Matronics Email Lists Forum Index Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
 
 Get Email Distribution Too!Get Email Distribution Too!    FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

is this a MOV and should I remove or replace it?

 
Post new topic   Reply to topic    Matronics Email Lists Forum Index -> AeroElectric-List
View previous topic :: View next topic  
Author Message
Ceengland



Joined: 11 Oct 2020
Posts: 378
Location: MS

PostPosted: Fri Jan 13, 2023 11:08 am    Post subject: is this a MOV and should I remove or replace it? Reply with quote

On 1/13/2023 12:41 PM, Robert L. Nuckolls, III wrote:

Quote:
At 04:12 PM 1/9/2023, you wrote:
Quote:
Hello Bob,

I tried researching this on your forums and did not find an answer.  I
also tried vans airforce and stumped them there for the most part.
Also stumped the eaa techs in my hangar.

My RV4 has an electrical diagram that apparently you created, in 1993,
for Ed Beach.  It shows a MOV in parallel with the master switch and
the starter switch.

See the attached images.  I find this potted block with 4 wires going
into it,  2 wires from the master and 2 from the starter switch.  The
block looks a little burned on top, though I am not sure what that
actually is.  I only just found the block as I am doing some minor
panel upgrades.

Are you familiar with a MOV in this form factor?  Is it an actual MOV
or diode, etc?  Any advice on what to do with it (everything works
fine as is).

Thanks,
Dave K

PS here is a link to my question on VAF
https://vansairforce.net/community/showthread.php?t=213172

   An excellent question my friend . . . thank you
   for bringing it up. Indulge me for a few moments
   of study in the history of MOVs (Metal Oxide
   Resistor) in DC power systems . . . but your
   welcome to skip to the short answer further
   down.

   In the earliest days of my participation in
   OBAM (Owner Built and Maintained) aircraft,
   I was some 20 years into a professional history
   with certified aviation. My jobs to that point
   were mostly focused on black box ('appliance' in
   FAA-speak) design, development and certification.
   This included a good working relationship with
   the systems folks but I had little need or
   interest in studying the physics of their
   activities.

   "Spike" was a popular but ill-defined concept
   that circulated amongst individuals with
   experience that ranged from the shade-tree
   mechanics to IR&D scientists. While design
   and qualification protocols already cited
   technical publications like DO160 and Mil-STD-704
   (quantified definitions of potential
   threats), there was a pervasive, popular concern
   for "spikes" being generated somewhere within
   the system that pose functional threats to
   "sensitive/vulnerable" components in the
   system.

   In my first tour of duty at Cessna (Circa
   1965), I recall the first studies of stored
   energy on inductive devices (like battery
   contactors and large relays).

   One of our electro-wizzards was
   a PHd physicist named Gordon Wood who bought
   a Hewlett-Packard, peak-reading voltmeter.
   This instrument captured and quantified
   battery contactor "spikes" on the order
   of hundreds of volts.

   WOW! . . . we sure wouldn't want
   that kind of threat wandering aimlessly
   about the electron highways in our
   airplanes!

   Contemporary avionics were just starting
   to receive their first transistors . . . too
   many of which were failing for reasons
   we didn't exactly understand . . . but
   for sure . . . the easy reaction was to
   hunt down and throttle those 'killer' spikes.

   That was the era when silicon junction
   diodes were becoming commonplace. There
   was some prior art in this arena wherein
   we find selenium rectifiers tied across
   contactor coils for the purpose of suppressing
   their stored energy during coil release.
 
   Cessna created a number of diode assemblies
   designed to make them assembly-line-friendly.
   The rest of the small aircraft community
   was similarly invested in 'taming
   spikes'.

   I was not involved in any design decisions
   or problem investigations. However, as a
   tech writer, I needed to be plugged into
   what was going on as it was my job to
   explain it to field technicians. The
   down-side of this relationship was that
   I would gain no more understanding of the
   fundamentals than was discovered and shared
   by my compadres across the isle.

   So . . . from about 1965 to 1985 or so,
   I had little cause to ponder the necessity
   for putting diodes across the contactor
   coils in airplanes.

   Then about 1988 the seeds were planted
   for publication of The AeroElectric
   Connection when I found myself gaining
   a toehold in Owner Built and Maintained
   aircraft. By then, the value of adding
   contactor coil energy suppression was
   'old news' but as a tech writer by 'birth'
   I pondered ways to introduce the practice
   and physics to my newest readership.

   Diodes were a natural solution to spike
   suppression but I'd become aware of a
   new 'spike warrior' on the block. Unlike
   the polarity sensitive diode, the Metal
   Oxide Varistor (MOV) didn't care about
   polarity of the offending energy. Cool!
   one could purchase low voltage versions
   of the MOV (18V or so) and those should
   tame the wily spikes and you couldn't
   wire them up wrong . . . they didn't care.

   So when I included them in first generation
   Z-figures, I thought I was doing a good
   thing . . . yeah . . . well . . .

   In many years since, we've had numerous
   spike suppression discussions here on the
   List and I've published some articles on
   the website. My own understanding of
   MOV functionality expanded in during
   my tours of duty in general aviation and
   bench studies in support of the 'Connection.

   To my dismay, I discovered that the MOV
   does not have a sharp conduction threshold
   such that an 18V MOV could allow a contactor
   energy spike to rise to as much as 50
   volts . . . while useful as a prophylactic
   against damaging spikes propagating through
   a SYSTEM, they would not serve to quench
   formation of the arc that strikes between
   the opening contacts of a SWITCH that controls
   the contactor! A diode, on the other hand,
   suppressed the spike to ZERO.

   MOVs were subsequently replaced with diodes
   in the Z-figures and in our discussions
   here on the List. Hence, THE SHORT ANSWER:
 
   I would replace any MOV's found on your ship's
   contactors with silicon rectifiers . . . current
   and voltage ratings not critical. You're more
   concerned with mechanical robustness and
   user-friendly installation. I recommend 3A
   devices of any voltage rating. 1N5400 through
   1N5406 are suitable. These are cheap and
   rugged.

   Here's a good way to buy them:

   https://tinyurl.com/2p82ml35

   . . . a fist full of devices for $10 delivered
   to your door.

   Some of you old timers may recall discussions
   on the List where I explored spike management
   philosophies and physics with a couple of readers
   about 20 years ago.

   One such thread included some bench test
   demonstrations captured and illustrated
   in this document.

http://aeroelectric.com/Reference_Docs/Contactors-Relays/60507_1_Spike_Suppression_Studies.pdf

   I'm still trying to find the narrative that
   goes with these scope traces. Suffice it to
   say that I kinda stubbed my toe with the MOV
   experience. The lowly silicon rectifier has
   proven to be the elegant solution for contactor
   spike suppression . . . in 1965, 2002 and
   today. 

  Bob . . .

  Un impeachable logic: George Carlin asked, "If black boxes
  survive crashes, why don't they make the whole airplane
  out of that stuff?"
If you have an Amazon Prime account, here's an even better deal"
https://www.amazon.com/LORESO-1N5404-Diode-Pack-Rectifier/dp/B09HWVQXZW/ref=sr_1_9?gclid=Cj0KCQiAn4SeBhCwARIsANeF9DKfCSDEtZlsLO3MmZfBuZoUzhmHrTyG3Ac9lV_Yw6D_dSphy-qx9bsaAnmvEALw_wcB&hvadid=616991091821&hvdev=c&hvlocphy=9013892&hvnetw=g&hvqmt=e&hvrand=18087607899855413765&hvtargid=kwd-27897519547&hydadcr=24663_13611861&keywords=1n5404%2Bdiode&qid=1673636601&sr=8-9&th=1
Virus-free.www.avast.com[url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]


- The Matronics AeroElectric-List Email Forum -
 

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

_________________
Charlie
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Matronics Email Lists Forum Index -> AeroElectric-List All times are GMT - 8 Hours
Page 1 of 1

 
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


Powered by phpBB © 2001, 2005 phpBB Group