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Odyssey % of charge (Correction)

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nuckollsr(at)cox.net
Guest

Posted: Thu Feb 23, 2006 8:35 am Post subject: Odyssey % of charge (Correction)

I stubbed my toe in interpretation of the graphs in an earlier

post. The revision is below:



At 08:22 AM 2/14/2006 +0000, you wrote:



 	  Quote: 	
		  



If the charging system is not working does anyone have an approximate % of

remaining capacity versus voltage for a Odyssey PC680 or similar?



What is a safe lower voltage limit one can discharge a PC680 to and not

cause permanent battery damage?


	




    <snip>



    Know that ALL lead-acid technologies are 95% used up

    at 11 volts for a 12-volt battery. See:



http://www.aeroelectric.com/Pictures/Curves/Capacity_vs_Voltage.gif



    This is a curve for a big biz jet battery where we see

    that for "light" loads (1 to 2x of capacity), the discharge

    voltage has a sharp "knee" that increases the negative

    going slope as it crosses 11v/22v line.



    This particular battery is capacity rated at CC levels

    of discharge i.e., it's a 37 a.h. battery that will give

    100% of rated capacity at 74 amps of discharge (typical

    for rating bizjet batteries that have a 30 minute emergency

    requirement). If one were to discharge this battery like

    most of the rest of the industry does (20 hour rate) then

    it would probably exhibit a capacity on the order of

    50 ampere-hours.



    Check out this curve from the datasheet on a Panasonic

    33 a.h. battery:



http://www.aeroelectric.com/Pictures/Curves/LA1233_Panasonic.gif

    Again, note the shape knee in the curve as it dives

    through 11 volts . . . all used up. In this case, the

    battery is not specifically rated for emergency power

    service in airplanes - it couldn't be called a

    33 a.h. device. If we run up the 30-minute line to

    11 volts, we find that the battery would have to be

    rated as a 26 a.h. device if intended for that kind

    of service.



    HERE'S THE POT HOLE - THE 30 MINUTE DISCHARGE CURVE

    OF 26.4 AMPS SAYS THE CAPACITY IS 26.4A X 0.5 HOURS

    OR 13.2 A.H., NOT 26 A.H.



    I SHOULD HAVE CAUGHT THAT . . . A 33 TO 26 REDUCTION

    IN APPARENT CAPACITY FOR A 15X LARGER DISCHARGE

    RATE DIDN'T RAISE THE FLAGS. FOUND IT WHILE ARCHIVING

    THE POST.



    Bob . . .

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Feb 24, 2006 5:37 am Post subject: Odyssey % of charge (Correction)

Robert L. Nuckolls, III wrote:



 	  Quote: 	
		       HERE'S THE POT HOLE - THE 30 MINUTE DISCHARGE CURVE

     OF 26.4 AMPS SAYS THE CAPACITY IS 26.4A X 0.5 HOURS

     OR 13.2 A.H., NOT 26 A.H.

 

     I SHOULD HAVE CAUGHT THAT . . . A 33 TO 26 REDUCTION

     IN APPARENT CAPACITY FOR A 15X LARGER DISCHARGE

     RATE DIDN'T RAISE THE FLAGS. FOUND IT WHILE ARCHIVING

     THE POST.


	


Welcome to Peukert's exponent. If you know the capacity at two different

discharge rates you can interpolate or extrapolate the capacity off the

battery at other discharge rates.



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
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