failure to close
and failure to open events.
Also, since solid state relays are immune from the failure modes of
mechanical relays, what are the "typical" causes of failures in solid
state relays?
They short, they fail to close. They are no
different than their electro-mechanical counterparts
for how failure manifests . . . different
only in the physics that precipitates the failure.
Solid state relays are immune to the effects of
contact arcing that produces erosion and/or
sticking . . . but they can still be degraded
by inappropriate application and/or extra-ordinary
external stresses.
Thanks for all your efforts with the aeroelectric list, I'm not there
yet but pedaling as fast as I can.
You're welcome . . . I'm pleased that you find
value in the effort.
Bob . . .
Message 4
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| Subject: | Re: RG400/RG142 BNC Male crimp connector |
Peter - I've got a couple, email me off list. Peter
On 03/01/2014 18:34, Peter Mather wrote:
>
> Hi
>
> I need urgently in the UK a couple of RG400/RG142 BNC Male crimp connectors.
> Trying to find anything suitable on the various (RS, Farnell, Mouser)
> websites seems impossible. Can anyone let me have a manufacturers part
> number?
>
> Thanks
>
> Peter
>
>
Message 5
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| Subject: | Re: Viking engine duel battery setup |
At 01:49 PM 1/3/2014, you wrote:
>for many of the same reasons that (I imagine) you put a "buss tie"
>contactor in the Z-14 drawings.
But what might those reasons be? In other words, we
add a component to a system to effect some desired
functionality that figures into the overall performance,
failure tolerance and risks.
If diodes were incorporated in the manner suggested
to feed the two batteries, how would we expect these
to operate and for what purpose?
I'm not trying to be obtuse here my friend. I
AM encouraging all of my readers to understand
the application of every component they choose
to add to their system. Suppose I offered a description
for the buss-tie contactor like, "This contactor
offers pilot control of the phramistat to prevent
inadvertent operation of the whatsadozit and
potential damage to the dingusfuzzy."
The inquiring builder would probably want some
detailed expansion on that statement . . . un-
fortunately, others will assume the statement
correct and useful based on the reputation
(deserved or otherwise) of the writer.
I encourage yourself and others to KNOW why
a part is included and UNDERSTAND what useful
things it will do for you. Hence my question
as to any value you perceive for having those
diodes in place as suggested.
Bob . . .
Message 6
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| Subject: | Re: Viking engine duel battery setup |
<file:///C:/DOCUME~1/User/LOCALS~1/Temp/??.htm>Not a problem
Bob...I'm busying myself attempting to master
the techniques necessary to assemble a 25 pin D-sub w/ mostly
shielded wires...Fred
Okay, I presume you've looked at this piece on
the website.
http://tinyurl.com/87lea6o
The shields do not have to come together inside
the connector back-shell. If there are a lot of them,
you can have a couple inches of un-shielded wires
allowing all the shield terminations to happen
outside the back-shell.
Bob . . .
Message 7
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| Subject: | Re: Viking engine duel battery setup |
Emacs!
Okay, referring to the abbreviated power distribution diagram
from the Viking installation literature, we see two batteries,
both 'protected' buy current limiters and paralleled onto
the system with independent contactors. One of the two batteries
is fitted with an always hot feeder routed to a 4-pole engine power
selection switch.
Years ago, I proposed a similar two-battery system which
could be automated to some degree with what was at that
time called the Aux Battery Management Module.
http://tinyurl.com/l353p5m
http://tinyurl.com/mrxbrtw
Back in those days, the notion was that at least one of
two electronic ignition systems and perhaps a boost pump
could be supported on an independent battery automatically
isolated from the rest of the airplane when an alternator
failure was detected (low voltage).
Let's revisit those notions in light of the Viking installation
documents that speak to a 'requirement' for a second battery
capable of running the engine for a minimum of 30 minutes.
First, how does one KNOW that battery #2 is capable of
meeting that requirement? It has to be sized -AND- maintained
such that the necessary energy available when needed.
Okay, what conditions would FORCE the use of #2 battery?
(a) no doubt the alternator is off line for what ever
reason and (b) and we KNOW that #1 battery is not capable
of carrying the engine + other endurance loads for at least
30 minutes.
Hmmmm . . . if we KNOW that #1 battery is overtaxed for
the task of supplied combined energy needs but that
#1 plus #2 battery WILL rise to the occasion, then what
is the value in having two batteries? Would a single
battery with a KNOWN capacity for the combined loads not
be a simpler, lighter and lower cost choice?
In other words, what combination of conditions pose such
risk that a second battery is needed to mitigate the risk?
Two batteries DOUBLES your battery maintenance expenses
and adds empty weight . . . all intended to mitigate a
rather rare event . . . alternator failure.
This line of reasoning is germane to the discussions
we were having on Fred's Exp-Bus integration which prompted
the crafting of Figure Z-7. It also applies to Les's question
about diodes suitable for battery isolation. Obviously, the
golden solution will include some assessment of loads over and
above those required to run the engine . . . along with
some decisions as to whether you're expecting to keep the panel all lit
up . . . or have crafted a plan-B that matches your skills
and confidence levels for getting down with a bare minimum
of panel equipment combined perhaps with flight bag back-up
hardware.
If Figure Z-7 were substituted for the figure above, are
there any unforeseen risks? Comments on the Viking drawing,
Figure Z-7 and perceptions of your individual FMEAs are solicited . . .
Bob . . .
Message 8
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| Subject: | Solid state DC/DC relay follow-up. |
The exemplar relay I ordered in last week arrived
and the performance is . . . shall we say . . .
disappointing.
I set up to switch a 12A load and voltage drop across
the 'contacts' was about 2.1 volts for an on-state
resistance of 0.175 ohms. Clearly way too high to
be a practical relay for more than a couple amps . . .
much less the 'rated' 100A.
I'm in a conversation with the supplier now . . . perhaps
I have an anomalous specimen . . . watch this
space.
Bob . . .
Message 9
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| Subject: | Re: Viking engine duel battery setup |
Bob,
As someone who has a Viking engine and who has been looking to modify Z-7 fo
r my electrical system, I'm very interested in this thread. First, where di
d you get the diagram at the top of your last posting? It's clearly differe
nt then the one sent by Les Goldner, which I also got from the Viking websit
e. It appears to be a system for Vikings unreleased turbo version.
I hesitate to make the following comment, since you chose not to answer my l
ast question about alternators running without batteries; but you asked for c
omments on Z-7 for this application. Viking claims that the alternator can r
un with the batteries disconnected and I believe that the diagram provided b
y Les allows for that. Your comment in an earlier thread that you wouldn't s
witch off the battery/batteries unless you were also disconnecting the alter
nator is a strong position. I understand that batteries that are properly m
aintained don't usually fail in a catastrophic manner, but is that never? C
an we quantify? Hard to separate failures due to inadequate maintenance and
others. In the absence of numbers but anecdotal experiences of failures (m
ine for one), why not have an allowance for running off the alternator only?
Seems prudent to me, so I'd like to understand why it isn't to you. Thank
s.
Tom
Sent from my iPad
> On Jan 4, 2014, at 9:13 AM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroel
ectric.com> wrote:
>
> <a6a5924.jpg>
>
>
> Okay, referring to the abbreviated power distribution diagram
> from the Viking installation literature, we see two batteries,
> both 'protected' buy current limiters and paralleled onto
> the system with independent contactors. One of the two batteries
> is fitted with an always hot feeder routed to a 4-pole engine power
> selection switch.
>
> Years ago, I proposed a similar two-battery system which
> could be automated to some degree with what was at that
> time called the Aux Battery Management Module.
>
> http://tinyurl.com/l353p5m
>
> http://tinyurl.com/mrxbrtw
>
> Back in those days, the notion was that at least one of
> two electronic ignition systems and perhaps a boost pump
> could be supported on an independent battery automatically
> isolated from the rest of the airplane when an alternator
> failure was detected (low voltage).
>
> Let's revisit those notions in light of the Viking installation
> documents that speak to a 'requirement' for a second battery
> capable of running the engine for a minimum of 30 minutes.
>
> First, how does one KNOW that battery #2 is capable of
> meeting that requirement? It has to be sized -AND- maintained
> such that the necessary energy available when needed.
>
> Okay, what conditions would FORCE the use of #2 battery?
> (a) no doubt the alternator is off line for what ever
> reason and (b) and we KNOW that #1 battery is not capable
> of carrying the engine + other endurance loads for at least
> 30 minutes.
>
> Hmmmm . . . if we KNOW that #1 battery is overtaxed for
> the task of supplied combined energy needs but that
> #1 plus #2 battery WILL rise to the occasion, then what
> is the value in having two batteries? Would a single
> battery with a KNOWN capacity for the combined loads not
> be a simpler, lighter and lower cost choice?
>
> In other words, what combination of conditions pose such
> risk that a second battery is needed to mitigate the risk?
> Two batteries DOUBLES your battery maintenance expenses
> and adds empty weight . . . all intended to mitigate a
> rather rare event . . . alternator failure.
>
> This line of reasoning is germane to the discussions
> we were having on Fred's Exp-Bus integration which prompted
> the crafting of Figure Z-7. It also applies to Les's question
> about diodes suitable for battery isolation. Obviously, the
> golden solution will include some assessment of loads over and
> above those required to run the engine . . . along with
> some decisions as to whether you're expecting to keep the panel all lit
> up . . . or have crafted a plan-B that matches your skills
> and confidence levels for getting down with a bare minimum
> of panel equipment combined perhaps with flight bag back-up
> hardware.
>
> If Figure Z-7 were substituted for the figure above, are
> there any unforeseen risks? Comments on the Viking drawing,
> Figure Z-7 and perceptions of your individual FMEAs are solicited . . .
> Bob . . .
Message 10
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| Subject: | Proposed new Z diagram? |
I'd like to start off by saying please be gentle. I'm not an expert and
this could be completely boneheaded.
I've been looking through the various Z diagrams, and although there are
parts of some that I like, I could not find one that is exactly what I
am (or think I am) looking for.
From being on this list for a decade or more, I know that Bob's first
question will be along the lines of "What are you looking for" followed
by "What elements do you want that aren't addressed by the current
diagrams". It is hard to put into words, but I'm going to try.
My aircraft will have an electrically dependent engine (electronic
ignition, gravity feed so no fuel pump) and an electrically dependent
panel (GRT HX EFIS and EIS). It will be used for IFR.
I know recently that we have been talking about how statistically
reliable alternators and batteries are, and have been considering a Z-7
based on a single alt and battery. Physics and statistics aside, I am
just not comfortable with this, and I want a dual battery
configuration. This is a personal choice. That led me to Z-19.
What I do not like about Z-19 is that it has two always hot power
buses. I want a system that when the contactor is off, the battery is
isolated except for the wires going to the contactor. Again, physics
and logic aside, this what I "want".
What I like about Z-19 is the redundancy providing power to the ECU and
Fuel Pump, and that it is an automatic redundancy. Both power buses are
providing power to the ECU at the same time from independent sources.
This led me to realize that I really do not care about having an
"endurance" bus, but what I really care about is having a "redundant"
bus, in other words there are a few devices in my setup that I want to
have the same automatic redundant power as offered by the engine part of
Z-19.
Taking parts of Z-19 that I like, and leaving parts out, I've attempted
to create a "redundant bus" diagram. It also incorporates an
"alternator only" operation simply by the fact of isolating the two
charging circuits and having the alternator on its own switch, although
I can't picture running in this mode.
Please excuse the crudeness of the drawing. I did it by hand, and just
took a picture of the paper afterwards.
Some parts I am not even sure are feasible, such as the diodes that
separate the two charging circuits (located just above the primary bus
in the drawing). I don't even know if diodes exist that will be able to
handle those loads, but I am sure that some sort of electro-whizzy would
probably do it.
Some notes:
I will be using a Fly EFII electronic ignition. Manufacturer
recommendation is a 10 amp CB/fuse for the coil charging circuit, and 5
amp for the ECU. I am told that overall the ignition draws 1.2 amps on
average for power usage purposes, but the coil charging currents can be
up to 10 amps. This current only flows for a few milliseconds.
Gravity feed for the fuel, so no fuel pump.
The GRT HX EFIS and the GRT EIS have multiple, internal diode isolated
power feeds built in which is why there are Pow "A" and Pow "B" feeds
for each of these devices.
This is a first pass, but I am thinking that I want GPS, NAV, COM, and
the Intercom to also have redundant power. I want enough to make an
instrument approach if needed, so usage and/or recommendations may
change this list.
Everything else is wired to the primary bus only (no access to the
secondary bus).
Not completely sure yet, but I anticipate the Aux battery to be smaller,
and mounted under the panel. It will be sized appropriately to offer at
least an hour of battery-only operation for items on the redundant bus
and to support the ignition. The main battery will be larger and
mounted in the tail for CG purposes.
Please critique, but be nice! :-)
Small version: http://deej.net/glastar/pics/electrical/redundant.jpg
Larger picture: http://deej.net/glastar/pics/electrical/redundant-large.jpg
-Dj
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
Message 11
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| Subject: | Re: Viking engine duel battery setup |
At 12:19 PM 1/4/2014, you wrote:
Bob,
As someone who has a Viking engine and who has been looking to modify
Z-7 for my electrical system, I'm very interested in this
thread. First, where did you get the diagram at the top of your last
posting? It's clearly different then the one sent by Les Goldner,
which I also got from the Viking website. It appears to be a system
for Vikings unreleased turbo version.
I got it from the Viking website using a link forwarded to
me by one of the list readers. The exact version is insignificant
at the moment as the points to ponder deal with the rationale for
two batteries as opposed to one.
I hesitate to make the following comment, since you chose not to
answer my last question about alternators running without batteries;
but you asked for comments on Z-7 for this application.
My apologies . . . didn't mean to ignore your question.
Never hesitate to jump right in the middle of my
lap if you believe some important link of communication
has broken. This list isn't about feelings, it's
about ideas . . . and even though GMCJetpilot found the
assertion incredible, I cannot be insulted and I welcome
logical persuasion.
Viking claims that the alternator can run with the batteries
disconnected and I believe that the diagram provided by Les allows for that.
Okay, that doesn't surprise me. I'm wondering to what extent
that operating mode has been tested.
Your comment in an earlier thread that you wouldn't switch off the
battery/batteries unless you were also disconnecting the alternator
is a strong position.
. . . yes . . . based on the legacy design goals
of yesteryear when the split-rocker master switch
was king.
But that was several generations ago in both alternator
and battery design. Odds are that most airplanes will continue
operating sans battery . . . but I suspect there are
limits that should be explored. I had some plans to
acquire a variable speed drive stand some years ago.
The goal was to explore the new alternator-only
paradigm.
I understand that batteries that are properly maintained don't
usually fail in a catastrophic manner, but is that never? Can we quantify?
I'll have to ask Skip about that. Concorde has done
countless failure analysis over the course of battery
evolution in aircraft and can probably offer us some
quantitative assessment.
Hard to separate failures due to inadequate maintenance and
others. In the absence of numbers but anecdotal experiences of
failures (mine for one), why not have an allowance for running off
the alternator only? Seems prudent to me, so I'd like to understand
why it isn't to you. Thanks.
I absolutely agree. But just as I was loath to
RECOMMEND the internally regulated alternator some
years back, my reluctance is not based on hard
negative data but a lack of hard positive data.
If Viking says they can run alternator only, I
rather suspect that they have at least determined
that the engine doesn't quit and the panel stays
lit with the batteries OFF. I wonder to what extent
any testing has been accomplished and documented upon
which a gray beard stuck in such traditions
can offer confident recommendation.
Thanks for asking . . .
Bob . . .
Message 12
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| Subject: | Re: Proposed new Z diagram? |
My aircraft will have an electrically dependent engine (electronic
ignition, gravity feed so no fuel pump) and an electrically dependent
panel (GRT HX EFIS and EIS). It will be used for IFR.
How is the engine dependent? Ignition? Fuel Injection?
Do you have the energy requirement numbers?
I know recently that we have been talking about how statistically
reliable alternators and batteries are, and have been considering a
Z-7 based on a single alt and battery. Physics and statistics
aside, I am just not comfortable with this, and I want a dual
battery configuration. This is a personal choice. That led me to Z-19.
One can ALWAYS add a second battery. Our builders
have been doing this for decades and the techniques
have been discussed at length on the List.
What I do not like about Z-19 is that it has two always hot power
buses. I want a system that when the contactor is off, the battery
is isolated except for the wires going to the contactor. Again,
physics and logic aside, this what I "want".
Any always hot busses are battery busses and they're
part and parcel of a considered FEMA and meeting
design goals. It's my wish that we can assist with
the crafting of your design goals based more on
understanding and planning and not so much on worries
that drive your discomfort.
What I like about Z-19 is the redundancy providing power to the ECU
and Fuel Pump, and that it is an automatic redundancy. Both power
buses are providing power to the ECU at the same time from
independent sources.
This led me to realize that I really do not care about having an
"endurance" bus, but what I really care about is having a "redundant"
bus, in other words there are a few devices in my setup that I want
to have the same automatic redundant power as offered by the engine
part of Z-19.
Redundant to meet what failure event. There's nothing
that prevents one from having as many batteries, alternators,
busses and switches as their creativity and physical space
allows . . . but in the TC aircraft world, the first goal
is to minimize weight, parts count, system complexity
and cost of ownership. At the same time, risk assessment
must necessarily drive all the above goals in the wrong
direction. The elegant design adds just enough but no more.
Taking parts of Z-19 that I like, and leaving parts out, I've
attempted to create a "redundant bus" diagram. It also incorporates
an "alternator only" operation simply by the fact of isolating the
two charging circuits and having the alternator on its own switch,
although I can't picture running in this mode.
Please excuse the crudeness of the drawing. I did it by hand, and
just took a picture of the paper afterwards.
Some parts I am not even sure are feasible, such as the diodes that
separate the two charging circuits (located just above the primary
bus in the drawing). I don't even know if diodes exist that will be
able to handle those loads, but I am sure that some sort of
electro-whizzy would probably do it.
Some notes:
I will be using a Fly EFII electronic ignition. Manufacturer
recommendation is a 10 amp CB/fuse for the coil charging circuit, and
5 amp for the ECU. I am told that overall the ignition draws 1.2
amps on average for power usage purposes, but the coil charging
currents can be up to 10 amps. This current only flows for a few milliseconds.
So have you arrived at a ball-park number
for total electrical system energy requirements?
You speak to a 60 minute battery-only ops goal
but can/should it be longer?
Gravity feed for the fuel, so no fuel pump.
The GRT HX EFIS and the GRT EIS have multiple, internal diode
isolated power feeds built in which is why there are Pow "A" and Pow
"B" feeds for each of these devices.
This is a first pass, but I am thinking that I want GPS, NAV, COM,
and the Intercom to also have redundant power. I want enough to make
an instrument approach if needed, so usage and/or recommendations may
change this list.
Everything else is wired to the primary bus only (no access to the
secondary bus).
Not completely sure yet, but I anticipate the Aux battery to be
smaller, and mounted under the panel. It will be sized appropriately
to offer at least an hour of battery-only operation for items on the
redundant bus and to support the ignition. The main battery will be
larger and mounted in the tail for CG purposes.
Please critique, but be nice!
You have described adjustments to an architecture
but it's not clear as to the reasoning behind those
moves. It seems as if you don't want any single failure
to cause to you drop to an energy efficient, endurance
mode . . . are you trying to keep everything lit up
no matter what?
You speak of a large main battery and a smaller
auxiliary battery. What's the physics behind these
sizing decisions?
Larger picture: http://deej.net/glastar/pics/electrical/redundant-large.jpg
Z-7 elects to drive a single engine bus
through diodes from two power paths. What in
your knowledge or experience suggests that
charging batteries through diodes offers
more attractive options?
Bob . . .
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| Subject: | Re: Viking engine duel battery setup |
Hi All
This is the Eggenfellner Aircraft Engines wiring diagram for a Subaru engine
(turbo'd). This where the E6T engine reference comes from.
Cheers
Les
Sent from my iPhone
> On Jan 4, 2014, at 9:13 AM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroel
ectric.com> wrote:
>
> <a6a5924.jpg>
>
>
> Okay, referring to the abbreviated power distribution diagram
> from the Viking installation literature, we see two batteries,
> both 'protected' buy current limiters and paralleled onto
> the system with independent contactors. One of the two batteries
> is fitted with an always hot feeder routed to a 4-pole engine power
> selection switch.
>
> Years ago, I proposed a similar two-battery system which
> could be automated to some degree with what was at that
> time called the Aux Battery Management Module.
>
> http://tinyurl.com/l353p5m
>
> http://tinyurl.com/mrxbrtw
>
> Back in those days, the notion was that at least one of
> two electronic ignition systems and perhaps a boost pump
> could be supported on an independent battery automatically
> isolated from the rest of the airplane when an alternator
> failure was detected (low voltage).
>
> Let's revisit those notions in light of the Viking installation
> documents that speak to a 'requirement' for a second battery
> capable of running the engine for a minimum of 30 minutes.
>
> First, how does one KNOW that battery #2 is capable of
> meeting that requirement? It has to be sized -AND- maintained
> such that the necessary energy available when needed.
>
> Okay, what conditions would FORCE the use of #2 battery?
> (a) no doubt the alternator is off line for what ever
> reason and (b) and we KNOW that #1 battery is not capable
> of carrying the engine + other endurance loads for at least
> 30 minutes.
>
> Hmmmm . . . if we KNOW that #1 battery is overtaxed for
> the task of supplied combined energy needs but that
> #1 plus #2 battery WILL rise to the occasion, then what
> is the value in having two batteries? Would a single
> battery with a KNOWN capacity for the combined loads not
> be a simpler, lighter and lower cost choice?
>
> In other words, what combination of conditions pose such
> risk that a second battery is needed to mitigate the risk?
> Two batteries DOUBLES your battery maintenance expenses
> and adds empty weight . . . all intended to mitigate a
> rather rare event . . . alternator failure.
>
> This line of reasoning is germane to the discussions
> we were having on Fred's Exp-Bus integration which prompted
> the crafting of Figure Z-7. It also applies to Les's question
> about diodes suitable for battery isolation. Obviously, the
> golden solution will include some assessment of loads over and
> above those required to run the engine . . . along with
> some decisions as to whether you're expecting to keep the panel all lit
> up . . . or have crafted a plan-B that matches your skills
> and confidence levels for getting down with a bare minimum
> of panel equipment combined perhaps with flight bag back-up
> hardware.
>
> If Figure Z-7 were substituted for the figure above, are
> there any unforeseen risks? Comments on the Viking drawing,
> Figure Z-7 and perceptions of your individual FMEAs are solicited . . .
> Bob . . .
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| Subject: | Re: Proposed new Z diagram? |
Hi Bob,
Thank you for your comments. Based on your response and questions
asked, I think you may have missed some points that I presented in my
initial post. I will try to elaborate and present my thoughts more clearly.
You ask several questions concerning the "why". As I mentioned,
ultimately, it is because I "want", not solely based on any particular
design based on physics, simple ideas, or statistical likelihood of any
component failing. When building or modifying an OBAM aircraft, "want"
is an important factor. This is why most of us build/fly experimental
aircraft versus spam cans, and as with most experimental aircraft, one
size does not necessarily fit all.
I want dual batteries and am not comfortable with just one. This is
not physics, these are those messy human "wants" and "feelings", which
can't be quantified easily, if at all.
I do not want an always hot power bus. I want a system that when
the contactor is off, the battery is isolated except for the wires going
to the contactor.
I want automatic redundancy to certain devices similar to that
offered in the engine section of Z-19.
Essentially, the "why" of the above doesn't really matter. These
are things that I "want" in my aircraft, and I'm trying to figure out
the best way to accomplish these goals safely. I am hoping that you and
others on the list are willing to help me to achieve this. The diagram
I presented is my first draft towards this goal, and is my first ever
attempt at an electrical design. It might be total felgercarb, which is
why I am asking for help.
I do have a few guidellines in my thinking. One is that from
others' experience, we know that in a one battery situation, the EFIS
and EIS can "brown out" and reboot when cranking the engine. I desire to
have the EFIS and EIS up and running before cranking the engine, thus a
second power source is required at least for these two items, which is
one small part of the design goals.
> How is the engine dependent? Ignition? Fuel Injection?
> Do you have the energy requirement numbers?
As mentioned, the engine is electrically dependent upon the
ignition system, comprised of the ECU and coil circuits. There is no
fuel pump (and no fuel injection). In particular, it is a Lycoming
O-320 in a Glastar, using gravity for fuel feed into a Rotec TBI
(Throttle Body Injector), which uses no electrical power. As outlined
in the initial post, the energy requirements are 1.2 amps to keep the
ignition running, but simply keeping the engine running is only part of
the goal.
> Any always hot busses are battery busses and they're
> part and parcel of a considered FEMA and meeting
> design goals. It's my wish that we can assist with
> the crafting of your design goals based more on
> understanding and planning and not so much on worries
> that drive your discomfort.
I have no desire or need for an always hot battery bus. When power
is turned off, I do not wish to have any parasitic load that can drain
the battery between flights, and I do not want to have any live buses.
These are design goals that I consider important for my electrical
system, but I fully agree that others may not share these same goals.
That's okay. :-)
> Redundant to meet what failure event. There's nothing
> that prevents one from having as many batteries, alternators,
> busses and switches as their creativity and physical space
> allows . . . but in the TC aircraft world, the first goal
> is to minimize weight, parts count, system complexity
> and cost of ownership. At the same time, risk assessment
> must necessarily drive all the above goals in the wrong
> direction. The elegant design adds just enough but no more.
All that is true, however, the most elegant design from an
engineering perspective may not be the most desired design from a user
perspective. I've stated up front that parts of the design are based on
what I "want", not just what is the most practical design based on
physics or simple ideas. As long as the engineering can support it,
including the "wants" can be just as important in meeting a design goal
as "elegance".
I am sitting here with Z-19 in one hand, and my proposed drawing in
the other, and to me my drawing looks much simpler than Z-19 with less
parts count, and in my mind seems to offer similar yet slightly
different functionality to incorporate my "wants" versus the Z-19
boilerplate. As I said, this is my first attempt ever at a design, so I
might be way off on this, and please, do not take this as an attack on
Z-19. I am simply using it as a comparison to your comment about parts
count and system complexity, especially since my diagram was based off
Z-19 initially.
>
> So have you arrived at a ball-park number
> for total electrical system energy requirements?
> You speak to a 60 minute battery-only ops goal
> but can/should it be longer?
The hour was picked as my personal comfort level. An hour should
be adequate to get the plane safely on the ground even in IFR
conditions. I do not have the exact numbers on all of the installed
equipment in the entire airplane, however, the total load on the
redundant bus is about 6 amps including the electronic ignition (COM not
transmitting). Unless I am missing something, I don't believe that
having those exact numbers at this time will change the basic design of
the electrical system. It will have an impact on the size of the
batteries chosen, and the values of fuses/CBs, though. Would you agree,
or have I misunderstood something?
Bear in mind that if the alternator fails, I have two separate
batteries that can provide power, so the total time should actually be
much longer than an hour especially if I turn off "extra" loads on the
main bus, but should be at least an hour from the aux battery if I don't
turn off anything. If one or the other battery or associated wiring and
circuitry should fail, the alternator and single battery remaining
should be able to run everything until the completion of the flight,
although more than likely I would make a precautionary landing in the
event of any type of problem.
> You have described adjustments to an architecture
> but it's not clear as to the reasoning behind those
> moves. It seems as if you don't want any single failure
> to cause to you drop to an energy efficient, endurance
> mode . . . are you trying to keep everything lit up
> no matter what?
I thought I described this clearly, but apparently I've not
communicated well. I'm trying to keep everything on the redundant bus
lit up as those are what I consider the critical items, and I mentioned
that this list of items may change as I use the system and/or receive
recommendations from others. In particular, in my initial email I
listed the electronic ignition, GPS, NAV, COM, and the Intercom to have
redundant power. At the moment, these are what I would consider minimum
to get the airplane safely on the ground in IFR conditions.
> You speak of a large main battery and a smaller
> auxiliary battery. What's the physics behind these
> sizing decisions?
Partly because I am rewiring an existing electrical system on an
already flying airplane. The main battery is located just behind the
baggage area, and I do not desire to relocate this.
The aux battery only needs to be large enough to run the redundant
bus for an hour, and will be mounted under the panel for CG reasons, so
it is helpful to have it be as small as practical from a physical
perspective.
As stated earlier, the electrical sizing of the batteries will be
made after all of the electrical loads are calculated, and are located
on either the main or redundant buses. Again, I'm not sure how the size
of the batteries will have any impact on the basic design of the
electrical system. Will selecting a 10ah versus a 12ah battery for the
aux, for example, have any effect at all on the basic electrical design
as depicted in the diagram?
> Z-7 elects to drive a single engine bus
> through diodes from two power paths. What in
> your knowledge or experience suggests that
> charging batteries through diodes offers
> more attractive options?
None, which is why I indicated diodes in the initial design. As I
stated, "I don't even know if diodes exist that will be able to handle
those loads". If they will, excellent, I chose correctly the first time
and I really have learned some things from following this list for the
past decade or so. If not, I was sure someone on here would point that
out and offer an alternative. Bear in mind that I'm still learning...
So we've gone through a couple of pages of questions and answers, but I
feel like I haven't really gotten any feedback at all on the diagram
itself as presented.
Will it work?
Are there any obvious or not so obvious flaws?
What are your concerns, if any, in the diagram as presented?
Have I communicated the basic design goals clearly enough to follow,
taking in to account the end-user "wants" in addition to ensuring that
the basic design will function properly?
http://deej.net/glastar/pics/electrical/redundant-large.jpg
Thanks,
-Dj
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
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