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tomblejwas(at)yahoo.com
Guest

Posted: Fri Oct 11, 2013 10:19 am Post subject: Relay for Critical Power Feed

Bob,



In Z-19, you use a diode bridge for critical power feeds.  Can a relay be used instead?  For example:  connect Power Source #1 to terminal 86 and to the critical component; connect Power Source #2 to terminal 30; and 87a to the critical component.  If both switched on, power comes from #1, otherwise power comes from whichever is switched on.  Seems that this has the advantage of no need for a heat sink and failure of the relay does not prevent power to the critical component.  What am I missing?  Thanks.



Tom



Sent from my iPad

edpav8r(at)yahoo.com
Guest

Posted: Fri Oct 11, 2013 3:30 pm Post subject: Relay for Critical Power Feed

That's a novel idea, Tom.  It would work, if you assume that failure of PS#1 always means instantaneous loss of power output.  This would immediately de-energize the relay coil and allow feed from PS#2.



If, however, PS#1 suffered a slow ramp-down of output voltage (as with a failed alternator leaving a battery to supply the bus), then bus voltage would likely sag below the minimum for operation of the critical component before the relay de-energized.



Relay coils exhibit substantial hysteresis; they require a higher voltage to energize than to de-energize.  A 12V-rated relay might energize at 9V rising, but not de-energize until 6V falling.  A 12V battery would be effectively dead long before the relay opened.



This is why the diode bridge works so well.  Whichever main bus has the higher voltage supplies the critical bus, and switchover is seamless, with no dropout during the change.



I have a bag of automotive relays on the shelf.  I'll try to remember to characterize their behavior when I get home on Monday and report back.



Eric

On Oct 11, 2013, at 11:18 AM, Thomas E Blejwas <tomblejwas(at)yahoo.com> wrote:

 	  Quote: 	
		   Bob,

 

 In Z-19, you use a diode bridge for critical power feeds.  Can a relay be used instead?  For example:  connect Power Source #1 to terminal 86 and to the critical component; connect Power Source #2 to terminal 30; and 87a to the critical component.  If both switched on, power comes from #1, otherwise power comes from whichever is switched on.  Seems that this has the advantage of no need for a heat sink and failure of the relay does not prevent power to the critical component.  What am I missing?  Thanks.

 

 Tom

edpav8r(at)yahoo.com
Guest

Posted: Tue Oct 15, 2013 12:32 am Post subject: Relay for Critical Power Feed

Following up on automotive relays.

I tested six 12V coil, 40A, SPDT automotive relays (Hsin Da 961A-1C-12DM) to determine "make" and "break" coil voltages.  I connected each one to a variable power supply, and clipped multimeter leads directly at the relay's coil contacts.  Make voltage was determined by slowly increasing voltage until the relay closed, break voltage by slowly decreasing until it opened.

Coil resistance ranged from 91.5 to 92.7 ohms.

Relay 1:  Make 6.81V  Break 3.85V

Relay 2:  Make 5.80V  Break 3.85V

Relay 3:  Make 5.87V  Break 2.03V

Relay 4:  Make 6.69V  Break 3.51V

Relay 5:  Make 6.42V  Break 3.15V

Relay 6:  Make 6.46V  Break 3.79V

Average:  Make 6.34V  Break 3.36V

Relays sat stationary on the bench during tests.  Vibration in real-world use would almost certainly alter these results just bit.

Next I did a very unscientific check of holding force.  I crimped PIDG fast-on connectors to two wires and connected them to the normally open relay contacts.  I fed 5V from a power supply, through a 100k resistor, through these wires, with an oscilloscope probe attached across the resistor.  I set the relay coil voltage from another power supply at 14.0V, so that the relay closed and the scope displayed a constant 5V DC.  I set the scope to trigger on a falling slope at 4.7V.  I then slapped the relay against the bench top in every direction except pins-down, until the contacts bounced.  A typical bounce waveform is attached.  I have no idea how many g it took to bounce the contacts, but it was a pretty solid smack.  Certainly much more severe than any turbulence I care to encounter!

Eric

On Oct 11, 2013, at 4:29 PM, Eric Page <edpav8r(at)yahoo.com> wrote:

 	  Quote: 	
		   That's a novel idea, Tom.  It would work, if you assume that failure of PS#1 always means instantaneous loss of power output.  This would immediately de-energize the relay coil and allow feed from PS#2.

 If, however, PS#1 suffered a slow ramp-down of output voltage (as with a failed alternator leaving a battery to supply the bus), then bus voltage would likely sag below the minimum for operation of the critical component before the relay de-energized.

 Relay coils exhibit substantial hysteresis; they require a higher voltage to energize than to de-energize.  A 12V-rated relay might energize at 9V rising, but not de-energize until 6V falling.  A 12V battery would be effectively dead long before the relay opened.

 This is why the diode bridge works so well.  Whichever main bus has the higher voltage supplies the critical bus, and switchover is seamless, with no dropout during the change.

 I have a bag of automotive relays on the shelf.  I'll try to remember to characterize their behavior when I get home on Monday and report back.

 Eric

 On Oct 11, 2013, at 11:18 AM, Thomas E Blejwas <tomblejwas(at)yahoo.com> wrote:

> Bob,

> 

> In Z-19, you use a diode bridge for critical power feeds.  Can a relay be used instead?  For example:  connect Power Source #1 to terminal 86 and to the critical component; connect Power Source #2 to terminal 30; and 87a to the critical component.  If both switched on, power comes from #1, otherwise power comes from whichever is switched on.  Seems that this has the advantage of no need for a heat sink and failure of the relay does not prevent power to the critical component.  What am I missing?  Thanks.

> 

> Tom

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tomblejwas(at)yahoo.com
Guest

Posted: Wed Oct 16, 2013 9:09 am Post subject: Relay for Critical Power Feed

Thanks Eric.  I was also missing the inherent redundancy in the bridge diode.  If the diode through which current is flowing fails, switching to the other power source (if it isn't already on) restores current.  The two buses might be connected, but that would not prevent power to the critical component.  



I will save the relay arrangement I described for switching between my fuel pumps.  If both are inadvertently energized, the pressure will exceed the capabilities of my fuel regulator.  The relay arrangement will prevent that.



Tom



Sent from my iPad

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Oct 16, 2013 9:32 am Post subject: Re: Relay for Critical Power Feed

I claim this is a better way to go and have sold lots of these to Aeroelectric builders doing Z-19



http://www.periheliondesign.com/powerschottkydiodes.htm

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

tomblejwas(at)yahoo.com
Guest

Posted: Thu Oct 17, 2013 5:41 pm Post subject: Relay for Critical Power Feed

Yes, this does look like a better choice for the feed to my ECU.  For my fuel pumps, I think having each pump connected to a different engine bus is a simpler way to go.



Tom



Sent from my iPad

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 19, 2013 10:54 am Post subject: Relay for Critical Power Feed

At 02:24 AM 10/15/2013, you wrote:

 	  Quote: 	
		  Following up on automotive relays.


	


   <snip>



 	  Quote: 	
		  Eric




	


   Good data sir! Thank you.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 19, 2013 10:54 am Post subject: Relay for Critical Power Feed

<snip>

 Relays sat stationary on the bench during tests.  Vibration in real-world use would almost certainly alter these results just bit.



 Next I did a very unscientific check of holding force.  I crimped PIDG fast-on connectors to two wires and connected them to the normally open relay contacts.  I fed 5V from a power supply, through a 100k resistor, through these wires, with an oscilloscope probe attached across the resistor.  I set the relay coil voltage from another power supply at 14.0V, so that the relay closed and the scope displayed a constant 5V DC.  I set the scope to trigger on a falling slope at 4.7V.  I then slapped the relay against the bench top in every direction except pins-down, until the contacts bounced.  A typical bounce waveform is attached.  I have no idea how many g it took to bounce the contacts, but it was a pretty solid smack.  Certainly much more severe than any turbulence I care to encounter!



 Eric



 

   I delayed joining this thread because I recalled

   a conversation we had here on the List some time

   back about contactors opening up under vibration . . .

   actually shock.



   That conversation spooled up after a builder posted

   a note stating that while working on his

   airplane, battery-only, he dropped a tool on his

   battery contactor and the EFIS rebooted. He repeated

   the experiment several times and then came to the

   List to inquire into the suitability of this device

   to its intended task.



   Of course, many tens of thousands of this style

   contactor had been used as battery master control

   on light airplanes for close to a century. Several

   companies offered similar products but most notably,

   White-Rodgers/Stancore and Cole-Hersee. The builder's

   problem presented in a Cole-Hersee part he had

   purchased from Van's.



   I had an exemplar C-H part which I set up on the bench

   not unlike Eric's experiment above. I was astounded to discover

   that what I thought was a relatively light tap with a

   box-wrench caused a demonstrable discontinuity in the

   contactor's conductivity.



   Hmmmm . . . bad contactor? I was selling W-R/S contactors

   at the time so I put one of those on the same test set up

   and guess what?  It did it too.



   "Holy contacts Batman, how can this be?"



   After some thought I came to two understandings about

   the nature of this phenomenon. First, striking the steel

   enclosure of the contactor with a steel tool was a

   shock force. In terms of g-levels it could have easily

   reached the big numbers. Certainly 10Gs and 100G would

   not have surprised me.



   Second, why did this not manifest before? Answer, it HAD,

   many, many times over the decades. But all of the

   applications that made these contactors popular DID NOT

   feature solid state electronics . . . particularly

   fitted with microprocessors that would re-set on

   microsecond notice.



   Then the lights came on. At some time toward the end

   of my tenure in the sales of contactors, W-R/S modified

   their 70 series devices to add plastic booties over

   the mounting feet.



 [img]cid:.0[/img]



    I wrote to W-R/C and called a rep to see if I could

    get an explanation for why those 'insulators' were

    added to the mounting. Never got a satisfactory

    answer . . . in fact never got any answer.



    But I'll be you $5 to your donut (used to be

    a dollar . . . but you know . . . inflation),

    that some new electric vehicle with modern,

    CPU driven controls demonstrated the same phenomenon

    reported by our brother builder in his

    airplane. The good folks at W-R/S couldn't do a thing

    about failure of some manufacturer to do DO-160

    style qualification to his fork lift controller

    . . . the next best thing was to modify the contactor

    for better resistance to hi-G pulses or shock.



    Of course, hitting the contactor with a wrench

    continues to produce the same demonstrable dis-

    continuity. The difference being that the same

    shocks delivered through the mounting feet are less

    likely to interrupt the flow of power through

    the contactor. 



    What's the likelihood of delivering such 10+

    G shock to the contactor in your airplane?

    VERY low, hence the exemplar service life of

    this device in airplanes . . . even machines

    fitted with electronics having twitchy reset

    characteristics.



    Nonetheless, the discovery was a surprise. At the

    time I was engaged in some relay life issues at

    Hawker-Beech and this discovery on the contactors

    prompted some explorations into smaller relays . . .

    particularly some mil-spec devices. Guess what?

    They do it too.



    I couldn't find the data plots I took on the contactor

    experiments. If I run across them in the future, I'll

    re-post this note alone with the data. I don't

    think I recorded any data on the $high$ relays,

    those investigations were never formally reported.



    Bottom line is that shock . . . fast rise, short duration

    high intensity transients are a special kind of

    vibration that gets spec'ed separately from the

    shake, rattle and roll of the airframe. This further

    emphasizes the need for good practice in the design

    of input power conditioning for particularly

    vulnerable avionics. Design practice that should

    happen INSIDE the box at the factory . . . not

    outside the box at the airplane.



    So the short answer to the topic question of this

    thread is, yes . . . plain vanilla contactors

    and relays are just as suited to control "critical"

    power as they ever were. The companion question is

    whether or not the designers of potentially vulnerable

    systems understood and considered the wild-and-wooly

    nature of DC power systems in all manner of vehicle.



    I have referred numerous non-aviation clients to

    DO-160 as a set of exemplar guidelines for successful

    marketing of a new product.



 

 

   Bob . . .

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Oct 20, 2013 5:18 am Post subject: Re: Relay for Critical Power Feed

Don't use Type-70 Stancore-White-Rodgers-Emerson-Tyco contactors in your aircraft. The reasons are plentiful: They have a 122 deg F maximum ambient. They are not water or fuel proof, they won't open against high currents or voltages. They are position sensitive and have low G-withstands. Disregard the fact that they have been used and failing for many years. There are better ways to go. Bob N. and I have argued this for years. Here are some excerpts from the archives:



So the manufacturer says, "mount plunger vertical, cap down". I checked 

into the engineering data on this part and of course the corporate 

conglomeratization has destroyed the engineering knowledge that built the 

part. The manufacturer PROMISED they'd get back to me.....BUT It's not DO-160 bubela. And it's only 122 deg F max operating temp. Etc. etc. 



I spent many hours tracking down the designers of this Stancor-White-Rogers Emerson Tyco Type-70. The only info that remains available seems to be the present specs. The available newly produced Type-70 specs simply make it unsuitable. Will it work, Yes. Will it fail? Yes, sooner than you'd like. It is entirely possible that Cessna had a custom model. Is Cessna still using these? Possibly, but certificated a/c tend to use old original technology until it bleeds. There's no reason you should follow them. 



 The Kilovac Czonkas II's are made in many types. There is a marine model too that is perfectly usable. (Blue Sea Systems p/n 9012)  But I don't have stock in Kilovac. There are many makers of newer stuff [Gigavac has come out with similar contactors]. 



For my airplane, I'll use a Flaming River Battery switch if I can, and an EV200 otherwise.... 



ps: Guess how Kilovac and Gigavac clamp coil voltages generated from the collapsing magnetic field? That's right...internal bidirectional zeners.



"Everything you've learned in school as "obvious" becomes less and less 

obvious as you begin to study the universe. For example, there are no 

solids in the universe. There's not even a suggestion of a solid. There 

are no absolute continuums. There are no surfaces. There are no straight 

lines." 

- R. Buckminster Fuller

_________________
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: Sun Oct 20, 2013 6:59 am Post subject: Relay for Critical Power Feed

At 08:18 AM 10/20/2013, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net>



 Don't use Type-70 Stancore-White-Rodgers-Emerson-Tyco contactors in your aircraft. The reasons are plentiful: They have a 122 deg F maximum ambient. They are not water or fuel proof, they won't open against high currents or voltages. They are position sensitive and have low G-withstands. Disregard the fact that they have been used and failing for many years. There are better ways to go. Bob N. and I have argued this for years. Here are some excerpts from the archives: 	


    "Better" is non quantitative. Just a few weeks ago

    I received a failed, 70-series contactor removed from

    a 70's model Cessna. The owner believed that it was

    the original contactor. We did a tear down and discovered

    that indeed, the contacts had become intermittent due

    to corrosion on contacts exacerbated by ingress of moisture.

    Mechanically the device was intact and functional . . .

    after 30+ years of service.



 [img]cid:.0[/img]



    Here's the mating set of contacts . . .



 [img]cid:.1[/img]



    For a device that has been operated for 30+ years

    "outside the spec sheet" envelope of limits it looks

    pretty good to me. Would this Cessna owner be well

    advised to install something "better"? 



    If "better" means that some other device will not succumb

    to moisture (sealed contact chamber) and it has higher

    ambient temperature ratings, then yes, this carry-over from

    the 1940's has some peers with improvements that have

    evolved over time . . . often crafted to meet the needs

    of a more antagonistic environment.



    But when cherry-picking of features that are "better"

    becomes a driving force in our decision making processes,

    then other authors on this List could opine that one

    should avoid the IO-360 in favor of some newer

    technology. Or perhaps we are well advised to abandon

    panel mounted switches . . . 



    We gave up these switches



 [img]cid:.0[/img]



    in favor of these . . .



 

 [img]cid:.1[/img]



   For reasons that are fairly obvious. But consider

   the constellation of simple-ideas that come with

   the use of this part in your airplane:



 [img]cid:.2[/img]



   There are 10 new metallic joints added to every

   current carrying path by the use of these switches.

   That's a fist-full of new opportunities for failure.

   But each opportunity for failure is exploited by 

   environmental conditions and craftsmanship of the

   installer.



   These switches HAVE suffered some interesting

   failures . . .



 [img]cid:.3[/img]



 

   Question: Have switches of this genre ever bubbled

   to the surface as a hazard so egregious as to generate

   an AD against hundreds of thousands of such devices

   flying for the past 70 years? 



   This switch has suffered that dubiou honor . . .



 [img]cid:.4[/img]



   Every owner of a Baron or Bonanza has a new item

   on his/her worry-list due to an un-foreseen deficiency

   in the design . . . a deficiency that took decades

   of field service before it bubbled up and people-paid-

   to-worry took notice.



   Even people-paid-to-worry have not banned the humble

   ol' workhorse that is the 70-series contactor from

   flying aboard airplanes. We can sing the ballad of

   dueling specsheets but the bottom line is that this

   product has a SERVICE HISTORY that demonstrates it

   to be good value. I.e. performance traded against

   cost of ownership while being attentive to

   increased risks.



   Since we're ALL building failure tolerant electrical

   systems I can confidently suggest that consideration

   of "better" contactors is driven more by our desire to

   own and drive a Benz as opposed to a Ford . . . in spite

   of the fact that both vehicles have high order

   probability of getting us from point A to point B over

   15 years and 200,000 miles at low risk . . . but with

   markedly different costs of ownership.



   Everything Eric has offered is true. The point of

   this discussion . . . indeed the point of this List

   is to sift the simple-ideas of any recipe for success

   and make decisions based on cost of ownership weighed

   against risk while sprinkling in some personal

   preferences for V-Power or EXP-Bus in with the gaggle

   of fuses and toggle switches. Just as S-K vs.

   Harbor Freight tools are judged in the marketplace,

   the value of a recipe-for success in our airplanes is

   demonstrated in the air. 



   It's not WHAT we choose to use but the UNDERSTANDING

   we bring to airplane to keep OPERABILITY high, RISKS

   low while fitting COST of ownership to our own bank

   accounts.  The 70-series contactor has demonstrated

   itself not to be a black hat lurking behind a rock

   awaiting the opportunity to give you a bad day in the

   cockpit. In 50 years of hammering on airplanes I can

   confidently assert that the greatest risks for failure

   to perform are human factors issues of installation,

   maintenance or operation. Failure to perform based

   inattention to specifications is VERY low on the list

   things cause pilots to break a sweat while airborne.

   Failure tolerant design strives to make any failure

   a MAINTENANCE and COST OF OWNERSHIP issue as opposed

   to a reason for breaking a sweat.



   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 20, 2013 7:19 am Post subject: Relay for Critical Power Feed

 	  Quote: 	
		  

I spent many hours tracking down the designers of this 

Stancor-White-Rogers Emerson Tyco Type-70.


	


   Those guys died years ago . . .



 	  Quote: 	
		    The only info that remains available seems to be the present 

 specs. The available newly produced Type-70 specs simply make it 

 unsuitable. Will it work, Yes. Will it fail? Yes, sooner than you'd like.


	


   Quantify "sooner" and "like" . . . and lay foundation

   for those numbers.



 	  Quote: 	
		  It is entirely possible that Cessna had a custom model.


	


   They did not.  Everything Cessna purchased in those

   days were catalog items folded into the qualified

   parts stream by virtue of words and illustrations

   on a piece of paper (we called them C-Drawings).

   Beech did the same thing on the W-31 breaker-switches.

   I did the same thing at Electro-Mech.



   But when C-H was selling thousands per year to

   Beech and Cessna versus hundreds of thousands per

   year to customers unwashed by the FARS, who do you think

   drove design decisions?



 	  Quote: 	
		  Is Cessna still using these?


	


   I'll have access to Cessna's great data-base-in-the-sky

   in a few weeks. I'll see what is being offered as spares

   for a 1970 C-172.



 	  Quote: 	
		  Possibly, but certificated a/c tend to use old original technology 

until it bleeds.


	


   Does the IO-360 bleed? Has the lead-acid

   battery been relegated to the pages of

   aviation history? Has the incandescent

   landing light been pried out and replaced

   with LED as a hazard to the airframe and

   occupants?



 	  Quote: 	
		  ps: Guess how Kilovac and Gigavac clamp coil voltages generated from 

the collapsing

magnetic field? That's right...internal bidirectional zeners.


	


   We explored the value of Benz versus Ford style

   coil suppression about 13 years ago. I went to the

   bench and did qualitative and quantitative measurements

   on the differences in performance and benefits derived

   therefrom. Did you find errors in either my process,

   measurement or reasoning?



http://tinyurl.com/nva2xdy



http://tinyurl.com/25wjo7w



http://tinyurl.com/jwxxav8





   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Oct 20, 2013 7:45 am Post subject: Re: Relay for Critical Power Feed

Your photo of the 30 year old contactor discloses: 30 years ago they looked like they were built better. The one you show is not the same one that is being used now.



I stand my ground: Published specification for the Type-70 contactor say not to use it in the applications for which it is being used. Regardless of the fact that one can get away with it, better solutions are at hand.



 	  Quote: 	
		  Does the IO-360 bleed? Has the lead-acid battery been relegated to the pages of aviation history? Has the incandescent landing light been pried out and replaced with LED as a hazard to the airframe and occupants? 

	




Strawman arguments Bob. You can do better.

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

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Oct 20, 2013 8:03 am Post subject: Re: Relay for Critical Power Feed

Attached disassembled Type-70 (minus cap).

type-70.jpg

Description:

Type-70 contactor

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208.6 KB

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

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Oct 20, 2013 8:10 am Post subject: Re: Relay for Critical Power Feed

Attached disassembled Type-70 (minus cap and copper coil). A long cost-cutting way down from the part you show.

type-70.jpg

Description:

Type-70 contactor

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_________________
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: Sun Oct 20, 2013 8:45 am Post subject: Relay for Critical Power Feed

Been having some problems with cut-n-paste between PhotoShop

 and my email client . . . the email client doesn't always

 keep the ducks lined up. The workaround seems to be to save

 the image to hard drive and then import to the email client as

 a file . . .



 Reposted with corrected images . . .



 At 08:18 AM 10/20/2013, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net>



 Don't use Type-70 Stancore-White-Rodgers-Emerson-Tyco contactors in your aircraft. The reasons are plentiful: They have a 122 deg F maximum ambient. They are not water or fuel proof, they won't open against high currents or voltages. They are position sensitive and have low G-withstands. Disregard the fact that they have been used and failing for many years. There are better ways to go. Bob N. and I have argued this for years. Here are some excerpts from the archives: 	


    "Better" is non quantitative. Just a few weeks ago

    I received a failed, 70-series contactor removed from

    a 70's model Cessna. The owner believed that it was

    the original contactor. We did a tear down and discovered

    that indeed, the contacts had become intermittent due

    to corrosion on contacts exacerbated by ingress of moisture.

    Mechanically the device was intact and functional . . .

    after 30+ years of service.



 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.7[/img] 



    Here's the mating set of contacts . . .



 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.8[/img] 



    For a device that has been operated for 30+ years

    "outside the spec sheet" envelope of limits it looks

    pretty good to me. Would this Cessna owner be well

    advised to install something "better"? 



    If "better" means that some other device will not succumb

    to moisture (sealed contact chamber) and it has higher

    ambient temperature ratings, then yes, this carry-over from

    the 1940's has some peers with improvements that have

    evolved over time . . . often crafted to meet the needs

    of a more antagonistic environment.



    But when cherry-picking of features that are "better"

    becomes a driving force in our decision making processes,

    then other authors on this List could opine that one

    should avoid the IO-360 in favor of some newer

    technology. Or perhaps we are well advised to abandon

    panel mounted switches . . . 



    We gave up these switches



 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.9[/img] 



    in favor of these . . .



 

 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.10[/img] 



   For reasons that are fairly obvious. But consider

   the constellation of simple-ideas that come with

   the use of this part in your airplane:



 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.11[/img] 



   There are 10 new metallic joints added to every

   current carrying path by the use of these switches.

   That's a fist-full of new opportunities for failure.

   But each opportunity for failure is exploited by 

   environmental conditions and craftsmanship of the

   installer.



   These switches HAVE suffered some interesting

   failures . . .



 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.12[/img] 



 

   Question: Have switches of this genre ever bubbled

   to the surface as a hazard so egregious as to generate

   an AD against hundreds of thousands of such devices

   flying for the past 70 years? 



   This switch has suffered that dubiou honor . . .



 [img]cid:7.1.0.9.0.20131020113308.02102cf0(at)aeroelectric.com.13[/img] 



   Every owner of a Baron or Bonanza has a new item

   on his/her worry-list due to an un-foreseen deficiency

   in the design . . . a deficiency that took decades

   of field service before it bubbled up and people-paid-

   to-worry took notice.



   Even people-paid-to-worry have not banned the humble

   ol' workhorse that is the 70-series contactor from

   flying aboard airplanes. We can sing the ballad of

   dueling specsheets but the bottom line is that this

   product has a SERVICE HISTORY that demonstrates it

   to be good value. I.e. performance traded against

   cost of ownership while being attentive to

   increased risks.



   Since we're ALL building failure tolerant electrical

   systems I can confidently suggest that consideration

   of "better" contactors is driven more by our desire to

   own and drive a Benz as opposed to a Ford . . . in spite

   of the fact that both vehicles have high order

   probability of getting us from point A to point B over

   15 years and 200,000 miles at low risk . . . but with

   markedly different costs of ownership.



   Everything Eric has offered is true. The point of

   this discussion . . . indeed the point of this List

   is to sift the simple-ideas of any recipe for success

   and make decisions based on cost of ownership weighed

   against risk while sprinkling in some personal

   preferences for V-Power or EXP-Bus in with the gaggle

   of fuses and toggle switches. Just as S-K vs.

   Harbor Freight tools are judged in the marketplace,

   the value of a recipe-for success in our airplanes is

   demonstrated in the air. 



   It's not WHAT we choose to use but the UNDERSTANDING

   we bring to airplane to keep OPERABILITY high, RISKS

   low while fitting COST of ownership to our own bank

   accounts.  The 70-series contactor has demonstrated

   itself not to be a black hat lurking behind a rock

   awaiting the opportunity to give you a bad day in the

   cockpit. In 50 years of hammering on airplanes I can

   confidently assert that the greatest risks for failure

   to perform are human factors issues of installation,

   maintenance or operation. Failure to perform based

   inattention to specifications is VERY low on the list

   things cause pilots to break a sweat while airborne.

   Failure tolerant design strives to make any failure

   a MAINTENANCE and COST OF OWNERSHIP issue as opposed

   to a reason for breaking a sweat.



   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 20, 2013 11:00 am Post subject: Relay for Critical Power Feed

At 11:10 AM 10/20/2013, you wrote:

 	  Quote: 	
		  



Attached disassembled Type-70 (minus cap and copper coil). A long 

cost-cutting way down from the part you show.


	


    Really?



    Are we privy to the conversations that transpired

    during the last 50 years worth of engineering/management/

    manufacturing/marketing meetings wherein the design

    features of this product like were decided?



    I'll invite our readers to review the library of

    70 series photos at http://tinyurl.com/kcc26jt



    These photos only go back to about 1960 . . . it seems

    likely that a 1940 tear-down would show yet other

    differences.



    I would guess that this product line has

    enjoyed a host of cost-cutting changes. Advancements

    in materials and automation are nearly always

    responsible for reductions in cost and/or improvements

    in meeting design goals.



    But consider that of the trio of failure teardowns

    illustrated in the library of pictures, 2 failures

    were the result of assembly error . . . a human

    factor I cited earlier today. The third failure

    occurred at or beyond any practical expectations

    for service life on the product . . . the thing

    operated as designed and expired gracefully

    (random intermittent). Further it was not a player

    in the classic trio of conditions that precede

    so many sad events in aviation and elsewhere.



    You seem to use the phrase "cost cutting" as

    an epithet. I have participated in dozens of

    tasks where cost-cutting was a mission

    imperative. However, in no instance was degradation

    of service life or performance considered a

    component of the acceptable solution. More often

    than not, the upgrade reduced costs while improving

    on the value of the product.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 20, 2013 11:00 am Post subject: Relay for Critical Power Feed

 	  Quote: 	
		   > Does the IO-360 bleed? Has the lead-acid battery been relegated 

 to the pages of aviation history? Has the incandescent landing 

 light been pried out and replaced with LED as a hazard to the 

 airframe and occupants?



Strawman arguments Bob. You can do better.


	


    Okay, strike that paragraph. What about the others?

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 21, 2013 9:00 am Post subject: Relay_for_Critical_Power_Feed

Fooey,



Seems I'm having difficulties with integration of my

email and image editing tools and the List-Server.

I can email myself and the message comes through as

expected in both Eudora and Outlook . . . but there

appears to be a disconnect with the List Server.



Here's a .pdf of the message with missing images.

I'll get with Matt to see if we can resolve the

issues.



   Bob . . .

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raymondj(at)frontiernet.n
Guest

Posted: Mon Oct 21, 2013 11:53 am Post subject: Relay for Critical Power Feed

raymondj(at)frontiernet.n
Guest

Posted: Mon Oct 21, 2013 12:27 pm Post subject: Relay_for_Critical_Power_Feed

Bob,

         

         FYI, The email you attached as a PDF came through to me as an         email without any problems.

         

         do not archive

               	  Quote: 	
		  Raymond Julian

Kettle River, MN.



"And you know that I could have me a million more friends,

and all I'd have to lose is my point of view." - John Prine 	
       On 10/21/2013 11:58 AM, Robert L. Nuckolls, III wrote:

     

     [quote]Fooey,       

       

       Seems I'm having difficulties with integration of my       

       email and image editing tools and the List-Server.       

       I can email myself and the message comes through as       

       expected in both Eudora and Outlook . . . but there       

       appears to be a disconnect with the List Server.       

       

       Here's a .pdf of the message with missing images.       

       I'll get with Matt to see if we can resolve the       

       issues.       

       

       

       

         Bob . . . [b]

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