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Final Review

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mprather(at)spro.net
Guest

Posted: Fri Nov 02, 2007 2:51 pm Post subject: Final Review

Going from 12V to 14V absolutely won't hurt the avionics.  It also doesn't

sound to me like the operation should cause any significant inductive kick

which would lead to a high power voltage excursion.



Consider that with the bus loaded (at least on some systems), if the

engine is brought to idle RPM, the bus voltage may sag significantly below

14V.  Increasing the RPM or reducing the bus load will increase the

voltage back to the regulator setup.



DO160 (the standard to which Avionics manufacturers should design their

products) allows for much larger swings than this..

Regards,



Matt-



 	  Quote: 	
		   Bob, and all,



 I have just completed a Velocity.  She just passed the FAA cert and, I am

 going thru the process once more of looking at all of my work and

 hopefully

 asking all the right questions.



 I have built a Velocity XLRG.  She has a 300 HP Lycoming IO-540.  The

 electrical design is my own with major influence from Bob Nuckols and this

 list.  Thanks for that.  She has two equal batteries (Odessy 925) and a

 single alternator (B&C 60 amp).  One mag and one elec ign.



 DC1 is direct wired into the main bus.  DC2 is direct wired into the

 Avionics/Essential bus.  The battery contactors have separate pilot

 controlled on/off switches.  They share a common hot bus bar thru separate

 schokey diodes.  In normal ops I plan to have both battery contactors

 closed

 for start.  Electrically the batt outputs will be isolated at this point.

 I

 have a 40 amp relay that is pilot controlled, to parallel the batteries

 after the engine is started.  I have a Garmin 480 GPS/NAV and a TruTrak

 Digi

 II VSGV and a GRT EFIS Horizon I to protect from starting circuit voltage

 sags and surges.



 Here is my question.



 After start, when the engine is stable at idle power, I will close the

 alternator field.  This action will cause the main bus (through a 60 amp

 current limiter) up to a nominal 14.2 volts.  Then I plan to close a two

 way

 solid state "bus tie" relay which sits electrically between the two bus

 terminal blocks.  This will bring the Avionics-Ess bus to the same 14.2

 volts and will serve as my DC2 charge wire path.



 So is this 12 to 14.2 voltage boost going to hurt my avionics if they are

 already on?  Should I leave them off until I have tied the system

 together?

 The amp loading on either bus as this point in the checklist is going to

 be

 minimal.



 Thanks,

 Terry Miles

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bobf(at)feldtman.com
Guest

Posted: Fri Nov 02, 2007 4:24 pm Post subject: Final Review

Simple question - why does anyone have their avionics "ON" when starting the engine, or the alternator for that matter - or when shutting down? Leave it all off til stable then turn on the avionics master. If you are worrying about unstable voltage with an air restart, you have bigger problems than whteher the EFIS comes back up quick (it does, seen the GRT do it in about 10 secs in a Cozy) 



bobf



On 11/2/07, Terry Miles <terrence_miles(at)hotmail.com (terrence_miles(at)hotmail.com)> wrote:[quote] [quote]  	  Quote: 	
		  Bob, and all,

 

I have just completed a Velocity.  She just passed the FAA cert and, I am going thru the process once more of looking at all of my work and hopefully asking all the right questions.

 

I have built a Velocity XLRG.  She has a 300 HP Lycoming IO-540.  The electrical design is my own with major influence from Bob Nuckols and this list.  Thanks for that.  She has two equal batteries (Odessy 925) and a single alternator (B&C 60 amp).  One mag and one elec ign.  

 

DC1 is direct wired into the main bus.  DC2 is direct wired into the Avionics/Essential bus.  The battery contactors have separate pilot controlled on/off switches.  They share a common hot bus bar thru separate schokey diodes.  In normal ops I plan to have both battery contactors closed for start.  Electrically the batt outputs will be isolated at this point.  I have a 40 amp relay that is pilot controlled, to parallel the batteries after the engine is started.  I have a Garmin 480 GPS/NAV and a TruTrak Digi II VSGV and a GRT EFIS Horizon I to protect from starting circuit voltage sags and surges.

 

Here is my question.

 

 	
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Gilles.Thesee(at)ac-greno
Guest

Posted: Fri Nov 02, 2007 4:42 pm Post subject: Final Review

Robert Feldtman a écrit :

 	  Quote: 	
		   Simple question - why does anyone have their avionics "ON" when starting the

 engine, or the alternator for that matter - or when shutting down? 

Robert,
	


Some installation have an EFIS to monitor engine or system parameters : 

voltage, RPM, oil pressure, temperatures, etc...

I would be reluctant to wait for the *voltage* to be stable before 

having any indication of revolutions or oil pressure at engine start.

Switching everything down for starting or shutting the engine is an old 

habit from sooo long ago.



 	  Quote: 	
		   whteher the EFIS comes back up quick (it does, seen the GRT do it in about

 10 secs in a Cozy)

   


	


I've just spent two days flying an airplane with a moving map GPS. This 

poorly engineered device kept resetting any time the voltage was 

sagging, when maneuvering the flaps on the ground, for instance.

A real nuisance. BTW, 10 seconds seems a bit long in flight.

On the other hand the little Dynon, or the Enigma are rock stable 

whatever the usual voltage variation....

Correctly designed aviation electronic devices are impervious to 

ordinary voltage fluctuations.



Best regards,

-- 

Gilles

http://contrails.free.fr

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Terry Watson

Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA

Posted: Fri Nov 02, 2007 5:33 pm Post subject: Final Review

Gilles,



Can you tell us the make and model of the flakey EFIS, and a little more

about the circumstances?



Terry

--

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Gilles.Thesee(at)ac-greno
Guest

Posted: Sun Nov 04, 2007 4:13 am Post subject: Final Review

Terry Watson a écrit :

 	  Quote: 	
		   Can you tell us the make and model of the flakey EFIS, and a little more

 about the circumstances?

   

Terry,
	




The instrument is some sort of Becker moving map about 6-7 years old. 

Considering the behaviour, I did not try to determine the exact 

denomination 

Anytime the voltage sags, the unit reboots : for instance on the ground 

with the engine idling, one must not move the electric wing flaps lest 

the GPS reboot...



Also, the display is not really sunlight readable : we had to use a map 

as a shade to accurately read the map. The associated Dynon is not much 

better in this respect, BTW.



Best regards,

-- 

Gilles

http://contrails.free.fr

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