Today's Message Index:
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1. 05:49 AM - Re: Avionics Master (donjohnston)
2. 08:25 AM - Re: Re: Avionics Master (Robert L. Nuckolls, III)
3. 10:39 AM - Re: Avionics Master (donjohnston)
4. 10:54 AM - Re: Re: Avionics Master (Sebastien)
5. 01:17 PM - Re: Ballasting Dsub connectors (Robert L. Nuckolls, III)
6. 06:54 PM - Alternator Field Circuit Fuse Blow (Valin Thorn)
Message 1
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Subject: | Re: Avionics Master |
Not to poke a sleeping bear...
I've got an avionics master not because I'm worried out spikes. My concern is
with the opposite. Sags.
I also have remote avionics (no power switches on the devices) with a VPX power
distribution system. When I'm starting up the EFIS will reboot if the voltage
gets too low (I'd have to check the doc's but I think it gets unhappy below
18 or maybe 20v). The radios are a bit more tolerant as they will handle much
lower voltages. Not sure about the GPS or audio panel.
The greater issue is that when the EFIS power sags, sometimes it won't reboot and
just goes into limbo. Then I have to go in to the VPX, shut off the breaker,
wait, and then reactivate the breaker to get the EFIS back up.
The EFIS doesn't reboot on every start. But if I've been fighting a stubborn hot
start then the battery can get a little tired. For the primary EFIS, I have
a small backup battery that powers the EFIS that during engine starts.
I could have put in a second backup battery for the other EFIS, or a switch for
the second EFIS. But it seems like the simplest solution is an avionics master.
This also allows me to power up the electrical system if I want to work on
the gear retract system, lights, etc., without powering up the avionics.
Just my .02
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=463750#463750
Message 2
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Subject: | Re: Avionics Master |
At 07:47 AM 12/6/2016, you wrote:
>
>Not to poke a sleeping bear...
>
>I've got an avionics master not because I'm worried out spikes. My
>concern is with the opposite. Sags.
>
>I also have remote avionics (no power switches on the devices) with
>a VPX power distribution system. When I'm starting up the EFIS will
>reboot if the voltage gets too low (I'd have to check the doc's but
>I think it gets unhappy below 18 or maybe 20v). The radios are a bit
>more tolerant as they will handle much lower voltages. Not sure
>about the GPS or audio panel.
Low voltage is generally not a stress to be
'handled' beyond the ability to make a graceful
recovery after the brown-out event. This
shortcoming is generally limited to devices
with micro-controllers that are not fitted
with brown-out protection features . . .
Failure to design such features into a modern
appliance is something akin to forgetting
to include a filler-spout on a fuel tank.
Pretty elementary.
In 50+ years of designing and fabricating
electro-whizzies for aircraft from Hawker
4000 to ultra-lights, I've never been
challenged by the notion that brown-outs of
any magnitude, rate and duration are a
special force to be wrestled with.
>
>
>The greater issue is that when the EFIS power sags, sometimes it
>won't reboot and just goes into limbo. Then I have to go in to the
>VPX, shut off the breaker, wait, and then reactivate the breaker to
>get the EFIS back up.
>
>The EFIS doesn't reboot on every start. But if I've been fighting a
>stubborn hot start then the battery can get a little tired. For the
>primary EFIS, I have a small backup battery that powers the EFIS
>that during engine starts.
>
>I could have put in a second backup battery for the other EFIS, or a
>switch for the second EFIS. But it seems like the simplest solution
>is an avionics master. This also allows me to power up the
>electrical system if I want to work on the gear retract system,
>lights, etc., without powering up the avionics.
>
>Just my .02
Unfortunately, there are numerous products offered
to the aviation markets that are not designed to the
spirit and intent of legacy rules-of-the-road for
aviation appliances.
Brownout mitigation has been discussed numerous
times over the years here on the List with a
variety solutions offered. They all have the
disadvantage of increased weight, system
complexity and potential electro-magnetic
compatibility issues (radio noise).
Do these affected systems not have their
own power switches? If not, then you're
not really adding an avionics master but
simply a power control switch to a device
that does not already have one. In such cases,
it seems prudent to have a separate switch
for each device . . . this gets
around the issue of generating single points
of failure for multiple appliances.
Cost of ownership for adding switches will
be lower than for adding more batteries
that need to be maintained throughout
the life of the aircraft . . . but only
serve a useful purpose for a few tens of
milliseconds every flight cycle.
Bob . . .
Message 3
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Subject: | Re: Avionics Master |
nuckolls.bob(at)aeroelect wrote:
> At 07:47 AM 12/6/2016, you wrote:
> Do these affected systems not have their own power switches?
Nope. These devices have no external controls.
> If not, then you're not really adding an avionics master but simply a power control
switch to a device that does not already have one. In such cases, it seems
prudent to have a separate switch for each device . . . this gets around the
issue of generating single points of failure for multiple appliances.
I thought about doing that. But I felt the additional wiring and switches to be
an added complication. Besides, each device can be powered on or off through
the VPX so that is my "individual device" switch. And my "Avionics Master" switch
can be bypassed from the VPX as well (should it fail).
So to me, that seems like a win-win. :D
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=463754#463754
Message 4
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Subject: | Re: Avionics Master |
All the Beech products I flew had a NC relay opened by turning the avionics master
switch off. If the switch failed and the avionics went dark, you just pulled
the breaker for the switch and the avionics came back on.
Seems like a simple solution to me.
Sebastien
> On Dec 6, 2016, at 10:38, donjohnston <don@velocity-xl.com> wrote:
>
>
>
> nuckolls.bob(at)aeroelect wrote:
>> At 07:47 AM 12/6/2016, you wrote:
>> Do these affected systems not have their own power switches?
>
> Nope. These devices have no external controls.
>
>
>> If not, then you're not really adding an avionics master but simply a power
control switch to a device that does not already have one. In such cases, it seems
prudent to have a separate switch for each device . . . this gets around
the issue of generating single points of failure for multiple appliances.
>
> I thought about doing that. But I felt the additional wiring and switches to
be an added complication. Besides, each device can be powered on or off through
the VPX so that is my "individual device" switch. And my "Avionics Master"
switch can be bypassed from the VPX as well (should it fail).
>
> So to me, that seems like a win-win. :D
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=463754#463754
>
>
>
>
>
>
>
>
>
Message 5
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Subject: | Re: Ballasting Dsub connectors |
At 11:14 AM 12/6/2016, you wrote:
>Bob
>
>For the illiteratti among us, please explain the concept behind the
>12 inch pigtails a bit more. My takeaway from the article was that
>12 inches of wire act as a "resistor" in series with the pin. Would
>you not need to tailor each pigtail to attain the correct
>resistance? Or, just by having this increased resistance, within a
>range, does it drive the pins to share current?
Correct. And thank you for that question. I should
have described that effect in the article. I've edited
it to include that explanation.
>The final takeaway was that, without the pigtails, one pin would hog
>the load, overload and fail, causing a cascade failure of the entire
>connector under load. Yes, no or should I go back to my corner?
Not at all . . . in fact, you've spotlighted
the need for further elaboration.
Bob . . .
Message 6
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Subject: | Alternator Field Circuit Fuse Blow |
Hello Bob,
First, let me say a big thank you for all your help over the years during
the design and build of the electrical system of our Lancair Legacy
airplane. We've been flying now for 14 months, have about 140 hours of
flight time, and the airplane received EAA's Kit Built Grand Champion Award
this year. The electrical system has been working very well. It's based on
your Z-12 single battery, dual alternator architecture.
We do have a slight mystery, though, that I would sure appreciate your
thoughts on. We've had the primary alternator's (100 A) field circuit fuse
blow (fuse not CB) while deploying the landing gear, on two occasions - once
two months ago and once this morning.
Here's some background info. We have a fuse tray that pulls out of the
panel holding blade type fuses that light up when they've blown -- saved a
bunch of real estate on the panel. The landing gear are powered by an
electric motor driven hydraulic pump that can pull almost 80 A at times. On
the first occasion the field fuse blew I'd eventually attributed it to being
because one of our two PC680 batteries (in series for 28 VDC) was heat
damaged from sitting down stream of the oil cooler and was not holding a
charge well and maybe not compensating for the big current draw from the
hydraulic pump motor as well as it should. The battery issue was corrected
(replaced) a couple months ago and all has been well until this morning when
the field fuse blew again on landing gear extension.
On both occasions the fuse blew on landing gear extension which seems to be
the least loaded gear operation since the weight of the gear and their gas
spring struts want to deploy the gear anyway - the pump can barely keep up.
But, we do have a modification to our landing gear system where the inboard
gear doors close after gear go down and the pump typically cycles very
quickly several time while it's closing the inboard doors. For more
background, we splurged on expensive hermetically sealed contactors rated
for 100 A continuous for switching the hydraulic pump motor -- Tyco Kilovac
EV100 relays with built in voltage suppression diodes.
I know you're the architect of the amazing crow bar over voltage protection
featured in our L3RC-28 linear alternator regulator from B & C Specialties.
In talking with TJ at B&C today, he said if the regulator sees over 32 VDC
for more than 5 milliseconds that the crow bar over voltage will short the
field circuit to trip the CB or fuse. We're both wondering if using a 5A
fuse vs. a 5A CB could make a difference.?
Anyway, what do you think about this? It has only happened twice. Could
the field current to drive a 100A alternator under a high load exceed the 5A
fuse limit? Should we try a 7A fuse? Is this likely from an over-voltage
condition and if so what's causing it? Could it be that the regulator isn't
dropping the field strength fast enough after the landing gear/hydraulic
motor stops running and causing an over voltage spike that's tripping the
crow bar over voltage circuit?
Thanks in advance for your help!
Valin Thorn
StarHawk Lancair Legacy -- N321TF
Sedona, Arizona
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