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How does the Cessna Ground pwr socket work?

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nuckolls.bob(at)aeroelect
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Posted: Mon Nov 11, 2013 2:06 pm Post subject: How does the Cessna Ground pwr socket work?

At 12:22 PM 11/11/2013, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Carlos Trigo" <trigo(at)mail.telepac.pt>



 Gents



 Just to be sure on how the Cessna (3-lug) ground power socket works:



 I followed figure Z-31A, where the third and thinner lug is connected to one

 of the contactor coil's terminal. 



 Where does that thinner lug on the Cessna female socket gets power to

 energize the contactor's coil?



 Thanks

 Carlos  

 	


   That ground power connector has been around

   for a very long time . . . it dates back to

   WWII or earlier.  The latest version MS3506



  http://tinyurl.com/nc6ybc3



   replaced the earlier version AN2552 back in

   the 60s



   

     The 'skinny' pin is smaller because it's not intended

     to carry much current . . . generally no more than what's

     needed to close the ground power contactor in the airplane.



     It's very robust for that current level because ground

     power jacks on an airplane take a beating . . . a contact

     physically sized for 2A or so wouldn't last long in the

     all-weather flight-line fast-moving-line-boy environment.



     The real 'magic' of this pin is based on its length.

     It's shorter than the other two. As you push a hot plug

     into the jack, the two current carrying pins are electrically

     engaged before the pilot pin . . . this means that the

     power pins cannot be loaded before they are engaged

     for carrying the load. Similarly, when you pull the plug,

     the pilot pin will break first, open the ground power

     contactor and prevent arcing at the power pins should

     they happen to be loaded at the break.



     Next time you're at an FBO and can take a peek

     at their ground power plug . . . I think every one

     I've seen had blackened and arc-pitted power contacts.

     No doubt damaged by hot-plugging or hot-disconnecting

     under load where the supported vehicle did not have

     a ground power contactor.



 

   Bob . . .    [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 11, 2013 2:19 pm Post subject: How does the Cessna Ground pwr socket work?

 	  Quote: 	
		  



Where does that thinner lug on the Cessna female socket gets power to

energize the contactor's coil?


	


  Oops!! . . . didn't answer the question. The pilot

  pin is often jumpered to the (+) power pin right

  next to it. In some cases, the ground power source

  control panel wants to manage the ground power

  contactor in the vehicle so a 3rd wire is

  brought back to the source for extra attention.



  In any case, the pilot pin gets + voltage from the same

  source as the adjacent power pin.



   Bob . . .

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trigo(at)mail.telepac.pt
Guest

Posted: Mon Nov 11, 2013 4:03 pm Post subject: How does the Cessna Ground pwr socket work?

Thanks Bob



Both explanations were welcome.

Got the general idea and the trick of the designer.



Best

Carlos  

--

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