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chasb(at)satx.rr.com
Guest

Posted: Mon Jan 20, 2014 9:36 pm Post subject: Strobe switches

Bob, et.al.,



I just replaced my fourth S700-1(or equivalent) strobe switch in about 200 hours of flying time. Both fast on terminals were badly burned as was about an inch of the 18ga. wire attached to the fast on. My first two switches were Carlings from B&C. Based on AeroElectric recommendations made some years back, I ordered a S700-1 equivalent switch from Honeywell - same result. Then I tried a switch from DigiKey, same result. I'm back to a Carling, at least for the short term. I have Carlings for the Nav lights, Landing and Wig Wag lights and instrument lights, and I have had no problem with any of them. The strobe switch is backed up by a 7 amp fuse which is recommended for the strobe system (Whelen) and it has never popped. The run of 18 ga. wire is about ten feet. Of all the switches, only the strobe switch gets real hot after only a few minutes of use.



I was searching B&C for a relay I could use to reroute the strobe heavy current wire, and discovered that B&C now advertises a MilSpec single pole switch (MS35058-22) that is the equivalent of the S700-1. The dimensions appear the same, with screw type connections rather than fast ons. It ain't cheap, but it would be worth it to avoid having to frequently replace a burnt out standard switch. Would this MilSpec switch be a viable solution to the strobe switch problem?



Charlie Brame

RV-6A,  N11CB

San Antonio

fvalarm(at)rapidnet.net
Guest

Posted: Mon Jan 20, 2014 11:20 pm Post subject: Strobe switches

What about using a relay to switch the strobe current?  Use the carling

switch to control the relay.



Bevan 



--

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 21, 2014 8:24 am Post subject: Strobe switches

 	  Quote: 	
		   The strobe switch is backed up by a 7 amp fuse which is recommended for the strobe system (Whelen) and it has never popped. The run of 18 ga. wire is about ten feet. Of all the switches, only the strobe switch gets real hot after only a few minutes of use. 	


   Can you tell where it's getting hot? We've

   had this (and similar) discussions on strobe

   controls over the years. I am mystified as

   to how the burning of switches and terminal

   crimps seems to be concentrated on the strobe

   systems . . . driven by relatively light

   protection (7A fuse).



  	  Quote: 	
		  I was searching B&C for a relay I could use to reroute the strobe heavy current wire, and discovered that B&C now advertises a MilSpec single pole switch (MS35058-22) that is the equivalent of the S700-1. The dimensions appear the same, with screw type connections rather than fast ons. It ain't cheap, but it would be worth it to avoid having to frequently replace a burnt out standard switch. Would this MilSpec switch be a viable solution to the strobe switch problem? 	


   Your question raises some interesting points.

   There seems to be something 'different' about

   the strobe system current draw profile that

   stresses the centers of highest-resistance

   in the power path. In the past, we've seen

   failures at the rivet joints on the switches,

   contacts within the switches, switch rockers,

   and less-than-idea crimps on terminals, etc.



   Yet the RMS or average current remains so

   low that a relatively fast protective device

   like a fuse doesn't complain. I would REALLY

   like to see the current profile on a strobe

   system that has repeatedly damaged its switch.

   There's got to be a characteristic unique to

   strobe supplies (perhaps just this model

   of supply) that's especially antagonistic

   to components in the power feeder.



   Getting to your specific questions. A

   relay would certainly transfer the stresses

   away from the switch . . . but any connecting

   devices in the power path (like crimps)

   would still see the 'abuse'.



   It might well be that a switch with molded

   terminal supports  . . .



 [img]cid:.0[/img]



   . . . would not offer the weaknesses of

   riveted joints . . . but crimps, threaded

   fasteners and internal contacts of the

   switch would still be getting 'hammered'.



   I do have a proof-of-concept, solid state

   relay that I'd be pleased to send you. I've

   like to get it into service on an often-flown

   airplane and perhaps yours is the best

   candidate. It appears that the strobes feeder

   in your airplane would be a good location to

   try the relay while potentially addressing

   your specific failure mode.



   Do you have access to any test equipment

   that might measure and record the current

   waveform impressed on the strobe switch

   in your airplane?

  

   I'm mulling over ideas for getting data

   of your airplane and then perhaps expanding

   the investigation to other airplanes to

   see if we can identify the controlling

   physics.



   There are tens of thousands of airplanes

   flying Carling switches in the strobe

   power feed path . . . the fact that a

   few folks here on the List have experienced

   serial failures of these switches is

   curious to say the least.



 

   Bob . . .

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Mauledriver(at)nc.rr.com
Guest

Posted: Tue Jan 21, 2014 9:28 am Post subject: Strobe switches

I experienced a burned out fast-on connector at my fuse panel on the 

16AWG strobe power lead between the fuse panel and the switch.  My 

strobe unit was a CreativAir Avi-Pak 60 watt, 4 outlet strobe power 

suppy intended for experimental aircraft use.  Three strobes were 

connected.  There was a 15amp fuse on the unit and a 15amp fuse on the 

fuse panel. This was on an RV10 and there was somewhere between 10 and 

20 feet of 16AWG wire in the switched power circuit.



I had difficulty identifying the burned out fast-on connector. The 

circuit remained intact despite it's inability to carry the required 

load.  In the course of problem determination, I decided to replace the 

unit.  (I later determined that the unit works just fine)



The CreativAir units are no longer available so I installed a unit from 

Nova Electronics - XPAK604X 60 watt, 4 outlet strobe power suppy.  It is 

also referred to as a SUPERPAK604X.  This unit seems to be intended for 

emergency vehicle use but is very similar to the CreativAir product, it 

looks like it is from the same manufacturer with the same dimensions and 

mounting hardware.



However, it can be powered by an unswitched line directly from the power 

circuit.  It is operated thru a separate control circuit. In the RV10 

this allowed me to reduce the power circuit from over 10 feet to less 

than 3 feet.  Where the old circuit was warm/hot to the touch, 

everything is now cool.



The XPAK604X was cheaper, had more strobe pattern options and used a 

control circuit which would seem to accomplish what a relay would do.

On 1/21/2014 2:19 AM, B Tomm wrote:

[quote] 



 What about using a relay to switch the strobe current?  Use the carling

 switch to control the relay.



 Bevan



 --

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 22, 2014 7:13 am Post subject: Strobe switches

At 11:27 AM 1/21/2014, you wrote:




I experienced a burned out fast-on connector at my fuse panel on the 

16AWG strobe power lead between the fuse panel and the switch.  My 

strobe unit was a CreativAir Avi-Pak 60 watt, 4 outlet strobe power 

suppy intended for experimental aircraft use.  Three strobes were 

connected.  There was a 15amp fuse on the unit and a 15amp fuse on 

the fuse panel. This was on an RV10 and there was somewhere between 

10 and 20 feet of 16AWG wire in the switched power circuit.



I had difficulty identifying the burned out fast-on connector. The 

circuit remained intact despite it's inability to carry the required 

load.  In the course of problem determination, I decided to replace 

the unit.  (I later determined that the unit works just fine)



   Do you still have this 'problem' system?



The XPAK604X was cheaper, had more strobe pattern options and used a 

control circuit which would seem to accomplish what a relay would do.



   Interesting. I wonder if they 'discovered' the

   features in their power demands that were so

   abusive of otherwise perfectly good switches . . .



   I'm gathering the hardware together to craft a

   mailable data acquisition system together that

   I can ship to a willing List member to gather

   some definitive data on their strobe systems.



   I'd like to acquire a library of data both

   from systems that have suffered failures in

   the power wiring . . . and some that didn't.



"When you can measure what you are speaking about,

    and express it in numbers, you know something about

    it, when you cannot express it in numbers, your knowledge

    is of a meager and unsatisfactory kind; it may be

    the beginning of knowledge, but you have scarcely,

    in your thoughts advanced to the stage of science."



                     ---- Lord Kelvin ----



    We've been watching these rare but significant

    events for some years . . . ignorant of the

    root cause. I'm thinking it's time to get some

    good numbers.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 22, 2014 7:16 am Post subject: Strobe switches

At 11:32 PM 1/20/2014, you wrote:

 --> AeroElectric-List message posted by: Charles Brame <chasb(at)satx.rr.com>



 Bob, et.al.,



 I just replaced my fourth S700-1(or equivalent) strobe switch in about 200 hours of flying time. Both fast on terminals were badly burned as was about an inch of the 18ga. wire attached to the fast on.



   Charlie, do you want to try the solid state

   relay? If you do install this relay . . .



 [img]cid:7.1.0.9.0.20140122091114.01120aa8(at)aeroelectric.com.0[/img] 



   . . . it will offer a plug-n-play port through which

   we can gather some good numbers when the DAS system

   goodies I've ordered get here . . .



 

 

   Bob . . .

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chasb(at)satx.rr.com
Guest

Posted: Wed Jan 22, 2014 8:56 am Post subject: Strobe switches

Bob,

Thanks for the response. See my answers to your questions in red below.

Charlie Brame

RV-6A  N11CB

San Antonio

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

Time: 08:24:54 AM PST US

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

Subject: Re: Strobe switches

 	  Quote: 	
		  The strobe switch is backed up by a 7 amp fuse which is 

recommended for the strobe system (Whelen) and it has never popped. 

The run of 18 ga. wire is about ten feet. Of all the switches, only 

the strobe switch gets real hot after only a few minutes of use.

	


  Can you tell where it's getting hot? 

With this latest switch failure the hot spots were the fast on connectors at the switch, and I did not notice the switch itself getting hot. The switch fast on tabs are externally riveted and became very loose. There is no signs of burning of the switch itself, though something caused the fast on tabs to become loose on the switch body. And both of the connectors (power in and power out) were burned. In one of the previous Carling failures, the switch was fried on the inside, and the switch itself got hot, including the bat handle. The power connector at the power pack is a Molex type pin plug and does not show any heat related distress. The power supply fast on at the fuse panel has also never shown any signs of heating. With a new switch installed, there is no evidence of any hot spots. However, after a period of time, the problem reoccurs. 

  We've had this (and similar) discussions on strobe

  controls over the years. I am mystified as

  to how the burning of switches and terminal

  crimps seems to be concentrated on the strobe

  systems . . . driven by relatively light

  protection (7A fuse).



 	  Quote: 	
		  I discovered that B&C now advertises a MilSpec single pole switch (MS35058-22) that is the equivalent of the 

S700-1. Would this MilSpec switch be a viable solution to the strobe switch problem? 	


  Your question raises some interesting points.

  There seems to be something 'different' about

  the strobe system current draw profile that

  stresses the centers of highest-resistance

  in the power path. In the past, we've seen

  failures at the rivet joints on the switches,

  contacts within the switches, switch rockers,

  and less-than-idea crimps on terminals, etc.



  Yet the RMS or average current remains so

  low that a relatively fast protective device

  like a fuse doesn't complain. I would REALLY

  like to see the current profile on a strobe

  system that has repeatedly damaged its switch.

  There's got to be a characteristic unique to

  strobe supplies (perhaps just this model

  of supply) that's especially antagonistic

  to components in the power feeder.



  Getting to your specific questions. A

  relay would certainly transfer the stresses

  away from the switch . . . but any connecting

  devices in the power path (like crimps)

  would still see the 'abuse'.



  It might well be that a switch with molded

  terminal supports  . . .



Emacs!

  . . . would not offer the weaknesses of

  riveted joints . . . but crimps, threaded

  fasteners and internal contacts of the

  switch would still be getting 'hammered'.



  I do have a proof-of-concept, solid state

  relay that I'd be pleased to send you. I've

  like to get it into service on an often-flown

  airplane and perhaps yours is the best

  candidate. It appears that the strobes feeder

  in your airplane would be a good location to

  try the relay while potentially addressing

  your specific failure mode.

I would be pleased to try your new solid state relay. However, I don't have any test equipment and am not sure I'm smart enough to use it if I had access. But I am open to ideas and suggestions.



  Do you have access to any test equipment

  that might measure and record the current

  waveform impressed on the strobe switch

  in your airplane?



  I'm mulling over ideas for getting data

  of your airplane and then perhaps expanding

  the investigation to other airplanes to

  see if we can identify the controlling

  physics.



  There are tens of thousands of airplanes

  flying Carling switches in the strobe

  power feed path . . . the fact that a

  few folks here on the List have experienced

  serial failures of these switches is

  curious to say the least.

In reading some of the other responses, I'd like to clarify the following: My system is a Whelen three light system with a single power pack. There have been no changes or additions to the system as it was received from the manufacturer. All bulbs and flash sequences were factory set and the cables from the power pack to the lights are factory supplied. The system is grounded at the power pack and the ground appears secure. I have seen no evidence of any other over voltage, over amperage damage to any other switches or devices. The regulator (a generic Ford regulator) seems to work as advertised. The strobe system is left on at all times and begins to operate when the master switch is turned on. In other words, the switch is rarely cycled on or off.



  Bob . . . 



 [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 22, 2014 11:48 am Post subject: Strobe switches

At 10:55 AM 1/22/2014, you wrote:

Bob,



Thanks for the response. See my answers to your questions in red below.



Charlie Brame

RV-6A  N11CB

San Antonio



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



Time: 08:24:54 AM PST US

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

Subject: Re: Strobe switches

The strobe switch is backed up by a 7 amp fuse which is

recommended for the strobe system (Whelen) and it has never popped.

The run of 18 ga. wire is about ten feet. Of all the switches, only

the strobe switch gets real hot after only a few minutes of use.



   Can you tell where it's getting hot?



With this latest switch failure the hot spots were the fast on 

connectors at the switch, and I did not notice the switch itself 

getting hot. The switch fast on tabs are externally riveted and 

became very loose. There is no signs of burning of the switch itself, 

though something caused the fast on tabs to become loose on the 

switch body. And both of the connectors (power in and power out) were 

burned. In one of the previous Carling failures, the switch was fried 

on the inside, and the switch itself got hot, including the bat 

handle. The power connector at the power pack is a Molex type pin 

plug and does not show any heat related distress. The power supply 

fast on at the fuse panel has also never shown any signs of heating. 

With a new switch installed, there is no evidence of any hot spots. 

However, after a period of time, the problem reoccurs.

   Good data. Thanks.

I would be pleased to try your new solid state relay. However, I 

don't have any test equipment and am not sure I'm smart enough to use 

it if I had access. But I am open to ideas and suggestions.



    Understand. Were your airplane sitting at Medicine Lodge

    Intergalactic Airport, there are a number of whippy

    tools on my shelf that would get us the data.  I've

    been considering ways to craft a DAS that could be

    mailed at cheap priority mail rates and be relatively

    simple to operate. I think I'm close to realizing

    that goal . . . you can be the first 'victim' . . .



    It will let us get data from YOUR installation,

    on the ground and in just a few seconds. It's

    basically a 1000 samples/second storage

    'oscilloscope' that records to a hard drive.



In reading some of the other responses, I'd like to clarify the 

following: My system is a Whelen three light system with a single 

power pack. There have been no changes or additions to the system as 

it was received from the manufacturer. All bulbs and flash sequences 

were factory set and the cables from the power pack to the lights are 

factory supplied. The system is grounded at the power pack and the 

ground appears secure. I have seen no evidence of any other over 

voltage, over amperage damage to any other switches or devices. The 

regulator (a generic Ford regulator) seems to work as advertised. The 

strobe system is left on at all times and begins to operate when the 

master switch is turned on. In other words, the switch is rarely 

cycled on or off.



   Also excellent data points.



   We'll move ahead as if we know what we're

   doing. Some of the goodies are coming from

   overseas but I can get the relay out to

   you this weekend. Shoot me your mailing

   address.



   As soon as you and I figure that we're doing

   a good thing, we'll bicycle the rig around

   and get data from as many other airplanes

   as we have willing participants.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 22, 2014 11:52 am Post subject: Strobe switches

Speaking of strobe switch failures, there was

a series of exchanges here on the list a few

years back where the Lister had experienced

a rash of failures . . . which produced an

understandable bad taste in his mouth for the

Carling switches.



Is that individual still on the List or does

anyone recall who it was?  I would be interesting

to know how the problem resolved.





   Bob . . .

Mauledriver(at)nc.rr.com
Guest

Posted: Wed Jan 22, 2014 5:39 pm Post subject: Strobe switches

Yes I still have the problem system and would be happy to send to you.  

Just let me know the address and it's on it's way.  No return required.



Thanks



On 1/22/2014 10:10 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 11:27 AM 1/21/2014, you wrote:

 

 <Mauledriver(at)nc.rr.com>



 I experienced a burned out fast-on connector at my fuse panel on the 

 16AWG strobe power lead between the fuse panel and the switch.  My 

 strobe unit was a CreativAir Avi-Pak 60 watt, 4 outlet strobe power 

 suppy intended for experimental aircraft use.  Three strobes were 

 connected.  There was a 15amp fuse on the unit and a 15amp fuse on the 

 fuse panel. This was on an RV10 and there was somewhere between 10 and 

 20 feet of 16AWG wire in the switched power circuit.



 I had difficulty identifying the burned out fast-on connector. The 

 circuit remained intact despite it's inability to carry the required 

 load.  In the course of problem determination, I decided to replace 

 the unit.  (I later determined that the unit works just fine)



   Do you still have this 'problem' system?



 The XPAK604X was cheaper, had more strobe pattern options and used a 

 control circuit which would seem to accomplish what a relay would do.



   Interesting. I wonder if they 'discovered' the

   features in their power demands that were so

   abusive of otherwise perfectly good switches . . .



   I'm gathering the hardware together to craft a

   mailable data acquisition system together that

   I can ship to a willing List member to gather

   some definitive data on their strobe systems.



   I'd like to acquire a library of data both

   from systems that have suffered failures in

   the power wiring . . . and some that didn't.



 "When you can measure what you are speaking about,

    and express it in numbers, you know something about

    it, when you cannot express it in numbers, your knowledge

    is of a meager and unsatisfactory kind; it may be

    the beginning of knowledge, but you have scarcely,

    in your thoughts advanced to the stage of science."



                     ---- Lord Kelvin ----



    We've been watching these rare but significant

    events for some years . . . ignorant of the

    root cause. I'm thinking it's time to get some

    good numbers.

   Bob . . .

 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

racerjerry

Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY

Posted: Thu Jan 23, 2014 5:57 am Post subject: Re: Strobe switches

I am very reluctant to throw in my two cents here, as there are much greater minds than mine on this list.  I figgerâ€™ that strobe power pack current characteristics may be causing switch arcing; slowly damaging the switch contact material, increasing contact resistance to the point where local heating and a snowball type failure occurs.  There are quite a few different materials used for switch contacts.   Depending on switch requirements and UL ratings; all contacts have their own characteristics and ability survive differing harsh environments.  Olâ€™ tungsten lamps are similarly known for their high initial current inrush characteristics and switches require a â€œTâ€ rating from UL, but these are AC switches and any arc is self extinguishing at the zero crossing point of the AC wave.  DC switches are a different animal.  DC switches require a quick snap action which is independent of operator manipulation.



One trick for switch survival in such instances is to use a double pole switch with both sets of contacts wired in series to double arc distance and contact separation speed.   (Thank you Mr. Tibolla, wherever you are).



Again, if I were to guess, I would first suspect the initial current draw of the large strobe capacitor would be the cause.  Any contact â€˜bounceâ€™ on switch closing would definitely aggravate things and hasten failure.  I too would want to check the current / voltage profile of that strobe.  Carling generally makes darned good switches.

_________________
Jerry King

rene(at)felker.com
Guest

Posted: Thu Jan 23, 2014 6:29 am Post subject: Strobe switches

Jerry, thanks for your input.  I learned a lot.  I do not have this problem in my airplane, but a better understanding of this failure mode will help me with future projects.



Do not archive



Rene' Felker

N423CF

801-721-6080



--

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Thu Jan 23, 2014 7:07 am Post subject: Re: Strobe switches

Here's my guess:



The only key difference in strobe supplies is their really big capacitors. When caps are flat (perhaps after long storage), their current demand is gigantic for a short time. Good design would put a peak current limiter like a CL-11 surge suppressor in the input circuit. 



An O-scope would show this, but maybe only on the first start after long storage. Furthermore the test design for this is tricky because the current you are trying to capture is very high and very short.



A solid state relay, or any other relay, probably isn't the solution to the problem.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 23, 2014 7:44 am Post subject: Strobe switches

At 07:57 AM 1/23/2014, you wrote:




I am very reluctant to throw in my two cents 

here, as there are much greater minds than mine 

on this list.  I figgerâ€™ that strobe power pack 

current characteristics may be causing switch 

arcing; slowly damaging the switch contact 

material, increasing contact resistance to the 

point where local heating and a snowball type failure occurs.



    I agree that some stress of this nature is in

    play. A stress that seems to be unique to a

    sub-set of the family of strobe products. I can't

    speak to the contact style of switches pre-Carling-

    rockers on the Cessnas. Without a doubt,

    the mechanical features of these switches went

    un-changed for decades and, perhaps, persist

    to this day. Here's a breakdown of the electron-

    pathway through a fast-on-tabbed Carling switch . . .



http://tinyurl.com/qcmyt4e



   There are quite a few different materials used 

for switch contacts.   Depending on switch 

requirements and UL ratings; all contacts have 

their own characteristics and ability survive 

differing harsh environments.  Olâ€™ tungsten 

lamps are similarly known for their high initial 

current inrush characteristics and switches 

require a â€œTâ€ rating from UL, but these are 

AC switches and any arc is self extinguishing at 

the zero crossing point of the AC wave.  DC 

switches are a different animal.  DC switches 

require a quick snap action which is independent of operator manipulation.



One trick for switch survival in such instances 

is to use a double pole switch with both sets of 

contacts wired in series to double arc distance 

and contact separation speed.   (Thank you Mr. Tibolla, wherever you are).



   Keep in mind that we've seen failures across

   the entire spectrum of metal-to-metal interfaces.



http://tinyurl.com/96yqmg



http://tinyurl.com/8zzkfbb



  Failures of terminals are almost always a

  failure to achieve gas-tight joining. Failure

  of the rivet joints are probably precipitated by

  degradation of the plastic housing material that

  relieves mate-up pressures between the tab and

  the contact-rivet. Degradation rooted in elevated

  temperatures at a slowly failing junction.



Again, if I were to guess, I would first suspect 

the initial current draw of the large strobe 

capacitor would be the cause.  Any contact 

â€˜bounceâ€™ on switch closing would definitely 

aggravate things and hasten failure.  I too would 

want to check the current / voltage profile of 

that strobe.  Carling generally makes darned good switches.



  Carling's demonstrated service history has

  offered no incentives for folks in the airplane

  business to boot them off the airplanes. At

  the same time, tens of thousands of these

  same switches have endured the test of time

  as controls for strobe lighting systems.



  Some years ago, a company that employed

  my services banned a particular brand of

  relay from the fleet of products . . . they

  purged stock and replaced with Brand-M

  based on anecdotal information that Brand-M

  demonstrated a 'longer service life' in the

  same abusive slot on the airplane. Brand-M

  STILL stuck but only 1/3rd as often.



  It took several years of P&P (play and ponder)

  to finally deduce root cause . . . an effect

  that was not covered in any of the relay engineering

  manuals but repeated demonstrated on my workbench.



  The 'fixes' I recommended based on findings

  were never implemented. The failure rate had

  dropped down enough to fall off the ten-worst-

  problems list and the bean-counters lost

  interest.



  Observations of anecdotes here on the List

  suggest that what ever differences

  exist across the family of strobe

  lighting systems, there IS a

  characteristic that will bring out the

  worst joint in any bus-voltage pathway to the

  strobe supply. The 'worst' has manifested

  mostly in failures in and around the strobe

  switch. But Listers have told us that the

  fast-on terminal to their fuse-block has

  proven to be the weak-link that succumbed

  to the ravages of whatever weapon their

  strobe brought to the fight.



  I think we've observed and analyzed enough

  history to suggest that an investigation

  into weaponry is in order. Hence my decision

  to acquire tools of investigation which,

  with the help of others here on the List,

  may peel back the layers of the onion

  and make all secrets known.



  Our work here on the strobe switch failure

  mystery has little to zero chance

  of causing anyone to change their designs.

  The best we can hope for is to identify

  root cause and craft tools to identify its

  recurrence so that some brands of strobes

  can be avoided.



  Ever hear of "too-little, too-late"? By the

  time we figure this out, xenon strobes may

  be on their way out of the marketplace and

  the 'problem' will simply go away. But there

  are simple-ideas and science to be identified

  that will give foundation for any future investigation

  into mysterious failures of perfectly good

  switches and terminals.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 23, 2014 7:45 am Post subject: Strobe switches

At 07:38 PM 1/22/2014, you wrote:

 	  Quote: 	
		  



Yes I still have the problem system and would be happy to send to you.

Just let me know the address and it's on it's way.  No return required.


	


   Sure.



   P.O. Box 130, Medicine Lodge, Ks, 67104-0130



   Thanks!

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 23, 2014 8:06 am Post subject: Strobe switches

At 09:07 AM 1/23/2014, you wrote:




Here's my guess:



The only key difference in strobe supplies is their really big 

capacitors. When caps are flat (perhaps after long storage), their 

current demand is gigantic for a short time. Good design would put a 

peak current limiter like a CL-11 surge suppressor in the input circuit.



   But we've seen failures in switches that are

   always left on. Initial inrush events, while

   most severe, occur only at turn-on . . . what

   we're seeing appears to be a manifestation of

   persistent RMS heating . . . i.e. a recurring

   condition during operation.



An O-scope would show this, but maybe only on the first start after 

long storage. Furthermore the test design for this is tricky because 

the current you are trying to capture is very high and very short.



   Actually, no worse that for getting

   a 100w landing light lit up from a cold

   start. Such inrush currents are generally

   limited by ship's wiring. Here's an exemplar

   plot for starting a 55W lamp.



http://tinyurl.com/mvugala



   Cold resistance of the lamp was measured

   at 150 mOhm, wiring added another 165

   mOhm for a total of 315 mOhm and a predictable

   inrush on the order of 14/.315 or 44A. If

   the bulb had a monster capacitor across it

   then the absolute max inrush would still

   be limited by a/c wiring to 14/.165 or

   84A.



   This is in the ballpark for expected tungsten

   lamp inrush values cited when switches are

   rated in the lab.  Ratings that assume the

   system integrator expects a service life in

   the thousands of cycles.



   We're witnessing failures in under 1000

   cycles . . . perhaps as few as 200 cycles.

   The failures include devices that don't have

   to switch . . . only carry the load.



   It may be that initial inrush is a factor

   but I'm guessing it's not the dominate

   effect. The fact that many strobe systems

   do not exhibit the problem while one

   system can duplicate the problem several

   times suggests that root cause can be

   chased down by comparing problem children

   with well behaved children . . .

A solid state relay, or any other relay, probably isn't the solution 

to the problem.



   A solid state relay will eliminate the failures

   with roots in contact resistance . . . but there

   are other metal-to-metal joints at risk. You're right,

   there's more going on here than can be explained

   by failure to observe switch ratings from the

   catalogs.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 28, 2014 5:03 am Post subject: Strobe switches

At 09:44 AM 1/23/2014, you wrote:

 	  Quote: 	
		  

<nuckolls.bob(at)aeroelectric.com>



At 07:38 PM 1/22/2014, you wrote:

>

>

>Yes I still have the problem system and would be happy to send to you.

>Just let me know the address and it's on it's way.  No return required.



   Sure.



   P.O. Box 130, Medicine Lodge, Ks, 67104-0130


	


    I received Bill's strobe supply and began

    to research its pedigree. Seems to be a custom

    device designed for Creativair (now defunct)

    and manufactured by Nova.



    The nameplate says 10-30 volts input

    which speaks to a modern, switchmode

    power supply topology. It also says

    70 watts in, 60 watts out and input

    current of 5.5A.



    Of course, that 5.5A figure is accurate

    only at the bus voltage where 70 watts

    of demand is satisfied or 70/5.5=12.7

    volts. At a bus voltage of 14 volts or

    more, input current would be expected to

    fall to about 5A. IN a 28v airplane, the

    current would be about half that.



    Bill says he supplied this device through

    a 7A fuse which held solid while other

    devices in the supply line were less

    happy about the nature of demands on

    their capabilities.



    We would probably do well to compile

    a listing of switch/terminal failures

    in strobe systems.



    Bill, would you repeat your narrative

    of what items in your strobe supply path

    failed . . . along with your best guess

    as to the epicenter of the failures?

    How many instances did you experience

    before you replaced the power supply?

   Bob . . .

FisherPaulA(at)johndeere.
Guest

Posted: Tue Jan 28, 2014 5:59 am Post subject: Strobe switches

If this is the "AVI-PAK" sold by CreativAir, then I have one too.  Mine has been in service for about 3.5 years (300+ flight hours) and I haven't noticed any problems... so far!  Last inspection was in July, and as soon as it warms up a little, I'll inspect all of the connections again just to be sure nothing is sneaking up on me.



I'd be very interested in any analysis of this device and what, if anything, we can do to prevent re-occurrence of this issue.



Paul A. Fisher 

RV-7A N18PF  

 



--

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 28, 2014 8:35 am Post subject: Strobe switches

At 07:58 AM 1/28/2014, you wrote:

 	  Quote: 	
		  

<FisherPaulA(at)johndeere.com>



If this is the "AVI-PAK" sold by CreativAir, then I have one 

too.  Mine has been in service for about 3.5 years (300+ flight 

hours) and I haven't noticed any problems... so far!  Last 

inspection was in July, and as soon as it warms up a little, I'll 

inspect all of the connections again just to be sure nothing is 

sneaking up on me.



I'd be very interested in any analysis of this device and what, if 

anything, we can do to prevent re-occurrence of this issue.


	


   Good idea. I'd also like to 'bicycle' the DAS

   system to you and get some data off your

   as-installed system.



   Bob . . .

FisherPaulA(at)johndeere.
Guest

Posted: Tue Jan 28, 2014 8:55 am Post subject: Strobe switches

Absolutely.  Happy to help.



 - Paul

Do not archive.



--

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