Today's Message Index:
----------------------
1. 12:10 AM - Alternate Feed Switch, is it a Master Switch?? (Leo Holler)
2. 04:38 AM - Re: Shunts ()
3. 05:05 AM - Re: Music Inputs (Emond)
4. 06:54 AM - Re: Re: Music Inputs (earl_schroeder@juno.com)
5. 08:36 AM - Re: Alternate Feed Switch, is it a Master Switch?? (Robert L. Nuckolls, III)
6. 11:57 AM - Re: Alternate Feed Switch, is it a Master Switch?? (Leo Holler)
7. 02:20 PM - Re: Re: Alternate Feed Switch, is it a Master Switch?? (Robert L. Nuckolls, III)
8. 05:44 PM - Re: Re: Alternate Feed Switch, is it a Master Switch?? (Richard T. Schaefer)
Message 1
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| Subject: | Alternate Feed Switch, is it a Master Switch?? |
Help! Am working on a new electrical system design (pretty much a standard Z-11)
for a complete re-wire of a certified ship. A friend tells me that a certified
aircraft can only have one Master Switch per FAA regs. Is the "Alternate Feed"
switch for the Endurance Bus considered a Master Switch? If so, how does
it reconcile with any regs? Or, is my friend wrong? I have read Sec. 23.1361,
regarding Master Switch arrangement, and I'm not totally comfortable in my interpretation
of what is being said. The section seems to infer that more than one
switch can be incorporated into a Master Switch arrangement, but with some
restrictions. Can someone shed some light on me regarding this matter?
I have been planning to locate the Alternate Feed switch immediately adjacent to
the main Master Switch and under a switch guard. Presumably, both switches would
only be on simultaneously for the short time after energizing the Endurance
Bus via the Alternate Feed and turning the main Master off after an alternator
or battery contactor failure.
Per 23.1361, am I restricted to no more than a 5 amp total load on the Endurance
Bus (that should be plenty)? Would I also be restricted to no more than a 5
amp protective device for the bus feed? My bus feed wire will be about 8" long.
Thanks to any of you "Masters" for any enlightenment you can share.
The FAR quoted above can be found at:
http://www.risingup.com/fars/info/part23-1361-FAR.shtml
Leo
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=176349#176349
Message 2
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The AMP meter is really a VOLT METER. Yep it has nothing to do with AMPS. (There
is an AMP and VOLT relation).
How does it work. The shunt causes a voltage drop across the shunt (due to resistance).
That resistance is a known calibrated value. The volt gauge is reads
volt drop. Since voltage drop is proportional to current (amps) the gauge can
read the volt drop as current or amps, as follows:
This is the famous OHMS law:
V = I x R
OR
Volts = Current (amps) X Resistance (ohms)
So what?
We know a shunt is "calibrated" to drop a certain volt for every every amp of
current. Shunts vary, but a typical 50 amp shunt has a 50 millivolt drop at 50
amps.
If you have 50 amps at 14 volts entering the shunt, the volts leaving the shunt
at 50 amps will be 50 millivolts (0.050v) lower or 13.95 volts.
One millivolt drop = one amp. So you need a gauge that is labeled from 0 to 50
amps (but has a range from 0 to 0.050 volts).
With a volt gage that reads millivolts from 0 to 50 millivolts (but labeled amps)
we have an AMP METER!
Again the meter is measuring voltage drop not amps. It just happens OHMS LAW
is handy and linear (usually); where current and volts are proportional based
on the resistance of the shunt.
Shunts can have higher or lower resistance. Not all have the 1 amp to 1 millivolts
ratio. That is OK as long as the scale and range of the gauge (analog or
digital) compatible or calibrated for that shunt. The 1 amp to 1 millivolt ratio
is handy since many volt gauges are calibrated in millivolts. Mini digital
panel volt meters are usually read millivolts.
You can make your own AMP meter from a small digital volt meter and a piece of
wire that has the 0.001 volt/amp (Ohm) resistance.
I hope that helps. George
__________________________________________________
Message 3
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| Subject: | Re: Music Inputs |
I had a music jack wired into my system. My audio panel is a Garmin 340. I
have a sonyericcson mobile phone with walkman capability. What I find is
that with the walkman at max volume output the sound through the headphones
is reasonable, engine off on the ground. However with the engine running at
cruise I can barely hear the music. Are there settings on the system I
should check ??
Dave Emond
Message 4
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| Subject: | Re: Music Inputs |
Hi Dave, If you want to add a another 'device', I've used one described in the following link: http://www.boostaroo.com/ Earl
Dave wrote:
I had a music jack wired into my system. My audio panel is a Garmin 340. I
have a sonyericcson mobile phone with walkman capability. What I find is
that with the walkman at max volume output the sound through the headphones
is reasonable, engine off on the ground. However with the engine running at
cruise I can barely hear the music. Are there settings on the system I
should check ??
Dave Emond
Message 5
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| Subject: | Re: Alternate Feed Switch, is it a Master Switch?? |
At 12:06 AM 4/12/2008 -0700, you wrote:
>
>Help! Am working on a new electrical system design (pretty much a standard
>Z-11) for a complete re-wire of a certified ship. A friend tells me that a
>certified aircraft can only have one Master Switch per FAA regs.
Ask him to cite the regulation. I've never read it anywhere.
We have lots of switches in TC aircraft OTHER than the DC
POWER MASTER switch that re-organize bus structures and/or
control alternative pathways to power sources. For example,
many offerings in recent years at HawkerBeech have a "clearance
delivery" switch that allows one to power up one radio directly
from the battery for the purpose of getting ATIS and Clearance
Delivery before powering up the whole airplane.
> Is the "Alternate Feed" switch for the Endurance Bus considered a
> Master Switch? If so, how does it reconcile with any regs? Or, is my
> friend wrong? I have read Sec. 23.1361, regarding Master Switch
> arrangement, and I'm not totally comfortable in my interpretation of what
> is being said. The section seems to infer that more than one switch can
> be incorporated into a Master Switch arrangement, but with some
> restrictions. Can someone shed some light on me regarding this matter?
>
>I have been planning to locate the Alternate Feed switch immediately
>adjacent to the main Master Switch and under a switch guard. Presumably,
>both switches would only be on simultaneously for the short time after
>energizing the Endurance Bus via the Alternate Feed and turning the main
>Master off after an alternator or battery contactor failure.
>
>Per 23.1361, am I restricted to no more than a 5 amp total load on the
>Endurance Bus (that should be plenty)? Would I also be restricted to no
>more than a 5 amp protective device for the bus feed? My bus feed wire
>will be about 8" long.
>
>Thanks to any of you "Masters" for any enlightenment you can share.
The 5-Amp rule presupposes that the battery feeder to the
E-bus Alternate Feed switch is LONG . . . 5A is the rule-
of-thumb for limiting always-hot feeders directly from
the battery that might pose a post-crash risk of fire.
It's pretty much a hip-shot number. Give me control over
the conditions and I can light off gasoline with a 1A
feeder and not open the breaker.
If you NEED to protect the alternate feed at more than
5A, then install a "mini-battery contactor" right at
the battery bus as suggested in:
http://www.aeroelectric.com/Pictures/Schematics/E-BusFatFeed.gif
http://www.aeroelectric.com/PPS/DCPwr/E-Bus/E-Bus_Heavy.pdf
This provides for local disconnect of feeders protected
at more than 5A.
>The FAR quoted above can be found at:
>
>http://www.risingup.com/fars/info/part23-1361-FAR.shtml
Okay, let's look at it:
Sec. 23.1361 - Master switch arrangement.
(a) There must be a master switch arrangement to allow ready disconnection
of EACH electric power source from power distribution systems, except as
provided in paragraph (b) of this section.
Note that the rules allow for MORE than one power source, hence more
than one switch . . .
The point of disconnection must be adjacent to the sources controlled by
the switch arrangement.
Yup, unless the feeder is limited to 5A or less as described below:
If separate switches are incorporated into the master switch arrangement, a
means must be provided for the switch arrangement to be operated by one
hand with a single movement.
Yeah . . . this is a tad silly. If one is concerned about getting
switching ALL potential hazards off with switches as a single movement
then the magneto switches should probably be included under the
one-movement-does-all mechanism. In the suggested switch layouts
shown in
http://www.aeroelectric.com/PPS/Mechanical/Switches.pdf
. . . switches that control all power including ignition are
grouped at one end of the array. Easy to locate and easy to get
turned OFF in a timely manner when circumstances call for it.
For a TC aircraft, you can craft a hinged "crash bar" that
provides the requested one-stroke operation of adjacent switches.
I had a discussion some years ago with a 172 owner who was
wanting to do the same thing you're doing. We discussed using
switch guards over adjacent switches and ganging them together
with a bonded plate so that slapping them down opened both
switches.
Now, this one-hand-operation is somehow magically ignored in
some TC aircraft where emergency batteries are used to power
up essential appliances . . . they are generally not fitted with
or even arranged such that one-handed operation is possible.
(b) Load circuits may be connected so that they remain energized when the
master switch is open, if the circuits are isolated, or physically
shielded, to prevent their igniting flammable fluids or vapors that might
be liberated by the leakage or rupture of any flammable fluid system; and
(1) The circuits are required for continued operation of the engine; or
(2) The circuits are protected by circuit protective devices with a rating
of five amperes or less adjacent to the electric power source.
(3) In addition, two or more circuits installed in accordance with the
requirements of paragraph (b)(2) of this section must not be used to supply
a load of more than five amperes.
(c) The master switch or its controls must be so installed that the switch
is easily discernible and accessible to a crewmember.
Since your proposed changes are not part of the original
TC on the as-built airplane, you're going to have to jump
STC/337 hoops. So this is between you and your local
regulators. What you're proposing has been done before
and is not a really big deal. It's just slight rearrangement
of the design goals that have been similarly addressed with
additions of the "clearance delivery" switch on modern
aircraft.
Bob . . .
Message 6
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| Subject: | Re: Alternate Feed Switch, is it a Master Switch?? |
Thanks Bob for an exceptional and thorough response. You very clearly took the
most of the "fog" out of my feeble interpretation of Section-23-1361. I'll be
able to better make my 337(Field Approval) case to FAA now, as well as educate
my friend.
> The point of disconnection must be adjacent to the sources controlled by
> the switch arrangement.
>
> Yup, unless the feeder is limited to 5A or less as described below:
Does the above mean that the 5A rule applies only if there is no disconnection
adjacent to the source? Also, do you consider the 8" unprotected run from battery
to Alternate Feed switch to be excessive? If so, I can fuse it, or add the
mini-contactor as you have suggested. Also, I have heard that new Cessnas have
Essential/Endurance buses installed. Have you or anyone else heard of this and,
if so, how did they handle the Master Switch arrangement? A local Cessna dealer
hinted that I could get their schematic by buying the CD for several hundred
dollars or by buying a new aircraft. [Shocked] This forum seems much more
user friendly. :D
Thanks again.
Leo
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=176423#176423
Message 7
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| Subject: | Re: Alternate Feed Switch, is it a Master Switch?? |
At 11:52 AM 4/12/2008 -0700, you wrote:
>
>Thanks Bob for an exceptional and thorough response. You very clearly took
>the most of the "fog" out of my feeble interpretation of Section-23-1361.
>I'll be able to better make my 337(Field Approval) case to FAA now, as
>well as educate my friend.
>
>
> > The point of disconnection must be adjacent to the sources controlled by
> > the switch arrangement.
> >
> > Yup, unless the feeder is limited to 5A or less as described below:
>
>
>Does the above mean that the 5A rule applies only if there is no
>disconnection adjacent to the source?
Yes. Things like hour meters, clocks, dome lights, etc have
been attached directly to the battery and protected with 5A
breakers or fuses for decades. This allows a battery fed,
always hot wire to snake its way through the airplane to
do the intended task irrespective of whether or not the
battery master switch was ON.
>Also, do you consider the 8" unprotected run from battery to Alternate
>Feed switch to be excessive?
Not sure about this question. The battery bus feeds should
always be protected by fuses or breakers, no matter how long.
The 8" rule is to avoid fusing things like jumpers that run
between the (+) side of a capacitor. bus isolation diode
(or similar device) and the power source. This is a special
case that doesn't apply to this conversation.
Whether your e-bus is simply switched or run through a
mini-battery contactor, it still gets protection right
at the battery.
> If so, I can fuse it, or add the mini-contactor as you have suggested.
I would recommend you go the mini-contactor route and
wire with 14AWG wire no matter what size fuse/breaker you
select. Even if you can get by with a 5A protected feeder
today, you may wish to upgrade it later. This is easily
accomplished if the local disconnect (relay) and wire
(14AWG) are already in place. The breaker or fuse can be
elevated to as high as 15A at a later time without taking
a hatchet to the wire bundles.
>Also, I have heard that new Cessnas have Essential/Endurance buses
>installed. Have you or anyone else heard of this and, if so, how did they
>handle the Master Switch arrangement?
I can find out. It would be pretty cool if they do this
now. About two years after I handed out several copies of the
'Connection to folks at the single-engine electrical engineering
group, a firewall mounted, single point ground system was
installed on production aircraft. I'll ask around.
> A local Cessna dealer hinted that I could get their schematic by buying
> the CD for several hundred dollars or by buying a new aircraft. [Shocked]
> This forum seems much more user friendly. :D
Yeah . . . I can get one for the asking. I'll see
what I can do.
Bob . . .
Message 8
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| Subject: | Re: Alternate Feed Switch, is it a Master Switch?? |
Before Cessna bought Columbia you could get the Columbia 400 wiring diagrams
from their web site. (have not checked lately). They have dual bus, dual
alternator with an essential bus diode fed from either bus.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Leo
Holler
Sent: Saturday, April 12, 2008 1:53 PM
Subject: AeroElectric-List: Re: Alternate Feed Switch, is it a Master
Switch??
Thanks Bob for an exceptional and thorough response. You very clearly took
the most of the "fog" out of my feeble interpretation of Section-23-1361.
I'll be able to better make my 337(Field Approval) case to FAA now, as well
as educate my friend.
> The point of disconnection must be adjacent to the sources controlled by
> the switch arrangement.
>
> Yup, unless the feeder is limited to 5A or less as described below:
Does the above mean that the 5A rule applies only if there is no
disconnection adjacent to the source? Also, do you consider the 8"
unprotected run from battery to Alternate Feed switch to be excessive? If
so, I can fuse it, or add the mini-contactor as you have suggested. Also, I
have heard that new Cessnas have Essential/Endurance buses installed. Have
you or anyone else heard of this and, if so, how did they handle the Master
Switch arrangement? A local Cessna dealer hinted that I could get their
schematic by buying the CD for several hundred dollars or by buying a new
aircraft. [Shocked] This forum seems much more user friendly. :D
Thanks again.
Leo
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=176423#176423
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