Matronics Email Lists :: View topic

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

MOV's
Goto page 1, 2 Next

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

aadamson(at)highrf.com
Guest

Posted: Sun Aug 20, 2006 4:55 pm Post subject: MOV's

Bob,



Just curious if a design element changed, or if they were there due to the

composite structure and some other phenomena.



In your "WireBook" for the Lancair IVP, you use MOV's across lots of

contactors, switches, etc.  And yet, your book doesn't show, nor discuss

them at least not as far as I've found.  Did something change since you did

that wirebook, or do you recommend them on composites?



Thanks in advanced,

Alan

nuckollsr(at)cox.net
Guest

Posted: Sun Aug 20, 2006 7:01 pm Post subject: MOV's

At 08:53 PM 8/20/2006 -0400, you wrote:



 	  Quote: 	
		  

<aadamson(at)highrf.com>



Bob,



Just curious if a design element changed, or if they were there due to the

composite structure and some other phenomena.



In your "WireBook" for the Lancair IVP, you use MOV's across lots of

contactors, switches, etc.  And yet, your book doesn't show, nor discuss

them at least not as far as I've found.  Did something change since you did

that wirebook, or do you recommend them on composites?


	


   Low voltage MOV's are hard to find and more expensive than

   diodes. Neat idea but not practical in low voltage DC systems.

   Hence the switch to diodes in later documents.



   Bob . . .



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

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

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

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Aug 21, 2006 10:02 am Post subject: Re: MOV's

Coil Suppression:



Mechanical relays and contactors depend upon magnetism generated by an electric current running through a wire coil. When the current stops, the magnetic field collapses. But the relay does not know the difference between a wire coil moving in a magnetic field (as in a generator) or a magnetic field moving in a wire coil (as in a collapsing magnetic field). Thus a large voltage—1000V to 1500V typically—is induced in the coil. This current goes the same direction the original current did—so it slows the contact opening—allowing arcing, chatter, bouncing, contact welding and even re-closure! Coil suppressions is required both to limit the damage to the relay contacts, and other parts in the system.



MOVs are considered to be better than diodes for coil suppression, although they have higher impedance. But MOVs typically have a limited lifetime.



Diodes are not the best devices for the task today. Not even the second-, third-, or fourth- best method. But in the 1960's they were the way to go. 



Perihelion Design sells 18V 600W Bi-Directional Zener Transient Voltage Suppressors (for 14.5V systems) that provide the most modern Third Millennium technical solution to relay coil suppression. We sell these as a set of twelve with the typical hardware needed to retrofit a small airplane.



Every manufacturer of bi-directional Zener transient voltage suppressors seems to have a trademarked name for these: Transils™, Surmetics™, Transorbs™, TranZorbs™, TransGuards™, Mosorbs™; the list is endless.  We call them SnapJacks™.



They also are offered in a range of voltages, packages, and wattages. Perihelion Design offers the 18 Volt 600 Watt axial lead version of these guys, commonly known to close friends as P6KE18CA, and includes some of the connectors and shrink tubing you may need to install them.



Basic Plan: SnapJacks are used to replace coil suppression diodes wherever they are now installed. For coils, contactors and relays that are internally equipped with a suppression diode, the best solution may be to buy the equivalent non-diode part. If possible, install the SnapJacks with the shortest leads possible consistent with strain relief and mechanical mounting of the part.



SnapJacks have NO POLARITY, regardless of any marking on the parts. Although the 600 W parts will work fine with the biggest relay, contactor, or motor that your aircraft could lift, you may wish to parallel two SnapJacks on the big loads for redundancy. In some cases diodes associated with contactors are there for switching logic purposes, not suppression. These should be left alone.



ref: http://relays.tycoelectronics.com/kilovac/appnotes/transients.asp



See: http://www.periheliondesign.com/suppressors/SnapJack.pdf

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

echristley(at)nc.rr.com
Guest

Posted: Tue Aug 22, 2006 6:05 am Post subject: MOV's

 	  Quote: 	
		  



Coil Suppression:



Diodes are not the best method today. Not even the second-, third-, or fourth-

best method. But in the 1960's they were the way to go.



  



In what aspect does the common, sub-$1, available-everywhere diode fall 
	


short enough to justify paying $30 for your single-source solution?



-- 

         ,|"|"|,              Ernest Christley       |

----===<{{(oQo)}}>===----    Dyke Delta Builder      |

        o|  d  |o        http://ernest.isa-geek.org  |

paulm(at)olypen.com
Guest

Posted: Tue Aug 22, 2006 8:47 am Post subject: MOV's

I get them for as little as under 25 cents each in qty of one (15 cents each 

for 100). All industrial electronic suppliers stock them in many types and 

brands.  $30 will get you 100 parts including shipping in some cases. The 

cost difference is not significant in the big picture.



Eric provides a value added KIT of parts etc its up to you to convert 

convenience for absolute cost. (Eric also posted the exact part number for 

those who wanted to get just the diodes from most any source as above)



Relays with internal diodes are available simply because of demand, not for 

technical reasons. Engineers resist change and if it seems to work why 

change?



Transorbs are better or (no worse in some opinions) and work in 100% of the 

cases. Its a "no brainier" for some of us.



While they may not appear to make a difference in a 5 amp resistive load 

with a small relay, Transorbs are proven to have a large advantage in 

inductive and larger current loads with larger or different type relays.



But so what! Bob has his "repeatable" test of one and is convinced he is 

right.



One size (test) does not fit all cases and perhaps its 90% (for diodes) for 

the average aircraft but clearly not 99.99% based on MY own lab repeatable 

tests.



The entire world, North America, and Europe for example, ALL say the same 

thing that Eric referenced about Diodes vs. Transorbs etc. Just who is out 

of step here????



There are hundreds in every modern auto. Given the number of autos made each 

year and yes Transorbs do cost more than simple diodes why would auto makers 

spend millions of $$ every year for them if the diode was as good and they 

could save all that money with diodes. Perhaps they know something not 

stated on this list??



If you look at the available data including the many references and read and 

understand the available info, its far more compelling than appears on the 

surface.



Is "good enough" OK if you can get better for little more?



I am unwilling to have another useless debate. It ends up with a lot of 

words/heat etc. and no opinion ever gets changed.



Paul

---

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Tue Aug 22, 2006 9:46 am Post subject: Re: MOV's

 	  Quote: 	
		  Coil Suppression: 



In what aspect does the common, sub-$1, available-everywhere diode fall 

short enough to justify paying $30 for your single-source solution? 

-- 

,|"|"|, Ernest Christley 	




Ernest,



See both of the links I posted, 



ref: http://relays.tycoelectronics.com/kilovac/appnotes/transients.asp 



See: http://www.periheliondesign.com/suppressors/SnapJack.pdf



but especially:



http://relays.tycoelectronics.com/kilovac/appnotes/fig48.asp



You are incorrect on several points-- These are not single sourced. Every manufacturer of bi-directional Zener transient voltage suppressors seems to have a trademarked name for these: Transils™, Surmetics™, Transorbs™, TranZorbs™, TransGuards™, Mosorbs™; the list is endless. We call them SnapJacks™. They are 18 Volt 600 Watt axial-lead bi-directional Zener transient voltage suppressors, part number P6KE18CA.



The kit includes:



(12) P6KE18CA

(24") of suitable heat shrink tubing,

(4) 1/4" faston solder adaptors

(10) 6-8-10 Multistud ring tongue connectors

(2) 1/4" ring tongues

(2) 5/16" ring tongues

(4) Faston tabs rivet or screw mount

(1) Instructions and technical details,

(1) Perihelion Design catalog

(1) Free first-class shipping



My accountant says I lost $xx,xxx on my little business in '04 and will maybe break even in '05 and '06, due entirely to my Space Shuttle Switch Guards that I sell to NASA (Perihelion Design parts are in orbit!) and the Military. 



Selling little SnapJack™ kits like this is a money loser no matter how you cut it, but I get to hang out with the most interesting people. That's worth a lot.

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

N6030X(at)DaveMorris.com
Guest

Posted: Tue Aug 22, 2006 9:54 am Post subject: MOV's

Ok, so translated into complete neophyte-speak, for the rest of "us", 

this means:



"

1. The experts disagree (as they do in high vs low wing)

2. You can use a diode or a transorb, but do use something.

3. Pick whichever you find cheaper and more readily available.

4. A transorb can be wired up either direction, while a diode must be 

wired with the correct polarity.

"



Dave Morris

N5UP



At 11:51 AM 8/22/2006, you wrote:

[quote]



I get them for as little as under 25 cents each in qty of one (15 

cents each for 100). All industrial electronic suppliers stock them 

in many types and brands.  $30 will get you 100 parts including 

shipping in some cases. The cost difference is not significant in 

the big picture.



Eric provides a value added KIT of parts etc its up to you to 

convert convenience for absolute cost. (Eric also posted the exact 

part number for those who wanted to get just the diodes from most 

any source as above)



Relays with internal diodes are available simply because of demand, 

not for technical reasons. Engineers resist change and if it seems 

to work why change?



Transorbs are better or (no worse in some opinions) and work in 100% 

of the cases. Its a "no brainier" for some of us.



While they may not appear to make a difference in a 5 amp resistive 

load with a small relay, Transorbs are proven to have a large 

advantage in inductive and larger current loads with larger or 

different type relays.



But so what! Bob has his "repeatable" test of one and is convinced 

he is right.



One size (test) does not fit all cases and perhaps its 90% (for 

diodes) for the average aircraft but clearly not 99.99% based on MY 

own lab repeatable tests.



The entire world, North America, and Europe for example, ALL say the 

same thing that Eric referenced about Diodes vs. Transorbs etc. Just 

who is out of step here????



There are hundreds in every modern auto. Given the number of autos 

made each year and yes Transorbs do cost more than simple diodes why 

would auto makers spend millions of $$ every year for them if the 

diode was as good and they could save all that money with diodes. 

Perhaps they know something not stated on this list??



If you look at the available data including the many references and 

read and understand the available info, its far more compelling than 

appears on the surface.



Is "good enough" OK if you can get better for little more?



I am unwilling to have another useless debate. It ends up with a lot 

of words/heat etc. and no opinion ever gets changed.



Paul

---

paulm(at)olypen.com
Guest

Posted: Tue Aug 22, 2006 12:32 pm Post subject: MOV's

Comments by your numbers.



1. I only know one "expert" that disagrees with the use of transorbs. I am 

sure they are more but the overwhelming majority of my engineering 

associates agree with the "true experts in the field" of  relays and 

contacts etc.



2. Sort of true in most cases. Not usually true with contactor type relays 

switching inductive loads for example. There are two issues the coil 

inductive kick that must be addressed that affects the driver of the coil 

and the relay contacts which can affect the switched load by delays (seldom) 

and slow opening which power contactors really have a large delay in many 

cases and the duration and magnitude of the slow opening of a large 

inductive load can be damaging.



3. Sure quality and use is trumped by price. 5 cents is better than 25 

cents. Using the same logic go to your rat shack and get plastic crimp 

terminals as they are cheaper and easier to find.



4. Transorbs are both uni-directional and bi-directional. True in one case 

and polarity is important in the other.



However a uni-directional transorb is no better than a diode, and is a diode 

in that use.



Paul



---

klehman(at)albedo.net
Guest

Posted: Tue Aug 22, 2006 12:53 pm Post subject: MOV's

True for a bi-directional transorb. But just to muddy the waters, I kind 

of like the more common uni-directional transorbs. They will still help 

with positive spikes (if you believe in positive spikes  ). Used 

across a contactor coil, they may delay the opening a smidge compared to 

a bidirectional transorb, but I suspect  that, like the common diode, 

they are more effective at preventing negative spikes (if you believe in 

negative spikes comining off contactor coils    ).   It seems to me 

that an 18 volt bidirectional transorb may still let negative spikes 

through that are  large enough to damage electrolytic capacitors and 

perhaps solid state devices, if there is no battery in the circuit.  I 

guess I used diodes on all the contactors and then added a few transorbs 

on the b-lead just because I could...



Are automobiles incorporating transorbs within some devices now? I've 

never come across one yet that I've noticed.



Ken



 	  Quote: 	
		   4. A transorb can be wired up either direction, while a diode must be 

 wired with the correct polarity.

 "

tonybabb(at)alejandra.net
Guest

Posted: Tue Aug 22, 2006 12:58 pm Post subject: MOV's

Dave,



As a neophyte thanks for leading me to the bottom line here - THANK YOU !!



Tony



--

nuckollsr(at)cox.net
Guest

Posted: Tue Aug 22, 2006 3:15 pm Post subject: MOV's

At 01:57 PM 8/22/2006 -0700, you wrote:



[quote]



Dave,



As a neophyte thanks for leading me to the bottom line here - THANK YOU !!



Tony



--

nuckollsr(at)cox.net
Guest

Posted: Tue Aug 22, 2006 6:34 pm Post subject: MOV's

At 01:33 PM 8/22/2006 -0700, you wrote:






Comments by your numbers.



1. I only know one "expert" that disagrees with the use of transorbs. I am 

sure they are more but the overwhelming majority of my engineering 

associates agree with the "true experts in the field" of  relays and 

contacts etc.



     Who's claiming to be an expert? Please cite the writings

     of any other individual who has measured, illustrated and

     explained variabilities and their effects in the manner

     which I've offered. The name, job title and organization

     of any such individual are unimportant. The numbers and

     explanations are.  Good data and experimental technique

     stands by itself because it (1) makes sense and/or (2)

     is easily supported (or refuted) by repeating the experiment.



     I can demonstrate at least three cases in the past 8 years

     where the best that some big-name companies could bring to

     bear on high dollar problems was insufficient to the task.

     Instead of getting their fast-turn advice on how best to

     deduce failures of their products, it took me months and

     in one case years to figure it out for myself. In the end,

     I knew more about some aspects of their product than they

     did.

2. Sort of true in most cases. Not usually true with contactor type relays 

switching inductive loads for example. There are two issues the coil 

inductive kick that must be addressed that affects the driver of the coil 

and the relay contacts which can affect the switched load by delays 

(seldom) and slow opening which power contactors really have a large delay 

in many cases and the duration and magnitude of the slow opening of a large 

inductive load can be damaging.



     If I read this correctly, you're citing the occasional

     system performance issue where a 12 mS dropout delay

     is okay but a 60+ mS delay causes problems. Yes, I've

     had to deal with a few systems where multiple relays could

     get into operating "races" and produce unpredictable and

     unsatisfactory performance. I know of no situation in OBAM

     aviation where this could be an issue.



     However, in the last sentence you seem to be speaking of

     contact spreading velocity which I've shown is mildly

     affected by the form of coil spike suppression.

3. Sure quality and use is trumped by price. 5 cents is better than 25 

cents. Using the same logic go to your rat shack and get plastic crimp 

terminals as they are cheaper and easier to find.



     Price has nothing to do with the design points under

     discussion. MOVs were attractive to me early on in spite

     of their price BECAUSE they were bi-directional devices.

     I reasoned that use of the MOV would prevent the occasional

     accidental mis-wiring that is possible with the decidedly

     uni-directional nature of diodes. However, they did not

     perform as well as diodes for the purpose of reducing stress

     on the controlling switch. Further, they were hard to find

     in very low conduction voltage ratings.



     I abandoned them in my writings after a few years in

     favor of readily available, lower cost, better performing,

     plain vanilla diode.

4. Transorbs are both uni-directional and bi-directional. True in one case 

and polarity is important in the other.



However a uni-directional transorb is no better than a diode, and is a 

diode in that use.



     In fact, you cannot use a uni-directional Transorb (or

     plain-vanilla zener) unless combined with a diode to

     prevent forward conduction as shown in multitudes of catalogs

     and literature on relays.



Paul



At 11:51 AM 8/22/2006, you wrote:




I get them for as little as under 25 cents each in qty of one (15 cents 

each for 100). All industrial electronic suppliers stock them in many types 

and brands.  $30 will get you 100 parts including shipping in some cases. 

The cost difference is not significant in the big picture.



       Agreed. Let us leave cost out of it.

Eric provides a value added KIT of parts etc its up to you to convert 

convenience for absolute cost. (Eric also posted the exact part number for 

those who wanted to get just the diodes from most any source as above)



Relays with internal diodes are available simply because of demand, not for 

technical reasons. Engineers resist change and if it seems to work why change?



      ???? Really. You don't speak very highly of engineers. Stuck

      in ruts (do they never seek to broaden their horizons?) Further,

      they're willing to accept anything that "seems" to work. Don't

      you think it's incumbent upon the savvy engineer to KNOW how

      and why things work and not rely on mortal perception? Perhaps

      I benefited from not having finished school if I avoided that

      upper level class: Ruts and Perceptions 425 - Recipes for

      Failure.



Transorbs are better or (no worse in some opinions) and work in 100% of the 

cases. Its a "no brainier" for some of us.



      How are they "better"?  I've never said that they SHOULD

      NOT be used or that they were somehow inferior. The only

      thing I've said and demonstrated was that there is no

      measurable value FOR using them.



      The difference between NO suppression (open circuit) and

      the most aggressive suppression (diode) was a spread of

      10% in arc-time during contact opening. A diode-transorb

      combo would fall somewhere in between. This means that

      the delta for diode-transorb versus diode-only could be

      as little as 1% and maybe as much a 9% . . . that was

      the point of the experiment, to put some bounds on a

      spread. Further, it's the only claim being made from

      analysis of the data.



While they may not appear to make a difference in a 5 amp resistive load 

with a small relay, Transorbs are proven to have a large advantage in 

inductive and larger current loads with larger or different type relays.



      Please cite the experiments and the resulting data.

      Keep in mind that off-the-shelf relays of ALL sizes

      are available with nothing, diode-zener and diode

      only coil suppression. If one technique were so

      decidedly favorable over another technique, why

      hasn't the relay and contactor industry all jumped

      onto one bandwagon as your "entire world" citation

      below suggests they should?



But so what! Bob has his "repeatable" test of one and is convinced he is right.



      I gathered data on one relay and tested three others of various

      sizes from 2 to 30 or so amps. The measured results with respect

      to effects on contact spreading velocity were similar. If the test

      was poorly crafted then it should be no big deal to demonstrate

      my error.



One size (test) does not fit all cases and perhaps its 90% (for diodes) for 

the average aircraft but clearly not 99.99% based on MY own lab repeatable 

tests.



      Please share the data of your tests. What size relay would

      you like to see data on? I have some real honkers. I think I

      could do a 400A interrupt experiment for you. Let us compare

      notes.



The entire world, North America, and Europe for example, ALL say the same 

thing that Eric referenced about Diodes vs. Transorbs etc. Just who is out 

of step here????



      Please cite the literature. You've cited applications literature

      on Transorbs before that was shown to be overstated or when it

      came to over-voltage and load-dump mitigation. You once advocated

      a generous sprinkling of Transorbs on the bus . . . one for every

      breaker as I recall.  The Transorb is a high power, low energy

      device well suited for mitigating short duration events . . .

      lightning strikes and ESD. I'm well aware of their usefulness. I

      stuck an array of Transorbs on an electro-whizzy just this weekend

      so that I could pass and ESD test in the lab tomorrow morning.



      At the same time, others here on the list have  shown that the

      Transorb is not suited to a load-dump mitigation without

      deliberate impedance limiting of the energy source (just

      like the manual says). In this discussion, we're definitely in

      the short duration, low energy realm where a Transorb thrives.



      But I'll say again, I'm not campaigning against Transorbs for

      this application. I'm only stating that there's no compelling

      evidence support superior performance over the lowly diode for

      coil suppression when it comes to fending off the contact-eating

      gremlins.



There are hundreds in every modern auto. Given the number of autos made 

each year and yes Transorbs do cost more than simple diodes why would auto 

makers spend millions of $$ every year for them if the diode was as good 

and they could save all that money with diodes. Perhaps they know something 

not stated on this list??



      Perhaps you have special knowledge of the reasoning behind their

      use? Yes, we use hundreds of them on airplanes too, but they're

      not used on large contactors in lieu of diodes . . . for the

      reasons I've cited.



If you look at the available data including the many references and read 

and understand the available info, its far more compelling than appears on 

the surface.



      Let us not talk about "surface" or "appearances". How about

      physics of test setups and numbers derived therefrom.



Is "good enough" OK if you can get better for little more?



I am unwilling to have another useless debate. It ends up with a lot of 

words/heat etc. and no opinion ever gets changed.



      It is not my wish to convince you or anyone else of anything

      sir. It's my intent to explain things and support my explanations

      with demonstrable fact and logical conclusions based on those

      facts. If I am in error, nobody would be happier to know the

      nature of the error than I. Go to the lab sir. Show us the

      data you've collected. I need to know how I screwed up. You

      name the test conditions and I'll repeat the test so we can

      compare results. This is where the debate becomes useful . . .

      not to you or I but to those who choose to read it and

      deduce facts of the matter for themselves.



      Bob . . .



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

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

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

nuckollsr(at)cox.net
Guest

Posted: Tue Aug 22, 2006 7:23 pm Post subject: MOV's

At 04:52 PM 8/22/2006 -0400, you wrote:



 	  Quote: 	
		  



True for a bi-directional transorb. But just to muddy the waters, I kind 

of like the more common uni-directional transorbs. They will still help 

with positive spikes (if you believe in positive spikes  ). Used across 

a contactor coil, they may delay the opening a smidge compared to a 

bidirectional transorb, but I suspect  that, like the common diode, they 

are more effective at preventing negative spikes (if you believe in 

negative spikes comining off contactor coils    ).   It seems to me that 

an 18 volt bidirectional transorb may still let negative spikes through 

that are  large enough to damage electrolytic capacitors and perhaps solid 

state devices, if there is no battery in the circuit.  I guess I used 

diodes on all the contactors and then added a few transorbs on the b-lead 

just because I could...



Are automobiles incorporating transorbs within some devices now? I've 

never come across one yet that I've noticed.



Ken



>4. A transorb can be wired up either direction, while a diode must be 

>wired with the correct polarity.

>"


	


    A contactor coil can generate spikes of either polarity. It

    depends on how you switch it. Here's a trace I took off the coil

    of a Cole-Hersee battery contactor with no coil suppression.

    I dug through the archives and found some more data on devices

    common to the OBAM aviation electrical systems. See:



http://www.aeroelectric.com/Pictures/Curves/CH_Bus_Noise_w_0p1_Cap.gif



    Here you see a 300+ volt POSITIVE spike because the controlling switch

    (battery master) is in the ground lead. Note that with as little as

    0.1 uF capacitor on the supply plus whatever the bench supply

    (3A regulated) impedance was, the spike noise coupled to the bus

    was on the order of one or two volts high. And this may have been

    a test setup artifact (meaning smaller than observed). The point of

    this setup was to show that coil spikes are a danger only to the

    controlling device (in this case, battery master switch) and NOT

    to other devices on the bus. These spikes DO NOT propagate about

    the system on the lookout for vulnerable electro-whizzies.



    The next trace  . . .



http://www.aeroelectric.com/Pictures/Curves/CH_w_120_Ohm.gif



    shows the coil suppression benefits of a simple resistor. In this

    case, 120 ohms. The spike is notably smaller, only 90 volts

    or so and again, the spike coupled to the bus was tiny by

    comparison and probably not "real".  Note the 22 mS release

    time for the contactor. The next trace . . .



http://www.aeroelectric.com/Pictures/Curves/CH_w_1n5400.gif



    shows what happens with the plain diode spike suppressor.

    Note the very slight upward inflection of trace #2 above

    bus voltage where the coil energy is staining against the

    diode's forward voltage drop as positive going spike is

    clamped off. Note the 75 mS release time. The next trace . . .



http://www.aeroelectric.com/Pictures/Curves/CH_w_2x18v_Transorbs.gif



    shows the results of a pair of 18v Transorbs (or zeners)

    hooked back to back to emulate the bi-directional device.

    Here the spike clamps off at an expected level of about 18 volts

    above bus voltage and we see a release time of about 14 mS.

    The next trace . . .



http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_without_Diode.gif

    Shows a Cole-Hersee contactor release time ploted at some

    other time without a diode but this time, I captured the

    release time of 11 mS. The next trace . . .



http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_with_Diode.gif

    is for the same relay and shows a 53 mS release time, again

    about 5x the no-diode time noted above. This data is proprotionally

    consistant with numbers I posted for the smaller relay

    earlier. Note also that one experiment with the CH contactor

    and diode yielded a 75 mS release time while the second

    was only 53 mS. This variability is to be expected and is

    driven by many factors including contactor temperature and

    manufacturing variables. The effects of any one suppression

    technique can be accurately compared only when all techniques

    are used on the same contactor and done with some effort to

    keep the contactor temperature constant for each experiment.



    Note that NONE of these traces went to the issue of contact

    spreading velocity and resulting arc durations . . . only changes

    in release time for the various techniques with a peripheral look

    at spike propagation to the bus.



    This series of traces serves to illustrate only the variability

    of release time which a number of articles have mistakenly

    assumed that proportionate decreases in contact spreading

    velocity automatically follow. I'll suggest that the

    assumed proportionality does not exist and that their is no

    demonstrable advantage for using one suppression technique over

    another in terms of performance. That suggests we're free to

    choose techniques based on price.  The plain vanilla diode is

    hard to beat for price and wide spread availability. However,

    I'd be delighted to be shown wrong if my suggestion is in error.



    Bob . . .

paulm(at)olypen.com
Guest

Posted: Tue Aug 22, 2006 7:49 pm Post subject: MOV's

I cannot let this get past as your statement is in fact TOTALLY technically 

incorrect (vs opinions).



Below requests for links must exclude your own as they need to be unbiased!



---

paulm(at)olypen.com
Guest

Posted: Tue Aug 22, 2006 7:49 pm Post subject: MOV's

As I have stated in my original post which you (apparently do not want to 

respond to) I will not get into a debate with you ever again (actually on 

ANY subject) and this subject (transorbs) has been debated between us 

starting nearly 10 years ago.



If you truly are interested in the reasons (pros and cons) of the various 

types of coil suppression please consider reviewing the references Eric 

posted as your reference had little info other than to illustrate the types 

of suppression relay delays. Yes (as you have stated) the total circuit (not 

just the coil) drives the suppression method and Transorbs always work and 

diodes only usually work.



I will not respond to your comments below (however erroneous some may be) as 

there is no point.



Paul

---

nuckollsr(at)cox.net
Guest

Posted: Tue Aug 22, 2006 7:57 pm Post subject: MOV's

At 10:46 AM 8/22/2006 -0700, you wrote:



 	  Quote: 	
		  

 > Coil Suppression:

 >

 > In what aspect does the common, sub-$1, available-everywhere diode fall

 > short enough to justify paying $30 for your single-source solution?

 > --

 > ,|"|"|, Ernest Christley

Ernest,



See both of the links I posted,



ref: http://relays.tycoelectronics.com/kilovac/appnotes/transients.asp


	




   Okay, lets take a look at this citation . . .

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

* Improving Relay Operate Time



        Coil suppression can have a profound effect on opening time

        which is usually called "release time". The citation speaks

        of "operate time" which is usually the time it takes for a

        relay to close - which is NOT affected by the popular coil

        suppression techniques.



* Calculating Pull-in & Drop-out Voltages at High or Low Temperatures

* Radiation Exposure at High Voltage; Is it a Problem?

* Power Conservation Schemes

* High Voltage Processing of Vacuum Relays



       These points are not germane to the discussion at hand and will

       be ignored for the moment.



"When a 28 Vdc relay coil is turned off, the inductive energy stored in it 

can create surge voltages to 1500 volts on a DC power line. With the 

increased use of solid state devices which are sensitive to spikes, relay 

coils must be suppressed to limit voltage spikes to a maximum of 50 to 80 

volts."



      The first paragraph uses impressive numbers . . . 1500 volts will scare

      the pants off most neophytes. Of course, it's easy to sign up to the 

notion

      that solid state devices should be "protected" from such horrific 

stresses.

      The paragraph ends with an assertion that bringing the offending 

spike down

      to the 50-80 volt range is the magic bullet. But there's a glaring 

error . . .

      that 1500 volt spike DOES NOT propagate out onto the bus but instead is

      impressed across the mechanism of the controlling device be it switch

      or transistor.



"The measure of successful coil suppression depends on the degree to which 

the method affects the operation of the relay. Improper or excessive 

suppression can cause the relay to suffer from a long release time, slow 

contact transfer, and contact bounce on break. All of these conditions will 

increase contact arcing when load switching, which will reduce relay life 

dramatically."



      Yes, slowed transfer and bounce are potentially hard on a relay.

      Delayed release is not hard on relays but may have an effect on

      system performance in time-critical situations . . . and were

      talking MILLISECOND criticality. The paragraph correctly infers that

      arcing is the proximate cause of reduced relay life.



"There are a number of common ways for a relay user to suppress relay coil 

transients and each has advantages and disadvantages. However, the most 

widely used methods utilize zener-diode and/or zener-zener combinations. 

These combinations are compact, provide excellent suppression, and do not 

affect relay release-time or contact life."



      We've already demonstrated that the favorably rated zener-zener

      technique has SOME effect on release time. It's less effect than

      diode only but the effect is not zero. What is inferred and not

      supported is that diode only has a profound effect on relay life . . .

      an assertion I don't understand based on experiments I've conducted

      over the years. I've not yet been able to confirm the assertion

      on any size relay I've worked with to date. If someone cares to

      show me an experiment that supports the assertion, I'd be pleased

      to know of it.



      In the mean time, I'm inclined to treat the words of the

      cited posting with skepticism. They take a couple of true

      statements, a false statement and then infer some golden

      actions to be taken based on those statements. As I stated

      in an earlier post, there's a LOT of writing like that

      in the wild . . .



      In this case, the errors are not harmful. There's nothing

      inherently wrong with the proposed "gold standard" but

      the writing does not foster understanding. Instead, lots

      of myths are launched and preached as gospel because they

      came from the Tyco-Amp or P&B bibles.



      Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Tue Aug 22, 2006 10:00 pm Post subject: MOV's

At 08:53 PM 8/22/2006 -0700, you wrote:



[quote]



I cannot let this get past as your statement is in fact TOTALLY 

technically incorrect (vs opinions).



Below requests for links must exclude your own as they need to be unbiased!



---

nuckollsr(at)cox.net
Guest

Posted: Tue Aug 22, 2006 10:21 pm Post subject: MOV's

At 08:19 PM 8/22/2006 -0700, you wrote:



 	  Quote: 	
		  



As I have stated in my original post which you (apparently do not want to 

respond to) I will not get into a debate with you ever again (actually on 

ANY subject) and this subject (transorbs) has been debated between us 

starting nearly 10 years ago.


	


   Yup, that conversation has been enshrined in bytes at



   http://aeroelectric.com/articles/spike.pdf



 	  Quote: 	
		  If you truly are interested in the reasons (pros and cons) of the various 

types of coil suppression please consider reviewing the references Eric 

posted as your reference had little info other than to illustrate the 

types of suppression relay delays. Yes (as you have stated) the total 

circuit (not just the coil) drives the suppression method and Transorbs 

always work and diodes only usually work.


	


   I've read those references. And I've explained what

   I've found in them that was in error. If you want

   to worship at the altars of Tyco-Amp or Potter-Brumfield

   based on your blind acceptance of their Word, that's

   your choice . . . but expect to be challenged when you

   preach philosophies you cannot yourself explain. You

   expose yourself as a propagandist and not as a teacher.



 	  Quote: 	
		  I will not respond to your comments below (however erroneous some may be) 

as there is no point.


	


   If you can't be a teacher then don't get into

   the sandbox to throw mud. Your drive-by insinuations

   that errors in my posting are unworthy of your

   time and effort is consistent with the behavior

   you favored 6 years ago. You stood off and threw

   rocks at my explanations and NEVER offered a single

   alternative supported by your own explanation of

   the underlying physics.



   You had plenty to complain about but never a

   plan consistent with anyone else's design goals but

   your own. You want to play? Fine. If not, then

   you know the way out. The unsubscribe link is:



http://www.matronics.com/subscribe/



   Bob . . .

paulm(at)olypen.com
Guest

Posted: Wed Aug 23, 2006 6:11 am Post subject: MOV's

Bob I love 99% of your posts. You are doing a great job in helping people 

understand and wire their aircraft and based on my limited accident 

investigation of auto engine powered aircraft.



I would guess you have saved hundreds of lives in the past 10 years.



The stupid things people do that do not know of your information is 

astounding.



However what I was asking for is independent backup of your conclusions as 

my background and experience as well as all the data I can find support my 

opinion not yours.



What is wrong with asking for independent backup. EVERY source (several 

beyond what has been mentioned recently) I can find that really evaluates 

(and stacks) the different suppression methods put the simple diode at the 

bottom and the bi-directional transorb (or its equivalent) at the top. Sure 

the different approaches are "application dependent" as which work better 

and which are not as good. My point is the transorb always is good (and at 

the top of the lost) so why not use it. No need to retrofit and replace 

diodes IF you were to go on and discuss the cases where the diode was not as 

good.



The only published paper that disagrees with me comes from you. How about an 

industry recognized paper that supports your position? Teachers must be able 

to backup what they say with independent references or the student can waver 

about that and anything else the teacher says. The "prove me wrong" is 

interesting but not useful as most students have no ability to try.



I have no interest in trying to prove what the industry says in unison. I 

did see the proving data in the EMI lab when I worked in aerospace that 

supported the industry and we simply proceeded on. Why not?, there was no 

significant mechanical, electrical or cost difference and in some cases 

there was a functional improvement. Sure 90% of the time a diode was just 

fine but in the other cases it was not.



I can and have been a teacher but you want to be a teacher and yet get upset 

when the student says "prove it". Using only your position (which differs 

from industry) is not enough for me (and some others unwilling to post) 

given the predictable results. A test by you of a single case or a couple of 

cases does not make the statement universally true in all cases.



Paul

---

paulm(at)olypen.com
Guest

Posted: Wed Aug 23, 2006 6:43 am Post subject: MOV's

Yes I remember that interchange and its a wonderful example how selective 

cut and paste can change what I was saying and its context.



Its a masterpiece.



Paul



---

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours Goto page 1, 2 Next
Page 1 of 2

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum