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recommendations for building a 24V battery?

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hdwysong

Joined: 06 Jun 2008
Posts: 21

Posted: Fri Jul 25, 2008 2:32 pm Post subject: recommendations for building a 24V battery?

I'm looking into building a 24V battery for an airborne payload with

the following spec's:



-  12AH minimum, no CCA requirement (not used for starting)

-  bolted terminals

-  no FAA/PMA approval required

-  no need for metal jackets, etc., to protect from the environment

-  hanging off of a bus fed by a 28V alternator



Several offerings from Odyssey (PC535/545/625/680), Panasonic

(LC-RD1217P), and Powersonic (PS-12180) fit the bill.  Thus far, the

Powersonic battery beats the rest on price and weight per AH.  Has

anyone had good/bad experience with Powersonic batteries?



The paperwork from Powersonic posts a charge voltage range of 14.4 to

14.7V and a float range of 13.5V to 13.8V.  First, is it valid to

simply double these for the 24V battery?  Second, the 28V bus will be

sitting between 28.5 and 28.9V nominally which is just under the

"charge" range (assuming doubling the 12V range is valid) but a volt

or so above the "float" range.  Probably not worth a worry but I want

to make sure.



Any other tricks/techniques/gotchas related to the care and feeding of

ganged batteries will be appreciated.



D

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hdwysong

Joined: 06 Jun 2008
Posts: 21

Posted: Sat Jul 26, 2008 4:42 pm Post subject: recommendations for building a 24V battery?

 	  Quote: 	
		     What are your battery-only energy storage requirements?


	


The system will draw a bit over 14A worst case and I can shed as much

as 4A without sacrificing functionality.  My design goal is to keep

the remaining 10A of "battery only" stuff alive (bus voltage >20V) for

at least an hour if the alternator drops offline.



 	  Quote: 	
		     Does the system DEPEND on a battery for functionality?

   In other words, would a failed battery contactor put

   the outcome of the flight at risk?


	


No, not as long as the alternator remains well behaved with the batt

contactor open.  BTW, our primary power source is a dedicated 28V 100A

alternator (National Airparts N300) wired per the "Z" diagrams with a

Zeftronics R25400 for voltage regulation and over-voltage protection.

The architecture also includes a "filter" cap sized per Nat'l Airparts

recommendations.



Have I made a mistake in assuming that this system will remain online

without the battery (e.g. - if the 28V battery contactor fails open)?

This is something that we can (and will, unless advised otherwise)

check out on the ground as part of a systems functional test.



 	  Quote: 	
		     What preventative maintenance program do you plan

   for replacing batteries before they're incapable of

   supporting battery only systems for the designed

   endurance mode?


	


Standard battery care/feeding is the plan (e.g. - battery tender when

down, periodic capacity testing as part of the preflight prep after

storage).  Replacement will occur when capacity tests show that

achieving the "1-hour battery only" target is not possible.



 	  Quote: 	
		      There's no objective data to suggest that any particular

    brand of battery is the better value in terms of

    $replacement$/service-hours. Periodic cap testing of the

    batteries in service is the 100% foolproof way to guarantee

    system performance irrespective of the batteries you choose

    to try.


	


Understood.  It will be interesting to compare the results from the

"cheap" battery tests against those from the $approved* battery that

rides around in my C150.  I have a hunch that the 3x cost doesn't

necessarily translate to 3x performance/service-hours...  



Thanks for your insight, Bob!



D

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