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Z13-8b Brown Out Relay Question ?

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Bill Schlatterer

Joined: 09 Jan 2006
Posts: 195

Posted: Fri Jun 13, 2008 7:11 pm Post subject: Z13-8b Brown Out Relay Question ?

Bob, I am having a little trouble understanding the charging circuit for the 7ah battery in Z13-8b.  What I see is that the normal E-Bus Alt Feed path is in place to activate the Aux Bat if needed to the Endurance bus.  The Brown-Out Battery Relay is normally energized by the starter circuit which disconnects the Aux Bat while starting but  leaves it in the circuit for normal charging at all other times.    

What I don't understand is why you would use a S701-4 relay instead of a simple D25 steering diode which has no moving parts?  Isn't this the same thing we are doing with the diode between the E-Bus and the Main Bus (allowing a one way current flow)?  Is there some advantage in using the relay over the diode in this "brown-out battery relay" position?  

[url=http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8B(BrownOutBattery).pdf]http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8B(BrownOutBattery).pdf[/url]  

  

Thanks Bill S  

7a finishing   

Z13/8/32/35  

     [quote][b]

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nuckolls.bob(at)cox.net
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Posted: Sat Jun 14, 2008 7:49 am Post subject: Z13-8b Brown Out Relay Question ?

At 10:06 PM 6/13/2008 -0500, you wrote:



 	  Quote: 	
		  Bob, I am having a little trouble understanding the charging circuit for 

the 7ah battery in Z13-8b.  What I see is that the normal E-Bus Alt Feed 

path is in place to activate the Aux Bat if needed to the Endurance 

bus.  The Brown-Out Battery Relay is normally energized by the starter 

circuit which disconnects the Aux Bat while starting but  leaves it in the 

circuit for normal charging at all other times.



What I don't understand is why you would use a S701-4 relay instead of a 

simple D25 steering diode which has no moving parts?  Isn't this the same 

thing we are doing with the diode between the E-Bus and the Main Bus 

(allowing a one way current flow)?  Is there some advantage in using the 

relay over the diode in this "brown-out battery relay" position?



<http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8B(BrownOutBattery).pdf>http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8B(BrownOutBattery).pdf 




	


   The relay has essentially zero voltage drop across it.

   The silicon rectifier has about .8 volts you could

   use a Schottky diode for about 0.5 volts depending

   on your e-bus loads. The design rationale is that

   the brown-out support battery get the recharging

   benefit from full bus voltage for normal operations.

   On the other hand, if you're not counting on the

   brown-out support battery as part of the endurance

   capacity, perhaps allowing the brown-out battery

   to live in the airplane at reduced capacity fits

   your design goals.



   I have it on my list of things to do in the lab

   to measure the difference in state of charge for

   small SVLA batteries when the recharge levels are

   0.5 and 0.8 volts below the main bus.



   In any case, I'm sure it's not a really big deal

   if you'd like to substitute a diode, particularly

   a Schottky device for the relay. The reason I

   suggested the relay was because I could not

   quantify the difference in state of charge based

   on good data. The "easy" way out was to suggest

   a switching device that did not put the battery's

   state of charge in question.



   Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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user9253

Joined: 28 Mar 2008
Posts: 1928
Location: Riley TWP Michigan

Posted: Sat Jun 14, 2008 5:19 pm Post subject: Re: Z13-8b Brown Out Relay Question ?

Bill S

Another advantage of using a relay is that the power can be interrupted close to the source, a nice feature to have in case of smoke in the cockpit.  One could think of the relay as a mini battery contactor.  Only a small size wire is required between the relay coil and cockpit switch.  Also, a diode would keep the E-Bus always hot.  With a diode, each load on the E-Bus would have to be shut off individually at the end of the flight to prevent the batteries from running down.

Joe Gores

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Joe Gores

Bill Schlatterer

Joined: 09 Jan 2006
Posts: 195

Posted: Sat Jun 14, 2008 7:17 pm Post subject: Z13-8b Brown Out Relay Question ?

Thanks Bob, I have the diode on a fused circuit going to the main bus so

that it charges when the master is on but doesn't drain if it's off.  Didn't

consider the reduced voltage through the diode as being insufficient to keep

the smaller battery "fully" charged.  I do get a .6 volt drop across the

D25.



Thanks for posting the diagram, made me think about it again.



Thanks Bill S

7a finishing 



--

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user9253

Joined: 28 Mar 2008
Posts: 1928
Location: Riley TWP Michigan

Posted: Sun Jun 15, 2008 3:45 am Post subject: Re: Z13-8b Brown Out Relay Question ?

Bill,

Oops, my mistake.  I thought you were talking about the Alternate Feed Relay and my first reply was in reference to that.

Joe

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