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AUX Battery

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tim2542(at)sbcglobal.net
Guest

Posted: Wed Oct 20, 2010 5:40 pm Post subject: AUX Battery

I'm designing my system using a small AUX Battery and single Alt. I want to charge the aux battery with a Schottkey diode.  The AUX battery will power the avionics during start to prevent brown out and can be used as clearance delivery and/or a backup bus for the EFIS/430W GPS/Comm. Others I know of who have done it this way also used a 50 ohm resistor in series with the diode for reasons no one can really explain to me. The battery is a small 7ah sealed unit and I plan to charge it thru the diode and a 7.5 amp fuse. Is there any reason to use a resistor in this configuration?   

Thanks, Tim Andres  

   

   

 (rnbraud(at)yahoo.com)   

   

       [quote][b]

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Thu Oct 21, 2010 6:07 am Post subject: Re: AUX Battery

 	  Quote: 	
		  Is there any reason to use a resistor in this configuration? 	


No, I see no reason to use a resistor.  If someone else used a resistor, they should be able to explain why.  Just because some other builder wired their plane wrong is no reason to do it the same way.  There have been arguments on this forum about what type of diode to use to minimize voltage drop.  Using a resistor does not minimize voltage drop.

  If there is a reason for using a resistor, it would be interesting to know how and why it was used.

Joe

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Oct 21, 2010 6:30 am Post subject: AUX Battery

At 08:34 PM 10/20/2010, you wrote:

  	  Quote: 	
		   I'm designing my system using a small AUX Battery and single Alt. I want to charge the aux battery with a Schottkey diode.  The AUX battery will power the avionics during start to prevent brown out and can be used as clearance delivery and/or a backup bus for the EFIS/430W GPS/Comm. Others I know of who have done it this way also used a 50 ohm resistor in series with the diode for reasons no one can really explain to me. The battery is a small 7ah sealed unit and I plan to charge it thru the diode and a 7.5 amp fuse. Is there any reason to use a resistor in this configuration? 	


   No. In fact the ideal aux battery charging circuit

   has a MINIMUM of voltage drop. The Shottky diode

   offers the closest solid state solution with drops

   averaging 0.3 to 0.5 volts. You can acquire these

   devices packaged for user-friendly installations

   from 



  https://matronics.com/aeroelectric/Catalog/AEC/9001/IM9001-700A.pdf 



   or

  http://www.periheliondesign.com/powerschottkydiodesfiles/PowerSchottky%20Manual.pdf 



   or loose parts from electronics suppliers of various

   sorts



  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MBRF40250TGOS-ND

 

   Alternatively, you can achieve essentially zero-volts

   drop for the charging circuit with incorporation of

   an Aux Battery Management Module that closes a relay

   between the two batteries only when the alternator is

   running (bus rises above 13.0 volts).



         



 

   Bob . . .    [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Oct 22, 2010 8:14 am Post subject: AUX Battery

At 09:07 AM 10/21/2010, you wrote:

 	  Quote: 	
		  

 > Is there any reason to use a resistor in this configuration?



No, I see no reason to use a resistor.  If someone else used a 

resistor, they should be able to explain why.  Just because some 

other builder wired their plane wrong is no reason to do it the same 

way.  There have been arguments on this forum about what type of 

diode to use to minimize voltage drop.  Using a resistor does not 

minimize voltage drop.

   If there is a reason for using a resistor, it would be 

 interesting to know how and why it was used.


	


     An excellent point. A series resistor

     in a small battery charging circuit is

     indicated for one purpose only and under

     a narrow set of circumstances.



     If the small battery is at risk for

     ever becoming totally discharged one might

     improve on battery performance by limiting

     the magnitude of recharge current when the

     system comes back up at normal voltages.

     The batteries I used in the recovery parachute

     controllers for HBC



http://www.aeroelectric.com/Pictures/Misc/Recovery_Parachute_Controller.jpg



     were 1.2 a.h. devices intended to be charged by and

     as back-up for ship's power. If ship's power was

     brought on with completely discharged batteries,

     the inrush to the little batteries would not be

     conducive to a long service lift. Hence, the charge

     loop included a 3 ohm resistor that would limit

     initial current flows to about 8 amps. This also

     prevented the initial recharge current to a dead

     battery from popping the 10A breaker on the ship's

     bus.



     Of course, this would mean that getting the batteries

     fully recharged would take longer. It also means that

     the charging loop could not be depended upon for

     power to run the system. That task was covered by

     a separate circuit.



     The decision for including such resistors depends

     on an assessment (and preventative maintenance

     program) for circumstances that might totally

     discharge the battery . . . and what you would

     do about it if such an event were discovered.



     I built a battery maintainer into the parachute

     controller intended to be plugged into AC mains

     for a minimum of two hours within the week prior

     to a flight where the parachute was to be armed.



     Further, preflight testing by ground

     crews before launch included a load test of the

     batteries. Hence, probability of the resistor ever

     being functionality tasked was very low.



     Joe's assessment is quite correct that inclusion

     of a resistor in the charge path of a battery demands

     a full understanding of it's purpose and the effect

     on system functionality under all anticipated

     conditions. 99% of the time, you don't need them.

   Bob . . .

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tim2542(at)sbcglobal.net
Guest

Posted: Fri Oct 22, 2010 8:52 am Post subject: AUX Battery

Thanks Bob, Joe.  The idea as I understood it was in regard to limiting the charge current just as you surmised. 

The Diode I'm using is a 9amp wire diode. I'll install it using your homeless components methods from the site, no resistor. 

Thanks,Tim



Sent from my iPhone



On Oct 22, 2010, at 9:13 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:



 	  Quote: 	
		   

 

 At 09:07 AM 10/21/2010, you wrote:

> 

> 

> 

> > Is there any reason to use a resistor in this configuration?

> 

> No, I see no reason to use a resistor.  If someone else used a resistor, they should be able to explain why.  Just because some other builder wired their plane wrong is no reason to do it the same way.  There have been arguments on this forum about what type of diode to use to minimize voltage drop.  Using a resistor does not minimize voltage drop.

>  If there is a reason for using a resistor, it would be interesting to know how and why it was used.

 

    An excellent point. A series resistor

    in a small battery charging circuit is

    indicated for one purpose only and under

    a narrow set of circumstances.

 

    If the small battery is at risk for

    ever becoming totally discharged one might

    improve on battery performance by limiting

    the magnitude of recharge current when the

    system comes back up at normal voltages.

    The batteries I used in the recovery parachute

    controllers for HBC

 

 http://www.aeroelectric.com/Pictures/Misc/Recovery_Parachute_Controller.jpg

 

    were 1.2 a.h. devices intended to be charged by and

    as back-up for ship's power. If ship's power was

    brought on with completely discharged batteries,

    the inrush to the little batteries would not be

    conducive to a long service lift. Hence, the charge

    loop included a 3 ohm resistor that would limit

    initial current flows to about 8 amps. This also

    prevented the initial recharge current to a dead

    battery from popping the 10A breaker on the ship's

    bus.

 

    Of course, this would mean that getting the batteries

    fully recharged would take longer. It also means that

    the charging loop could not be depended upon for

    power to run the system. That task was covered by

    a separate circuit.

 

    The decision for including such resistors depends

    on an assessment (and preventative maintenance

    program) for circumstances that might totally

    discharge the battery . . . and what you would

    do about it if such an event were discovered.

 

    I built a battery maintainer into the parachute

    controller intended to be plugged into AC mains

    for a minimum of two hours within the week prior

    to a flight where the parachute was to be armed.

 

    Further, preflight testing by ground

    crews before launch included a load test of the

    batteries. Hence, probability of the resistor ever

    being functionality tasked was very low.

 

    Joe's assessment is quite correct that inclusion

    of a resistor in the charge path of a battery demands

    a full understanding of it's purpose and the effect

    on system functionality under all anticipated

    conditions. 99% of the time, you don't need them.

 

 

  Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Oct 22, 2010 1:50 pm Post subject: AUX Battery

At 11:49 AM 10/22/2010, you wrote:

 	  Quote: 	
		  



Thanks Bob, Joe.  The idea as I understood it was in regard to 

limiting the charge current just as you surmised.

The Diode I'm using is a 9amp wire diode. I'll install it using your 

homeless components methods from the site, no resistor.


	


  What's the capacity of your aux battery?

   Bob . . .

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tim2542(at)sbcglobal.net
Guest

Posted: Fri Oct 22, 2010 3:11 pm Post subject: AUX Battery

7ah 

Tim



Sent from my iPhone



On Oct 22, 2010, at 2:48 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:



 	  Quote: 	
		   

 

 At 11:49 AM 10/22/2010, you wrote:

> 

> 

> Thanks Bob, Joe.  The idea as I understood it was in regard to limiting the charge current just as you surmised.

> The Diode I'm using is a 9amp wire diode. I'll install it using your homeless components methods from the site, no resistor.

 

 What's the capacity of your aux battery?

 

 

  Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 23, 2010 9:21 am Post subject: AUX Battery

What's the capacity of your aux battery?



At 06:08 PM 10/22/2010, you wrote:

AeroElectric-List message posted by: tim2542(at)sbcglobal.net



7ah



Tim



     Okay, it's not one of those "tiny" things and

     will probably be okay with the simple diode in

     the charging feeder.



                        CAUTION



     Any builders on the List who are relatively new

     or perhaps were not paying close attention to battery

     discussions in past years, I advise a review of the

     following publications:



Chapters 2 and 17 of the AeroElectric Connection



http://www.aeroelectric.com/articles/neveragain/neveragain.html



http://www.aeroelectric.com/articles/neveragain/neveragain_1.html



http://www.aeroelectric.com/articles/neveragain/neveragain_2.html



http://www.aeroelectric.com/articles/battery.pdf



http://www.aeroelectric.com/articles/rg_bat.html



http://www.aeroelectric.com/articles/Batteries/Multiple_Battery_Myths_A.pdf



http://www.aeroelectric.com/articles/bat_iso2.pdf



http://www.aeroelectric.com/articles/Batteries/Deltran_Odyssey_Floobydust.html



http://www.aeroelectric.com/articles/WestMountain_CBAII.pdf



     Bottom line is that if you are carrying ANY

     number of battery(ies) on board for the purpose

     of alternator failure mitigation, then

     you need to SIZE the task - how much time to do

     you EXPECT any battery to perform as back-up power?

     Then you need A PLAN to make sure those requirements

     will be met.



     This is especially important for so-called AUX

     batteries that are not NORMALLY expected to

     do anything. If the battery doesn't crank the

     engine . . . nor is it occasionally used to

     supply some noteworthy run-time for ground maintenance,

     then HOW DO YOU KNOW the thing is even useful?



     The heavy iron guys periodically capacity test

     all ship's batteries and replace them when they

     fall below established limits for meeting

     s/b power needs.



     With out A PLAN, it's a high order risk that

     the battery won't be there for you at such

     time you DO need it.



     If no plan, then depending on an AUX battery (or

     even the ship's main battery) to bail you

     out is problematic. You're may be investing

     $acquisition$, space, weight and fuel to wrap

     yourself in a lead-acid security blanket.



     Cap meters like . . .



http://www.westmountainradio.com/content.php?page=cba



     are excellent pieces of test equipment that will load

     the battery exactly like you'll expect to load it

     during S/B service in your airplane. If not this

     class of device, then



http://www.aeroelectric.com/articles/Poor_Man%27s_Cap_Tester.pdf



     or just put a new battery in every two years. But

     have requirements assured by a plan.

   Bob . . .

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