Today's Message Index:
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1. 08:18 AM - Re: 2 alternators and 3 questions (Pat Little)
2. 09:02 AM - Re: 2 alternators and 3 questions (Robert L. Nuckolls, III)
3. 07:32 PM - Aera 660 Bare Wire Cradle Question (farmrjohn)
4. 07:50 PM - Re: Aera 660 Bare Wire Cradle Question (user9253)
Message 1
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| Subject: | Re: 2 alternators and 3 questions |
I appreciate your suggestions, Art.
In my loads analysis the left column, which is colored, corresponds to
your *Maximum
*column, and I use this for wire sizing (hence the color codes, just as a
quick visual for me to know which PIDG I'll be using). The other columns to
the right show which circuits will be in use during various phases of
flight (so I only show starter contactor when starting, and flap motor is
present in some phases of flight but reduced somewhat to account for air
loads on the flaps - it only shows the max 4A during descent when
presumably the motor is working against the air loads). My final,
right-most, column of numbers is an attempt to show average currents, which
I think corresponds to your *Typical *column.
Maybe all the numbers in my phase-of-flight columns should be average, and
ignore transient peaks?
I would love to be able to run both alternators all the time but I don't
think I can (at least not without giving the pilot extra work to do)
because my secondary alternator has a thermal restriction and needs to be
kept below 17A. Depending on details of how the the two alternators behave
at high currents, i.e., how their voltages droop as current increases, the
secondary may exceed 17A when pitot heat is on and would need to be
cosseted even though the bus voltage, with both alternators contributing,
is still plenty above LV warn level. So, the pilot would have to monitor
the secondary's current which is extra work. And I agree that is a Bad
Idea.
Pat
On Wed, May 22, 2019 at 6:08 AM Art Zemon <art@zemon.name> wrote:
> Pat,
>
> I encourage you to reexamine your load analysis. Here are three points
> from your Main Bus section:
>
> - Flaps motor - 4 amps. The flaps motor rarely operates. This current
> can be supplied by the battery if the alternator does not have suffici
ent
> capacity.
> - Stater contactor - 4 amps. Once the engine is running, the starter
> contactor disengages and draws no current.
> - Strobe Lights - 4.5 amps. Like you, I have AeroLEDs Pulsar NSP
> lights on my wing tips and the pair draws 2.40 amps continuous, not 4.
50.
>
> It looks like I just saved you 10.1 amps. =F0=9F=99=82
> As a point of comparison is the load analysis for my airplane. It is in
> the right column of this drawing.
>
> overview.pdf
> <https://drive.google.com/a/zemon.name/file/d/0BzOP2gb9_3RQSU5qbVN1ckJNOU
k/view?usp=drive_web>
>
> As for your cockpit procedures, they seem like they will certainly work
> but it is way more effort than I would want to oblige myself to. I fly wi
th
> both alternator on 100% of the time. If the primary fails, the backup
> automatically steps in. No pilot action required. If the load is too high
> for the standby alternator, I will see a low voltage alert and can shed
> some load. The only two things that I anticipate needing to turn off woul
d
> be pitot heat (which is almost certainly off anyway) and autopilot servos
.
>
> Just my opinion, of course: Since we are designing our own airplanes, we
> have the ability to reduce pilot workload as much as possible. Doing so i
s
> a Really Good Idea.
>
> -- Art Z.
>
>
> On Wed, May 22, 2019 at 1:30 AM Pat Little <roughleg@gmail.com> wrote:
>
>> Bob (and Art and Joe),
>> Many thanks for your feedback. I realize from your replies that I didn't
>> explain why I am proposing an e-bus which is normally for reducing batte
ry
>> loads, but since my Stby alternator has a strict current limit I think t
he
>> e-bus has a role to play in my system. Here is how I think my design wou
ld
>> work, which I hope will make it clear why I am adding the electrical
>> complexity of the e-bus to achieve a reduction in pilot workload:
>>
>> 1) cruise flight, main alternator ON and stby alt OFF - ammeter shows
>> current from main alternator (our EMS only has a single ammeter gauge)
>> 2) main alternator fails - LV warning alerts the pilot, he sees current
>> is zero and deduces main alternator has failed (or maybe the breaker has
>> popped which makes it easier to see what has happened)
>> 3) battery carries the loads for a short while
>> 4) pilot turns the e-bus alternate feed ON, and the master OFF - this
>> reduces the electrical loads below the 17A limit of the stby alternator
>> 5) pilot turns Stby Alt ON. The EMS now shows current from Stby Alt (the
>> Stby Alt switch is a 3PDT that swaps the ammeter shunt signals as well a
s
>> controlling the relay) and pilot can verify loads <17A
>> 6) continue flight to destination
>>
>> In this sequence the benefit of the e-bus is that it gives the pilot a
>> few simple actions to perform in order to ensure the Stby alternator is
>> happy, and the process doesn't require a lot of heads-down work.
>>
>> NOTE - the above scenario assumes worst-case electrical loads. If the
>> pitot heat is not being used then it would be simpler to just turn on St
by
>> alt and not use the e-bus alt feed.
>>
>> So, how to choose a system architecture to achieve this?
>>
>> Given that I am proposing to use the Stby alt with the master OFF (e-bus
>> alternate feed ON) I need the output of the Stby alt to feed into the
>> system upstream of the battery contactor, and that is what Z-13 shows,
>> whereas Z-12 has it going in downstream where it won't work for my propo
sed
>> design. That is why I want to base my design on Z-13. However, Z-12 show
s
>> the B&C regulator, which is what I have for my main alternator, so i wou
ld
>> be incorporating some elements from Z-12 into my drawing.
>>
>> I have a loads analysis (I based it on one of the examples from your sit
e
>> Bob) and I'm attaching it. It is still somewhat incomplete but I'd welco
me
>> you thoughts.
>>
>> Cheers,
>> Pat
>>
>>
>>
Message 2
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| Subject: | Re: 2 alternators and 3 questions |
>
>Maybe all the numbers in my phase-of-flight columns should be
>average, and ignore transient peaks?
Yes . . .
>I would love to be able to run both alternators all the time but I
>don't think I can (at least not without giving the pilot extra work
>to do) because my secondary alternator has a thermal restriction and
>needs to be kept below 17A. Depending on details of how the the two
>alternators behave at high currents, i.e., how their voltages droop
>as current increases, the secondary may exceed 17A when pitot heat
>is on and would need to be cosseted even though the bus voltage,
>with both alternators contributing, is still plenty above LV warn
>level. So, the pilot would have to monitor the secondary's current
>which is extra work. And I agree that is a Bad Idea.
Your gut is right . . . AMMETERS are
bad flight management instrumentation.
Your various "plans" based on flight
conditions are predictable. That's
what the load analysis is all about.
We've built millions of airplanes
with no ammeters in them. It's only
since the glass cockpit guys started
adding them to the list of features
that pilots are beginning to think
that (1) gee, if I can go measure a current,
why not? (2) but which current and for
what operational purpose? (3) now
that I can track that feature in flight,
what are my pilot duties (work load)
to observe and react to what I see?
The answer to all three questions is
zilch, zip, nada . . .
If you've need to observe a manufacture's
limit on an alternator load, then factor
that into which switches are ON and OFF
for the pre planned flight conditions
(those columns in the load analysis).
Ammeters are diagnostic instruments
used to deduce malfunctions and
plan repairs . . . on the ground.
If you need to fiddle with the switches
in flight while watching an ammeter,
you've failed to exploit the value
of the load analysis.
Bob . . .
Message 3
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| Subject: | Aera 660 Bare Wire Cradle Question |
NOOB question: I have a Garmin Aera 660 that I'd like to use their bare wire cradle
to connect to aircraft power and utilize the 232 and audio outputs. Is
the best way to do that is connect all nine wires in a D-sub connector to provide
connections to the other devices? If so, would it be best to use a male of
female connector? For now the planned distribution would be audio for warnings
to Garmin GTR 200 and gps position information to the ELT. At some point
the second 232 output would be for navigational display. This is in addition to
the power and ground for the 660 itself. Thanks.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=489352#489352
Message 4
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| Subject: | Re: Aera 660 Bare Wire Cradle Question |
If the GPS has a male connector and the aircraft wiring has the female connector,
then there is less chance of accidentally shorting out the power wires.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=489353#489353
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