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Protection For Auxillary Power Jacks

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Bill Denton

Joined: 10 Jan 2006
Posts: 97
Location: Chicago, IL USA

Posted: Mon Feb 05, 2007 3:50 pm Post subject: Protection For Auxillary Power Jacks

Assume that one wanted to install four "cigarette lighter" auxillary power jacks in an airplane, with two on the panel and two in the rear passenger area. Anywhere from none to all four might be used at any given time.



Would it be acceptable practice to put all of these on a single breaker?



Would it be acceptable to have more than one on a single breaker?



Or, should each jack have a separate breaker?



Thanks!

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mprather(at)spro.net
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Posted: Mon Feb 05, 2007 4:50 pm Post subject: Protection For Auxillary Power Jacks

My preference (bias)?  No breakers - just fuses..



Either way, (as has been said) the cigarette lighter connection isn't all

that spiffy except that lots of portable electronics are designed to use

them.  I've seen up to about 5A run through one with good success.  Maybe

it's safe to run more than that through them.  Need to research that some

more.



Whatever, as is the case when choosing wire and circuit protection for any

other application, the breaker/fuse must be small enough to protect the

skinniest wire/component being used in the circuit.



So, I don't see a way to provide protection for the plug and the wire if

you gang them, assuming you want to support the max capability of the

plug.  If you assume the plug will support 5A, you put a 5A breaker/fuse

on the circuit.  If you gang multiple plugs onto the same breaker then 5A

is still the largest circuit protection you can select.  However, if you

don't mind imposing a total power budget on your users - not letting them

use more than 5A total, then by all means put them all on one breaker.



If it were mine, depending on where my breaker/fuse panel is and how

accessible it is in flight, I'd split the load into at least two chunks. 

If one of the devices craps out (shorts its power supply), or your kid

tries to drive two laptops into one plug (adapter on top of adapter), only

half the cig buss will be dead.  I would probably build it with one per

adapter.  Or maybe two fuses for the front and one to cover the pair in

the rear - 3 total.



I think one big thing to consider is whether the adapters will be used for

mission-convenient/comfortable appliances.  I don't say mission-critical

because I kind of think cigarette adapters aren't appropriate for

mission-critical power sources.  My handheld GPS probably isn't mission

critical, but I'd like it's power source to be very stable none the less.

Regards,



Matt-

 	  Quote: 	
		   

 <bdenton(at)bdenton.com>



 Assume that one wanted to install four "cigarette lighter" auxillary power

 jacks in an airplane, with two on the panel and two in the rear passenger

 area. Anywhere from none to all four might be used at any given time.



 Would it be acceptable practice to put all of these on a single breaker?



 Would it be acceptable to have more than one on a single breaker?



 Or, should each jack have a separate breaker?



 Thanks!





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=93067#93067

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khorton01(at)rogers.com
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Posted: Mon Feb 05, 2007 4:50 pm Post subject: Protection For Auxillary Power Jacks

On 5 Feb 2007, at 18:50, Bill Denton wrote:



 	  Quote: 	
		   

 <bdenton(at)bdenton.com>



 Assume that one wanted to install four "cigarette lighter"  

 auxillary power jacks in an airplane, with two on the panel and two  

 in the rear passenger area. Anywhere from none to all four might be  

 used at any given time.



 Would it be acceptable practice to put all of these on a single  

 breaker?



 Would it be acceptable to have more than one on a single breaker?



 Or, should each jack have a separate breaker?



 Thanks!




	


No problem with all on one breaker.  But, that breaker must be large  

enough to handle the total possible load.  And, all wiring must be  

sized so that it wouldn't overheat if current up to the breaker size  

was going through it.  E.g., let's say you except no more than 2.5  

amps per circuit.  The breaker must be able to handle 10 amps,  

without opening.  You need some margin, so you decide to use a 15 amp  

breaker.  Now you need to make sure all wiring is large enough to  

handle up to 15 amps, because a short would put that much current in  

the wire before the breaker popped.



If you use 4 separate breakers, then the breaker size can be smaller,  

and that will allow the use of smaller wires.



Total weight, complication, and cost are probably lowest by putting  

all four through one breaker, unless the wire runs would be quite  

long.  If the wire runs are long enough, it might be lighter to go  

with four breakers.



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

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nuckollsr(at)cox.net
Guest

Posted: Mon Feb 05, 2007 6:44 pm Post subject: Protection For Auxillary Power Jacks

At 03:50 PM 2/5/2007 -0800, you wrote:



 	  Quote: 	
		  



Assume that one wanted to install four "cigarette lighter" auxillary power 

jacks in an airplane, with two on the panel and two in the rear passenger 

area. Anywhere from none to all four might be used at any given time.



Would it be acceptable practice to put all of these on a single breaker?


	


   Problem with one breaker/fuse does all is that a fault in one

   system takes down all systems. If you don't use fuse blocks with

   the necessary spares, then suggest in-line fuse holders with

   one fuse for each accessory.



http://www.aeroelectric.com/Pictures/Fuses/ifh-2.jpg



   Cigarette lighter jacks are about the poorest excuse for a connector

   without being completely worthless. For use in aircaft, consider

   these devices from Radio Shack.



http://www.aeroelectric.com/Pictures/Connectors/274-010.jpg



http://www.aeroelectric.com/Pictures/Connectors/274-013.jpg



   These are REAL connectors. They're more compact than the cigar

   lighter and have a positive locking feature that prevents the

   plug from being inadvertently dislodged.



   Bob . . .



        Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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willslau(at)alumni.rice.e
Guest

Posted: Tue Feb 06, 2007 3:28 am Post subject: Protection For Auxillary Power Jacks

Regardless of the protection scheme, take a look at these plugs and sockets.

www.powerletproducts.com	These come highly recommended by one of my

motorcyle riding friends, and are what I'm planning to use.



William Slaughter

RV-8

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