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Dual Alternator, Dual Battery, Single Bus

 
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nuckolls.bob(at)aeroelect
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PostPosted: Mon Jan 26, 2015 8:09 pm    Post subject: Dual Alternator, Dual Battery, Single Bus Reply with quote

At 15:20 2015-01-26, you wrote:
Quote:


Thanks Joe,
That article rings of a familiar tone. Maybe that where "I was also more
recently told that modern avionics, with their internal protection, do not
need such isolation."
Dan


Actually, the av master was borne on a compelling
but flawed premise . . .

About 1966, when transistors were starting to show
up in aircraft radios (pnp germanium with 30v ratings)
Cessna (and I suspect others . . . don't know for sure
but I was at Cessna) were experiencing a rash of radio
failures in new, ready-to-deliver airplanes . . .

. . .and yes . . . it seems that radios left ON during
engine start were the most affected. It was surmised
that a 'spike' from the starter got 'em. It stood to
good reason. That starter thingy draws hundreds of amps,
was very inductive . . . it HAD to be a potential source
of inductive 'kick back' deleterious to those relatively
fragile.

The Avionics Master was borne . . . and yes . . . the
failures went away. In retrospect, it was not an
inductive 'spike' that got the radios but brownout.

The 'Airplane Patch' east of the plant would park hundreds
of airplanes waiting for delivery . . . none of which had
guaranteed battery integrity . . . a 6v sag to the 14v radio
during a starter 'grunt' was the most likely cause. Further,
while DO-160 (and its predecessors DO-138 and DO-108)
was definitely around, it was not as rigorous with
respect to bus voltage aberrations.

In years since, solid state devices have become very
robust in that they are designed to EXPECT the very
abuse that rolled a NavCom 300 T.U. in 1967.

By the time yours truly was designing transistors into
airplanes in the 1975 time frame, the idea that I would
want to 'take it off the bus' during an engine start
was rather humorous . . . the industry had learned
how to live in the vehicular DC power environment.
It was no big deal . . . yet the seeds of concern for
'spiking' a radio persisted as did the avionics master
switch.

Bob . . .

Bob . . .


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ARGOLDMAN(at)aol.com
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PostPosted: Mon Jan 26, 2015 8:37 pm    Post subject: Dual Alternator, Dual Battery, Single Bus Reply with quote

The below not withstanding, Dynon recommends starting and stopping the engine with the /Skyview not connected to the ships buss. They recommend starting the engine on the skyview backup battery so that you can see the engine instruments and connecting to the ships power after start. What do they know that we don't?

Rich

In a message dated 1/26/2015 10:11:07 P.M. Central Standard Time, nuckolls.bob(at)aeroelectric.com writes:
Quote:
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

At 15:20 2015-01-26, you wrote:
Quote:
--> AeroElectric-List message posted by: "Dan Brown" <dbrown2(at)nycap.rr.com>

Thanks Joe,
That article rings of a familiar tone. Maybe that where "I was also more
recently told that modern avionics, with their internal protection, do not
need such isolation."
Dan


Actually, the av master was borne on a compelling
but flawed premise . . .

About 1966, when transistors were starting to show
up in aircraft radios (pnp germanium with 30v ratings)
Cessna (and I suspect others . . . don't know for sure
but I was at Cessna) were experiencing a rash of radio
failures in new, ready-to-deliver airplanes . . .

. . .and yes . . . it seems that radios left ON during
engine start were the most affected. It was surmised
that a 'spike' from the starter got 'em. It stood to
good reason. That starter thingy draws hundreds of amps,
was very inductive . . . it HAD to be a potential source
of inductive 'kick back' deleterious to those relatively
fragile.

The Avionics Master was borne . . . and yes . . . the
failures went away. In retrospect, it was not an
inductive 'spike' that got the radios but brownout.

The 'Airplane Patch' east of the plant would park hundreds
of airplanes waiting for delivery . . . none of which had
guaranteed battery integrity . . . a 6v sag to the 14v radio
during a starter 'grunt' was the most likely cause. Further,
while DO-160 (and its predecessors DO-138 and DO-108)
was definitely around, it was not as rigorous with
respect to bus voltage aberrations.

In years since, solid state devices have become very
robust in that they are designed to EXPECT the very
abuse that rolled a NavCom 300 T.U. in 1967.

By the time yours truly was designing transistors into
airplanes in the 1975 time frame, the idea that I would
want to 'take it off the bus' during an engine start
was rather humorous . . . the industry had learned
how to live in the vehicular DC power environment.
It was no big deal . . . yet the seeds of concern for
'spiking' a radio persisted as did the avionics master
switch.

Bob . . .

Bob . . . ========================= Use utilities Day ================================================ - MATRONICS WEB FORUMS ================================================ - List Contribution Web Site sp; ===================================================


[quote][b]


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dbrown2(at)nycap.rr.com
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PostPosted: Tue Jan 27, 2015 3:05 am    Post subject: Dual Alternator, Dual Battery, Single Bus Reply with quote

There is a similar note in the Garmin G3X installation manual (Note 14, P. 22-1, Rev. P) that recommends power inputs are connected to an aux battery or stabilized power input during engine start in order to maintain minimum LRU input voltage and minimize the chance of the system restarting during engine cranking.

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of ARGOLDMAN(at)aol.com
Sent: Monday, January 26, 2015 11:37 PM
To: aeroelectric-list(at)matronics.com
Subject: Re: Re: Dual Alternator, Dual Battery, Single Bus

The below not withstanding, Dynon recommends starting and stopping the engine with the /Skyview not connected to the ships buss. They recommend starting the engine on the skyview backup battery so that you can see the engine instruments and connecting to the ships power after start. What do they know that we don't?



Rich



In a message dated 1/26/2015 10:11:07 P.M. Central Standard Time, nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com) writes:
Quote:

--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

At 15:20 2015-01-26, you wrote:
Quote:
--> AeroElectric-List message posted by: "Dan Brown" <dbrown2(at)nycap.rr.com (dbrown2(at)nycap.rr.com)>

Thanks Joe,
That article rings of a familiar tone. Maybe that where "I was also more
recently told that modern avionics, with their internal protection, do not
need such isolation."
Dan


Actually, the av master was borne on a compelling
but flawed premise . . .

About 1966, when transistors were starting to show
up in aircraft radios (pnp germanium with 30v ratings)
Cessna (and I suspect others . . . don't know for sure
but I was at Cessna) were experiencing a rash of radio
failures in new, ready-to-deliver airplanes . . .

. . .and yes . . . it seems that radios left ON during
engine start were the most affected. It was surmised
that a 'spike' from the starter got 'em. It stood to
good reason. That starter thingy draws hundreds of amps,
was very inductive . . . it HAD to be a potential source
of inductive 'kick back' deleterious to those relatively
fragile.

The Avionics Master was borne . . . and yes . . . the
failures went away. In retrospect, it was not an
inductive 'spike' that got the radios but brownout.

The 'Airplane Patch' east of the plant would park hundreds
of airplanes waiting for delivery . . . none of which had
guaranteed battery integrity . . . a 6v sag to the 14v radio
during a starter 'grunt' was the most likely cause. Further,
while DO-160 (and its predecessors DO-138 and DO-108)
was definitely around, it was not as rigorous with
respect to bus voltage aberrations.

In years since, solid state devices have become very
robust in that they are designed to EXPECT the very
abuse that rolled a NavCom 300 T.U. in 1967.

By the time yours truly was designing transistors into
airplanes in the 1975 time frame, the idea that I would
want to 'take it off the bus' during an engine start
was rather humorous . . . the industry had learned
how to live in the vehicular DC power environment.
It was no big deal . . . yet the seeds of concern for
'spiking' a radio persisted as did the avionics master
switch.

Bob . . .

Bob . . . Use utilities Day ======================= - MATRONICS WEB FORUMS ======================= - List Contribution Web Site sp; =
http://www.matronics.com/Navigator?AeroElectric-List
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user9253



Joined: 28 Mar 2008
Posts: 1435
Location: Riley TWP Michigan

PostPosted: Tue Jan 27, 2015 3:45 am    Post subject: Re: Dual Alternator, Dual Battery, Single Bus Reply with quote

Quote:
The below not withstanding, Dynon recommends starting and stopping the engine with the /Skyview not connected to the ships buss. They recommend starting the engine on the skyview backup battery so that you can see the engine instruments and connecting to the ships power after start. What do they know that we don't?
Rich

Where did you read that? Please post a link to Dynon manual and page.

The Dynon SkyView Pilot’s User Guide - Revision Q page 2-1 says, "SkyView’s robust power protection allows it to be powered on during engine start."
According to Bob's teachings, there are no high voltage spikes during engine starting. The only concern is a brownout. Dynon's SkyView automatically switches to its own backup battery during brownout conditions. No action is required by the pilot as the power transfer is automatic.
Joe


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user9253



Joined: 28 Mar 2008
Posts: 1435
Location: Riley TWP Michigan

PostPosted: Tue Jan 27, 2015 4:11 am    Post subject: Re: Dual Alternator, Dual Battery, Single Bus Reply with quote

Below is a quote from SkyView System Installation Guide - Revision R page 2-5.

Quote:
SkyView Can Be On During Engine Start SkyView units incorporate robust power protection that allows them to be powered on during engine start for full engine monitoring. SkyView displays require a minimum of 10V, and during engine start, it’s common for the electrical system to temporarily drop below 10V. If an SV-BAT- 320 backup battery is not installed, SkyView may shut off / reboot. If you wish to monitor your engine prior to engine start, an SV-BAT-320 backup battery should be installed so that the SkyView display can switch to the SV-BAT-320 when its power inputs are not receiving at least 10V. The SkyView display will switch from SV-BAT-320 to ship’s power when its power inputs receive voltage above 10V.


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PostPosted: Tue Jan 27, 2015 7:48 am    Post subject: Re: Dual Alternator, Dual Battery, Single Bus Reply with quote

The Garmin G3X installation manual says:
Quote:
TO MINIMIZE THE CHANCE OF THE SYSTEM RESETTING DURING ENGINE CRANKING, THE OPTIONAL REDUNDANT (DIODE OR'D) POWER INPUTS MAY BE CONNECTED TO AN AUXILIARY BATTERY . . .OR STABILIZED POWER INPUT. . .

The Garmin manual does not recommend using backup power during engine start. It says that OPTIONAL backup power MAY be used.
Both Garmin and Dynon say that having optional backup power will prevent rebooting during engine cranking, which I think is a good idea because rebooting is annoying. But neither company says that not having backup power will damage their units. And neither company recommends disconnecting their units from the aircraft electrical system during engine starting.
The point that I am trying to make is that an avionics master switch to protect avionics is unnecessary. Installing an avionics master switch introduces a single point of failure. If that switch fails, avionics go dark.
Joe


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