Today's Message Index:
----------------------
1. 09:24 AM - Re: Re: Toggle Switches with Fast-On Tabs (Robert L. Nuckolls, III)
2. 02:50 PM - Re: Re: Toggle Switches with Fast-On Tabs (Vernon Little)
3. 03:15 PM - Re: Re: Toggle Switches with Fast-On Tabs (Robert L. Nuckolls, III)
4. 05:02 PM - Re: Re: Toggle Switches with Fast-On Tabs (William Slaughter)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Toggle Switches with Fast-On Tabs |
At 06:52 PM 9/24/2008 -0700, you wrote:
>
>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 (8) 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 !@#$@#$ 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 . . .
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Toggle Switches with Fast-On Tabs |
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
>
> 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
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Toggle Switches with Fast-On Tabs |
At 02:49 PM 9/25/2008 -0700, you wrote:
><rv-9a-online@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.
>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.
>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.
>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- )
----------------------------------------
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: 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
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Thursday, September 25, 2008 5:13 PM
Subject: RE: AeroElectric-List: Re: Toggle Switches with Fast-On Tabs
<nuckolls.bob@cox.net>
At 02:49 PM 9/25/2008 -0700, you wrote:
><rv-9a-online@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.
>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.
>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.
>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- )
----------------------------------------
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|