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Coil Suppression Techniques

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john_rv10(at)yahoo.com
Guest

Posted: Wed May 21, 2008 1:24 pm Post subject: Coil Suppression Techniques

Eric, 



Thank you for this contribution.



I am planning to use a relay to switch power to my avionics/endurance busses. Normal loads at switch on/turn off would be in the order of 10 amps at 12 volts. What relay would you recommend and would you draw a simple diagram for a non electrical person showing how and where to wire the P6KE18CA bidirectional zener?



Thanks once again,

John



--

Max Johansson

Joined: 09 Jan 2006
Posts: 25
Location: Helsinki, Finland

Posted: Thu May 22, 2008 12:38 am Post subject: Coil Suppression Techniques

Eric   

This seems to be a well studied subject and after studying your results the method of parallelling a relay or contactor with an opposite direction diode seems to be the quick and dirty but still quite adequate method for the homebuilder.     

Now a very practical question:     

Is a 0.1 dollar 1N4001...4004 or similar diode strong enough to handle the collapsing energy of any relay or contactor used in a homebuilt ?  

best regards  

Max  

(just now wiring my 701 starter circuit)  

    [quote][b]

_________________
Max

Max Johansson, Helsinki, Finland
Building a CH701SP-912S
on CZAW amphibian floats

jetboy

Joined: 22 Jul 2006
Posts: 233

Posted: Thu May 22, 2008 2:41 am Post subject: Re: Coil Suppression Techniques

Max,

  1N5404 thru -8 series should do well with much more margin. I fitted one to the master solenoid on a Cessna150 once because the A&P in their collective wisdom neglected that small part as depicted it the Cessna parts book when replacing the old solenoid  and damaged my master switch. 



My CH701 has a diode installed as required by the ACS ignition/start switch instructions and I think this one may have come with the switch.



Ralph

_________________
Ralph - CH701 / 2200a

nuckolls.bob(at)cox.net
Guest

Posted: Thu May 22, 2008 5:18 am Post subject: Coil Suppression Techniques

At 11:27 AM 5/22/2008 +0300, you wrote:



 	  Quote: 	
		  Eric



This seems to be a well studied subject and after studying your results 

the method of parallelling a relay or contactor with an opposite direction 

diode seems to be the quick and dirty but still quite adequate method for 

the homebuilder.



Now a very practical question:



Is a 0.1 dollar 1N4001...4004 or similar diode strong enough to handle the 

collapsing energy of any relay or contactor used in a homebuilt


	


  Yes. Electrically the 1A diode is fine for about everything

  on the airplane. Recall that in the realm of reactive devices

  that store energy, the discharge begins at the same magnitude

  as the charging source. If you charge a capacitor to 100 volts, you

  get a reaction that starts at 100v and goes down from there

  when you discharge it.



  If you charge and inductor up to 1A, then when you release

  it from the charging source, the delivered reaction starts

  a 1A and goes down from there.  Diodes have a steady state

  capability which is exemplified in their ratings . . . I.e,

  the 1N4001 is a 1A device. However, they also have transient

  ratings at much higher currents. For example, consulting the

  1N400x data sheet at:



http://aeroelectric.com/Mfgr_Data/Semiconductors/1N4001.pdf



  we read about an 8.3 mS non repetitive peak forward surge

  current rating of 30A. By "non-repeating", they don't

  mean "one time ever" but "just don't do this often." So as

  a transient current clamp on a manually operated contactor

  found in our airplanes the 1N400x series devices are

  electrically fine.



  However, I have often suggested that the larger siblings

  to the 1N400x (1N540x) devices have some mechanical

  advantages. They're still small but MUCH more robust

  than the little fellers. I selected these parts as

  power steering and coil suppressors of choice for the

  line of contactors I used to sell (which B&C still

  does). See:



http://www.aeroelectric.com/Pictures/Contactors/s701-1l.jpg



http://www.aeroelectric.com/Pictures/Contactors/s701-2.jpg



   The red PIDG terminal gets a good connection on

   the larger wires for these devices and the wires

   are robust enough to support the diode body under

   vibration levels typical of installations for

   these contactors.



   Radio Shack offers both sizes of diode:



http://aeroelectric.com/Pictures/Misc/RS_Diodes.jpg



   Since a prohibition against Radio Shack parts has

   been suggested, I'll share an observation that there

   were times in the history of many suppliers of consumer/

   experimenter parts where their offerings included

   industrial surplus parts of unknown but not necessarily

   evil pedigree. This includes a now premier supplier

   of goods (Digikey) who started out as a mail

   order supplier of industrial surplus that advertised

   in ham radio and experimenter electronics magazines.



   RS still handles experimenter's assortments of components

   that are reminiscent of "grab bags" offered in years

   gone by . . .



http://tinyurl.com/5jhbu6



http://tinyurl.com/42jn9v



   . . . but these days, when you are responsible for

   managing inventory in thousands of stores, millions

   of catalogs, and a really big website, you don't

   spend time scrounging the back alleys of industrial

   trash cans looking for "floor sweepings".



   These components are so cheap that it simply doesn't

   pay to spend the time to salvage and then inventory

   less than factory-fresh components.



   The times they are a changing.



   As a final note, this thread is not intended to

   discourage anyone from using more sophisticated

   transient control techniques if that process rings

   their chimes. Information provided here is offered

   as a prophylactic against decision making based

   on poorly interpreted data, marketing hype, or sage

   advice from those who would disseminate but will not

   or cannot also teach.



     Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Thu May 22, 2008 10:11 am Post subject: Re: Coil Suppression Techniques

 	  Quote: 	
		  Eric 

This seems to be a well studied subject and after studying your results the method of parallelling a relay or contactor with an opposite direction diode seems to be the quick and dirty but still quite adequate method for the homebuilder. Now a very practical question: Is a 0.1 dollar 1N4001...4004 or similar diode strong enough to handle the collapsing energy of any relay or contactor used in a homebuilt ? 

best regards 

Max 	




The coil's collapsing magnetic field when the contactor is de-energized induces a high current that travels in the same direction as the original holding current, but is of much greater magnitude. This is why the relay contacts chatter and arc on opening, can re-close (and even weld closed). This is bad for everything electrical, especially contacts. 



The bidirectional zeners are very cheap, and well worth it. The kit I sell will do your whole airplane, or go to Digikey if you want to save a few bucks and buy a dozen P6KE18CA. 



The question you imply, "Would it do for the homebuilder?"....My answer is NO, Bob's is YES. Take your pick.



But Tyco, Potter and Brumfield, Kilovac, Gigavac, Zettler, 



Here's what Gigavac says: COIL SUPRESSION



"....coil suppression techniques such as single diode, resistor capacitor combination, resistor, or varistor noticeably slow down the release time of the relay and can effect the life of the relay or the use of the relay in the application. In carry-only applications, the release time may not be important so these less expensive coil suppression techniques can be used. However, if the release/reset time is important, or if the contacts are to interrupt a load, do not use these techniques and use the recommended zener-zener or diode-zener combination." (underlining mine) Gigavac makes the GX-11 which is a great battery and starter contactor for your airplane, they also make really big high-current, high-voltage stuff. 



Diodes were 1960's technology. There's a better way now.

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

bob(at)bob-white.com
Guest

Posted: Thu May 22, 2008 11:06 am Post subject: Coil Suppression Techniques

On Thu, 22 May 2008 11:11:37 -0700

"Eric M. Jones" <emjones(at)charter.net> wrote:

 	  Quote: 	
		   

 The coil's collapsing magnetic field when the contactor is de-energized induces a high current that travels in the same direction as the original holding current, but is of much greater magnitude. This is why the relay contacts chatter and arc on opening, can re-close (and even weld closed). This is bad for everything electrical, especially contacts. 

 

 The bidirectional zeners are very cheap, and well worth it. The kit I sell will do your whole airplane, or go to Digikey if you want to save a few bucks and buy a dozen P6KE18CA. 

 

 The question you imply, "Would it do for the homebuilder?"....My answer is NO, Bob's is YES. Take your pick.

 

 But Tyco, Potter and Brumfield, Kilovac, Gigavac, Zettler, 

 

 Here's what Gigavac says: COIL SUPRESSION

 

 "....coil suppression techniques such as single diode, resistor capacitor combination, resistor, or varistor noticeably slow down the release time of the relay and can effect the life of the relay or the use of the relay in the application. In carry-only applications, the release time may not be important so these less expensive coil suppression techniques can be used. However, if the release/reset time is important, or if the contacts are to interrupt a load, do not use these techniques and use the recommended zener-zener or diode-zener combination." (underlining mine) Gigavac makes the GX-11 which is a great battery and starter contactor for your airplane, they also make really big high-current, high-voltage stuff. 

 

 Diodes were 1960's technology. There's a better way now.

 

 --------

 Eric M. Jones

 www.PerihelionDesign.com

 113 Brentwood Drive

 Southbridge, MA 01550

 (508) 764-2072

 emjones(at)charter.net

 

 

I think we need to revisit the physics here.  The collapsing field
	


induces a high VOLTAGE which is the opposite polarity of the applied

voltage.  The faster the current decreases, the higher the voltage

spike.  The suppression diode gives the current a place to go allowing

it to decay more slowly, producing a lower voltage, reducing the

arcing on the switch controlling the relay.  The current will never

exceed the original current flowing in the coil.



Use of the suppression diode delays opening the relay because the

current continues to flow for a longer time.  The important point is

that the suppression diode protects the switch controlling the relay.

The effects on the relay contact arcing are secondary.



Bob W.

-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

3.8 Hours Total Time and holding

Cables for your rotary installation - http://roblinstores.com/cables/

longg(at)pjm.com
Guest

Posted: Thu May 22, 2008 11:42 am Post subject: Coil Suppression Techniques

Thanks Bob et al,



This is all very academic and provides excellent reading. Unfortunately

I won't soon be a fellow in the IEEE and I have an airplane to build.



Given the list of manufacturer's provided is there one who makes a

quality relay with built in zener or combo protection for which I won't

need to break out the heath kit?



I want to use the relay to load my essential bus (alternate feed) as in

Z-19. My expect load will be 25 amps. This is in keeping with the max

load for the heat sink'd diode coming from the main bus. 



Glenn

--

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Thu May 22, 2008 11:51 am Post subject: Re: Coil Suppression Techniques

 	  Quote: 	
		  induces a high VOLTAGE which is the opposite polarity of the applied voltage. The faster the current decreases, the higher the voltage 

spike. The suppression diode gives the current a place to go allowing 

it to decay more slowly, producing a lower voltage, reducing the 

arcing on the switch controlling the relay. The current will never 

exceed the original current flowing in the coil. 



Use of the suppression diode delays opening the relay because the 

current continues to flow for a longer time. The important point is 

that the suppression diode protects the switch controlling the relay. 

The effects on the relay contact arcing are secondary. Bob W. 

-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com 

3.8 Hours Total Time and holding 

Cables for your rotary installation - http://roblinstores.com/cables/

	




If it were only so, what a nice world it would be!  Please read:



http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf

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

bob(at)bob-white.com
Guest

Posted: Thu May 22, 2008 12:32 pm Post subject: Coil Suppression Techniques

On Thu, 22 May 2008 12:51:56 -0700

"Eric M. Jones" <emjones(at)charter.net> wrote:



 	  Quote: 	
		   

 

 

 > induces a high VOLTAGE which is the opposite polarity of the applied voltage. The faster the current decreases, the higher the voltage 

 > spike. The suppression diode gives the current a place to go allowing 

 > it to decay more slowly, producing a lower voltage, reducing the 

 > arcing on the switch controlling the relay. The current will never 

 > exceed the original current flowing in the coil. 

 > 

 > Use of the suppression diode delays opening the relay because the 

 > current continues to flow for a longer time. The important point is 

 > that the suppression diode protects the switch controlling the relay. 

 > The effects on the relay contact arcing are secondary. Bob W. 

 > -- 

 > N93BD - Rotary Powered BD-4 - http://www.bob-white.com 

 > 3.8 Hours Total Time and holding 

 > Cables for your rotary installation - http://roblinstores.com/cables/

 > 

 

 

 If it were only so, what a nice world it would be!  Please read:

 

 http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf

 

 --------

 Eric M. Jones

 www.PerihelionDesign.com

 113 Brentwood Drive

 Southbridge, MA 01550

 (508) 764-2072

 emjones(at)charter.net

 


	


OK, I've read it.  What's your point?



Quote: 

"When an electromechanical relay is de-energized rapidly by a mechanical

switch or semiconductor, the collapsing magnetic field produces a

substantial voltage transient in its effort to disperse the stored

energy and oppose the sudden change of current flow."



Note that this high voltage is not connected to the relay contacts and

there is no mention of high currents being generated.  It just doesn't

happen.  The high voltage is impressed across the switch controlling

the relay.  As Ralph (jetboy) recently posted, the A&P left off the

diode resulting in the master switch being destroyed in his C150.



All the problems with relay contact opening are associated with the

slower opening time.



Another quote:

"The optimum switching life (for normally-open contacts) is therefore

obtainew with a totally unsuppressed relay and statements of rated

electrical life are usually based on this premise."



In other words, for best contact life, don't use suppression.  So why

do we use it?  To protect the controlling switch!



Bob W. 



-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

3.8 Hours Total Time and holding

Cables for your rotary installation - http://roblinstores.com/cables/

john_rv10(at)yahoo.com
Guest

Posted: Thu May 22, 2008 2:08 pm Post subject: Coil Suppression Techniques

Bob,



Reading all these comments, two questions come to mind.



1. Have you done the tests below with a zener-zener or a diode-zener

combination to see how they compare with their IN 540x cousins?



2. Have you collected data on the effect on the switch controlling the relay

to compare the four conditions:-

	No protection

	IN540x protection

	Zener-zerner protection

	Diode-zener protection?



The data from question 1 will show us the effects on the relay under the

various conditions being discussed. The data from Q2 will show us the

effects on the switch controlling the relay under those same conditions. It

seems both lots of data are required to determine the best way to protect

the switch and at the same time protect the relay? - or am I missing

something in this debate?



Thanks once again,

John 



--

nuckolls.bob(at)cox.net
Guest

Posted: Thu May 22, 2008 7:36 pm Post subject: Coil Suppression Techniques

At 08:03 AM 5/23/2008 +1000, you wrote:



 	  Quote: 	
		  



Bob,



Reading all these comments, two questions come to mind.



1. Have you done the tests below with a zener-zener or a diode-zener

combination to see how they compare with their IN 540x cousins?


	


   Absolutely. The the worse case voltage spike occurs with zero

   suppression (where all energies are dissipated in the arcing

   across spreading switch contacts). The best scenario for arcing

   control is the plain vanilla diode where arcing is minimal

   because the negative going spike that would normally go -300 volts

   plus is clamped off at ground thus limiting the voltage stress

   across the switch contacts to 14 volts.

 	  Quote: 	
		  2. Have you collected data on the effect on the switch controlling the relay

to compare the four conditions:-

         No protection

         IN540x protection

         Zener-zerner protection

         Diode-zener protection?


	


   Sure. They all work within the limits of their physics.

   Even a plain resistor adds significant value for arc

   reduction . . . even if the least efficient of the lot.

   A capacitor/resistor combination works too. Recall the

   "condenser" across the points on an Kettering ignition

   system distributor? There's a LOT of ways each offering

   trade offs. But to date, I've discovered no simpler, easier

   to implement technique than use of the plain-vanilla

   diode.

 	  Quote: 	
		  The data from question 1 will show us the effects on the relay under the

various conditions being discussed. The data from Q2 will show us the

effects on the switch controlling the relay under those same conditions. It

seems both lots of data are required to determine the best way to protect

the switch and at the same time protect the relay? - or am I missing

something in this debate?


	


   I looked at all these variations and quite frankly they

   performed well. I thought I had the traces on

   my hard drive but I don't find them. If I get time tomorrow,

   I'll go plot them again.



   I've not included them in my offerings of data because

   they are all middle-ground for performance between NO

   suppression and the ULTIMATE suppression of a plain-vanilla

   diode.



   With one exception. At one time I personally embraced low

   voltage MOV's as viable contact preservation devices

   but discarded them after I went to the bench to check

   performance when a reader told me of his own experiments

   where visible arcing was not attenuated by any observable

   amount with MOVs. I was properly embarrassed and dutiful

   in correcting the gaff. It's one of those things that

   happens when understanding based on data sheets does

   not mesh with real world experiences.



   The debate here is not whether the alternative systems

   do their job. The debate is whether there is return

   on investment for acquiring "specialized"

   components sold not upon hard data and repeatable

   experiment. The only support is a kind of "new and

   improved" marketing hype based on poorly extrapolated

   conclusions in a "celebrity" document.  In this case,

   engineers that published under the Tyco trade name.



   It appears Eric is unwilling to be a teacher based on

   his personal understanding of the physics supported

   by a willingness to explain it. I am saddened by

   this. I'll go get the data on the alternative techniques

   tomorrow.



   Bob . . .

john_rv10(at)yahoo.com
Guest

Posted: Fri May 23, 2008 2:09 am Post subject: Coil Suppression Techniques

Bob,



You are a LEGEND.



Thanks again,

John



--

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Fri May 23, 2008 6:23 am Post subject: Re: Coil Suppression Techniques

 	  Quote: 	
		  induces a high VOLTAGE which is the opposite polarity of the applied voltage. The faster the current decreases, the higher the voltage 

spike. The suppression diode gives the current a place to go allowing 

it to decay more slowly, producing a lower voltage, reducing the 

arcing on the switch controlling the relay. The current will never 

exceed the original current flowing in the coil. 



Use of the suppression diode delays opening the relay because the 

current continues to flow for a longer time. The important point is 

that the suppression diode protects the switch controlling the relay. 

The effects on the relay contact arcing are secondary. 



Bob W. 	
 



Actually, Eric is in bed with the cold/flu. And Paul M. keeps calling me up to rant about politics.....Jeeeze.



Let's clear the air regarding coil suppression.



When the relay is closed (and as I said this is targeted mainly at contactor relays), the relay coil has a large amount of energy stored in its inductor. When the relay coil switch is opened, the field collapses and a problematic  high voltage is produced (the voltage depends on the several construction variables). I think we agree to this point.



Now, it might seem that the current produced by the collapsing field is opposite its normal direction. This is not so. The coil current is in the same direction, but the relay coil has changed from being the Load to being the Generator. If you look at the diode direction, you will see that a current in the opposite direction could not flow at all, and the diode would serve no purpose.



I agree with Bob W. that the coil suppressor protects the switch and anything else that provides power to the relay. It also provides other beneficial effect. However, not having a coil suppressor is not an option.



Indeed, the best way to preserve the contactor's own power contacts is to have NO coil suppressor and just rip them apart as fast and as far as possible as possible. But everything else would suffer.



The common (and historic) coil suppression technique that minimized damage to other components like the on/off switch was to shunt the coil with a reversed bias diode (a diode arranged so that it does not normally conduct current). Now when the coil's magnetic field collapses, it induces a

current that is shorted by the diode. The current flows through the coil and stops in a very short time, lowering the voltage by lengthening the field collapse time. 



This longer field collapse time is deleterious to the power contacts, and (by Tyco P&B's information) can actually cause momentary re-closure which manifests as chatter, bouncing, etc. I assume this depends on the load, and the particulars of the contactor.



But this approach raises some red flags:

1) The diode must not be driven over-current. 

2) The delay to opening must be minimized.

3) The suppression device should last longer than the contactor.

4) The ground bounce oscillations should be handled. (for inductive loads)



Now this is where Bob N. and I part company. Bob runs tests and depends on experience, I just read technical papers and study spec sheets. I claim one should dump the diode and use a newer approach. Bob N. claims the diode is good enough. I claim the major purveyors of contactors now use back-to-back zeners or bidirectionals. Bob N. can show lots of relays that use diodes.



There you go.

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

bob(at)bob-white.com
Guest

Posted: Fri May 23, 2008 7:36 am Post subject: Coil Suppression Techniques

On Fri, 23 May 2008 07:23:10 -0700

"Eric M. Jones" <emjones(at)charter.net> wrote:

 	  Quote: 	

 > induces a high VOLTAGE which is the opposite polarity of the applied voltage. The faster the current decreases, the higher the voltage 

 > spike. The suppression diode gives the current a place to go allowing 

 > it to decay more slowly, producing a lower voltage, reducing the 

 > arcing on the switch controlling the relay. The current will never 

 > exceed the original current flowing in the coil. 

 > 

 > Use of the suppression diode delays opening the relay because the 

 > current continues to flow for a longer time. The important point is 

 > that the suppression diode protects the switch controlling the relay. 

 > The effects on the relay contact arcing are secondary. 

 > 

 > Bob W.

 Actually, Eric is in bed with the cold/flu. And Paul M. keeps calling me up to rant about politics.....Jeeeze.

 Let's clear the air regarding coil suppression.

 When the relay is closed (and as I said this is targeted mainly at contactor relays), the relay coil has a large amount of energy stored in its inductor. When the relay coil switch is opened, the field collapses and a problematic  high voltage is produced (the voltage depends on the several construction variables). I think we agree to this point.

 **** Now, it might seem that the current produced by the collapsing field is opposite its normal direction. This is not so. The coil current is in the same direction, but the relay coil has changed from being the Load to being the Generator. If you look at the diode direction, you will see that a current in the opposite direction could not flow at all, and the diode would serve no purpose.

 I agree with Bob W. that the coil suppressor protects the switch and anything else that provides power to the relay. It also provides other beneficial effect. However, not having a coil suppressor is not an option.

 Indeed, the best way to preserve the contactor's own power contacts is to have NO coil suppressor and just rip them apart as fast and as far as possible as possible. But everything else would suffer.

 The common (and historic) coil suppression technique that minimized damage to other components like the on/off switch was to shunt the coil with a reversed bias diode (a diode arranged so that it does not normally conduct current). Now when the coil's magnetic field collapses, it induces a

 current that is shorted by the diode. The current flows through the coil and stops in a very short time, lowering the voltage by lengthening the field collapse time. 

 This longer field collapse time is deleterious to the power contacts, and (by Tyco P&B's information) can actually cause momentary re-closure which manifests as chatter, bouncing, etc. I assume this depends on the load, and the particulars of the contactor.

 But this approach raises some red flags:

 1) The diode must not be driven over-current. 

 2) The delay to opening must be minimized.

 3) The suppression device should last longer than the contactor.

 4) The ground bounce oscillations should be handled. (for inductive loads)

 Now this is where Bob N. and I part company. Bob runs tests and depends on experience, I just read technical papers and study spec sheets. I claim one should dump the diode and use a newer approach. Bob N. claims the diode is good enough. I claim the major purveyors of contactors now use back-to-back zeners or bidirectionals. Bob N. can show lots of relays that use diodes.

 There you go.

 --------

 Eric M. Jones

 www.PerihelionDesign.com

 113 Brentwood Drive

 Southbridge, MA 01550

 (508) 764-2072

 emjones(at)charter.net

OK, that's better.  You have stated the physics correctly.

The only minor point I might make is that the fourth paragraph is not

entirely accurate (marked **** above).  I wouldn't expect the current

produced by the collapsing field to be in the opposite direction.  What

I did say was that the voltage generated by the collapsing field was

of the opposite polarity to the originally applied voltage.  If that

weren't true, the diode wouldn't provide any benefit.

As to the usefulness of a suppression technique more complex than a

diode, it seems to me that Bob N.'s test have shown that the effect on

the contactors used in OBAM aircraft is fairly minor.  It's interesting

that the table shown in the PDF you referenced earlier shows the

relationship between various suppression techniques and drop out time

when the important factor is armature velocity.  Did the engineers that

wrote this paper take any data on armature velocity? They don't say.

Did they test hundreds of relays to failure? The don't say.  A tech

paper needs to be based on experience or it's of little value.  Bob's

data shows a reduction in armature velocity.  That is consistent with

statements in the PDF.  Bob has characterized the reduction and

concluded that it's minor, based on his invaluable experience.

Bob W.

-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

3.8 Hours Total Time and holding

Cables for your rotary installation - http://roblinstores.com/cables/

nuckolls.bob(at)cox.net
Guest

Posted: Fri May 23, 2008 11:45 am Post subject: Coil Suppression Techniques

At 07:23 AM 5/23/2008 -0700, you wrote:

 	  Quote: 	

 > induces a high VOLTAGE which is the opposite polarity of the applied 

 voltage. The faster the current decreases, the higher the voltage

 > spike. The suppression diode gives the current a place to go allowing

 > it to decay more slowly, producing a lower voltage, reducing the

 > arcing on the switch controlling the relay. The current will never

 > exceed the original current flowing in the coil.

 >

 > Use of the suppression diode delays opening the relay because the

 > current continues to flow for a longer time. The important point is

 > that the suppression diode protects the switch controlling the relay.

 > The effects on the relay contact arcing are secondary.

 >

 > Bob W.

Actually, Eric is in bed with the cold/flu. And Paul M. keeps calling me 

up to rant about politics.....Jeeeze.

Let's clear the air regarding coil suppression.

When the relay is closed (and as I said this is targeted mainly at 

contactor relays), the relay coil has a large amount of energy stored in 

its inductor. When the relay coil switch is opened, the field collapses 

and a problematic  high voltage is produced (the voltage depends on the 

several construction variables). I think we agree to this point.

   yes except that "large" is not quantified. We're

   talking a handful of millijoules.

 	  Quote: 	
		  Now, it might seem that the current produced by the collapsing field is 

opposite its normal direction. This is not so. The coil current is in the 

same direction, but the relay coil has changed from being the Load to 

being the Generator. If you look at the diode direction, you will see that 

a current in the opposite direction could not flow at all, and the diode 

would serve no purpose.

I agree with Bob W. that the coil suppressor protects the switch and 

anything else that provides power to the relay. It also provides other 

beneficial effect. However, not having a coil suppressor is not an option.

   ???? Tens of thousands of aircraft have flown out their

   lifetimes (and millions of cars ditto) with no coil

   collapse suppression on a variety of inductive loads.

   Service life of the controlling devices was perhaps

   less than what MIGHT be achieved but running without

   it was and still is AN OPTION in numerous antique

   vehicles including airplanes.

 	  Quote: 	
		  Indeed, the best way to preserve the contactor's own power contacts is to 

have NO coil suppressor and just rip them apart as fast and as far as 

possible as possible. But everything else would suffer.

   Agreed . . . but "everything else" and "suffering"

   are non-identified and non-quantified.

 	  Quote: 	
		  The common (and historic) coil suppression technique that minimized damage 

to other components like the on/off switch was to shunt the coil with a 

reversed bias diode (a diode arranged so that it does not normally conduct 

current). Now when the coil's magnetic field collapses, it induces a

current that is shorted by the diode. The current flows through the coil 

and stops in a very short time, lowering the voltage by lengthening the 

field collapse time.

   agreed

 	  Quote: 	
		  This longer field collapse time is deleterious to the power contacts, and 

(by Tyco P&B's information) can actually cause momentary re-closure which 

manifests as chatter, bouncing, etc. I assume this depends on the load, 

and the particulars of the contactor.

   I've never seen a spreading contact re-reclose. Have

   you some examples of where this has been observed?

   Chatter, bouncing . . . yes ALL contacts in switches,

   relays and contactors do not close and stay closed

   on first contact. I've seen as few as 2 or 3 closures-

   before-stable and as many as dozens. I counted over 25

   bounces in one of traces I recently published  Mercury

   wetted relays and solid-state switches are some exceptions.

 	  Quote: 	
		  But this approach raises some red flags:

1) The diode must not be driven over-current.

   Sure . . . but even the most delicate of silicon

   power rectifiers is not at risk for over-current

   in situations common to our aircraft.

 	  Quote: 	
		  2) The delay to opening must be minimized.

   Why? There ARE the occasional condition where

   TIMING is important. I've wrestled with "relay

   races" in circuits where relay-logic combinations

   were polluted because relay timing was not consistent

   or carefully accommodated.

   In every situation we're considering here, the

   relay or contactor is manually operated by

   crew . . . whether or not the contacts begin

   to move 1 mS or 50 mS after the pilot hits

   the switch is transparent to both the operator

   and to system performance.

 	  Quote: 	
		  3) The suppression device should last longer than the contactor.

   ??? Have you seen a contactor kill its own

   collapse suppressor? I just measured the inductance

   of an S701-1 contactor at 45 mH. LI^2/2 = (.045 x

   .9 x .9)/2 = 18 millijoules.  The 1N4001

   is rated to take 30A (1v drop) for 8.3 mS for

   250 millijoles. My favorite diode 1N5400

   is good for 200A for 8.3 mS for a spike

   catching capability of 1660 millijoules.

   I can't imagine where we'd encounter an energy-

   stress situation for coil suppression.

 	  Quote: 	
		  4) The ground bounce oscillations should be handled. (for inductive loads)

   Not sure how you're using "ground bounce". Inductance

   across a ground system is an issue within devices

   where very fast, tiny signals are handled. The

   ground system in a vehicle is exceedingly variable,

   difficult to control which is why we assume that

   products installed in an airplane should be able to

   withstand a variety of butt-ugly noises including

   "ground bounce". A diode across a relay coil has no

   significance to the generation or suppression of

   ground bounce as I perceive the phrase. If you

   have another perception, I'll need to understand

   it before I can intelligently discuss it.

 	  Quote: 	
		  Now this is where Bob N. and I part company. Bob runs tests and depends on 

experience,

   . . . repeatable experiments are the ingredients

   that go into recipes for success.

 	  Quote: 	
		  I just read technical papers and study spec sheets.

   the printed word is an exceedingly important

   communications tool for teachers with simple-ideas

   to explain. At the same time, anyone can write down

   ideas that are easily mis-interpreted or are just

   plain wrong. One must always be wary of poorly

   explained ideas promoted only with convincing words.

   No teacher is insulted by honorable skepticism.

 	  Quote: 	
		    I claim one should dump the diode and use a newer approach. Bob N. 

 claims the diode is good enough.

   . . . for relays and contactors as WE use them

   in OUR airplanes. I will happily use any alternative

   technique that improves on performance, reliability

   or cost of ownership. Here's an example of arc

   suppression added across the contacts of my products

   control relay:

http://aeroelectric.com/Pictures/Relays/Relay_with_Arc_Suppression_s.jpg

   Here the concern was for the effects of an inductive

   load on ME as the controlling device. I had no

   control over configuration of load so I had to

   cover the bases in the design of my product and

   put suppression on not on my coil but my contacts!

 	  Quote: 	
		    I claim the major purveyors of contactors now use back-to-back zeners or 

 bidirectionals. Bob N. can show lots of relays that use diodes.

   I don't thing we have "parted company" if you're

   agreeing that the diode is . . .

  (1) the ultimate transient suppressor from a energy

  management perspective, convenience and cost

  of ownership and . . .

  (2) causes an extended but insignificant

  drop-out delay for the ways we use relays

  and contactors and . . .

  (3) offers an insignificant influence upon

  service life for applications under discussion.

  I'll go plot the performance characteristics

  of 6-8 different ways to manage stored energy

  in a contactor coil. I'll also discuss the

  fact that selection of arc suppression techniques

  depend on the whole suite of design considerations

  that may go beyond starter/master switch and starter/

  battery contactor service life.

  Bob . . .

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