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a couple of specific wiring questions

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sportav8r(at)gmail.com
Guest

Posted: Mon Jan 22, 2007 6:50 pm Post subject: a couple of specific wiring questions

First, I want to make sure I'm okay using a D-sub connector to carry

flap motor loads in an RV.  I think 16 AWG is recommended for the

motor wiring; will a single D-sub pin carry the current, or should I

double-up on pins?



Second, there is a wide range of recommendations and practice

regarding the B-lead wiring for the SD-8 alternator.  The Z 13/8

diagram shows 12 AWG for this run; the documents from B&C show 14 AWG,

 yet the wire they supply (potted into the regulator) is 16 AWG.

Given that these critters can only do about 10A flat-out, are we

sizing for voltage drop concerns here?  It's not just academic: I can

fuselink-protect a 16 AWG wire, maybe even a 14 AAWG one, but above

that it means buying ANL's.  Besides, there's the 2-gram weight

difference to obsess over 



-Bill B

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nuckollsr(at)cox.net
Guest

Posted: Tue Jan 23, 2007 10:21 am Post subject: a couple of specific wiring questions

At 09:26 AM 1/20/2007 -0500, you wrote:



 	  Quote: 	
		  



First, I want to make sure I'm okay using a D-sub connector to carry

flap motor loads in an RV.  I think 16 AWG is recommended for the

motor wiring; will a single D-sub pin carry the current, or should I

double-up on pins?


	


   How much current does the motor draw worst case? D-sub pins

   are RATED at 5A in low density loads. For longevity in aircraft

   environments I de-rate the pins to 3A.



   You CAN parallel pins for higher current conductors if you

   pay careful attention to the physics. The problem to be

   solved is making paralleled pins in a connector SHARE

   the total load. When mated resistance of the pin is say

   5 +/- 2 milliohms, then there is a small but non-zero

   statistical probability for direct paralleling pins as

   low as 3 milliohms and as high as 7 milliohms.



   Here's a technique I developed for adding "ballasting

   resistance" to each pin . . .



http://www.aeroelectric.com/Pictures/Wiring_Technique/Paralleled_DSub_Pins.pdf



   This was designed into and qualified on the following

   product:



http://www.aeroelectric.com/Pictures/Misc/GQM_Power_Dist.jpg



http://www.aeroelectric.com/Pictures/Misc/GQM_1st_Ops_Flight.jpg



   Now, I've discussed a way to make your system live

   long and prosper using a d-sub connector . . . but why

   a d-sub?  I needed the d-sub in the design cited above

   for compactness, convenience of dropping a connector

   right onto an ECB combined with a need to run lots

   of wires on and off the board with currents ranging

   from 22A down to microamps.



   Are you sure something like a



http://preview.tinyurl.com/2ccop5



   Isn't more appropriate to your task? Just a suggestion.

   The d-sub will perform just fine within the limits

   driven by the physics described above.



 	  Quote: 	
		  Second, there is a wide range of recommendations and practice

regarding the B-lead wiring for the SD-8 alternator.  The Z 13/8

diagram shows 12 AWG for this run; the documents from B&C show 14 AWG,

yet the wire they supply (potted into the regulator) is 16 AWG.

Given that these critters can only do about 10A flat-out, are we

sizing for voltage drop concerns here?  It's not just academic: I can

fuselink-protect a 16 AWG wire, maybe even a 14 AAWG one, but above

that it means buying ANL's.  Besides, there's the 2-gram weight

difference to obsess over 


	


    The Z-Figures are architecture drawings and not intended

    to be the final word on sizes for anything. Some SD-8's were

    installed on the ass-end of a LongEz and drove electronics

    and batteries at the head-end. Fatter than usual wires

    were used to improve on regulator performance. As you've

    noted, the alternator's output is rated at 10A max so as

    long as logistics and special performance issues are not

    a consideration 16AWG wire and 15A fusing would be most

    adequate. Don't get bogged down in ANY variabilities between

    the various Z-figures. EACH system needs to be evaluated

    for wire and fuse sizing based on the physics of YOUR

    proposed installation.



    Bob . . .

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sportav8r(at)gmail.com
Guest

Posted: Tue Jan 23, 2007 12:16 pm Post subject: a couple of specific wiring questions

Thanks most kindly.



Since I have a short run from the dynamo to the bus, I won't bother

with the 12 AWG concept.  Even 14 AWG seems a tad heavy for the

proposed 8 amp service, and the wiring will never see much use unless

the main alternator fails or goes OV (IR).



As for the flap harness connector, I had already leaned towards the

Molex and that is clearly the way to go, without always wondering if I

should have derated those pins and ballasted the wires.



-Bill



On 1/23/07, Robert L. Nuckolls, III <nuckollsr(at)cox.net> wrote:

 	  Quote: 	
		   



 At 09:26 AM 1/20/2007 -0500, you wrote:



 >

 >

 >First, I want to make sure I'm okay using a D-sub connector to carry

 >flap motor loads in an RV.  I think 16 AWG is recommended for the

 >motor wiring; will a single D-sub pin carry the current, or should I

 >double-up on pins?



    How much current does the motor draw worst case? D-sub pins

    are RATED at 5A in low density loads. For longevity in aircraft

    environments I de-rate the pins to 3A.



    You CAN parallel pins for higher current conductors if you

    pay careful attention to the physics. The problem to be

    solved is making paralleled pins in a connector SHARE

    the total load. When mated resistance of the pin is say

    5 +/- 2 milliohms, then there is a small but non-zero

    statistical probability for direct paralleling pins as

    low as 3 milliohms and as high as 7 milliohms.



    Here's a technique I developed for adding "ballasting

    resistance" to each pin . . .



 http://www.aeroelectric.com/Pictures/Wiring_Technique/Paralleled_DSub_Pins.pdf



    This was designed into and qualified on the following

    product:



 http://www.aeroelectric.com/Pictures/Misc/GQM_Power_Dist.jpg



 http://www.aeroelectric.com/Pictures/Misc/GQM_1st_Ops_Flight.jpg



    Now, I've discussed a way to make your system live

    long and prosper using a d-sub connector . . . but why

    a d-sub?  I needed the d-sub in the design cited above

    for compactness, convenience of dropping a connector

    right onto an ECB combined with a need to run lots

    of wires on and off the board with currents ranging

    from 22A down to microamps.



    Are you sure something like a



 http://preview.tinyurl.com/2ccop5



    Isn't more appropriate to your task? Just a suggestion.

    The d-sub will perform just fine within the limits

    driven by the physics described above.



 >Second, there is a wide range of recommendations and practice

 >regarding the B-lead wiring for the SD-8 alternator.  The Z 13/8

 >diagram shows 12 AWG for this run; the documents from B&C show 14 AWG,

 >yet the wire they supply (potted into the regulator) is 16 AWG.

 >Given that these critters can only do about 10A flat-out, are we

 >sizing for voltage drop concerns here?  It's not just academic: I can

 >fuselink-protect a 16 AWG wire, maybe even a 14 AAWG one, but above

 >that it means buying ANL's.  Besides, there's the 2-gram weight

 >difference to obsess over 



     The Z-Figures are architecture drawings and not intended

     to be the final word on sizes for anything. Some SD-8's were

     installed on the ass-end of a LongEz and drove electronics

     and batteries at the head-end. Fatter than usual wires

     were used to improve on regulator performance. As you've

     noted, the alternator's output is rated at 10A max so as

     long as logistics and special performance issues are not

     a consideration 16AWG wire and 15A fusing would be most

     adequate. Don't get bogged down in ANY variabilities between

     the various Z-figures. EACH system needs to be evaluated

     for wire and fuse sizing based on the physics of YOUR

     proposed installation.



     Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

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