Matronics Email Lists :: View topic - Low voltage indicator with dual alternators

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Low voltage indicator with dual alternators

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jul 08, 2013 12:29 pm Post subject: Low voltage indicator with dual alternators

 	  Quote: 	
		  My operational goals for the Z-14 included being able to run much of the panel 

 on one battery while still having a fully charged battery for starting.  The

 idea being that I wanted to be able to enter flight plans and even check weather

 before engine start.  That's worked out well.  I can connect the buses for starts

 if needed and that works well as well. 	


    Okay, but consider the ENERGY needed to do these two tasks.

    Suppose you turn on three electro-whizzies for a total drain

    of 3A (a lot for solid state gizmos) and take 5 minutes to

    herd all the ducks into place. That 12v x 3A x 300 seconds

    for a total of 11,000 watt-seconds.



    Now, lets crank the engine at 200A x 12v x 10 seconds

    for a total of 24,000 watt-seconds.



    How much energy is available for use in a 18 a.h.

    SVLA battery?  At a 3A rate will give it up over 5 hours

    at an average voltage of 11.5 for a total of about 650,000

    watt-seconds.



    In other words, the task of conducting pre-flight activities

    and starting the engine are not big demands on a well

    maintained battery.



  	  Quote: 	
		   

 However, I normally start with the buses separated because if I go parallel, the voltage drop causes my 3 MDFs to re-boot. 	


   How much 'stuff' do you have to turn on before engine

   start? On the Beech products we used to offer a mini-ebus

   switch that would let you fire up a comm radio directly

   from the battery. Your comm radio probably needs 0.2A receive,

   and maybe 1.5A transmit. A long winded pre-flight activity

   might need 1000 watt-seconds.



   I'm thinking that the bus from which all your 'kitchen

   sink' accessories is powered also powers the comm radio

   and you have no way to power up the comm radio independently?

   You might want to consider moving a comm radio to a

   battery bus and adding . . .



   COMM RADIO . . . . . Check OFF

   

   . . . . to your shutdown checklist.



   Bottom line is that with two batteries on board, you've

   got perhaps a million watt-seconds to burn. Doing your

   starts in parallel will reduce relative abuse to the batteries

   and extend their service life. Letting the 'kitchen sink'

   accessories clock in after engine start may not be

   a significant delay in your departure plans.



 

   Bob . . .    [quote][b]

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

Mauledriver(at)nc.rr.com
Guest

Posted: Wed Jul 10, 2013 6:30 am Post subject: Low voltage indicator with dual alternators

On 7/8/2013 4:29 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		          	  Quote: 	
		  My operational goals         for the         Z-14 included being able to run much of the panel 

         on one battery while still having a fully charged battery for         starting.  The

         idea being that I wanted to be able to enter flight plans and         even check         weather

         before engine start.  That's worked out well.  I can connect         the buses for starts

         if needed and that works well as well. 	
       

          Okay, but consider the ENERGY needed to do these two       tasks.

          Suppose you turn on three electro-whizzies for a total       drain

          of 3A (a lot for solid state gizmos) and take       5 minutes to

          herd all the ducks into place. That 12v x 3A x 300       seconds

          for a total of 11,000 watt-seconds.

       

          Now, lets crank the engine at 200A x 12v x 10 seconds

          for a total of 24,000 watt-seconds.

       

          How much energy is available for use in a 18 a.h.

          SVLA battery?  At a 3A rate will give it up over 5       hours

          at an average voltage of 11.5 for a total of about       650,000

          watt-seconds.

       

          In other words, the task of conducting pre-flight       activities

          and starting the engine are not big demands on a well

          maintained battery.

     	
     That was my assumption going in.  My original thought was that I'd     be able to turn everything on, do my flight plan input, clearance     copy and whatever, then turn the key and start her up.  Thinking     there would be little need to manage energy through th pre-start, I     do not have an avionics master or bus or even power switches on my     MFDs.  

     

     The fly in the ointment has been tendency for the MFDs (3 GRT HX     units) to reboot during an interconnected start.

     

     The energy draw is probably a bit more than one might expect but I     don't have actual current draw measurements to validate.  For     planning purposes I assumed 4.5A for the 3 MFDs combined, 1A for the     dual AHRS,  .6A for ADSB weather, 2.1A for the G430.  Add 1 amp for     the contactor and (unknown) for the panel fans.  That's 12v x 8.2A x     300secs = 29,520 watt-secs.  That doesn't include the AP and audio     panel which are on the same bus and are turned off at shutdown.  It     is the minimum I want for pre-start duck herding but I'm thinking I     need to find a way to mitigate it.

     (BTW, Thanks so much for engaging me on this - This has become a big     task on my improvement list for the year)

      	  Quote: 	
		  

        	  Quote: 	
		   

         However, I normally start with the buses separated because if I         go         parallel, the voltage drop causes my 3 MDFs to re-boot. 	
       

         How much 'stuff' do you have to turn on before engine

         start? On the Beech products we used to offer a mini-ebus

         switch that would let you fire up a comm radio directly

         from the battery. Your comm radio probably needs 0.2A       receive,

         and maybe 1.5A transmit. A long winded pre-flight activity

         might need 1000 watt-seconds.

     	
     How much?  I need at least one MFD (weather, input of pre-flight     values), the G430 (flight plan input & comm).  But powering up     only 1 MFD is a compromise - 3 are configured.  With anything less,     many error msgs are generated.

     

     Is all this pre-start duck herding necessary or desirable? Yes and     Yes

     Virtually 99% of my flying is IFR.  Single pilot in and out of the     NY/PHL/WASH axis requires lining them up and knocking them down or     getting called on every miss.  The reality is more nuanced however.      In winter, I start it, then begin the flight planning/clearance     getting process.  No electron problems except that the MFDs     sometimes reboot on an interconnected cold weather start.  In     summer, temperatures demand minimizing the time with the RV10 gull     wing doors closed.  We're very comfortable sitting in the cockpit     fooling around as long as a breeze is blowing thru  with the doors     providing some shade.  Engine start requires the doors be closed and     from that point on, it's sweaty and miserable until takeoff despite     the strong stream of 'fresh' air blowing on our sun baked     carcasses.  The net is - I will hurry and/or skip some pre-flight,     post-start planning activities until airborne and I invariably pay     for that.  Actually, I just don't let that happen any longer.

      	  Quote: 	
		  

         I'm thinking that the bus from which all your 'kitchen

         sink' accessories is powered also powers the comm radio

         and you have no way to power up the comm radio independently?

         You might want to consider moving a comm radio to a

         battery bus and adding . . .

       

         COMM RADIO . . . . . Check OFF

         

         . . . . to your shutdown checklist.

     	
     Done.  The SL30 is on the other bus and other non-essential stuff is     shut down during shut down, but the whole G430 needs to be online     for flight planning.  I don't consider it a kitchen sink - just the     essentials in this bit intensive world.

     

     It just occured to me that several non-bus essentials aren't even     included; the cell phone for remote IMC releases and the iPad. Most     NY/WASH/PHL clearances, make that 'all' such clearances, require     victor airway translation for G430 input.  Entry of the 8-10 step     clearance into the iPad is required in order to figure out that     actual waypoints for entry into the G430.  It's usually desirable to     make sure I 'get it' before  taking off over NYC and heading toward     the Wash SFRA, which means that it then gets mostly input into the     G430 before engine start.  Ah, the joys of the paper-less cockpit!

      	  Quote: 	
		  

         Bottom line is that with two batteries on board, you've

         got perhaps a million watt-seconds to burn. Doing your

         starts in parallel will reduce relative abuse to the       batteries

         and extend their service life. Letting the 'kitchen sink'

         accessories clock in after engine start may not be

         a significant delay in your departure plans.

       

     	
     Well, in summer I need the essential sink before start.  Point well     taken, but no doubt about the need here.

     

     However, I'd like to get back to interconnected parallel starts with     all my essential stuff on.  I'm thinking the core problem is not the     load involved but rather the tendency for the  GRT MFDs to re-boot.      I started looking at power wiring options for the GRTs.  This     paragraph from the installation guide may be useful:

      	  Quote: 	
		  The majority of the current flow into the display unit       will occur on the bus with the 

       highest voltage. So if the voltage of the main bus or power source       falls below 

       that of the secondary bus or power supply, the secondary bus will       power the 

       display units and operation will not be interrupted. Since it is       desirable to not 

       have the display units and AHRS connected to the power supply       supplying power 

       to the engine starter during the engine start (to maximize the       current available for 

       the starter, and possibly extend the life of the CCFL backlight in       the display unit),

       this feature allows the fitting of a small (3-5AH) auxiliary       battery to one of the 

       power input connections provide power to the EFIS during engine       start. If an 

       auxiliary battery is fitted, provisions should be made to keep it       charged.

     	
     What do you think?

      [quote][b]

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum