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Battery Choices - what is too small AH capacity?

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mikefapex

Joined: 05 Jul 2007
Posts: 70
Location: Colorado

Posted: Tue Aug 12, 2008 12:05 pm Post subject: Battery Choices - what is too small AH capacity?

I am close to completing my not-so-little Z-19 upgrade and have a question about battery choices.



I originally had an Odyssey 545 14 AH battery, weight about 12 lbs. It cranked the engine fine but I am not sure how much life it would supply in a dead alternator condition (I know this is important and plan to test/quantify). 



A buddy loaned me an Odyssey 310 (8AH, 6lb) and I was thinking that two of these would make a light, compact package. And paralleled for starting would work, I'm sure. Also, the 310 has very small terminals (size M4), I see that as a challenge to making a good connection.



But in searching this list I can find no mention of batteries used smaller than about 12 AH capacity, so I am wondering if there is some lower AH practical limit I should not go below?



Adding a second 545 is doable but I would be obviously giving up useful payload capacity (which the Z-19 system has already reduced). 



Suggestions are appreciated, thanks in advance,



Mike

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jfogarty(at)tds.net
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Posted: Tue Aug 12, 2008 1:35 pm Post subject: Battery Choices - what is too small AH capacity?

Mike,  I have had a dead alternator in my Cardinal and all I did was look 

for the nearest airport and then landed, the next day was a nice vfr day and 

I few home on the same dead alternator and now dead battery, the plane does 

not care, it is just what works for you.  I would save the weight.



Jim

---

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mikefapex

Joined: 05 Jul 2007
Posts: 70
Location: Colorado

Posted: Tue Aug 12, 2008 1:56 pm Post subject: Re: Battery Choices - what is too small AH capacity?

Jim,



I think I am a bit more limited, my engine (Suzuki 1.3L) must have power to run (either alternator or battery). No mag magic for me. I am all about saving the weight but trying to stay with the good ideas of the Z-19 design (dual batteries).



Thanks,



Mike

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klehman(at)albedo.net
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Posted: Tue Aug 12, 2008 6:18 pm Post subject: Battery Choices - what is too small AH capacity?

Mike

I use two 8 AH Dekka AGM batteries on my 2.2 liter subaru with Z-14. One 

of them will crank the engine fine and with EFI it starts immediately. 

However they normally automatically parallel for cranking. At least 500 

starts over a couple of years so far and still going strong. Of course 

with Z-14, one dead alternator is not an issue even with an electrically 

dependent engine.

Ken



mikef wrote:

 	  Quote: 	
		   

 

 I am close to completing my not-so-little Z-19 upgrade and have a question about battery choices.

 

 I originally had an Odyssey 545 14 AH battery, weight about 12 lbs. It cranked the engine fine but I am not sure how much life it would supply in a dead alternator condition (I know this is important and plan to test/quantify). 

 

 A buddy loaned me an Odyssey 310 (8AH, 6lb) and I was thinking that two of these would make a light, compact package. And paralleled for starting would work, I'm sure. Also, the 310 has very small terminals (size M4), I see that as a challenge to making a good connection.

 

 But in searching this list I can find no mention of batteries used smaller than about 12 AH capacity, so I am wondering if there is some lower AH practical limit I should not go below?

 

 Adding a second 545 is doable but I would be obviously giving up useful payload capacity (which the Z-19 system has already reduced). 

 

 Suggestions are appreciated, thanks in advance,

 

 Mike

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Beemer

Joined: 26 Aug 2006
Posts: 87
Location: Middle Georgia

Posted: Wed Aug 13, 2008 3:06 am Post subject: Re: Battery Choices - what is too small AH capacity?

Mike,

I have the same question for my Kitfox with a G10 Suzi, I am planning to install Z-19RB, and have issues with weight. Right now, I'm planning on installing a 17ah in the tail for the Primary Eng bus, and a 12ah behind the seat for the Secondary bus.



My real question is how long will they last once the alt goes dead? no way to know, unless we figure out how much amperage the ECM, coil, and fuel pump are using. Right now, I have no idea.



I suppose it's a situation where an 8ah and a 12ah, or two 8ah would work, but would it leave enough time, say 15-30 minutes to descend and reach an airport? No idea.



I don't want to carry more weight than I have to, but I don't want to design in an off-field landing, either. I guess if we were to figure out how much juice is being used to keep the engine alive, we could calculate the time given by the battery size(s).



Sound right?

Bradley

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_________________
Beemer
KF2 (and now an M3!)
Suzuki G10 three-banger
Middle Georgia

mikefapex

Joined: 05 Jul 2007
Posts: 70
Location: Colorado

Posted: Wed Aug 13, 2008 11:16 am Post subject: Re: Battery Choices - what is too small AH capacity?

Ken and others,



That is good info on the battery usage. I'll look into the Dekka, I especially like the larger battery contacts as compared to the PC310 M4 bolts (they are so small they can hardly be called bolts....). I also replied in another thread, that I think the purchase of the West Mountain battery tester is probably money well spent (or something similar bought or built). Auto conversion guys like me need to know that if the alternator goes south, there really is a backup of some duration. 



Bob K has good guidelines for determining battery capacity, and I think taking the extra step with a quantitative measure is good.



Fly safe, 



Mike

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mikefapex

Joined: 05 Jul 2007
Posts: 70
Location: Colorado

Posted: Wed Aug 13, 2008 12:15 pm Post subject: Re: Battery Choices - what is too small AH capacity?

Ken,



You wrote: 8 AH Dekka AGM batteries



Can you describe the battery terminals on these Dekka batteries? Even a digital photo would be helpful. I have #2 welding cable with #2 lug terminals from the main contactor to the main battery terminals. I'm a bit concerned my existing battery terminals are too small for long term use & vibration resistance.



Thanks,



Mike

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Sam

Joined: 18 May 2008
Posts: 135

Posted: Wed Aug 13, 2008 4:59 pm Post subject: Battery Choices - what is too small AH capacity?

I purchased one of the West Mountain units for the same reason that you are concerned about, Mike.  It's a nifty tool.



I was surprised to find the 11 a.h. battery I had laying around the shop was actually only good for 7 a.h.

  	  Quote: 	
		  	
Sam



On Wed, Aug 13, 2008 at 2:06 PM, mikef <mikefapex(at)gmail.com (mikefapex(at)gmail.com)> wrote:

 [quote]--> AeroElectric-List message posted by: "mikef" <mikefapex(at)gmail.com (mikefapex(at)gmail.com)>

  

 Ken,

 

 Your conservative approach is probably a good one to begin estimating. I plan to experiment with actual battery only run times to back up the theory.

 

 I am also thinking about purchasing one of those West Mountain battery testers. At $109 it is probably money well spent. I know we go on forever with the 'little extras' in OBAM but I don't want to be looking for a field and thinking 'damn, just $109.....' .

  

 Mike

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=198424#198424

 

 

 

 

 

 

 

 

 

 

 [b]

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_________________
Sam Hoskins
www.samhoskins.blogspot.com

jmcburney(at)pobox.com
Guest

Posted: Thu Aug 14, 2008 8:08 am Post subject: Battery Choices - what is too small AH capacity?

If you need to know actual current draw, check out

www.sears.com/shc/s/p_10153_12605_03482369000P.  DC clamp-on ammeter, works

well for this kind of situation, not too expensive.  Just be sure you're

clamping around the wire that you really want to read.  It's easy to get on

the wrong side of a terminal.  (Don't ask how I know -- I know!)



Do not archive



Blue skies and tailwinds



Jim

CH-801

DeltaHawk diesel

Augusta GA

90% done, 90% left

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