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Toggle Switches with Fast-On Tabs
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fvalarm(at)rapidnet.net
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Posted: Wed Sep 24, 2008 11:58 am Post subject: Toggle Switches with Fast-On Tabs

Vern,



I agree with the experiment.  Be sure to add a couple switches and tools to

the A/C repair kit.  Probably a good thing to have on all our airplanes

especially when away from home base.



Bevan



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rv-9a-online(at)telus.net
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Posted: Wed Sep 24, 2008 1:21 pm Post subject: Toggle Switches with Fast-On Tabs

Good idea.  I'll keep the list posted on any developments.  



Vern



[quote] --

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dale.r(at)cox.net
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Posted: Wed Sep 24, 2008 5:54 pm Post subject: Toggle Switches with Fast-On Tabs

Vernon Little wrote:

 	  Quote: 	
		   Update on my findings.



 One question that I had was if vibration could be working the rivets loose

 on the Carling switches.  Given that I believe the rivets to be suspect to

 begin with-- even new switches have loose rivets-- vibration may be a

 trigger for a cascade of overheating problems.

   


	


Vern,



   If you have loose rivets on a new switch, the manufacturer

has a QA problem.  A tab that is not held in intimate contact

the inner component with sufficient force to resist

movement by finger pressure has already begun to fail.



   If I got switches like that from two or more production

lots, that manufacturer would be off my supplier list.



Dale R.

Mesa, AZ

COZY MkIV #0497

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rv-9a-online(at)telus.net
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Posted: Wed Sep 24, 2008 6:19 pm Post subject: Toggle Switches with Fast-On Tabs

Yup, mine too.



Do not archive.



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nuckolls.bob(at)cox.net
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Posted: Thu Sep 25, 2008 8:24 am Post subject: Toggle Switches with Fast-On Tabs

At 06:52 PM 9/24/2008 -0700, you wrote:

 	  Quote: 	
		  



Vernon Little wrote:

>Update on my findings.

>

>One question that I had was if vibration could be working the rivets loose

>on the Carling switches.  Given that I believe the rivets to be suspect to

>begin with-- even new switches have loose rivets-- vibration may be a

>trigger for a cascade of overheating problems.

>



Vern,



   If you have loose rivets on a new switch, the manufacturer

has a QA problem.  A tab that is not held in intimate contact

the inner component with sufficient force to resist

movement by finger pressure has already begun to fail.



   If I got switches like that from two or more production

lots, that manufacturer would be off my supplier list.


	


    Upon further reflection on the switch failure experiences

    of members of this List and examination of several corpses

    I'll suggest there is good reason to look very closely at

    the installation of these devices . . . in particular,

    providing sufficient service-slack on individual leads

    so that forces from a vibrating wire bundle cannot

    be transferred to the riveted fast-on tabs.



    The first failure we looked at . . .



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



    led us to believe that the point-of-origin for the

    cascade of effects was at the pivot saddle for the

    moveable contact bar . . .



    Subsequent postmortems showed no signs of internal

    heating source at the pivot saddle or contacts.

    These pictures are typical of carcass condition

    for all subsequent teardowns . . .



http://aeroelectric.com/Pictures/Switches/Carling_Failures/



    If one evaluates the construction of this product

    for a sense of mechanical weak-spots, the attachment

    of the tabs with hollow rivets has to be high on the

    list of concerns.  Poor design? Not if used within

    established limits.



    All failures subsequent to the first showed significant

    effects of heating outside the switch in the form of

    discolored tabs, discolored insulation grips, loose

    rivets. There WAS enough effect of heating to take the

    temper out of the teeter-totter . . .



http://aeroelectric.com/Pictures/Switches/Carling_Failures/BRA_08.JPG



    but no indication that the source of that heat

    was the pivot saddle or electrical-contacts.

    In every case, things DID get hot outside the switch.

    In one case, probability of poor connection

    within a heat-damaged PIDG terminal was discounted . . .



http://aeroelectric.com/Pictures/Misc/VL_Crimp_Tool_1.jpg



    This suggests a modification of hypothesis for root cause.

    If vibration forces on the tabs compromises the gas-tight

    integrity of the joints at (3), (7) or ( of



http://aeroelectric.com/Pictures/Switches/Toggle_Switch_with_Fast-On_Tabs.jpg



    then the products of corrosion begin followed by an

    increase of resistance, followed by increased heating,

    followed by more corrosion . . . We can make this go

    faster yet by continuing to shake the fast-on tab with

    the same forces that precipitated the initial failure.



    Obviously, the higher the service-current for the switch,

    the faster things run down hill. So it's easy to

    understand why continuous duty, moderate current loads

    would produce the highest population of failures. But

    we've heard that a battery master . . . probably the lightest

    loaded switch in the airplane has also suffered a failure.



    I've received a number of e-mails from folks suggesting that

    "things are going to !(at)#$(at)#$ in a hand-basket now that

    Carling is assembling in Mexico". One could jump on that

    band-wagon IF there was a significant number of failures

    spread over a broad spectrum of users. Keep in mind that

    the OBAM aircraft community uses perhaps 0.0001% of all

    switches assembled with this process. Of all such switches

    in service, the OBAM aircraft community offers some of the

    highest levels of vibration and stresses that are byproducts of

    that vibration. Further, we've seen rashes of failures on

    the same aircraft over a spread of manufacturing date codes.



    I'll suggest there's good reason to fully explore extra-

    ordinary stresses on the rolled-rivet joints that result

    from conditions of installation.



    Bob . . .

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rv-9a-online(at)telus.net
Guest

Posted: Thu Sep 25, 2008 1:50 pm Post subject: Toggle Switches with Fast-On Tabs

Hi Bob, see my commments:



 	  Quote: 	
		       ...Further, we've seen rashes of failures on

     the same aircraft over a spread of manufacturing date codes.


	


I've had 3, possibly 4 switch failures in my RV-9A.  Another RV-9A had 2

similar failures.  All except one were Carling switches

 	  Quote: 	
		   

     I'll suggest there's good reason to fully explore extra-

     ordinary stresses on the rolled-rivet joints that result

     from conditions of installation.

 

     Bob . . .


	


I am reasonably convinced that the combination of vibration, terminal rivet

construction and high current loading is causing these failures.  I will

continue my experiment with a straight switch substitution to see if the

Micro Switch brand has higher vibration tolerance.  I will report any

failures or successes in the next 100 hours of operation.



Even if the new switches are successful, after 100 hours I will secure the

wiring harness more positively to minimize vibration. The combination of

(potentially) better switches and proper wire grooming will hopefully give

me long term reliability.



I hope others have learned from the problems I've had and are looking at

their own installations for potential problems.  Good Luck to everybody.



Thanks,

Vern

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nuckolls.bob(at)cox.net
Guest

Posted: Thu Sep 25, 2008 2:15 pm Post subject: Toggle Switches with Fast-On Tabs

At 02:49 PM 9/25/2008 -0700, you wrote:

 	  Quote: 	

<rv-9a-online(at)telus.net>

Hi Bob, see my commments:

 >     ...Further, we've seen rashes of failures on

 >     the same aircraft over a spread of manufacturing date codes.

I've had 3, possibly 4 switch failures in my RV-9A.  Another RV-9A had 2

similar failures.  All except one were Carling switches

   Understand.

 	  Quote: 	
		  I am reasonably convinced that the combination of vibration, terminal rivet

construction and high current loading is causing these failures.  I will

continue my experiment with a straight switch substitution to see if the

Micro Switch brand has higher vibration tolerance.  I will report any

failures or successes in the next 100 hours of operation.

   I can guarantee that the MicroSwitch product is immune from

   this failure mode.

 	  Quote: 	
		  Even if the new switches are successful, after 100 hours I will secure the

wiring harness more positively to minimize vibration. The combination of

(potentially) better switches and proper wire grooming will hopefully give

me long term reliability.

   Bundle securement is not so important as UNCOUPLING

   of the bundle with respect to the tabs. Imagine a wire

   bundle that runs right behind the switches. Pigtails

   should not coming out of the bundle directly to the switch.

   Instead, use about 2" of wire that exits the bundle AWAY

   from the switch and then does a 180-degree turn to drop

   onto the fast-on tab.

 	  Quote: 	
		  I hope others have learned from the problems I've had and are looking at

their own installations for potential problems.  Good Luck to everybody.

   I'm not sure we've confirmed anything yet. It's not

   an electrical ratings issue and unlikely to be a QA

   issue. This leaves us with mechanical issues that

   exceed design limits. The soft-coupling of bundle-to-

   tab by way of long service loops would absolutely

   break the offending force path.

   If you were to splice 2" pieces to your existing

   pigtails and allow them to make a lazy curl in

   the bundle to tab transition, I'll bet the Carlings

   would perform to expectations.

        Bob . . .

        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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willslau(at)comcast.net
Guest

Posted: Thu Sep 25, 2008 4:02 pm Post subject: Toggle Switches with Fast-On Tabs

Hi Bob,

Can you furnish a list of the Microswitch part numbers to correlate to the

various switch configurations as shown in Fig 11-14, particularly the

progressive transfer switches? I have some of the Carlings on hand, but am

considering switching to the more robust product line before installing

anything. Thanks.



William Slaughter

RV-8



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nuckolls.bob(at)cox.net
Guest

Posted: Sat Sep 27, 2008 6:32 am Post subject: Toggle Switches with Fast-On Tabs

At 06:27 PM 9/25/2008 -0500, you wrote:

 	  Quote: 	
		  

<willslau(at)comcast.net>



Hi Bob,

Can you furnish a list of the Microswitch part numbers to correlate to the

various switch configurations as shown in Fig 11-14, particularly the

progressive transfer switches? I have some of the Carlings on hand, but am

considering switching to the more robust product line before installing

anything. Thanks.



William Slaughter

RV-8


	


   There's a Microswitch catalog for the TL series devices on

   my server at:



http://aeroelectric.com/Mfgr_Data/Switches/Microswitch_TL-Series.pdf



   There is a correlation between the dash-numbers I adopted

   (and B&C retained) for identifying switch functionality.



   An S700-1-3 is a Micoroswitch 1TL1-3

   An S700-2-10 is a Microswitch 2TL1-10



   etc.



   Bob . . .

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