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Problems Soldering DB-25 Connectors

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art(at)zemon.name
Guest

Posted: Mon Nov 28, 2016 7:50 pm Post subject: Problems Soldering DB-25 Connectors

Bob,



I found your explanation about the ballasting 22 AWG pigtails. It was in an email to me, not on your website. I will use this to update my blog post.

    -- Art Z.



On Thu, Sep 22, 2016 at 9:01 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 08:22 PM 9/21/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "rampil" <ira.rampil(at)gmail.com (ira.rampil(at)gmail.com)>



 Be careful about dry joints, the solder should be bright and shiny all around 

 the joint. 	


   . . .  which is easy to achieve with 63/37 solder featuring

   quality flux.



  	  Quote: 	
		   If the wire is carrying just signal, clipping a strand or two should 

 be fine . . . 	




   I've attached 18 AWG wires to solder-cups by trimming

   back excess strands. This was a system with long runs

   of wire where voltage drop was an issue. There are

   companies that make special adapters to put too-large

   wires into 20AWG solder-cups but trimming the strands

   is more compact and works good too.



  	  Quote: 	
		   (with adequate strain relief). 	


   The backshell is were wire-support takes place.

   Heat shrink is more of a hedge against pin-to-pin

   shorts by conductive contaminants . . . a thing

   that just doesn't happen in a clean work environment.

   

  	  Quote: 	
		  Power carrying wire demand more careful consideration

 about potential resistive heating and voltage drop. 	


   Sort of . . . but pin-to-socket interface within

   the connector is the driving concern about path

   resistance. 20AWG wire is 10 milliohms per FOOT,

   22AWG is 16 mOhms/Ft. A single pin-to-socket

   interface on a d-sub can present 3 millioms of

   resistance over a millimeter. Variability in

   resistance between pin-to-socket interface within

   a connector gives rise to the prohibition for

   paralleling pins to increase current handling

   of any one path.



   I designed and qualified a paralleled d-sub pin

   process at Beech that was used in both targets

   and production aircraft. This involved EXTENDING

   each pin in a paralleled array with say 12" of

   22AWG wire before the pin-paths were joined in

   parallel. This ADDS 16 milliohms resistance to

   each 1-3 milliohm pin-to-socket variability.

   This 'ballasting' resistance forces the sharing

   of current across an array of paralleled pins.



   The short answer is that concerns for heating

   due to current flow reside in the pins . . .

   not the wires.



 

   Bob . . .  

	




-- 

https://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 29, 2016 8:50 am Post subject: Problems Soldering DB-25 Connectors

At 09:45 PM 11/28/2016, you wrote:

  	  Quote: 	
		  Bob,



 I found your explanation about the ballasting 22 AWG pigtails. It was in an email to me, not on your website. I will use this to update my blog post. 	


   Oops . . . my bad. I'll update my own

   postings as well. Thanks!



 

 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Dec 05, 2016 9:36 am Post subject: Problems Soldering DB-25 Connectors

At 10:48 AM 11/29/2016, you wrote:

  	  Quote: 	
		  At 09:45 PM 11/28/2016, you wrote:

  	  Quote: 	
		  Bob,



 I found your explanation about the ballasting 22 AWG pigtails. It was in an email to me, not on your website. I will use this to update my blog post. 	


   Oops . . . my bad. I'll update my own

   postings as well. Thanks! 	


    It took a little bit but I've uploaded the 

    paralleled d-sub pins saga at



  http://tinyurl.com/jx96vpd



    . . .even got it indexed.  Man! I need to

   spend more time on the website. There's about

   a dozen updates I need to post. Anybody got some

   36 hour days for sale?



 

 

   Bob . . .

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