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Combining alternator wires?

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Jul 16, 2013 8:26 am Post subject: Combining alternator wires?

I've looked through the archives because I'm sure this is in there, but I can't find it. 



I've got a Velocity-XL, 28v system, single battery (up front), dual alternators (60a & 20a). The battery and starter contactors are both up front next to the battery. 



With respect to the B-leads from the two alternators, does each one need to have a separate wire up to the nose? Or can I install a single wire from the firewall to the front that both alternators can tie in to? If I can do the single wire approach, would all three wires need protection with ANL current limiters, or just the two lines from the alternators?

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nuckolls.bob(at)aeroelect
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Posted: Tue Jul 16, 2013 8:47 am Post subject: Combining alternator wires?

At 11:26 AM 7/16/2013, you wrote:

 	  Quote: 	
		  



I've looked through the archives because I'm sure this is in there, 

but I can't find it.



I've got a Velocity-XL, 28v system, single battery (up front), dual 

alternators (60a & 20a). The battery and starter contactors are both 

up front next to the battery.



With respect to the B-leads from the two alternators, does each one 

need to have a separate wire up to the nose? Or can I install a 

single wire from the firewall to the front that both alternators can 

tie in to? If I can do the single wire approach, would all three 

wires need protection with ANL current limiters, or just the two 

lines from the alternators?


	


   If it were my airplane, the starter contactor

   would be as close as practical to the starter

   on the firewall.



   The starter contactor becomes a  fat-wire tie

   point to bring alternator b-leads to the bus

   by tying their current limiters to the hot side of

   the contactor.



   So yes, the single wire approach

   works for all three devices . . . a wire which

   you already have in place.



   Bob . . .

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Jul 16, 2013 10:19 am Post subject: Re: Combining alternator wires?

 	  Quote: 	
		  The starter contactor becomes a  fat-wire tie

   point to bring alternator b-leads to the bus

   by tying their current limiters to the hot side of

   the contactor. 	




Thanks!



Follow up question:  I can't find a 20a current limiter for the backup alternator. B&C only has them down to 40a. Do I use a regular 20a CB? Or look elsewhere for a 20a current limiter?

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jul 16, 2013 2:13 pm Post subject: Combining alternator wires?

At 01:19 PM 7/16/2013, you wrote:

 	  Quote: 	
		  

 > The starter contactor becomes a  fat-wire tie

 >    point to bring alternator b-leads to the bus

 >    by tying their current limiters to the hot side of

 >    the contactor.

Thanks!



Follow up question:  I can't find a 20a current limiter for the 

backup alternator. B&C only has them down to 40a. Do I use a regular 

20a CB? Or look elsewhere for a 20a current limiter?


	


   Use an ATC inline fuseholder with a 30

   A fuse in it.



http://tinyurl.com/lusgrmw



   I have these for sale at:



http://tinyurl.com/cgr42l5



   you might find them in a local automotive

   parts house.



   Bob . . .

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steve(at)tomasara.com
Guest

Posted: Wed Jul 17, 2013 6:46 am Post subject: Combining alternator wires?

Don J. said:

 	  Quote: 	
		   With respect to the B-leads from the two alternators, does each one need to have

 a separate wire up to the nose? Or can I install a single wire from the firewall

 to the front that both alternators can tie in to? If I can do the single

 wire approach, would all three wires need protection with ANL current limiters,

 or just the two lines from the alternators?

Bob K. replied:
	


 	  Quote: 	
		      If it were my airplane, the starter contactor

     would be as close as practical to the starter

     on the firewall.



     The starter contactor becomes a  fat-wire tie

     point to bring alternator b-leads to the bus

     by tying their current limiters to the hot side of

     the contactor.


	


If it were my airplane (and this is the way I layed it out in my LongEz 

though I have yet to bother installing a starter and it's a single 

alternator configuration):



I would put the ANL and both contactors up in the nose.  The ANL in my 

installation is to protect against current flowing out the battery to a 

short in the wire going back to the alternator(s).  The alternator(s) 

themselves current limit to a degree much more than a battery does.  

This wire only has to be sized to match the needs of the alternators.



The fat starter wire is only live when the starter is being activated.



The "cost" of this approach is the weight of the separate alternator 

wire, the benefit to me was eliminating the un-protected, always hot 

when the master is on, large wire running the whole length of the 

aircraft.  Acceptable though this may be, I wasn't comfortable with it.



A minor side benefit is that I had a better place to put the ANL and 

starter contactor up in the nose than back on/near the firewall.



Boulder/Longmont, Colorado

Restoring (since 1/07) and flying again (8/11!): N45FC O235 Longeze 

Cothern/Friling CF1 (~1000 Hrs)

Flying (since 9/86): N43732 A65 Taylorcraft BC12D

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