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Avionics Back-Up Power

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trigo(at)mail.telepac.pt
Guest

Posted: Fri Aug 29, 2008 7:05 am Post subject: Avionics Back-Up Power

Bob and the group  

   

Since I had to put some weight in the tail of my RV-9A, I decided to install a battery as back-up power to some avionics, the EFIS, the COMM Radio and the Transponder.  

   

My GRT EFIS has 2 power inputs, which are internally controlled (EFIS uses the electrons from the highest source), so this is easy to wire.  

However, the Radio (SL-30) and the Transponder (GTX-330) only have 1 power input, therefore the question:  

   

  - How should I wire power, both from Main Battery and Back-Up Battery, to the COMM Radio and the Transponder?  

   

Help appreciated  

Carlos  

       [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Fri Aug 29, 2008 7:28 am Post subject: Avionics Back-Up Power

At 04:04 PM 8/29/2008 +0100, you wrote:



 	  Quote: 	
		  Bob and the group



Since I had to put some weight in the tail of my RV-9A, I decided to 

install a battery as back-up power to some avionics, the EFIS, the COMM 

Radio and the Transponder.



My GRT EFIS has 2 power inputs, which are internally controlled (EFIS uses 

the electrons from the highest source), so this is easy to wire.



However, the Radio (SL-30) and the Transponder (GTX-330) only have 1 power 

input, therefore the question:



   - How should I wire power, both from Main Battery and Back-Up Battery, 

 to the COMM Radio and the Transponder?


	


    How big a battery is it? How many batteries does the airplane

    carry already . . . in other words do you already have an

    AUX battery?



    Bob . . .

        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

trigo(at)mail.telepac.pt
Guest

Posted: Fri Aug 29, 2008 8:18 am Post subject: Avionics Back-Up Power

 	  Quote: 	
		   >  

 >Since I had to put some weight in the tail of my RV-9A, I decided to  

 >install a battery as back-up power to some avionics, the EFIS, the COMM  

 >Radio and the Transponder.  

 >  

 >  

 >My GRT EFIS has 2 power inputs, which are internally controlled (EFIS uses  

 >the electrons from the highest source), so this is easy to wire.  

 >  

 >However, the Radio (SL-30) and the Transponder (GTX-330) only have 1 power  

 >input, therefore the question:  

 >  

 >  

 >   - How should I wire power, both from Main Battery and Back-Up Battery,  

 > to the COMM Radio and the Transponder?  

   

     How big a battery is it? How many batteries does the airplane  

     carry already . . . in other words do you already have an  

     AUX battery?  

   

     Bob . . .  

   
	


I don't know exactly, because I still don't know the exact weight I need for W & B, but I am planning for a battery around 10Ah  

   

I do have 2 other batteries, Main and AUX, since my engine is an electron-dependant Subaru.  

   

Carlos  

       [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Sat Aug 30, 2008 5:06 am Post subject: Avionics Back-Up Power

>     How big a battery is it? How many batteries does the airplane

 >     carry already . . . in other words do you already have an

 >     AUX battery?

 >

 >     Bob . . .



I don't know exactly, because I still don't know the exact weight I need

for W & B, but I am planning for a battery around 10Ah I do have 2 other

batteries, Main and AUX, since my engine is an electron-dependant Subaru.



     Hmmmm . . . this is a bit problematic. Battery installation

     philosophy in A/C calls for local disconnect (battery contactor

     or relay). We also need to size the wiring so expected loads

     and recharge currents do not experience too large voltage

     drop. Finally, all wires need to be properly protected against

     faults.



     A 10 a.h. battery is good for about 10# of 'ballast'. If

     you went further back on the airframe, could you get down

     to say 5# of ballast? The reason for asking is that my present

     image of this system suggests a plastic battery relay (one

     of those 70A plastic things). A local fuse (use MAXI fuse

     holder to make the battery(+) to battery relay jumper. Run

     the battery feeder forward to the battery bus that runs

     the panel during alternator out operations.  We don't

     want to leave that feeder hot while the airplane is

     shut down . . . you need another relay at the forward

     end of the feeder too and protect that end with another

     MAXI fuse. The wire probably wants to be 10AWG and the

     fuses at both ends are MAX30. Now you need a third battery

     switch that closes both relays during flight operations.



     This is electrically messy . . . not much better from

     the pilot workload perspective either. As I mentioned

     earlier, it might be better to minimize total added weight

     by moving it as far back on the airframe as possible . . .

     an letting it be dead-weight thus avoiding the bow-

     of-spaghetti-wiring.



     Bob . . .

trigo(at)mail.telepac.pt
Guest

Posted: Sat Aug 30, 2008 6:48 am Post subject: Avionics Back-Up Power

Bob  

Thanks for your explanation and suggestions.  

   

Anyway, which is the reason you say "we don't want to leave that feeder hot while the airplane is shut down” ?  

If it’s not so important, 2 relays and 1 switch could be avoided, and pilot workload as well…  

   

Carlos  

   

   

 	  Quote: 	
		   -----Original Message-----  

 From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-  

 server(at)matronics.com] On Behalf Of Robert L. Nuckolls, III  

 Sent: sábado, 30 de Agosto de 2008 14:05  

 To: aeroelectric-list(at)matronics.com  

 Subject: RE: Avionics Back-Up Power  

   

 --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"  

 <nuckolls.bob(at)cox.net>  

   

  >     How big a battery is it? How many batteries does the airplane  

  >     carry already . . . in other words do you already have an  

  >     AUX battery?  

  >  

  >     Bob . . .  

   

 I don't know exactly, because I still don't know the exact weight I need  

 for W & B, but I am planning for a battery around 10Ah I do have 2 other  

 batteries, Main and AUX, since my engine is an electron-dependant Subaru.  

   

      Hmmmm . . . this is a bit problematic. Battery installation  

      philosophy in A/C calls for local disconnect (battery contactor  

      or relay). We also need to size the wiring so expected loads  

      and recharge currents do not experience too large voltage  

      drop. Finally, all wires need to be properly protected against  

      faults.  

   

      A 10 a.h. battery is good for about 10# of 'ballast'. If  

      you went further back on the airframe, could you get down  

      to say 5# of ballast? The reason for asking is that my present  

      image of this system suggests a plastic battery relay (one  

      of those 70A plastic things). A local fuse (use MAXI fuse  

      holder to make the battery(+) to battery relay jumper. Run  

      the battery feeder forward to the battery bus that runs  

      the panel during alternator out operations.  We don't  

      want to leave that feeder hot while the airplane is  

      shut down . . . you need another relay at the forward  

      end of the feeder too and protect that end with another  

      MAXI fuse. The wire probably wants to be 10AWG and the  

      fuses at both ends are MAX30. Now you need a third battery  

      switch that closes both relays during flight operations.  

   

      This is electrically messy . . . not much better from  

      the pilot workload perspective either. As I mentioned  

      earlier, it might be better to minimize total added weight  

      by moving it as far back on the airframe as possible . . .  

      an letting it be dead-weight thus avoiding the bow-  

      of-spaghetti-wiring.  

   

      Bob . . .  

   

   
	


       [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Sat Aug 30, 2008 1:35 pm Post subject: Avionics Back-Up Power

At 03:47 PM 8/30/2008 +0100, you wrote:



 	  Quote: 	
		  Bob



Thanks for your explanation and suggestions.



Anyway, which is the reason you say "we don't want to leave that feeder 

hot while the airplane is shut down ?



If it s not so important, 2 relays and 1 switch could be avoided, and 

pilot workload as well&


	


   It's just not done (at least in the TC aircraft world) both for maintenance

   and crash safety. How would you propose to wire it?



   Bob . . .

trigo(at)mail.telepac.pt
Guest

Posted: Sun Aug 31, 2008 8:49 am Post subject: Avionics Back-Up Power

 	  Quote: 	
		   --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"  

 <nuckolls.bob(at)cox.net>  

 At 03:47 PM 8/30/2008 +0100, you wrote:  

 >Bob  

 >  

 >Thanks for your explanation and suggestions.  

 >  

 >  

 >  

 >Anyway, which is the reason you say "we don't want to leave that feeder  

 >hot while the airplane is shut down ?  

 >  

 >If it s not so important, 2 relays and 1 switch could be avoided, and  

 >pilot workload as well&  

    It's just not done (at least in the TC aircraft world) both for maintenance  

    and crash safety. How would you propose to wire it?  

    Bob . . .  

I am thinking in installing the battery in the tail deck (under the RV-9A tail fairing), in order to obtain the longest arm to help with the Balance of the aircraft.  

The (-) terminal will be connected to a local Ground (which is the same I used for the tail light), and the (+) terminal connected to a 16A fuse located near the battery. (Is this fuse adequate to protect the wire and the battery from any inadvertent short along the hot wire?)  

By the way, regarding your observation that the wire should not be hot after shutdown, because of maintenance and crash safety, my humble opinion is that, in case of maintenance it is easy to disconnect the battery or pull out the fuse, and in case of crash I do have many hot wires around…  

From the fuse I will run an AWG#14 wire to a buss behind the instrument panel. Actually I’m planning this “buss” to be the “out” terminal of a diode, and I am thinking to connect the Main Battery to the “In” terminal of the Diode, to charge the Back-Up Battery.  

From that “buss” (the “out” terminal of the diode) I would run wires to each of the Avionics to be fed with back-up power.  

And that’s where I come back to my initial question:  

 How do I wire from this back-up “buss”, which is permanently hot, to each of the Avionics (Comm Radio and Transponder) which only have one power input?  

I am prepared to be technically fustigated but please be gentle….  

Carlos  

       [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Sun Aug 31, 2008 4:51 pm Post subject: Avionics Back-Up Power

I am thinking in installing the battery in the tail deck (under the RV-9A 

tail fairing), in order to obtain the longest arm to help with the Balance 

of the aircraft.



The (-) terminal will be connected to a local Ground (which is the same I 

used for the tail light), and the (+) terminal connected to a 16A fuse 

located near the battery. (Is this fuse adequate to protect the wire and 

the battery from any inadvertent short along the hot wire?).



     Sure, fuses are fast and tend to limit energy in

     the fault to the lowest practical values.



By the way, regarding your observation that the wire should not be hot 

after shutdown, because of maintenance and crash safety, my humble opinion 

is that, in case of maintenance it is easy to disconnect the battery or 

pull out the fuse, and in case of crash I do have many hot wires around…



     If this meets your design goals, then go for it!



 From the fuse I will run an AWG#14 wire to a buss behind the instrument 

panel. Actually I’m planning this “buss” to be the “out” terminal of a 

diode, and I am thinking to connect the Main Battery to the “In” terminal 

of the Diode, to charge the Back-Up Battery.

 From that “buss” (the “out” terminal of the diode) I would run wires to 

each of the Avionics to be fed with back-up power.



And that’s where I come back to my initial question:



How do I wire from this back-up “buss”, which is permanently hot, to each 

of the Avionics (Comm Radio and Transponder) which only have one power input?



    Okay, you already have two batteries and you've

    suggested that the always hot wire does not violate

    your design goals. You've also stated a desire not

    to add switches.



I am prepared to be technically fustigated but please be gentle….



    Not a problem. If I understand your design goals

    accurately, then how about simply adding the second

    battery in parallel to the battery that is already

    tasked with running the panel when the alternator is

    off line.  Fuses at both ends protects the wire,

    minimized parts count and avoids voltage drops

    associated with diodes.



    There's much M-Squared (mythology and misunderstanding)

    about paralleling batteries. It is true that any number

    of batteries may be paralleled for the purpose of

    charging them on a constant voltage source. All

    batteries will accept what ever energy they are capable

    of holding. Any number of batteries may be paralleled

    for the purpose of discharging them and aside from

    shorted-cell failures (exceedingly rare in RG batteries)

    all paralleled batteries will deliver all their contained

    energy to the load irrespective of their size or condition.



    Energy storage abilities of the tail-battery will

    be seamlessly added to those of the existing panel-

    battery if you simply parallel them.



    For the purposes of supporting good recharging times

    on the tail battery and minimizing voltage drop on that

    long run, I'll suggest 10AWG wire and 20A MAXI fuses at both

    ends.



    Bob . . .

mrspudandcompany(at)veriz
Guest

Posted: Mon Sep 01, 2008 8:45 am Post subject: Avionics Back-Up Power

Hmmmm . . . this is a bit problematic. Battery installation

     philosophy in A/C calls for local disconnect (battery contactor

     or relay). We also need to size the wiring so expected loads

     and recharge currents do not experience too large voltage

     drop. Finally, all wires need to be properly protected against

     faults.

     Bob . . .





Bob,

 	  Quote: 	
		  From one of your recent postings, you mentioned that battery install

philosophy calls for a local disconnect.  In the Z19RB the wires off the
	


busses at the 2 batteries are always hot.  Are you saying that the fat wires

must be short or disconnected and it is OK to have small fused wires, always

hot going to the instrument panel and elsewhere?

Thanks,



Roger

trigo(at)mail.telepac.pt
Guest

Posted: Mon Sep 01, 2008 10:05 am Post subject: Avionics Back-Up Power

Bob



As usual you've been very useful.

Thanks for your help



Carlos

[quote] --

wilenius(at)sympatico.ca
Guest

Posted: Tue Sep 02, 2008 5:11 am Post subject: Avionics Back-Up Power

Carlos,

  

  You've probably thought of this but ... could you not move the 2nd  battery backwards into the tail? Too much W&B shift?

  

 regards,

  

 Dave

 [quote]   --

trigo(at)mail.telepac.pt
Guest

Posted: Tue Sep 02, 2008 5:42 am Post subject: Avionics Back-Up Power

Hi Dave  

   

I did thought of that but   

   1 - my Aux Batt is also an Odissey PC625 which doesn’t fit under the tail fairing, and if I decided to put it somewhere between the baggage area and the tail tip, I would not be able to service/replace it  

   2 – I need the Aux battery to be an exclusive back-up to my electron-dependant engine, in case of alternator death and Main Battery is out of electrons  

   

I know that 3 batteries look really overkill, mainly to Total Weight ….  

   

Thanks anyway  

Carlos  

   

           

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Dave Wilenius

 Sent: terça-feira, 2 de Setembro de 2008 14:09

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: Avionics Back-Up Power  

  

     

Carlos,  

    

   

    

 You've probably thought of this but .. could you not move the 2nd battery backwards into the tail? Too much W&B shift?  

    

   

    

regards,  

    

   

    

Dave  

  [quote]  

--

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