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e-bus diode

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tomcostanza

Joined: 19 Oct 2008
Posts: 49

Posted: Sun Feb 28, 2010 8:57 am Post subject: e-bus diode

Bob (et al),



I'm about to wire the panel, and am wondering about the e-bus diode.  In particular, I'm looking at Z-11.  It appears to me that the diode only needs to be there when the main contactor is disengaged, and the e-bus alternate feed switch is closed.  When operating normally, the diode could be a piece of wire.  So why isn't the e-bus alternate feed switch a DPDT with one pole shorting the diode when in "normal" operation.  During normal operation, would I not drop 0.6 volts across the diode?  I have found empirically, that an 0.6 volt drop equals about a 10% deficit in the output of my comm transmitter (5w to 4.5w).



I do realize that Bob has probably forgotten more than I'll ever know about this stuff, so am I over-thinking this?  Or is there something I'm missing?



Clear skies,

-Tom

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_________________
Clear Skies,
Tom Costanza
-- in year 17 of a 3 year project

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Feb 28, 2010 11:11 am Post subject: e-bus diode

At 10:57 AM 2/28/2010, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "tomcostanza" <Tom(at)CostanzaAndAssociates.com>



 Bob (et al),



 I'm about to wire the panel, and am wondering about the e-bus diode.  In particular, I'm looking at Z-11.  It appears to me that the diode only needs to be there when the main contactor is disengaged, and the e-bus alternate feed switch is closed.  When operating normally, the diode could be a piece of wire.  So why isn't the e-bus alternate feed switch a DPDT with one pole shorting the diode when in "normal" operation. 	


    The design goal was to minimize parts count for reducing

    risk of mis-positioned switches during a re-configuration to

    battery only operations. The diode absolutely prevents

    back-feeding the main bus from the e-bus.



  	  Quote: 	
		   During normal operation, would I not drop 0.6 volts across the diode?  I have found empirically, that an 0.6 volt drop equals about a 10% deficit in the output of my comm transmitter (5w to 4.5w).



 I do realize that Bob has probably forgotten more than I'll ever know about this stuff, so am I over-thinking this?  Or is there something I'm missing?   A  "voltage drop" on the order of .6 to

.7 volts is not significant

   with respect to operation of equipment on the e-bus. That

   tiny drop in output, while measureable, would not be

   noticed by anyone listening to you at the other end.



   Consider that the alternate feedpath to the e-bus is there

to

   provide 10.5 to 12.5 volts to the equipment when the

alternator

   is off line . . . 10.5 to 12.5 is all you're going to get

out

   of a battery. Nonetheless, we reasonably expect equipment

on

   the e-bus to function in a useful manner.



   When the alternator is working, the main bus is 13.8 to

14.6

   volts . . . throw away 0.7 volts in

the e-bus normal feed diode

   and you have 13.1 to 13.9 volts on the e-bus. Still

higher

   than with battery-only operations.



   Bottom line is that the diode drop affects performance in

no

   way that anyone would notice.



[/b] 	


   Bob . . .    [quote][b]

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