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Catch diode location

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Oct 15, 2010 2:33 pm Post subject: Catch diode location

In the attached, I don't understand the pathway for the inductive spike of the Grnd Pwr contactor to dissipate. I thought that the diode symbol always pointed to positive.



And where does the catch diode go/orient on the Stby Alt Contactor?



Thank you,

John

Z8 w-SB ALT-GPJ conceptual rev b .pdf

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Fri Oct 15, 2010 2:46 pm Post subject: Re: Catch diode location

Or use bidirectional Zeners like you should and don't worry about it.

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

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Fri Oct 15, 2010 3:46 pm Post subject: Catch diode location

John;  

   

In all cases the "spike catcher" diode goes across the coil just as it does and is shown on the battery contactor and with that same orientation. The drawing you've attached has no "spike catcher" on the ground power contactor. If you wish that feature it would have to be added. The diodes currently shown are for polarity protection to prevent energizing the contactor should the connect ground power be reverse polarity, and to allow the light to indicate polarity.   

The direction of the diode symbol depends on what use you are trying to make of the diode. Its orientation to prevent "reverse flow" may be different than if its purpose is to provide an alternate path for induced voltages. You can also use a bidirectional zener as Eric suggests for spike suppression, but these won't work for directing current flow such as in the reverse polarity protection circuit. Different purpose, different characteristics, different functions, different connections. (Sometimes able to be achieved by the same component however)  

   

Bob McC  

   

> -----Original Message-----  

> From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-  

> server(at)matronics.com] On Behalf Of jonlaury  

> Sent: Friday, October 15, 2010 6:34 PM  

> To: aeroelectric-list(at)matronics.com  

> Subject: Catch diode location  

>   

> --> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>  

>   

> In the attached, I don't understand the pathway for the inductive spike of the Grnd  

> Pwr contactor to dissipate. I thought that the diode symbol always pointed to  

> positive.  

>   

> And where does the catch diode go/orient on the Stby Alt Contactor?  

>   

> Thank you,  

> John  

>   

>   

>   

>   

> Read this topic online here:  

>   

> http://forums.matronics.com/viewtopic.php?p=315902#315902  

>   

>   

>   

>   

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> http://forums.matronics.com//files/z8_w_sb_alt_gpj_conceptual_rev_b__838.pdf  

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_________________
Bob McC
Falco #908
(just starting)

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Oct 15, 2010 5:00 pm Post subject: Re: Catch diode location

Eric and Bob McC,

My EFIS maker, Advanced Flight Systems, wants spike suppression on every relay.

OK, so I can just put a bi-directional zener across all the relay/contactor coils in the plane and I'm good for spike catching? Including the Alt 2 relay?



I've also got a small 5vdc coil (40ma) driven by an optical switch (another relay). Does it get a spike catcher too?



So how does one size a bi-di-zener for spike catching?



Thanks,

John

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Fri Oct 15, 2010 7:23 pm Post subject: Catch diode location

John;



Yes, or just use the 1N5400's you've already shown for your battery

contactor on everything. Either will work. The perceived disadvantage to the

plain diode is that it does slow the reaction time of the device slightly,

but this will be undetectable for all practical intents and purposes.

(Advantages, really cheap, available anywhere)

Check Eric's website for explanations of the zeners. (Which he happens to

sell under the name "snapjack". They are also available from the major

electronics suppliers as bi-directional zeners)

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

Any coil carrying a current will generate some level of reverse voltage when

switched off. So technically, yes, your small 5vdc coil will exhibit the

effect. Is it of any significance? Most likely not, especially as many

optical switches have suppression built in. The greatest effects are from

relatively large currents in relatively large inductors. (Like the one amp

of holding current in the multi turn winding of the battery contactor)



Bob McC

[quote] --

_________________
Bob McC
Falco #908
(just starting)

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sat Oct 16, 2010 5:04 am Post subject: Re: Catch diode location

Modern relay and contactor manufacturers recommend using bidirectional Zeners for coil suppression, NOT diodes. 



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 voltageâ€”1000V to 1500V typicallyâ€”is induced in the coil. This current goes the same direction the original current didâ€”so it slows the contact openingâ€”allowing arcing, chatter, bouncing, contact welding and even re-closure.



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



Or buy your own, I recommend P6KE18CA for general purposes. Another advantage is you can't put them in the wrong direction. They are symmetrical.

_________________
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: Sat Oct 16, 2010 6:19 am Post subject: Catch diode location

At 08:04 AM 10/16/2010, you wrote:

 	  Quote: 	
		  



Modern relay and contactor manufacturers recommend using 

bidirectional Zeners for coil suppression, NOT diodes.


	


     . . . an assertion that appears to be based

     upon a paper published by Tyco authors that

     in-expertly speak to issues not relevant

     to the manner in which we use diodes on

     our relays and contactors. Furhter, they

     made mis-interpreted the significance of

     their own data.



     This was examined at length some years

     ago Eric and you offered no evidence

     or analysis contrary to the explanations

     I demonstrated and published. If you have

     some personally developed rationale for

     contradicting what I wrote, please bring

     it forward.



   Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Sat Oct 16, 2010 7:11 am Post subject: Re: Catch diode location

Eric and Bob McC,



Thank you both for spelling it all out for me. I like the bi-di- zener solution because it's idiot proof and perfect for people like me that have just enough electronic knowledge to be dangerous. 

Eric, your schematics of all the different scenarios are priceless. With all the other sorts of subjective decisions involved in building my plane, it's REALLY a luxury to have an experienced person say "Here, do it this way".



Contributions, like yours, to this forum, really make it sing.



John

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sat Oct 16, 2010 7:39 am Post subject: Re: Catch diode location

The application of relay coil suppression with DC relays

www.ciitechnologies.com/appnotes/app_pdfs/13c3311.pdf



Coil Suppression Can Reduce Relay Life

relays.tycoelectronics.com/appnotes/app_pdfs/13c3264.pdf



Coil Suppression

www.leachintl2.com/english/english2/vol6/properties/how7.htm



Coil Suppression Techniques:

www.newark.com/pdfs/techarticles/crydom/May2010_SolidStatements.pdf



You want more?



Using diodes for coil suppression is Soooooooooooo 1900's Bob. Come on board to the next century.

_________________
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: Sat Oct 16, 2010 8:56 am Post subject: Catch diode location

At 10:39 AM 10/16/2010, you wrote:

 	  Quote: 	
		  

Using diodes for coil suppression is Soooooooooooo 1900's Bob. Come 

on board to the next century.


	


    Eric.  Those papers were crafted for exploring

    the tradeoffs for relays designed to operate

    under rated loads for tens to hundreds of

    thousands of cycles. And yes, SOME of the

    studies show a benefit for not clamping the

    recoil spike at near zero volts with a diode and

    instead allowing it to rise to some level determined

    by a zener.



    THIS forum of discussion is not about crafting

    electrical systems for military or space-grade

    vehicles. On average, the GA light aircraft

    flies 50 hours a year. OBAM aircraft as a class

    are probably higher. So let us say after 20

    years, the airplane MIGHT have 3000 hours on

    it. How many THOUSANDS of operations might

    any given relay or contactor see on such a

    vehicle? Certainly not hundreds of thousands

    nor even tens of thousands. How many of our

    relays are loaded such that they switch rated

    loads for every cycle?



    Adding super-suppression to a relay might

    produce a 10-20% improvement in laboratory

    life tests running at rated loads . . . probably

    NO improvement for lightly loaded or dry-circuit

    switching.



    The point is my friend that there is no value

    to be secured for NOT buying coil suppression

    devices at Radio Shack as opposed to the

    "ideal" device ordered in from remote sources

    for more money and time.



    You have taken a few facts and morphed them

    into a level of significance that is simply

    not applicable to the customers you and I

    serve for the airplanes they are building.



    The next century? Hammers have been around for

    thousands of years . . . but that does not mean that

    the task of driving a nail is not well served

    by keeping a few hammers in my toolbox.



    The point of my writing for this audience is

    to tailor a suggestion for adequate performance

    at the least cost and time . . . i.e. the

    elegant solution. The solutions may or may not

    comport with findings produced in a laboratory

    that will never study what we do on the OBAM

    GA aircraft.

   Bob . . .

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