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Switch problem

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chasb(at)satx.rr.com
Guest

Posted: Tue Sep 02, 2008 6:19 pm Post subject: Switch problem

Bob, et., al.,



My strobe lights blows its fuse. After replacing the 10A fuse, it blew again when the Master Switch was turned on with the strobe power off. The wire from the power bus to the switch checked okay. However, the fast-on for the wire that goes to the strobe power pack was charred.  A continuity check of the switch shows a closed circuit from the common terminal to the exterior switch mounting bolt and knob, regardless of the switch position.  So, I think I have isolated the problem to the panel mounted strobe power switch being shorted out internally.



 Questions: 

Do I have the right switch for the situation? The switch is a B&C 700 series, 1-3 On-On. Its on a 12 volt system. A single hot wire goes from the power bus to the switch and from the switch to the power pack. The power pack is locally grounded. All wires are 18 gauge. 

Are these type switch failures common? 

Any ideas of what could have caused the short?

Charlie Brame

RV-6A  N11CB

San Antonio



 [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Tue Sep 02, 2008 8:44 pm Post subject: Switch problem

At 09:17 PM 9/2/2008 -0500, you wrote:

 	  Quote: 	
		  Bob, et., al.,



My strobe lights blows its fuse. After replacing the 10A fuse, it blew 

again when the Master Switch was turned on with the strobe power off. The 

wire from the power bus to the switch checked okay. However, the fast-on 

for the wire that goes to the strobe power pack was charred.  A continuity 

check of the switch shows a closed circuit from the common terminal to the 

exterior switch mounting bolt and knob, regardless of the switch 

position.  So, I think I have isolated the problem to the panel mounted 

strobe power switch being shorted out internally.



  Questions:



Do I have the right switch for the situation? The switch is a B&C 700 

series, 1-3 On-On. Its on a 12 volt system. A single hot wire goes from 

the power bus to the switch and from the switch to the power pack. The 

power pack is locally grounded. All wires are 18 gauge.



Are these type switch failures common?


	


   I didn't think so . . . but it seems you've duplicated

   a failure mode effect that was discovered in a strobe

   system about 2 years ago. See:



http://tinyurl.com/2a2qqp

 	  Quote: 	
		  Any ideas of what could have caused the short?


	


   The working hypothesis is discussed in the failure

   analysis. It would be interesting to get a current

   draw signature from your strobe system . . . and

   to find out if its the same brand as the one

   involved in the earlier incident.



   These switches are rated for plenty of current to

   carry the strobe system currents I'm familiar with

   but there may be something curious afoot here. In

   any case, consider replacing the Carling device

   with something heavier . . . A Honeywell Microswitch

   11TS95



http://sccatalog.honeywell.com/pdbdownload/images/11ts95.series.chart.1.pdf



http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=480-3066-ND



   Bob . . .

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

Posted: Tue Sep 02, 2008 9:36 pm Post subject: Switch problem

Bob.  I've had a Carling B&C 1-3 switch sitting on my desk for a couple of

years that I pulled out of my Whelen strobe circuit with almost identical

failure symptoms.  I pulled it apart and it looks virtually identical to the

failed switch shown in your article.



Is this a coincidence?  Three switches failing in identical fashions in

identical applications... Sounds like an intrinsic application problem.  I

have my suspicions about the Whelen strobe pack.  Is there any indication of

what the strobe unit was for the other failed switches?



Thanks,

Vern Little



--

nuckolls.bob(at)cox.net
Guest

Posted: Wed Sep 03, 2008 3:47 am Post subject: Switch problem

At 10:30 PM 9/2/2008 -0700, you wrote:

 	  Quote: 	
		  

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



Bob.  I've had a Carling B&C 1-3 switch sitting on my desk for a couple of

years that I pulled out of my Whelen strobe circuit with almost identical

failure symptoms.  I pulled it apart and it looks virtually identical to the

failed switch shown in your article.


	


   You mentioned this a couple of weeks ago . . . and I wondered

   if you were the reader who supplied me the carcass of the

   failed switch in the article.

 	  Quote: 	
		  Is this a coincidence?  Three switches failing in identical fashions in

identical applications... Sounds like an intrinsic application problem.  I

have my suspicions about the Whelen strobe pack.  Is there any indication of

what the strobe unit was for the other failed switches?


	


   Not a coincidence. What about the Whelen product makes you

   believe it's unique among strobe systems with respect

   to power demands.  Three similar failures in so short a

   period of time tends to support your suspicions but I'm

   curious as to what you might know that I've not yet

   discovered.



   What kind of switch did you put in place of the failed

   switch and how much time do you have on it?

   Bob. . .

chasb(at)satx.rr.com
Guest

Posted: Wed Sep 03, 2008 5:58 am Post subject: Switch problem

Bob & Vernon,



Thanks for the rapid replies. I find it interesting that each of the  

failures were in a strobe circuit



In my case, it was also a Whelen Strobe System with a single power  

pack driving three strobes. It had been in intermittent use for less  

than 50 hours.



I have already ordered a new Carling switch from B&C. I think I will  

reverse the current flow through the switch as you suggested in your  

article. If it blows again, I will switch to the Honeywell  

Microswitch 11TS95 as you recommended.



Charlie Brame

RV-6A  N11CB

San Antonio



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



Time: 10:36:26 PM PST US

From: "Vernon Little" <rv-9a-online(at)telus.net>

Subject: RE: Switch problem

Bob.  I've had a Carling B&C 1-3 switch sitting on my desk for a  

couple of

years that I pulled out of my Whelen strobe circuit with almost  

identical

failure symptoms.  I pulled it apart and it looks virtually identical  

to the

failed switch shown in your article.



Is this a coincidence?  Three switches failing in identical fashions in

identical applications... Sounds like an intrinsic application  

problem.  I

have my suspicions about the Whelen strobe pack.  Is there any  

indication of

what the strobe unit was for the other failed switches?



Thanks,

Vern Little



--

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

Posted: Wed Sep 03, 2008 7:12 am Post subject: Switch problem

Hi Bob, I replaced the failed switch with another Carling/B&C switch.  I've

had some trouble with loose rivets on some of these switches which I thought

was the root cause of the thermal problems.



I will be inspecting the replacement switch later today.  The external

evidence of problems is a burnt fast-on and discolored terminals.  I have

about 100 hours on the replacement.



Thanks,

Vern



 	  Quote: 	
		  Bob.  I've had a Carling B&C 1-3 switch sitting on my desk for a couple 

of years that I pulled out of my Whelen strobe circuit with almost 

identical failure symptoms.  I pulled it apart and it looks virtually 

identical to the failed switch shown in your article.


	


   You mentioned this a couple of weeks ago . . . and I wondered

   if you were the reader who supplied me the carcass of the

   failed switch in the article.

 	  Quote: 	
		  Is this a coincidence?  Three switches failing in identical fashions in 

identical applications... Sounds like an intrinsic application problem.  

I have my suspicions about the Whelen strobe pack.  Is there any 

indication of what the strobe unit was for the other failed switches?


	


   Not a coincidence. What about the Whelen product makes you

   believe it's unique among strobe systems with respect

   to power demands.  Three similar failures in so short a

   period of time tends to support your suspicions but I'm

   curious as to what you might know that I've not yet

   discovered.



   What kind of switch did you put in place of the failed

   switch and how much time do you have on it?

   Bob. . .

nuckolls.bob(at)cox.net
Guest

Posted: Wed Sep 03, 2008 9:12 am Post subject: Switch problem

At 08:08 AM 9/3/2008 -0700, you wrote:

 	  Quote: 	
		  

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



Hi Bob, I replaced the failed switch with another Carling/B&C switch.  I've

had some trouble with loose rivets on some of these switches which I thought

was the root cause of the thermal problems.



I will be inspecting the replacement switch later today.  The external

evidence of problems is a burnt fast-on and discolored terminals.  I have

about 100 hours on the replacement.



Thanks,

Vern


	


   Thanks for taking the time to track this. This basic

   switch configuration has been around for a VERY long time

   in airplanes. The rocker switches with fast-ons used in

   the Cessna product late in the 60s used this manufacturing

   processes.



   Certainly, many tens of thousands of strobe systems

   have been controlled with this switch. It will

   be interesting to see what you find.



   Bob . . .

glineberry(at)earthlink.n
Guest

Posted: Thu Sep 04, 2008 1:11 pm Post subject: Switch problem

Interestingly I have had almost the same problem.  With a little over 200 hours on the aircraft my Whelen strobe system stopped working.  It did not open the 10A fuse, but when switched on the strobes would flash for about 10 seconds and then stop.  I was thinking that it was a problem with the Whelen unit but it is in a very difficult place to get to in my RV8 (under the floor) so I haven’t yet gone to the effort to take up the floor to check it out.  I looked at the fuse block and things looked good.  Until I read this thread I didn’t think about looking at the switch…..my mistake.  When I examined the switch today I discovered that the blue insulation on the Fast-On connectors had darkened considerably, indicating that they have been getting hot.  They are still firmly attached to the wire but it appears there is an internal problem in the switch that is causing excessive heat.  It is the B&C 1-3 switch referenced in this discussion.  I have just ordered a few of the Honeywell switches from Digi-Key and will replace it with one of those.  I don’t know what the actual current draw on the circuit is, but I have a 10A fuse that has not opened, so I would think that the B&C switch should handle it.  On the other hand, it appears that there is some other factor afoot here in the strobe circuit that the 1-3 does not like.  We’ll see how the Honeywell switch handles it.  

       [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Fri Sep 05, 2008 3:34 am Post subject: Switch problem

At 02:10 PM 9/4/2008 -0700, you wrote:



 	  Quote: 	
		  Interestingly I have had almost the same problem.  With a little over 200 

hours on the aircraft my Whelen strobe system stopped working.  It did not 

open the 10A fuse, but when switched on the strobes would flash for about 

10 seconds and then stop.  I was thinking that it was a problem with the 

Whelen unit but it is in a very difficult place to get to in my RV8 (under 

the floor) so I haven t yet gone to the effort to take up the floor to 

check it out.  I looked at the fuse block and things looked good.  Until I 

read this thread I didn t think about looking at the switch&..my mistake.


	


    Not a mistake . . . just an unhappy discovery that

    one ingredient in your system's recipe for success may

    not be performing as-advertised.



 	  Quote: 	
		    When I examined the switch today I discovered that the blue insulation 

 on the Fast-On connectors had darkened considerably, indicating that they 

 have been getting hot.  They are still firmly attached to the wire but it 

 appears there is an internal problem in the switch that is causing 

 excessive heat.


	


    A logical deduction.



 	  Quote: 	
		  It is the B&C 1-3 switch referenced in this discussion.  I have just 

ordered a few of the Honeywell switches from Digi-Key and will replace it 

with one of those.


	


    I'd really like to put my hands on the overheated switch

    for teardown, documentation and analysis.



 	  Quote: 	
		  I don t know what the actual current draw on the circuit is, but I have a 

10A fuse that has not opened, so I would think that the B&C switch should 

handle it.  On the other hand, it appears that there is some other factor 

afoot here in the strobe circuit that the 1-3 does not like.  We ll see 

how the Honeywell switch handles it.


	


    Agreed. There are valuable experiments to conduct

    for the purpose of clearer understanding. It's

    interesting to see how the act of bringing one

    event to forums like these triggers a cascade of

    recollection and consideration of similar events.

    Situations that might have been pushed aside as isolated

    events for individuals but raise flags of common

    concerns for the group when the knowledge is pooled

    together.



    The strobe supply is unique among loads on the bus.

    For those of you who are interested, take a peek at:



http://www.aeroelectric.com/Pictures/Curves/Strobe_Supply_Current.pdf



    This is the current plot on a small strobe system I

    was able to document some years ago. We were investigating

    the effectiveness of various filter techniques for

    the purpose of reducing the whining noise that some

    strobes put out onto the bus.



    The bottom two plots of this figure show the unfiltered

    supply current draw of the system at two different

    sample rates. Of particular interest is the fast rate

    plot (second one up). Here we can clearly see the

    modulation of on-current that is indicative of the

    audio rate switching of the high voltage power

    supply.



    The third plot was measured after a 10KuF capacitor

    was placed across the strobe supply leads. Note that

    the switching noise is for all practical purposes

    gone. The fourth plot is with one of the now discontinued

    audio noise filters from Radio Shack. It too proved to

    be an effective suppressor of the audio rate noise

    but note the little spike at the onset of current

    draw.



    This is a GREAT illustration of the potential for

    unintended consequences of an otherwise good thing.

    This spike is a ringing at the resonant frequency of

    the filter's inductor and capacitor. While the

    combination of components DID relieve us of the

    audio rate noise, it produces a new stimulus that

    might now be perceived as a once-per-flash "tick"

    at some other place in the system.



    Clearly, this experiment suggests that the stand-alone

    capacitor is effective and offers the least

    risk for unintended byproducts of an otherwise

    effective solution.



    Now the problem before us is one of discovering the

    energy signature that offends a switch that should

    be sufficient to the task based on its ratings.



    Neal, are you following this thread? We were discussing

    an experiment to deduce the suitability of smaller gage

    shielded wire when used as the connection between strobe

    supply and the flash-tubes. Any chance you could get your

    hands on a 'scope with digital data recording features

    like a Tek TDS2012? These new gee-whizz scopes plot

    .jpg screen shots AND ascii sample plots to a thumbdrive.

    REALLY slick. If you could get the current plots from

    your system the same time you do the flash intensity

    experiments, it might lend some insight as to why the

    switches that control the strobes are barfing.



    If push came to shove, I could mail you my 'scope for

    a few days to get the measurements. Let's talk about

    this.



    Another interesting piece of data from the plots

    I cited above. Note that the POWER required to run

    this little feller was 1.3 a-s per cycle x 14 volts

    or 18 watts. THIS is the number that drives your

    load analysis for the purpose of sizing batteries

    and alternators. Note that it is smaller than the

    value derived by simply multiplying bus votlage by

    peak current draw of 2.7 amps (38 watts).



    Bob . . .

Neal.George(at)hurlburt.a
Guest

Posted: Fri Sep 05, 2008 5:07 am Post subject: Switch problem

Neal, are you following this thread? 



I'm trying.  The water's deep and I'm short.



	Any chance you could get your hands on a 'scope with digital

data recording features like a Tek TDS2012? 



Maybe.  I'll ask around and see what I can find.



neal

nuckolls.bob(at)cox.net
Guest

Posted: Fri Sep 05, 2008 12:02 pm Post subject: Switch problem

At 08:02 AM 9/5/2008 -0500, you wrote:

 	  Quote: 	
		  

TES/TBM" <Neal.George(at)Hurlburt.AF.MIL>





     Neal, are you following this thread?



I'm trying.  The water's deep and I'm short.



         Any chance you could get your hands on a 'scope with digital

data recording features like a Tek TDS2012?



Maybe.  I'll ask around and see what I can find.


	


   Thanks!



   Bob . . .

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

Posted: Fri Sep 05, 2008 3:20 pm Post subject: Switch problem

I checked the switch that I installed as a replacement for the one that I

fried about 100 hours ago.  No sign of external damage or discoloration on

the new switch.



My failed switch was installed in 2005, purchased somewhat earlier.  I had

two switches that had loose rivets, so I'm wondering if there was a QC

problem with the Carling switches made about that time.  It would be

interesting to see the date codes on the failed switches.



My failed switch says C0344 Mexico.  My guess was this is a date code (44th

week in 2003?).  The one Bob analysed says 9936 Mexico on it.



Vern



--

glineberry(at)earthlink.n
Guest

Posted: Fri Sep 05, 2008 9:37 pm Post subject: Switch problem

Bob:  

Thank you for your analysis.  I would have been happy to send you the offending switch, but I have already dismantled it in order to satisfy my curiosity.  The only real visual sign was some arc pitting on the contact surfaces.  I believe that over time this pitting caused a high resistance that did two things.  First, there was a voltage drop across this resistance which in series with the strobe unit caused the unit to stop working because of reduced voltage.  When that happened I shut the circuit off and did not use it anymore.  Second, the resistance at the pitted contacts generated enough heat to discolor the blue insulation on the Fast-On connectors, but I caught it before any further heat damage occurred.  The switch components looked normal except for the pitting.  Nothing anywhere near the fried specimen you referenced earlier.  I temporarily installed a new 1-3 switch today and ran the system for ½ hour and noticed no heat increase on the fasteners.  But I wouldn’t expect that until many switch actuations and subsequent pitting of the contacts.  I will put the Honeywell switch in when it arrives and keep an eye on it.  If it shows any signs of impending failure I will research a Mil-Spec switch that might be a good replacement.  

   

Gary Lineberry  

RV8    N18BL  

       [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Sat Sep 06, 2008 5:03 am Post subject: Switch problem

At 10:35 PM 9/5/2008 -0700, you wrote:



 	  Quote: 	
		  Bob:



Thank you for your analysis.  I would have been happy to send you the 

offending switch, but I have already dismantled it in order to satisfy my 

curiosity.  The only real visual sign was some arc pitting on the contact 

surfaces.  I believe that over time this pitting caused a high resistance 

that did two things.  First, there was a voltage drop across this 

resistance which in series with the strobe unit caused the unit to stop 

working because of reduced voltage.  When that happened I shut the circuit 

off and did not use it anymore.  Second, the resistance at the pitted 

contacts generated enough heat to discolor the blue insulation on the 

Fast-On connectors, but I caught it before any further heat damage 

occurred.  The switch components looked normal except for the 

pitting.  Nothing anywhere near the fried specimen you referenced 

earlier.  I temporarily installed a new 1-3 switch today and ran the 

system for ½ hour and noticed no heat increase on the fasteners.  But I 

wouldn t expect that until many switch actuations and subsequent pitting 

of the contacts.  I will put the Honeywell switch in when it arrives and 

keep an eye on it.  If it shows any signs of impending failure I will 

research a Mil-Spec switch that might be a good replacement.


	


    The Honeywell parts will be a cut-above the

    Carling devices. I'm sure we're looking for

    QA issues too. Loose rivets is one likely

    root cause. The housings for these switches is

    a molded and somewhat brittle plastic with

    rather thin walls. The staking-height for

    rivets that hold the contacts and terminals

    together on the housing is an exceedingly close

    tolerance process. A few thousandths too tight

    and you crush the housing, too loose and you

    loose gas-tightness in the joint and corrosion

    gets you.



    The failure I illustrated in the website

    article seems to have initiated as a poor

    fit of the radii of mating parts at the

    teeter-totter pivot. Do you still have the

    parts from your failed switch? I'd like to have

    them even if you've already disassembled it.



    Bob . . .

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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

chasb(at)satx.rr.com
Guest

Posted: Sat Sep 06, 2008 1:23 pm Post subject: Switch problem

Bob,



I'll have my shorted out switch in the mail on Monday.

Charlie Brame

RV-6A  N11CB

San Antonio



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

Time: 04:34:28 AM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

Subject: Re: Switch problem

At 02:10 PM 9/4/2008 -0700, you wrote:

 	  Quote: 	
		   Interestingly I have had almost the same problem.  With a little  

 over 200

 hours on the aircraft my Whelen strobe system stopped working.  It  

 did not

 open the 10A fuse, but when switched on the strobes would flash for  

 about

 10 seconds and then stop.  I was thinking that it was a problem  

 with the

 Whelen unit but it is in a very difficult place to get to in my RV8  

 (under

 the floor) so I haven t yet gone to the effort to take up the floor to

 check it out.  I looked at the fuse block and things looked good.   

 Until I

 read this thread I didn t think about looking at the switch&..my  

 mistake.




	


     Not a mistake . . . just an unhappy discovery that

     one ingredient in your system's recipe for success may

     not be performing as-advertised.

 	  Quote: 	
		    When I examined the switch today I discovered that the blue  

 insulation

 on the Fast-On connectors had darkened considerably, indicating  

 that they

 have been getting hot.  They are still firmly attached to the wire  

 but it

 appears there is an internal problem in the switch that is causing

 excessive heat.




	


     A logical deduction.

 	  Quote: 	
		   It is the B&C 1-3 switch referenced in this discussion.  I have just

 ordered a few of the Honeywell switches from Digi-Key and will  

 replace it

 with one of those.




	


     I'd really like to put my hands on the overheated switch

     for teardown, documentation and analysis.

 	  Quote: 	
		   -------------snip---------------------------------------

     Bob . . .

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