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RG Batteries: I learned something last night

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nuckolls.bob(at)aeroelect
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Posted: Sun Oct 30, 2011 5:55 pm Post subject: RG Batteries: I learned something last night

At 10:18 AM 10/30/2011, you wrote:




I can report results that seem similar. For a new 9AH dekka vrla 

battery discharged at 6 amps (2 ohm resistance) I measure 56 minutes 

to 11.00 volts or 5.6 AH.



For a 6+ year old but 5 years in service identical battery (420 

flight hours) that has never been deep discharged or been on a 

maintainer, I measure 52 minutes to 11.00 volts or 5.2 AH again at 6 

amps discharge rate. All tests were done with the battery stabilized 

at a 66*F basement room temperature for several days after top up 

with a Schumaker 1162.



    Interesting!



I don't have an easy way to compare the cranking capabilities other 

than last winter the two paralleled batts in my Z-14 system seemed to 

crank a bit slower than normal.



   Hmmm . . . a pair of 9 a.h. batteries seems a bit light.

   How even are you swapping them out?



  It cranked fine all summer but I have just replaced the oldest 

battery anyway. Hasn't been much colder than freezing yet to compare 

this winter. I too am surprised that the old battery delivered 93% of 

the capacity of the newer one at a 6 amp discharge rate.



I'll attempt to compare the current flow from each battery while 

cranking (clamp on dc ammeter) the next time I fly. (I have the 

automatic parallel option during cranking). Should give an indication 

of how another 4 year in service batt compares to the new one for cranking.



   The 'definitive' test is done with some adjustable

   high current load, a timer and a voltmeter. Something

   like:



http://aeroelectric.com/Pictures/Battery_Testers/HF91129_4.jpg



   Our load measurements would not be comparable given the big

   differences in battery sizes. But doing the load test on your

   'new' and 'old' battery conducted in the same manner would yield

   some useful data. Your observations for discharge under a

   static load are interesting. Thanks for sharing!



   I'll be talking to my long time friend and battery guru

   in the next few weeks, I'll ask him about these observations.



   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 31, 2011 6:56 am Post subject: RG Batteries: I learned something last night

At 11:59 PM 10/30/2011, you wrote:

  	  Quote: 	
		  A few years back, we had a dead short on the battery cable before the contactor that drained the battery dead, dead, dead. I arrived and removed the short after about 2 hours. The battery read ~ 5v at that time. Charged it overnight and put it back in service. Several weeks later I replaced it when it failed to start the engine, charged it and did a CBA II capacity test on it at 4 amps. It delivered just under 24 ah - not bad for a severely abused 24 ah battery. I'm still using it as a shop battery. 	


    This is exactly the sort of event that can 

    be recovered. There's a process described in the

    Concorde maintenance documents for doing one or

    more recharge/discharge cycles on a badly abused

    battery. If (as the instance you describe) the

    recovery is started soon, a lot if not all of the

    battery's before-incident condition can be

    restored.



    Thanks for the input!



    Bob . . .     [quote][b]

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