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New Design Schemes and Brownout Operation

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 09, 2020 10:09 am Post subject: New Design Schemes and Brownout Operation

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
Guest

Posted: Thu Apr 09, 2020 5:19 pm Post subject: New Design Schemes and Brownout Operation

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: 33
Location: Saline MI

Posted: Sat Apr 11, 2020 8:44 am Post subject: Re: New Design Schemes and Brownout Operation

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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