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AeroElectric-List Digest: 11 Msgs - 09/12/08

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nuckolls.bob(at)cox.net
Guest

Posted: Sat Sep 13, 2008 9:09 am Post subject: AeroElectric-List Digest: 11 Msgs - 09/12/08

At 08:48 AM 9/13/2008 -0700, you wrote:

 	  Quote: 	
		  Vern,



you quoted Carling switch ratings, but if you read further down on the 

page, you find the following:



"Types of Loads:

  An electric load is the amount of electric power delivered or required 

 at any specific point or points on a system. The requirement originates 

 at the energy consuming equipment of the consumers. More simply put, a 

 load is the piece of equipment you turn on and off.


	


   <snip>

 	  Quote: 	
		  Are you sure you are using the switches within their rated specs???????????



My experience using AC rated switches on DC circuits with high inrush 

currents (landing/taxi lights and strobes in particular) is failure after 

failure.



Eric....this includes ROCKER SWITCHES TOO!.... Cessna rocker switches used 

in the 70's for example (AC rated "Mr Coffee Maker switches).



My $.02 worth......



Scott A Klemptner

bmwr606 on Yahoo IM


	




    Scott,



    Keep in mind that RATINGS have to do with SWITCH

    SERVICE LIFE generally given in the tens of thousands of

    cycles with various conditions. Our use of switches in

    light aircraft is exceedingly light-duty in terms

    of service life.



    For example, a master switch (one of those cited in

    the constellation of failures) operates ONCE PER FLIGHT-CYCLE

    and carries very small currents compared to the switch's

    RATINGS.



    Scott, please review the arguments offered in the

    piece at:



http://www.aeroelectric.com/articles/Switch_Ratings.pdf



    and explain where you find discrepancies of fact or

    logic. I'll suggest that had Vern sat in his airplane

    one afternoon and put 1000 cycles on any of the failed

    switches, he would NOT have experienced a

    failure. Yet, over a period of many flight hours

    and a mere handful of operations he experienced

    failures that speak to long term effects of ENVIRONMENT

    that include DEFICIENCIES of process either in fabrication

    of the switch as described here . . .



http://www.aeroelectric.com/articles/Anatomy_of_a_Switch_Failure/Anatomy_of_a_Switch_Failure.html



    or installation of the switch as hypothesized in

    my earlier treatise published this morning.



    The old AC vs. DC as a critical driving force in

    switch life is a myth. Further, it is clear that the

    study before us has nothing to do with switch

    life in terms of ratings, operating cycles, or

    application. Root cause of these failures will be

    loss of conduction integrity in one or more of the

    ten metal-to-metal joints that make up the switch's

    current path.



    Bob . . .

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nuckolls.bob(at)cox.net
Guest

Posted: Sat Sep 13, 2008 9:28 am Post subject: AeroElectric-List Digest: 11 Msgs - 09/12/08

At 12:52 PM 9/13/2008 -0400, you wrote:

 	  Quote: 	
		  

<retasker(at)optonline.net>



A comment on the below comments:



If you look at the schematic Vern posted, you would see that he is using 

NTC surge limiters on each light.  These minimize startup surges caused by 

the very low cold filament resistance of the lamps.



On the other hand, it depends on the time constants of the NTC surge 

limiters vs the time constants of the lamp filaments as to whether these 

are effective when in wig-wag mode.



Dick Tasker


	


   A couple of years ago, the effectiveness/value of surge

   limiters in Wig-Wag systems was discussed here on the List.

   I went to the workbench and took this trace from the

   operating current of a 55W halogen lamp flashed at

   about 2 flashes per second.



http://www.aeroelectric.com/Pictures/Curves/Wig_Wag_Currents.jpg



   Note that the first time the lamp gets power we

   see the characteristic cold-filament inrush current.

   However, on subsequent turn-ons, the lamp does not

   have enough time to cool such that the 7x inrush

   experience is repeated.



   Bob . . .

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