Today's Message Index:
----------------------
1. 07:12 AM - Re: Aviation wire (Steve Stearns)
2. 07:39 AM - Re: Shunt Questions (Robert L. Nuckolls, III)
3. 08:00 AM - Re: Re: Aviation wire (Kent or Jackie Ashton)
4. 08:10 AM - Re: Aviation wire (Robert L. Nuckolls, III)
5. 08:16 AM - Re: Re: Aviation wire (Alec Myers)
6. 08:23 AM - Re: Re: Aviation wire (Alec Myers)
7. 11:44 AM - Re: Re: Shunt Questions (Eric Page)
8. 12:29 PM - Shelf life of electrical components in humid and dry environments (Dan)
9. 12:46 PM - Questions about Architecture Design (MFleming)
10. 01:00 PM - Crowbar let the smoke out (Finn Lassen)
11. 03:06 PM - Re: Re: Shunt Questions (Robert L. Nuckolls, III)
12. 03:09 PM - Re: Shelf life of electrical components in humid and dry environments (Robert L. Nuckolls, III)
13. 03:32 PM - Re: Crowbar let the smoke out (Robert L. Nuckolls, III)
14. 05:56 PM - Re: Questions about Architecture Design (Robert L. Nuckolls, III)
15. 05:59 PM - Z101 has been released under Rev A (Robert L. Nuckolls, III)
16. 07:45 PM - Re: Questions about Architecture Design (user9253)
17. 09:43 PM - Re: Questions about Architecture Design (MFleming)
Message 1
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| Subject: | re: Aviation wire |
Bob said: "
*The Teflon wire is a bit fussy to strip.See: https://tinyurl.com/bol9x2n
<https://tinyurl.com/bol9x2n>"*
My 2 cents: When I obtained my Longeze (now about 10 years ago) it had a
lot of Teflon wire in it (apparently it was the "the thing" when it was
built) and after inspecting the plane, I pulled *all* of the wiring out and
re did all of it. I chose mostly Tefzel (which is neither here nor there
as far as my point goes) but I will *never* use Teflon in the plane (or a
car for that matter, but 30 AWG solid teflon is *great* for rework wire on
circuit boards). For me the "creep" issue is so bad as to be a show
stopper. Any place the wire got pulled over an edge (presumably during
install) the edge just opened up the wire. It didn't cut it but it
did displace the insulation (creep) all the way down to the wire. Even
when carefully installing tefzel wire great care must be taken to avoid
inadvertent wire-chafing related problems.
Example: I *thought* I had always been really careful but minor a
seemingly-minor re-routing of my Alternator b-lead wire back by the
alternator inadvertently took out the slack in the wire near the forward
engine mount which turned into a short on a sharp engine mount edge
bushing. Fortunately I had an ANL installed up by the master contactor
(and I don't have raw fuel spraying around under the cowl) so it was a none
event. The tefzel wire is much more durable (but clearly not durable
enough in this case) than the Teflon. (Useful tip for doing an out-of-town
field repair, on a Sunday, and you need an ANL: They are now commonly used
for automobile subwoofers and can be found super cheap at places like Car
Toys and Best Buy).
I counsel that anyone choosing to put straight teflon wire in their
aircraft be especially paranoid about protecting what, in my experience, is
a very fragile insulation layer.
Best regards to all,
Steve Stearns
O235 Longeze
Taylorcraft BC12D
Boulder/Longmont CO
Message 2
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| Subject: | Re: Shunt Questions |
At 07:25 PM 5/24/2020, you wrote:
>Bob, I hope you and yours are well!
>
>I have a question on shunts, but for my camper, not an aircraft. I
>thought maybe you prefer I don't clutter up the AeroElectric list
>with non-aircraft topics! (But tell me if you'd rather I send this
>to the list.)
Not that far off-topic. No doubt there
are other List members with at least
an academic if not practical interest
in DIY data acquisition. A pretty smart
cookie once opined:
"I often say that when you can measure what you
are speaking about, and express it in numbers,
you know something about it; but when you cannot
measure it, when you cannot express it in numbers,
your knowledge is of a meagre and unsatisfactory kind."
-- Lord Kelvin
>I would like to build some data logging for the DC system in my VW camper.
>
>https://sbw.org/sbwsty/
>
>There's a photo of my van's (messy) wiring closet here:
>
>https://sbw.org/westybattery/
>
>I have two lead-acid batteries, starting and house. Right now, just
>two charging sources, the alternator and a ProSport marine charger.
>Thinking of adding solar.
>
>I'd like to monitor several current flows:
>
>- From the alternator to the house battery.
>- From the ProSport to the house battery.
>- From the house battery to the appliances.
>- In future, from the solar charge controller to the house battery.
>
>I don't NEED all of those, of course. Just curious. So I'll need
>several shunts. B&C offers only one, 50mv at 20A, if I
>understand. So 2.5 milliohms?
>
>I think a different shunt might be better, because I'm planning to
>use this breakout board:
>
>https://www.adafruit.com/product/904
>
>It comes with a 100 milliohm shunt (a 1% resistor), intended to
>measure up to 3.2A at the INA219B chip's max differential
>320mv. The resolution at 3.2A is .8mA. I would put a shunt in
>parallel to measure a higher current, ideally one that produces
>close to 320mv for good resolution.
>
>For example, the if the alternator can produce 60A, would I maybe
>choose this 20A/100mv shunt (5 milliohms), which would produce 300mv at 60A?
>
>https://www.newark.com/canadian-shunt/la-20-100/shunt/dp/73K4805
>
>Is it silly to give up 300mv just to get higher resolution?
>
>Will it get too hot, dissipating 18W vs. the 2W it's rated for?
>
>B&C sells their shunt for $5, where the shunts from Newark are much
>more spendy. Is there somewhere better to buy them?
>
>Is there a simpler way to do this?
>
>Another interesting part of the project will be how to get the data
>up to the cloud: I'm thinking WiFi when it's available and APRS
>otherwise. And maybe BLE to an app on my phone. Adafruit has lots
>of radios I can experiment with.
>
>But first I need to gather the data.
>
>Thanks!
I have all but abandoned metallic shunts for current
measurement - especially when the millivolt data
is to processed in low level digital electronics.
We can revisit your shunt questions but I'll
suggest you consider this product:
https://tinyurl.com/yaxv58ax
These are closed loop, hall-effect sensors priced
about the same as the metallic shunts. Beauty
of these critters is total isolation, very
good linearity, repeatability and accuracy.
Best yet, one device can measure a huge
range of currents.
I stock the 6A version for about all applications.
I can run 5 passes of 22AWG wire through the
aperture and get plus/minus 1.2A full scale.
Alternatively, a single pass of 22AWG 1 foot
long through the aperture spliced in parallel
with 10AWG 1 foot long outside the aperture
gives me approx 10x multiplier for plus/minus
60A full scale.
You can situate the sensor local to the stimulus
of interest and extend the leads on a shielded,
twisted pair for direct interface with your
a/d converter. You don't need those high common
mode gain chips to do achieve an interface.
You WILL need some a/d ports to process your
hall sensor data.
I've acquired high quality data at the ends
of 40' leads in all manner of noisy environments.
The attached photo is one example of one
application. This board includes a 5v, 3-terminal
regulator enabling me to use the device
'barefoot' with a digital VOM at the observation-
end of the leads. For applications such as yours,
I'd probably solder a shielded pair directly to
the module pins and 'pot' the connections with
E-6000.
If you'd like some boards to mount and terminate
the wires in a connector, I think I've got a
few laying around. Also, if you'd like to
go for the metalic shunts, I think I've
got a few dozen 20A shunts available for the
asking . . . but you don't want to overload
these things by much . . . maybe 50%. They're
easy to 'smoke'.
LONG time no hear my friend! Pleased to know
that you're still alive, kicking and curious!
Bob . . .
Message 3
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| Subject: | Re: re: Aviation wire |
Possibly what you had was not Teflon but something else. Tefzel is just
a Dupont tradename for various Teflon types. Better to specify a
Mil-W-22759/__ spec or a Mil-W-16878/__ but even those come in different
insulations. I have been pretty happy with a PEFE wire or and FEP wire.
I could not tell much difference in handling. The -16878 wire comes in
more colors. Here is a chart
> On May 25, 2020, at 10:09 AM, Steve Stearns <steve@tomasara.com>
wrote:
>
> Bob said: "The Teflon wire is a bit fussy to strip.
> See: https://tinyurl.com/bol9x2n"
>
> My 2 cents: When I obtained my Longeze (now about 10 years ago) it
had a lot of Teflon wire in it (apparently it was the "the thing" when
it was built) and after inspecting the plane, I pulled *all* of the
wiring out and re did all of it. I chose mostly Tefzel (which is
neither here nor there as far as my point goes) but I will *never* use
Teflon in the plane (or a car for that matter
Message 4
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| Subject: | Re: Aviation wire |
At 09:09 AM 5/25/2020, you wrote:
Bob said: "The Teflon wire is a bit fussy to strip.
See: https://tinyurl.com/bol9x2n"
My 2 cents: When I obtained my Longeze (now
about 10 years ago) it had a lot of Teflon wire
in it (apparently it was the "the thing" when it
was built) and after inspecting the plane, I
pulled *all* of the wiring out and re did all of
it. I chose mostly Tefzel (which is neither here
nor there as far as my point goes) but I will
*never* use Teflon in the plane (or a car for
that matter, but 30 AWG solid teflon is *great*
for rework wire on circuit boards). For me the
"creep" issue is so bad as to be a show stopper.
Any place the wire got pulled over an edge
(presumably during install) the edge just opened
up the wire. It didn't cut it but it did
"displace the insulation" (creep) all the way
down to the wire. Even when carefully installing
tefzel wire great care must be taken to avoid
inadvertent wire-chafing related problems.
<snip>
Your experience clearly illustrates the importance
of artful wire routing and support. Every airframe
shop I've worked in treated wire bundles like fuel
lines . . . do not, repeat DO NOT allow wires,
pipes, control cables, etc. to ride in contact with
the airframe . . . even if it is SMOOTH. I had a brake
failure about 2 am one morning in my '57 Chevy when
a steel brake line had laid against a rubber
power steering hose wherein the gap was 'lubricated'
with greasy sand and dust. Wore a hole in the line.
Just last week, I repaired apiece of steel line on
local kid's truck where the line was laying 'gently'
against an axle housing. 200K miles of vibration
wore a hole in it.
I think I've shared the story of a C90 on short
final to Clovis NM suffering total elevator
control disconnect due to cable chaffing against
8AWG windshield de-ice power feeder. Insulation
wore through, copper arced 'gently' against a
steel cable which eventually parted.
I counsel that anyone choosing to put straight
teflon wire in their aircraft be especially
paranoid about protecting what, in my experience,
is a very fragile insulation layer.
You bet . . . but not limited to ANY particular material.
Time, motion, pressure and contaminants are as
relentless as the Colorado River carving the Grand
Canyon. It's not a question of whether or not
it will fail . . . just a matter of when.
Best regards to all,
Steve Stearns
Thanks for sharing!
Bob . . .
Message 5
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| Subject: | Re: re: Aviation wire |
On the subject of different colours, Im not sure about 16878, but Allied Wire and
Cable will happily vend you 22759/16 in ten different colours:
Black, Brown, Red, Orange, Yellow, Green, Blue, Violet Grey and White.
They also do reel ends for cheap: right now you can have 155 of -20 in blue for
11.45 (0.6 cents per foot) or 90 of orange -22 for $4.83 (0.9 cents per foot).
On May 25, 2020, at 10:56 AM, Kent or Jackie Ashton <kjashton@vnet.net> wrote:
Possibly what you had was not Teflon but something else. Tefzel is just a Dupont
tradename for various Teflon types. Better to specify a Mil-W-22759/__ spec
or a Mil-W-16878/__ but even those come in different insulations. I have been
pretty happy with a PEFE wire or and FEP wire. I could not tell much difference
in handling. The -16878 wire comes in more colors. Here is a chart
> On May 25, 2020, at 10:09 AM, Steve Stearns <steve@tomasara.com> wrote:
>
> Bob said: "The Teflon wire is a bit fussy to strip.
> See: https://tinyurl.com/bol9x2n"
>
> My 2 cents: When I obtained my Longeze (now about 10 years ago) it had a lot
of Teflon wire in it (apparently it was the "the thing" when it was built) and
after inspecting the plane, I pulled *all* of the wiring out and re did all
of it. I chose mostly Tefzel (which is neither here nor there as far as my point
goes) but I will *never* use Teflon in the plane (or a car for that matter<Wire16878-22759.jpg>
Message 6
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| Subject: | Re: re: Aviation wire |
Sorry - got my arithmetic wrong - thats 7 cents per foot, and 5 cents per foot,
respectively.
On May 25, 2020, at 11:13 AM, Alec Myers <alec@alecmyers.com> wrote:
On the subject of different colours, Im not sure about 16878, but Allied Wire and
Cable will happily vend you 22759/16 in ten different colours:
Black, Brown, Red, Orange, Yellow, Green, Blue, Violet Grey and White.
They also do reel ends for cheap: right now you can have 155 of -20 in blue for
11.45 (0.6 cents per foot) or 90 of orange -22 for $4.83 (0.9 cents per foot).
On May 25, 2020, at 10:56 AM, Kent or Jackie Ashton <kjashton@vnet.net> wrote:
Possibly what you had was not Teflon but something else. Tefzel is just a Dupont
tradename for various Teflon types. Better to specify a Mil-W-22759/__ spec
or a Mil-W-16878/__ but even those come in different insulations. I have been
pretty happy with a PEFE wire or and FEP wire. I could not tell much difference
in handling. The -16878 wire comes in more colors. Here is a chart
> On May 25, 2020, at 10:09 AM, Steve Stearns <steve@tomasara.com> wrote:
>
> Bob said: "The Teflon wire is a bit fussy to strip.
> See: https://tinyurl.com/bol9x2n"
>
> My 2 cents: When I obtained my Longeze (now about 10 years ago) it had a lot
of Teflon wire in it (apparently it was the "the thing" when it was built) and
after inspecting the plane, I pulled *all* of the wiring out and re did all
of it. I chose mostly Tefzel (which is neither here nor there as far as my point
goes) but I will *never* use Teflon in the plane (or a car for that matter<Wire16878-22759.jpg>
Message 7
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| Subject: | Re: Shunt Questions |
Gents,
Another good option is Allegro MicroSystems' line of Hall effect sensors.
=C2- You can get them from all of the usual suspects on eBay, Amazon, Ali
Express, etc., mounted on a small PCB.=C2- You just feed your current of
interest through the screw terminals, connect the output to an ADC input on
your micro and scale the reading in your code.=C2- They work well, are v
ery small, generate virtually no heat and cost very little.
The unidirectional sensors output 0V with no current flow, while the bidire
ctional sensors output half the supply voltage with no current flow (5V sup
ply = 2.5V no-current output; current in one direction produces output >2
.5V and current in the other direction produces output <2.5V).
A couple of caveats.=C2- 1. Avoid laying another current-carrying wire ov
er the surface of the sensor IC, as it can disturb the Hall sensor inside.
=C2- 2. The zero-current output of the bidirectional ICs is ratiometric w
ith the supply voltage, so be sure your sensor supply is the same as your A
DC reference.
Search links for sensor modules on eBay:
-- ACS712 (5A, 20A and 30A sensors):=C2-https://preview.tinyurl.com/ybc55
6k5
-- ACS724 (40A and 50A sensors):=C2-https://preview.tinyurl.com/y9xfbehu
-- ACS758 (50A and 100A sensors):=C2-https://preview.tinyurl.com/ybqcwoqt
Sensor IC datasheets:
-- ACS712:=C2-https://preview.tinyurl.com/ybbckmf5
-- ACS724:=C2-https://preview.tinyurl.com/yafr2oms
--ACS758:=C2-https://preview.tinyurl.com/yxoukcv4
Eric
At 07:25 PM 5/24/2020, you wrote:
I'd like to monitor several current flows:
- From the alternator to the house battery.
- From the ProSport to the house battery.
- From the house battery to the appliances.
- In future, from the solar charge controller to the housebattery.
Message 8
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| Subject: | Shelf life of electrical components in humid and dry |
environments
Hi all,
I am completing my Lancair ES, finally! I am finalizing wiring that was planned
15 years ago! I chose Z-14, Bobs dual electric system, planning two 17 AH batteries
in the rear of the airplane, and I acquired all the components years
ago. I installed the battery contactors and a ground power contactor in the rear
of the airplane and ran all the wiring required from the rear to the front
years ago. The components in the airplane sat in a pretty humid environment,
and other components said in boxes in a dryer environment. My question is whether
I need to worry about shelf life of any of these components. For example,
if the contactors test OK, are they good to go, or should I replace them?
Generally, what components in Z-14, if any, would be susceptible to degradation
from sitting?
Cheers,
Dan
Message 9
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| Subject: | Questions about Architecture Design |
I hope these questions are not too rudimentary or repetitive.
I'm moving in on finalizing the wiring design for my RV-7. A few question have
nagged me for a while and I'm eager to better understand the rules or rationals
for these conundrums.
I'm basically speaking to Z101.
(1) The 6AWG wire from the battery contactor to the main bus is unprotected and
not length limited. My calculations show I can use a smaller wire. Is the 6AWG
permitted to be downsized or is it integral to safety?
(2) Since I don't have an electrically dependent engine (one p-mag) I'm planning
the Clearance Delivery bus be secondarily fed from the main bus through a diode.
Should I fuse the wire (18AWG) or come directly off the bus? Also, I have
no need for a battery bus. My plan is to feed the clearance delivery relay (Relay
needed? 3.8amps max) from the battery side of the battery contactor...is
this acceptable?
(3) I am going to have an avionics bus (sorry, I just don't want all that stuff
running when I start), so the same question. Do I fuse the 18AWG wire to the
avionics bus? I see that most endurance busses are not fused...not sure why not?
(4) Fuselinks depicted in a lot of the Z drawings. How do I size them and where
do I get them?
(5) Relay vs switch. Is there a rule of thumb for when to add a relay instead of
using a beefy switch?
Thanks in advance.
Michael Fleming
--------
Michael Fleming
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496506#496506
Message 10
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| Subject: | Crowbar let the smoke out |
Happened to turn on master switch (relay) and saw smoke coming from the
OV circuit. (Made from the AEC9003-14A schematic more than two decades ago.)
I thought that was rather rude of it.
The SCR is the one that fried.
No problems many times before. Must have seen a spike from alternator
field winding.
But very worrisome that it did NOT pop the 5 amp W23-X1A1G-5 pull breaker.
The schematic specifies 20 AWG wires, and I used thicker -- perhaps 12
or 14, and very short, about three inches total for ground and + wires.
Maybe that was the problem?
Finn
Message 11
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| Subject: | Re: Shunt Questions |
At 01:40 PM 5/25/2020, you wrote:
>Gents,
>
>Another good option is Allegro MicroSystems' line of Hall effect
>sensors. You can get them from all of the usual suspects on eBay,
>Amazon, AliExpress, etc., mounted on a small PCB. You just feed
>your current of interest through the screw terminals, connect the
>output to an ADC input on your micro and scale the reading in your
>code. They work well, are very small, generate virtually no heat
>and cost very little.
>
>The unidirectional sensors output 0V with no current flow, while the
>bidirectional sensors output half the supply voltage with no current
>flow (5V supply = 2.5V no-current output; current in one direction
>produces output >2.5V and current in the other direction produces
>output <2.5V).
>
>A couple of caveats. 1. Avoid laying another current-carrying wire
>over the surface of the sensor IC, as it can disturb the Hall sensor
>inside. 2. The zero-current output of the bidirectional ICs is
>ratiometric with the supply voltage, so be sure your sensor supply
>is the same as your ADC reference.
I've used these with success. They are
not quite so 'tight' for accuracy, etc. but
if your error budget will tolerate them, they
perform as advertised.
Bob . . .
Message 12
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| Subject: | Re: Shelf life of electrical components in humid |
and dry environments
At 02:24 PM 5/25/2020, you wrote:
>
>Hi all,
>
>I am completing my Lancair ES, finally! I am
>finalizing wiring that was planned 15 years
>ago! I chose Z-14, Bob=99s dual electric
>system, planning two 17 AH batteries in the rear
>of the airplane, and I acquired all the
>components years ago. I installed the battery
>contactors and a ground power contactor in the
>rear of the airplane and ran all the wiring
>required from the rear to the front years
>ago. The components in the airplane sat in a
>pretty humid environment, and other components
>said in boxes in a dryer environment. My
>question is whether I need to worry about shelf
>life of any of these components. For example,
>if the contactors test OK, are they good to go,
>or should I replace them? Generally, what
>components in Z-14, if any, would be susceptible to degradation from
sitting?
I don't think you have anything to be worried about.
Bob . . .
Message 13
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| Subject: | Re: Crowbar let the smoke out |
At 02:56 PM 5/25/2020, you wrote:
>
>Happened to turn on master switch (relay) and saw smoke coming from
>the OV circuit. (Made from the AEC9003-14A schematic more than two
>decades ago.)
>
>I thought that was rather rude of it.
>
>The SCR is the one that fried.
>
>No problems many times before. Must have seen a spike from
>alternator field winding.
>
>But very worrisome that it did NOT pop the 5 amp W23-X1A1G-5 pull breaker.
Yeah, it probably opened the chip
bonds on the SCR before the breaker
could even respond.
>The schematic specifies 20 AWG wires, and I used thicker -- perhaps
>12 or 14, and very short, about three inches total for ground and + wires.
>
>Maybe that was the problem?
Yup. You'll notice that the z-figures
show crowbar ov modules at the end of the
feeder to the alternator field switch . . .
and wire sized more to the task of
supplying a 3A alternator field. 20AWG.
The W23 breakers are slower than the
miniature devices but this isn't a
show stopper if you limit the fault
current with judicious wire sizes and
lengths.
This limits trip current to some value
within limits for the SCR. I've had
customers install their AEC fabricated
modules right at the breaker on a legacy
bus bar . . . they even shortened the
factory supplied leads. Their modules
suffered the same fate the first time
they tripped.
Bob . . .
Message 14
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| Subject: | Re: Questions about Architecture Design |
At 02:44 PM 5/25/2020, you wrote:
>
>I hope these questions are not too rudimentary or repetitive.
>
>I'm moving in on finalizing the wiring design for my RV-7. A few
>question have nagged me for a while and I'm eager to better
>understand the rules or rationals for these conundrums.
>
>I'm basically speaking to Z101.
>
>(1) The 6AWG wire from the battery contactor to the main bus is
>unprotected and not length limited. My calculations show I can use a
>smaller wire. Is the 6AWG permitted to be downsized or is it
>integral to safety?
It would be better for this to be 'robust'. I.e.
take it's place in the constellation of power
distribution feeders . . . I wouldn't go smaller
than 8AWG but unless you already have some 8 and
don't need to buy some 6, I'd use the 6. Here's
one source of many . . .
https://tinyurl.com/ya4756q6
You'll like working with this 'fat' wire.
>(2) Since I don't have an electrically dependent engine (one p-mag)
>I'm planning the Clearance Delivery bus be secondarily fed from the
>main bus through a diode.
Yup, that's what Z101 shows.
>Should I fuse the wire (18AWG) or come directly off the bus?
How many devices on your clearance delivery
bus?
>Also, I have no need for a battery bus. My plan is to feed the
>clearance delivery relay
>(Relay needed? 3.8amps max) from the battery side of the battery
>contactor...is this acceptable?
Sure . . . your 'battery bus' is the hot side terminal . . .
It just has one feeder departing the 'bus'. I recommend
10A local in-line fuse and 18AWG wire to your CD switch.
>(3) I am going to have an avionics bus (sorry, I just don't want all
>that stuff running
>when I start) . . .
What is the 'down side' for having 'all that stuff
running' during start? Z101 as depicted supports all
auxiliary busses with independent feed paths. What
are your plans for an avionics bus?
> so the same question. Do I fuse the 18AWG wire to the avionics bus?
>I see that most endurance busses are not fused...not sure why not?
They are fused at the battery source for alternate feed.
Not fused in normal feed from the main bus because
wires are short(*).
>(4) Fuselinks depicted in a lot of the Z drawings. How do I size
>them and where do I get them?
You make them from fuse link wire. Where do you
plan to incorporate them?
>(5) Relay vs switch. Is there a rule of thumb for when to add a
>relay instead of using a beefy switch?
Depends on how much wire you want to run
the 'high current' through. Which switch(es) are
you talking about? If you're switching 7A or
less, you could consider eliminating relays.
Bob . . .
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| Subject: | Z101 has been released under Rev A |
I've combed Z101 several times and I think
the major 'nits' have been eliminated. I removed
'preliminary' status and published as Rev -A-
at:
https://tinyurl.com/yavoutjh
Doesn't mean it's 'carved in stone' . . . just
ready for some serious builder consideration.
Error call outs and suggestions always welcome.
Bob . . .
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| Subject: | Re: Questions about Architecture Design |
The main power bus is one of the most reliable things on an airplane. It is
connected to 2 power sources, a battery and an alternator. There are no
fuses to blow in the main power feeder. An avionics bus has a switch that
can fail. And if it is protected by a fuse, that is one more unnecessary
failure point. It is a bad idea to have two fuses in series. If a load fuse
blows, the bus fuse could also blow and disable all avionics. Eliminate the
avionics bus. Yeah, I know you are concerned about voltage spikes during
engine start. But there is no such thing. Who are you going to believe,
flight instructors and mechanics who do not even own an oscilloscope and
base their advice on 1950 technology, or an electrical engineer (Bob) who
has worked for major aircraft companies and has tested starter motors in
a laboratory and proved that there are no voltage spikes? I do not have
an avionics bus. My airplane has been started hundreds of times with all
avionics turned on. No avionics have failed. Yes, some do reboot from
voltage sag which is annoying. Brownout protection can be installed if
desired. Give me the name of a modern avionics manual and page
number that states that their product must be powered off during engine
start. There are none. Make your airplane safer, and less complicated by
not having an avionics bus.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496516#496516
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| Subject: | Re: Questions about Architecture Design |
nuckolls.bob(at)aeroelect wrote:
> At 02:44 PM 5/25/2020, you wrote:
>
> >
> > I hope these questions are not too rudimentary or repetitive.
> >
> > I'm moving in on finalizing the wiring design for my RV-7. A few question
have nagged me for a while and I'm eager to better understand the rules or rationals
for these conundrums.
> >
> > I'm basically speaking to Z101.
> >
> > (1) The 6AWG wire from the battery contactor to the main bus is unprotected
and not length limited. My calculations show I can use a smaller wire. Is the
6AWG permitted to be downsized or is it integral to safety?
>
> It would be better for this to be 'robust'. I.e.
> take it's place in the constellation of power
> distribution feeders . . . I wouldn't go smaller
> than 8AWG but unless you already have some 8 and
> don't need to buy some 6, I'd use the 6. Here's
> one source of many . . .
>
> https://tinyurl.com/ya4756q6 (https://tinyurl.com/ya4756q6)
>
> You'll like working with this 'fat' wire.
>
>
> > (2) Since I don't have an electrically dependent engine (one p-mag) I'm planning
the Clearance Delivery bus be secondarily fed from the main bus through
a diode.
>
> Yup, that's what Z101 shows.
>
>
> > Should I fuse the wire (18AWG) or come directly off the bus?
>
> How many devices on your clearance delivery
> bus?
>
>
> > Also, I have no need for a battery bus. My plan is to feed the clearance delivery
relay
> > (Relay needed? 3.8amps max) from the battery side of the battery contactor...is
this acceptable?
>
> Sure . . . your 'battery bus' is the hot side terminal . . .
> It just has one feeder departing the 'bus'. I recommend
> 10A local in-line fuse and 18AWG wire to your CD switch.
>
>
> > (3) I am going to have an avionics bus (sorry, I just don't want all that stuff
running
> > when I start) . . .
>
> What is the 'down side' for having 'all that stuff
> running' during start? Z101 as depicted supports all
> auxiliary busses with independent feed paths. What
> are your plans for an avionics bus?
>
>
> > so the same question. Do I fuse the 18AWG wire to the avionics bus?
> > I see that most endurance busses are not fused...not sure why not?
>
> They are fused at the battery source for alternate feed.
> Not fused in normal feed from the main bus because
> wires are short(*).
>
>
> > (4) Fuselinks depicted in a lot of the Z drawings. How do I size them and where
do I get them?
>
> You make them from fuse link wire. Where do you
> plan to incorporate them?
>
>
>
> > (5) Relay vs switch. Is there a rule of thumb for when to add a relay instead
of using a beefy switch?
>
> Depends on how much wire you want to run
> the 'high current' through. Which switch(es) are
> you talking about? If you're switching 7A or
> less, you could consider eliminating relays.
>
>
> Bob . . .
How many devices on your clearance delivery
bus?
Four, Primary EFIS, GPS, Comm and strobes so I don't forget to turn off the clearance
delivery switch.
Sure . . . your 'battery bus' is the hot side terminal . . .
It just has one feeder departing the 'bus'. I recommend
10A local in-line fuse and 18AWG wire to your CD switch.
Got it.
What is the 'down side' for having 'all that stuff
running' during start? Z101 as depicted supports all
auxiliary busses with independent feed paths. What
are your plans for an avionics bus?
OK, I gave my avionics wiring diagram a hard look. If I eliminate the avionics
bus and move those devices to the main bus, I only have two items that might reboot
during start, they are the Garmin GMC-507 auto pilot head and the #2 MFD.
The rest are on the TCW IBBS 6ah back-up battery.
The autopilot head I'm not concerned about. Currently the second power pin on the
#2 MFD (GDU-470) is not being used. I could run a Keep Alive wire from the
Garmin GAD-27 which conditions the line voltage during engine start and prevents
any annoying reboots from the #2MFD.
This sound simple and appealing. I'll give it s good look tomorrow.
You make them from fuse link wire. Where do you
plan to incorporate them?
I currently show a 16awg fuselink on the ALT 'B' line just before the starter solenoid.
Depends on how much wire you want to run
the 'high current' through. Which switch(es) are
you talking about? If you're switching 7A or
less, you could consider eliminating relays.
The clearance delivery switch would be a candidate to eliminate the relay. 3.8A
on the clearance delivery bus.
-M
--------
Michael Fleming
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496517#496517
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