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AUX BAttery Charging

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jack.byrne(at)bigpond.com
Guest

Posted: Thu Feb 21, 2008 10:31 pm Post subject: AUX BAttery Charging

All.



I have a 4AMP/HR battery as an AUX battery for my EFIS.

I am charging it via the main bus.



Bus-5amp fuse-diode-aux bat. 18G wire

The Diode has the #'s 339 and IN5400 on it.



The 5 amp fuse blows!



How can I get around this. I am assuming the AUX bat is drawing a greater current if it gets depleted a resonable amount and this is blowing th fuse.



Do I need to increase the size of the wire and fuse?

What is the max AMPs that will be drawn by the AUX bat?



Thanks

Chris Byrne

SYDNEY

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mprather(at)spro.net
Guest

Posted: Fri Feb 22, 2008 7:21 am Post subject: AUX BAttery Charging

That sounds like a decent mix of components to get the job done.  What's

the voltage on the aux battery?



The max amps will depend on the state of charge and the internal

resistance of the battery and the voltage drop across the diode.  I would

have guessed that 5A would be plenty.



Is this diode a two-lead device (anode and cathode only - I see that it's

listed as a rectifier diode)?  Do you only have two of the leads

connected?



I assume you have it wired like this:



main_bus --> 5A fuse --> diode --> +lead on aux battery



What model/brand/specs is the aux battery?

Regards,



Matt-



 	  Quote: 	
		   

 All.



 I have a 4AMP/HR battery as an AUX battery for my EFIS.

 I am charging it via the main bus.



 Bus-5amp fuse-diode-aux bat. 18G wire

 The Diode has the #'s 339 and IN5400 on it.



 The 5 amp fuse blows!



 How can I get around this. I am assuming the AUX bat is drawing a greater

 current if it gets depleted a resonable amount and this is blowing th

 fuse.



 Do I need to increase the size of the wire and fuse?

 What is the max AMPs that will be drawn by the AUX bat?



 Thanks

 Chris Byrne

 SYDNEY

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nuckolls.bob(at)cox.net
Guest

Posted: Fri Feb 22, 2008 7:59 am Post subject: AUX BAttery Charging

At 05:25 PM 2/22/2008 +1100, you wrote:



 	  Quote: 	
		  

All.



I have a 4AMP/HR battery as an AUX battery for my EFIS.

I am charging it via the main bus.



Bus-5amp fuse-diode-aux bat. 18G wire

The Diode has the #'s 339 and IN5400 on it.



The 5 amp fuse blows!



How can I get around this. I am assuming the AUX bat is drawing a greater 

current if it gets depleted a resonable amount and this is blowing th fuse.



Do I need to increase the size of the wire and fuse?

What is the max AMPs that will be drawn by the AUX bat?



Thanks

Chris Byrne

SYDNEY


	


   What you're experiencing is one of several reasons

   I crafted the aux battery management module some

   years ago. See:



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

http://www.aeroelectric.com/Catalog/AEC/9005/9005-701B.pdf



   The AEC9005 product has been discontinued and

   will be replaced by a newer design. In the mean

   time, there's no reason that folks can craft a

   similar device themselves.



   However, understand that it's real easy to get

   wrapped around the "aux battery isolation" axle.



   Whether your system has two or ten batteries

   in the system, the generalized operating scenario

   says for normal operations, ALL batteries can

   be hard-connected to the charging system. By

   "hard" I'm saying closed contacts of a switch

   or relay.



   When and if the low volts warning light comes

   on, we now have the task of SEPARATING each

   of the batteries into it's unique duties for

   mitigating the effects of alternator failure.

   The time that a pilot has to effect this

   separation IS NOT a tense, borderline emergency

   situation demanding millisecond response.



   It's perfectly okay if battery isolation is

   immediate and automatic by means of diodes

   and/or aux battery management systems . . .

   but if the pilot decided to finish a cup

   of coffee or fold some maps before manually

   opening the connection pathways that isolate

   various batteries, the outcome of the flight

   would not be measurably different.



   The sum total of energy on the batteries

   needs to be a known quantity, part of your

   plan-B for dealing with alternator failure.

   It's my fondest wish that everyone who reads

   these words is PLANNING, DESIGNING, and

   MAINTAINING their battery management philosophy

   for HOURS of no-sweat, alternator failure-management

   flight. This is diametrically opposed to the

   FAA blessed notion of carrying a minimum of

   30-minutes of EMERGENCY operation.



   So, it's a perfectly okay thing if your aux battery

   charging path were simply replaced with a switch

   as opposed to the diode mentioned. It's also

   perfectly okay that the aux battery charging

   feeder be some kind of boss-hog conductor. Say

   14AWG and 15A fuse. Now, keep in mind that there

   are huge current sources at BOTH ends of this feeder

   so BOTH ends should be fused if the feeders are

   of significant length.



   No doubt what you've observed is a demonstration

   of the capability for even a very small battery

   to ACCEPT charging currents at rates much higher

   than the anticipated loads on the battery itself.

   This is why I like to place ALL batteries close

   together, tie them together in a cluster with

   hard contacts and short, fat wires. This is why

   you don't see any fuses or long feeders in the

   Z-figures to wire multiple batteries.



   When the various and sundry manufacturer's

   of products recommend some itty-bitty "back

   up" battery to support their customer's desire

   to keep the product working, the dirty little

   details of the physics for making seamless

   installation the battery can start jumping

   up to nibble at your heels.



   If your airplane's electrical system will

   benefit from multiple power sources over

   and above the classic single-battery/single-

   alternator architecture, first add the second

   alternator if you can (Z-13/. If a second

   battery is your only viable option, then consider

   a REAL battery sitting right next to the

   MAIN battery and connected to the system

   by a fat wire and hard switched contactor.



   In your particular case, it may be that you're

   too far down the path of adding an itty-bitty

   backup battery to the system so consider

   first upsizing the feeders and their protection

   levels. If the wires either side of the diode

   are relatively short, say 6-12" you can leave

   the fuses out entirely. I'd upsize the diode

   to one leg of a more robust device like:



http://www.aeroelectric.com/Pictures/Wiring_Technique/diode_wiring.jpg



   Bob . . .

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jack.byrne(at)bigpond.com
Guest

Posted: Fri Feb 22, 2008 3:56 pm Post subject: AUX BAttery Charging

Thanks to Bob, Matt and Max for your replies.



Bob the AUX Batt is just being used to power the EFIS during engine cranking. I lose the EFIS initialization and have to sit in the one spot for 2 mins after engine start for the GYRO's to align. It is also a last ditch power source for the SBY ADI (TRUTRACK) in case every thing turns to poo.



I have the Z13/8. One main batt and 35 AMP ALT and the B & C 8 AMP ALT.



I think I will try and optimise the setup I have. The wires to and from the diode are less than 12 inches. I had see your AUX BATT drawing but wanted to try and keep this as simple as possible, providing it works of course.

THanks again guys.



Chris Byrne

SYDNEY

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nuckolls.bob(at)cox.net
Guest

Posted: Sun Feb 24, 2008 10:45 am Post subject: AUX BAttery Charging

At 10:52 AM 2/23/2008 +1100, you wrote:



 	  Quote: 	
		  



Thanks to Bob, Matt and Max for your replies.



Bob the AUX Batt is just being used to power the EFIS during engine 

cranking. I lose the EFIS initialization and have to sit in the one spot 

for 2 mins after engine start for the GYRO's to align. It is also a last 

ditch power source for the SBY ADI (TRUTRACK) in case every thing turns to poo.



I have the Z13/8. One main batt and 35 AMP ALT and the B & C 8 AMP ALT.


	


    Then your concerns for supporting the ADI with

    a second battery are overkill. 13/8 is exceedingly

    unlikely to leave you with a dark panel.



 	  Quote: 	
		  I think I will try and optimise the setup I have. The wires to and from 

the diode are less than 12 inches. I had see your AUX BATT drawing but 

wanted to try and keep this as simple as possible, providing it works of 

course.


	


    Then parallel a second, small battery with the main

    battery a-la Z-35 . . .



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z35A.pdf



    Power your protected electro-whizzies from

    the Aux Battery Bus. Leave it's master switch

    OFF until after the engine is started. The

    S704-1 relay is only a 100 mA load and not

    a major no-value-added load during alternator

    out operations . . . which you're not going to

    experience anyway with two alternators. Dump

    the diode and fuse.



    Bob . . .

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schaefer(at)rts-services.
Guest

Posted: Sun Feb 24, 2008 1:44 pm Post subject: AUX BAttery Charging

This is a function of the internal resistance of the battery.

A good battery will draw more current.

This is a bad idea to charge this in this manner. 

It's OK to use this to maintain the battery. But if you use the battery you

should remove it and charge it on a regular charger and then re-install it

to the circuit.

--

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