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New Design Schemes and Brownout Operation

 
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nuckolls.bob(at)aeroelect
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PostPosted: Thu Apr 09, 2020 10:09 am    Post subject: New Design Schemes and Brownout Operation Reply with quote

At 11:06 AM 4/9/2020, you wrote:
Quote:
Bill,

Here is my electrical plan. I have SDS EFI, GRT Sport EX x 2, GPS175, EIS and GTR-200 x 2. The SDS EFI runs from the ENG BUS. The GRTs get primary power from the VP-X and secondary power from the E-BUS. The #2 GTR-200, GPS175, EIS, Stratus, GMA240, encoder and ARINC get power from the E-BUS. The number one priority is to keep the ENG BUS and E-BUS alive for continued emergency flight IFR.


Looks pretty much like Z01 . . .



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Thu Apr 09, 2020 5:19 pm    Post subject: New Design Schemes and Brownout Operation Reply with quote

At 07:08 PM 4/9/2020, you wrote:
Quote:
--> AeroElectric-List message posted by: "wsimpso1" <wsimpso1(at)comcast.net>

Given the current state of knowledge, do we appear to be better
off with a 7-10 AH battery on a brownout bus or with the boosters,
or even both?

a battery supported brown-out bus is not
terribly elegant. The energy needed to
support the 'victim' electro-whizzies
is minuscule . . . 15V output at say
6A for (heaven forbid!) 10 Seconds
is a total of 900 Watt-Seconds. An
8 a.h. bat discharged at the same rate
is good for about an HOUR for about
300,000 Watt-Seconds. Further, it
weighs about 8 pounds and has a
short service life.

A booster will happily deliver
to the necessary load with a
weight penalty of less than 1
pound and a service life that probably
exceeds the life of the airplane.

Quote:
Anybody have some brands and model numbers that
are known to be reliable for these DC-DC gadgets
that could be used as brownout boosters?

These are not safety of flight
items. They are used for mere seconds
at the beginning of each flight . . .
failure to perform only means that
potential brown-out victims will
reset after engine start and continue
to work normally. Ergo, failure of
the device is at worst an inconvenience
requiring some attention when you get back
to your home field.

Quote:
Which gives better reliability (scores better on FMEA)
for backup power - backup batteries on the individual
boxes or a single battery, switch, and relay?

These are not BACKUP POWER . . . they
are a band-aid sadly needed because
some popular electro-whizzies did
didn't take DO160 qualification testing
to heart and make their product
brown-out resistant -OR- capable of
fast reboot . . . like 1-2 seconds.

Internal or external BACKUP batteries
called out by suppliers are yet another
band-aid. The supplier of every really
cool gizmo wants to believe that it's
always going to be there for you. They
correctly observe that they have no
control over YOUR choices for architecture.
So, the safe thing to do from a marketing
perspective is to include internal
backup battery or call for an external
backup battery in their installation
recommendations.

The downside is the same as cited above
for brown-out bus support. They're
a limited life product that demands
preventative maintenance for continue
airworthiness . . .

The discussions going to refinement
of Z01 strive to achieve bullet-proof
power sources not only for the really
slick electro-whizzies . . . but ALL
accessories needed for comfortable
termination of flight.

I suggest that goal can be achieved
with ONE . . . count 'em . . . ONE
well cared for battery and up to two
modern offerings for engine driven
power sources.


Bob . . .


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wsimpso1



Joined: 04 Nov 2018
Posts: 26
Location: Saline MI

PostPosted: Sat Apr 11, 2020 8:44 am    Post subject: Re: New Design Schemes and Brownout Operation Reply with quote

First, thanks for the response, I appreciate the thoughtful response.

To specifics:

I do believe that a DC-DC booster makes sense for prevention of brownout reboots over adding a battery. I was hoping that we could narrow the field some. Going on a search/shop/install/repeat cycle is something I would like to avoid. Any brands that are obviously bad news or look like they should be OK is a big help.

The AeroElectric Connection has talked FMEA and MTBF. I was trained on FMEA in 1980 and have done a lot of work with them over a successful engineering career, and believe in their value. I was hoping that we could talk relative scores of the various systems when performed by someone who has more than the guesses I would have to apply to the process. Frankly, if I can add a couple switches and contactors plus another battery to reduce the likelihood of dead stick and dark panel by an order of magnitude, I am likely to do it. On the other hand, if Z-14 and the newly developing scheme are on par with each other, I will go for simpler and lighter every time...

That said, I did a quick FMEA using pessimistic values for MTBF of alternators, regulators, drive mechanisms, switches, contactors, and wiring, and even then, two alternators and reasonably fresh battery gets reliability beyond 99.9% for a thousand hours of operation. The value of redundancy is pretty high.

I am beginning to see the value in the advice I have received... Thanks Bob!

Billski


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