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AGM batteries question

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Phil White

Joined: 10 Jan 2006
Posts: 45
Location: Downers Grove, IL

Posted: Wed Nov 25, 2009 11:36 am Post subject: AGM batteries question

I am building an RV with Mazda rotary engine that is electric-dependent, 

so I will have 2 batteries, and probably 2 alternators.  It came time to 

purchase batteries, and I presumed I would use the Odyssey PC-680 16AHr 

AGM units.  A web search didn't find any bargains (lowest was $118 each, 

if memory serves).

    A search for AGM batteries led me to Gruber Power Systems, who make 

an 18 AHr unit nearly identical in size and capacity to the Odyssey 680, 

but only $42 each.  I have purchased a pair, and am in process of 

mounting and wiring them, but I wonder if anyone has experience with or 

has tested Gruber batteries, or others like them, to determine if they 

are well suited to aircraft use.

    I did notice that the terminals are noticably thinner than what one 

sees on the Odysseys, being a half inch tall and wide, but only 1/16" 

thick protruding up from the battery top.  Makes me wonder if these 

batteries won't supply the high current needed for starting an engine, 

only having long life in lower current demand applications.



    Any experience you can share?



Phil in IL

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 26, 2009 9:30 am Post subject: AGM batteries question

At 01:29 PM 11/25/2009, you wrote:

 	  Quote: 	
		  



I am building an RV with Mazda rotary engine that is 

electric-dependent, so I will have 2 batteries, and probably 2 

alternators.  It came time to purchase batteries, and I presumed I 

would use the Odyssey PC-680 16AHr AGM units.  A web search didn't 

find any bargains (lowest was $118 each, if memory serves).

    A search for AGM batteries led me to Gruber Power Systems, who 

 make an 18 AHr unit nearly identical in size and capacity to the 

 Odyssey 680, but only $42 each.  I have purchased a pair, and am in 

 process of mounting and wiring them, but I wonder if anyone has 

 experience with or has tested Gruber batteries, or others like 

 them, to determine if they are well suited to aircraft use.


	


   ANY reasonable battery is suited to aircraft use IF your

   system is designed and crafted for failure tolerance.



   In other words, assuming your system is designed such

   that failure of a battery brings you to an unplanned

   arrival with the earth, then NO battery (or its accessory

   connection hardware) can offer at 100.00% level of

   certainty for no unhappy days in the cockpit.



   First, set up design goals that include conducing

   failure mode effects analysis on your proposed system.

   You need to KNOW than no single failure of any fragile

   or wearing component will present a hazard. If such

   components are identified, they are (1) increased in

   robustness to achieve reliability of prop-bolts or

   (2) backed up by a plan-b. In the case of wearing

   components (like batteries, tires, oil, alternator

   belts, etc.) you craft a preventative maintenance plan

   that identifies and replaces a sub-standard component

   long before its ability to deliver to design goals

   is compromised.



 	  Quote: 	
		      I did notice that the terminals are noticably thinner than what 

 one sees on the Odysseys, being a half inch tall and wide, but only 

 1/16" thick protruding up from the battery top.  Makes me wonder if 

 these batteries won't supply the high current needed for starting 

 an engine, only having long life in lower current demand applications.


	


   Starting the engine is the LEAST of your concerns.

   Battery sizing (energy stored in a NEW battery)

   and performance tracking (energy stored in a USED

   battery) are the drivers for your battery selection

   and maintenance activities.



 	  Quote: 	
		      Any experience you can share?


	


   Be wary of anecdotal experiences. There are many, MANY

   combinations of condition and stress that drive the

   performance of a battery. Some combinations can make

   a platinum plated super-battery look like a brick of

   lead while other conditions induce owners to heap praises

   upon their bargain-barn battery.



   If selected, installed and maintained with rudimentary

   knowledge of requirements to meet design goals ANY

   battery (including your $42 find) is a candidate

   for exploration.



   You will have to judge for yourself whether your

   choice has performed to satisfactory cost-of-ownership

   values. You won't have that answer for several years.

   In the mean time, be VERY wary of those who extol

   the virtues of their own choices: "My Excalibur 1000

   cranking-amp battery has been spinning my engine for

   6 years now . . . best battery I've ever owned."

   Ask that fellow how long that battery runs his

   electro-whizzies if the alternator quits. It's

   almost a sure bet he can't tell you.



See:

http://www.aeroelectric.com/Mfgr_Data/Batteries/Concorde/owner_manual_new.pdf



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



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



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



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



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



    The short answer to your question is: Yeah, that battery

    should be included in your suite of choices. Plan

    on doing periodic capacity and load-dump testing to

    insure continued flight-worthiness in concert with

    your design goals.



See chapter 17 of:



https://matronics.com/aeroelectric/Catalog/pub/pub.html#P-Book



    In the mean time, what are you building? What's your

    proposed electrical system architecture look like?

    Have you done a load analysis of all the electro-whizzies

    on your airplane to size your energy requirements

    for normal and abnormal operating conditions?



    Bob . . .

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