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Engine start on Z14 with different size batteries

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 28, 2012 7:49 am Post subject: Engine start on Z14 with different size batteries

At 04:40 AM 6/28/2012, you wrote:



 	  Quote: 	
		  In my architecture Bus 1 with the big battery is the sole starter 

cranking bus for normal operations. Accordingly all "starter current 

path" wires on Bus 1 are 2 AWG to reduce resistance during engine start.


	


   Unless your batteries are in the tail, 2AWG is heavier

   than necessary but certainly not an electrical performance

   issue.



 	  Quote: 	
		  By comparison I calculate that the largest wire on Bus 2 could be 8 

AWG for normal operations on that bus including Xfeed operations to 

bus 2 (for non cranking operations).


	


   If your batteries are up front and the small battery

   is not intended to crank the engine, then probably 12AWG

   is sufficient on the aux alternator side . . .

 	  Quote: 	
		  However it occurs to me that if my Bus 1 battery (Odyssey 680) was 

struggling to crank the engine in a remore location I would be 

tempted to switch on the Xfeed and get whatever current boost I 

could from the smaller Odyssey 310 on bus 2.



My question is this:   What size wire do I need to incorporate in 

the "starter current" path of bus 2 to facilitate assisted engine 

cranking on the odd occasion from the smaller battery. Presumably 

bigger would always be better....but what's reasonable.


	


   We're talking seconds here. 20A through a 22 AWG wire

   wont 'burn' the wire. 12AWG or perhaps 10AWG in your aux

   alternator system is quite adequate to the task even

   if you find yourself tempted to 'boost' the larger battery's

   abilities with the smaller battery. But I'll suggest that

   a ground power system capable of jump-starting from a

   ground vehicle is a much better hedge against soggy batteries

   in remote locations.



   If you plan to frequent remote locations, then keeping a

   sharp eye on the condition of the larger battery is

   important. You need to replace it when it drops to 70%

   or less of capacity . . . this isn't an endurance issue,

   it's a cranking issue for ventures into higher risk airports.



   Being able to 'stack' the 7.5 a.h. battery on top of a soggy

   17 a.h. battery is poor insurance irrespective of wire

   sizes.

   Bob . . .

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dick(at)minetfiber.com
Guest

Posted: Thu Jun 28, 2012 10:16 am Post subject: Engine start on Z14 with different size batteries

Question;



See below. How is the test performed to see if the battery has at least 70% 

capacity?



Dick Wildman

7S5

 	  Quote: 	
		     If you plan to frequent remote locations, then keeping a

   sharp eye on the condition of the larger battery is

   important. You need to replace it when it drops to 70%

   or less of capacity . . . this isn't an endurance issue,

   it's a cranking issue for ventures into higher risk airports.



   Being able to 'stack' the 7.5 a.h. battery on top of a soggy

   17 a.h. battery is poor insurance irrespective of wire

   sizes.

   Bob . . .


	




 	  Quote:

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