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Master contactor catch diode failure

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jdubner

Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR

Posted: Tue Jun 27, 2017 10:56 am Post subject: Master contactor catch diode failure

What would be the root cause of this charred diode and wiring?



   https://i.imgur.com/e3FcBgf.jpg

   https://i.imgur.com/Sl9foF6.jpg



This is in a friend's RV-9A and the diode was wired (properly) across the master 

contactor's coil.  The wire runs to the master switch (split-rocker type) where 

a ground is applied.  Both the contactor and the diode were supplied by Van's 

Aircraft.



http://vansaircraft.com/cgi-bin/store.cgi?ident=1498576754-172-723&browse=electrical&product=master-sw

http://vansaircraft.com/cgi-bin/store.cgi?ident=1498576754-172-723&browse=electrical&product=diodes



This incident happened the instant the master power was turned on.  Could the 

diode have failed in a shorted condition, vaporizing itself and the wire when 

the switch applied a ground?



After replacing the diode and wiring, operation seems normal.



-- 

Joe

_________________
Independence, OR

Bob McC

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

Posted: Tue Jun 27, 2017 11:53 am Post subject: Master contactor catch diode failure

The most obvious answer is that the original diode was installed backwards. Maybe the supplied "packaged" assembly from Vans was incorrectly assembled under the heat shrink causing full battery voltage and hence current to forward bias the diode leading to its action as a fuse. The new assemblies shown in your photos leave no possible clue as to the direction the encapsulated diode is oriented. The external red band is fine and dandy, but if the diode under the shrink was accidentally reversed there is no way to know without "testing". I would suggest your "test" proved conclusively it was incorrect.   

Bob McC   [quote]    

--------

_________________
Bob McC
Falco #908
(just starting)

jdubner

Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR

Posted: Tue Jun 27, 2017 1:16 pm Post subject: Re: Master contactor catch diode failure

 	  Bob McC wrote: 	
		  The most obvious answer is that the original diode was installed backwards. 	


That was my initial thought too but the aircraft had 29 hours TTSN with that configuration.



The RV-9A owner told me this incident happened on the first master switch actuation after battery replacement due to a totally discharged battery.  There was a battery charger involved but the owner assured me it was always connected properly.  And the master contactor actuated, at least momentarily, because the Dynon EFIS turned on (and continued to run on its internal battery).

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 28, 2017 3:04 am Post subject: Master contactor catch diode failure

At 02:52 PM 6/27/2017, you wrote:



  	  Quote: 	
		  The most obvious answer is that the original diode was installed backwards. Maybe the supplied "packaged" assembly from Vans was incorrectly assembled under the heat shrink causing full battery voltage and hence current to forward bias the diode leading to its action as a fuse. The new assemblies shown in your photos leave no possible clue as to the direction the encapsulated diode is oriented. The external red band is fine and dandy, but if the diode under the shrink was accidentally reversed there is no way to know without "testing". I would suggest your "test" proved conclusively it was incorrect. 	


   Agreed . . . with one other possibility . . . 

   I have encountered plastic diodes that

   were incorrectly marked. Band on the

   wrong end. It's rare but I think I've

   seen it a couple of times. Further,

   they were a one-of event, not a 'batch'

   problem.



   I'm not sure this is possible but it's

   certainly low probability given modern

   manufacturing and grading techniques

   for diodes. But these days, there are

   diodes and then there are DIODES. Without

   knowing the critter's pedigree, we'll never

   know.



   In any case, replacing the diode is the

   permanent fix.



 

 

   Bob . . .

billhuntersemail(at)gmail
Guest

Posted: Wed Jun 28, 2017 6:21 am Post subject: Master contactor catch diode failure

How does one (me) check a diode when it is installed on the contactor? 

I assume that you want to have the master switch off and use DC resistance. Does it matter what polarity to connect the leads?  

Thanks, 

Bill Hunter   At 02:52 PM 6/27/2017, you wrote:



  	  Quote: 	
		  The most obvious answer is that the original diode was installed backwards. Maybe the supplied "packaged" assembly from Vans was incorrectly assembled under the heat shrink causing full battery voltage and hence current to forward bias the diode leading to its action as a fuse. The new assemblies shown in your photos leave no possible clue as to the direction the encapsulated diode is oriented. The external red band is fine and dandy, but if the diode under the shrink was accidentally reversed there is no way to know without "testing". I would suggest your "test" proved conclusively it was incorrect. 	


 Â  Agreed . . . with one other possibility . . . 

 Â  I have encountered plastic diodes that

 Â  were incorrectly marked. Band on the

 Â  wrong end. It's rare but I think I've

 Â  seen it a couple of times. Further,

 Â  they were a one-of event, not a 'batch'

 Â  problem.



 Â  I'm not sure this is possible but it's

 Â  certainly low probability given modern

 Â  manufacturing and grading techniques

 Â  for diodes. But these days, there are

 Â  diodes and then there are DIODES. Without

 Â  knowing the critter's pedigree, we'll never

 Â  know.



 Â  In any case, replacing the diode is the

 Â  permanent fix.



 

 

 Â  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 28, 2017 11:40 am Post subject: Master contactor catch diode failure

At 09:20 AM 6/28/2017, you wrote:



  	  Quote: 	
		  How does one (me) check a diode when it is installed on the contactor? 	


  Just unhook one end (the small terminal) and use

  your ohmmeter function to test continuity through

  the diode. One configuration will show SOME value

  of resistance, reversing the leads will show

  infinite resistance.



 

  	  Quote: 	
		  I assume that you want to have the master switch off and use DC resistance. Does it matter what polarity to connect the leads? 	


  You test BOTH ways . . . looking for basically

  NO conduction one way (off scale high resistance)

  and some value of resistance the other way . . .

  the exact value unimportant as it will vary

  from one ohmmeter to another.



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 28, 2017 11:47 am Post subject: Master contactor catch diode failure

At 04:16 PM 6/27/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jdubner" <jdubner(at)yahoo.com>



 

 Bob McC wrote:

 > The most obvious answer is that the original diode was installed backwards.



 That was my initial thought too but the aircraft had 29 hours TTSN with that configuration.



 The RV-9A owner told me this incident happened on the first master switch actuation after battery replacement due to a totally discharged battery. 	


   THIS IS NOT GOOD . . . If the diode WAS good

   and fried after battery replacement, then the

   battery was hooked up BACKWARDS . . . This

   fries the catch diode and potentially, lots

   of other stuff.



   Years ago, I used to recommend adding a fuse

   in series with the battery master contactor

   wire that runs off to the master switch.

   When paired with a catch diode on the contactor

   the diode shorts out reversed voltage to the

   contactor preventing closure while the fuse

   blows preventing wire damage . . . and perhaps

   damage to the diode as well.



   But it sounds like this event went on long

   enough to open the diode, close the contactor

   and to put battery energy onto the ship's bus . . .

   

   



 

 

   Bob . . .

billhuntersemail(at)gmail
Guest

Posted: Wed Jun 28, 2017 11:50 am Post subject: Master contactor catch diode failure

Thanks,  

Also, how warm do contactors get when they are energized? 

I have two contactors mounted in a well underneath the backseat of my airplane.Â  This well is about three inches deep 20 inches wide and 12 inches long and it's completely sealed with no cooling air and since it is constructed of foam core fiberglass It is Well insulated and therefore none of the heat can get conducted out of the airplane.  

I felt them and the contactors do get warm but the question is how warm can they get and do they need any cooling air? Inflight only one contactor will be energized however on the ground during maintenance I will have both contactors energized. 

THANKS AGAIN FOR YOUR HELP  

Bill Hunter  On Jun 28, 2017 12:44 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote: 	  Quote: 	
		    At 09:20 AM 6/28/2017, you wrote:



  	  Quote: 	
		  How does one (me) check a diode when it is installed on the contactor? 	


 Â Just unhook one end (the small terminal) and use

 Â your ohmmeter function to test continuity through

 Â the diode. One configuration will show SOME value

 Â of resistance, reversing the leads will show

 Â infinite resistance.



 

  	  Quote: 	
		  I assume that you want to have the master switch off and use DC resistance. Does it matter what polarity to connect the leads? 	


 Â You test BOTH ways . . . looking for basically

 Â NO conduction one way (off scale high resistance)

 Â and some value of resistance the other way . . .

 Â the exact value unimportant as it will vary

 Â from one ohmmeter to another.



 

 Â  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 28, 2017 12:11 pm Post subject: Master contactor catch diode failure

At 02:50 PM 6/28/2017, you wrote:



  	  Quote: 	
		  Thanks, 



 Also, how warm do contactors get when they are energized? 	


   Too hot to touch but not hot enough to 'sizzle spit'



  http://tinyurl.com/mpcgp3t



  http://tinyurl.com/k6bwdqo



 

  	  Quote: 	
		  I have two contactors mounted in a well underneath the backseat of my airplane.Â  This well is about three inches deep 20 inches wide and 12 inches long and it's completely sealed with no cooling air and since it is constructed of foam core fiberglass It is Well insulated and therefore none of the heat can get conducted out of the airplane. 



 I felt them and the contactors do get warm but the question is how warm can they get and do they need any cooling air? Inflight only one contactor will be energized however on the ground during maintenance I will have both contactors energized.



 THANKS AGAIN FOR YOUR HELP 	


   Materials used in construction of these devices

   is rated for operating at temperatures well in

   excess of 100C . . . but of course, hotter than

   you would want to touch.



 

 

   Bob . . .

billhuntersemail(at)gmail
Guest

Posted: Wed Jun 28, 2017 12:49 pm Post subject: Master contactor catch diode failure

Thanks Bob!!!  

The next time I have them humming for two hours at room temperature I will lick them to see if spit sizzles.  

Thanks again,  

Bill Hunter  On Jun 28, 2017 1:15 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote: 	  Quote: 	
		    At 02:50 PM 6/28/2017, you wrote:



  	  Quote: 	
		  Thanks, 



 Also, how warm do contactors get when they are energized? 	


 Â  Too hot to touch but not hot enough to 'sizzle spit'



  http://tinyurl.com/mpcgp3t



  http://tinyurl.com/k6bwdqo



 

  	  Quote: 	
		  I have two contactors mounted in a well underneath the backseat of my airplane.Ã‚Â  This well is about three inches deep 20 inches wide and 12 inches long and it's completely sealed with no cooling air and since it is constructed of foam core fiberglass It is Well insulated and therefore none of the heat can get conducted out of the airplane. 



 I felt them and the contactors do get warm but the question is how warm can they get and do they need any cooling air? Inflight only one contactor will be energized however on the ground during maintenance I will have both contactors energized.



 THANKS AGAIN FOR YOUR HELP 	


 Â  Materials used in construction of these devices

 Â  is rated for operating at temperatures well in

 Â  excess of 100C . . . but of course, hotter than

 Â  you would want to touch.



 

 

 Â  Bob . . .

ceengland7(at)gmail.com
Guest

Posted: Wed Jun 28, 2017 1:56 pm Post subject: Master contactor catch diode failure

Do be aware that the temp it will get a       *lot* hotter in your sealed up insulated box than it will sitting       on your kitchen counter. I wouldn't do what you're talking about,       because I wouldn't want to melt my aircraft in that area.       Component life might be a secondary issue, in this case (pardon       the pun).

       

       On 6/28/2017 3:48 PM, William Hunter wrote:

     

      	  Quote: 	
		         

Thanks Bob!!!        

The next time I have them humming for two hours at         room temperature I will lick them to see if spit sizzles.        

Thanks again,        

Bill Hunter        On Jun 28, 2017 1:15 PM, "Robert L.         Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>         wrote:          	  Quote: 	
		                          At 02:50 PM 6/28/2017, you wrote:

               

                	  Quote: 	
		  Thanks,                 

                 

                 Also, how warm do contactors get when they are                 energized? 	
             

             Â  Too hot to touch but not hot enough to 'sizzle spit'

             

                            http://tinyurl.com/mpcgp3t

             

                            http://tinyurl.com/k6bwdqo

               

               

                           	  Quote: 	
		  I have two                 contactors mounted in a well underneath the backseat of                 my                 airplane.Ã‚Â  This well is about three inches deep 20                 inches wide and                 12 inches long and it's completely sealed with no                 cooling air and since                 it is constructed of foam core fiberglass It is Well                 insulated and                 therefore none of the heat can get conducted out of the                 airplane.                 

                 

                 I felt them and the contactors do get warm but the                 question is how warm                 can they get and do they need any cooling air? Inflight                 only one                 contactor will be energized however on the ground during                 maintenance I                 will have both contactors energized.

                 

                 THANKS AGAIN FOR YOUR HELP 	
             

             Â  Materials used in construction of these devices

             Â  is rated for operating at temperatures well in

             Â  excess of 100C . . . but of course, hotter than

             Â  you would want to touch.

             

             

             

               Â  Bob . . .                        

         	
       

     	
     

     	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Wed Jun 28, 2017 4:32 pm Post subject: Re: Master contactor catch diode failure

I agree with Charlie.  The heat given off by a fire (caused by hot contactors) will be a whole lot hotter than the heat given off by contactors exposed to circulating air.  What is the purpose of an insulated box?

  At what temperature will the diode start conducting in the reverse direction?  Nobody knows how hot it will get inside of the box because it depends on several factors: size of box, how well it is sealed, insulating properties of the box, ambient air temperature, wattage of the contactor, length of time contactor is energized.

_________________
Joe Gores

billhuntersemail(at)gmail
Guest

Posted: Wed Jun 28, 2017 5:33 pm Post subject: Master contactor catch diode failure

I appreciate everyone's opinions and suggestions!!! 

The airplane is a Velocity (pusher) so it is constructed of fiberglass foam sandwich panels and I was trying to move as much of the heavy electrical cables aft closer to the engine so I placed these components under the rear bench seat. The rear seat "pedestal" (support structure) is a fiberglass box integral with the fuselage also constructed with fiberglass foam sandwich panels that equate to an "enclosed box".  

I thought that this was an "elegant solution" to utilize this empty space as an electrical equipment box however I didn't really think about the BTU output of these contactors.  

I guess I could cut some vent openings into the pedestal and that would introduce some cabin ambient air into the box (four feet away from the heater floor vents) however this would not be forced air ventilation but still much better than an enclosed, sealed, and very insulated box.  

Thanks,  

Bill Hunter  On Jun 28, 2017 5:37 PM, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 I agree with Charlie.Â  The heat given off by a fire (caused by hot contactors) will be a whole lot hotter than the heat given off by contactors exposed to circulating air.Â  What is the purpose of an insulated box?

 Â  At what temperature will the diode start conducting in the reverse direction?Â  Nobody knows how hot it will get inside of the box because it depends on several factors: size of box, how well it is sealed, insulating properties of the box, ambient air temperature, wattage of the contactor, length of time contactor is energized.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=470566#470566

 

 

 

 

 

 

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donvansanten(at)gmail.com
Guest

Posted: Wed Jun 28, 2017 6:44 pm Post subject: Master contactor catch diode failure

I would put the battery contactor as close to the battery as possible and the starter contactor on thd engine side of the firewall. This is how the RV 10 is done, battery in rear battery contactor inches away and starter contactor on the front of the firewall. I realize that your are building a pusher but this will work fine. This also keeps the heay generating contactors out in the open and seperated from each other.



On Jun 28, 2017 18:37, "William Hunter" <billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote: 	  Quote: 	
		  

I appreciate everyone's opinions and suggestions!!! 

The airplane is a Velocity (pusher) so it is constructed of fiberglass foam sandwich panels and I was trying to move as much of the heavy electrical cables aft closer to the engine so I placed these components under the rear bench seat. The rear seat "pedestal" (support structure) is a fiberglass box integral with the fuselage also constructed with fiberglass foam sandwich panels that equate to an "enclosed box".  

I thought that this was an "elegant solution" to utilize this empty space as an electrical equipment box however I didn't really think about the BTU output of these contactors.  

I guess I could cut some vent openings into the pedestal and that would introduce some cabin ambient air into the box (four feet away from the heater floor vents) however this would not be forced air ventilation but still much better than an enclosed, sealed, and very insulated box.  

Thanks,  

Bill Hunter  On Jun 28, 2017 5:37 PM, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 I agree with Charlie.Â  The heat given off by a fire (caused by hot contactors) will be a whole lot hotter than the heat given off by contactors exposed to circulating air.Â  What is the purpose of an insulated box?

 Â  At what temperature will the diode start conducting in the reverse direction?Â  Nobody knows how hot it will get inside of the box because it depends on several factors: size of box, how well it is sealed, insulating properties of the box, ambient air temperature, wattage of the contactor, length of time contactor is energized.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=470566#470566

 

 

 

 

 

 

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 eferrer" target="_blank">http://forums.matronics.com

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 29, 2017 3:47 am Post subject: Master contactor catch diode failure

At 09:36 PM 6/28/2017, you wrote:

  	  Quote: 	
		  I would put the battery contactor as close to the battery as possible and the starter contactor on thd engine side of the firewall. This is how the RV 10 is done, battery in rear battery contactor inches away and starter contactor on the front of the firewall. I realize that your are building a pusher but this will work fine. This also keeps the heay generating contactors out in the open and seperated from each other. 	


   I like that . . .



   Starter contactors on firewall become a tie-point

   for the altenrator's b-lead to tie into the fat-wire

   system. Battery contactors are generally only

   inches away from Battery(+).



 

   Bob . . .

Robert Reed

Joined: 22 Oct 2009
Posts: 331
Location: Dallas/Ft.Worth

Posted: Thu Jun 29, 2017 5:58 am Post subject: Master contactor catch diode failure

I am using your Z-14 dual alternator and dual battery design with the batteries under the pilot and copilot seats, battery contactor within 6 inches of battery.  The crossover contactor and starter contactor on firewall with 2 inch crossover connection to starter contactor.  Alternator B-leads connect to crossover input and starter input lead.  Overvoltage connections just before connection to contactors.  Any issues you can foresee?





Bob Reed



       From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Thursday, June 29, 2017 6:48 AM

 Subject: Re: Re: Master contactor catch diode failure

  

 

  At 09:36 PM 6/28/2017, you wrote:

  	  Quote: 	
		  I would put the battery contactor as close to the battery as possible and the starter contactor on thd engine side of the firewall. This is how the RV 10 is done, battery in rear battery contactor inches away and starter contactor on the front of the firewall. I realize that your are building a pusher but this will work fine. This also keeps the heay generating contactors out in the open and seperated from each other. 	


   I like that . . .



   Starter contactors on firewall become a tie-point

   for the altenrator's b-lead to tie into the fat-wire

   system. Battery contactors are generally only

   inches away from Battery(+).



     Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 29, 2017 12:18 pm Post subject: Master contactor catch diode failure

At 08:56 AM 6/29/2017, you wrote:

  	  Quote: 	
		  I am using your Z-14 dual alternator and dual battery design with the batteries under the pilot and copilot seats, battery contactor within 6 inches of battery. 	


   Okay



  	  Quote: 	
		   The crossover contactor and starter contactor on firewall with 2 inch crossover connection to starter contactor. 	


   Okay



  	  Quote: 	
		  Alternator B-leads connect to crossover input and starter input lead. 	


   Okay



 

  	  Quote: 	
		   Overvoltage connections just before connection to contactors.  Any issues you can foresee? 	




   Not sure what this means . . . what hardware are

   you using for regulators . . . do they

   have ov protection built in?



 

 

   Bob . . .

Robert Reed

Joined: 22 Oct 2009
Posts: 331
Location: Dallas/Ft.Worth

Posted: Thu Jun 29, 2017 12:49 pm Post subject: Master contactor catch diode failure

Bob,

"Always double check before hitting send...a motto I clearly forgot."





What I meant to say was I placed the ANL Current Limiters Before the connections from the B-Lead to the Starter Lead and Crossover Lead. (50 amp primary, 30 amp secondary)

I am using the B & C Regulators (LR3C-14) on both circuits.



       From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Thursday, June 29, 2017 3:19 PM

 Subject: Re: Re: Master contactor catch diode failure

  

 

  At 08:56 AM 6/29/2017, you wrote:

  	  Quote: 	
		  I am using your Z-14 dual alternator and dual battery design with the batteries under the pilot and copilot seats, battery contactor within 6 inches of battery. 	


   Okay



  	  Quote: 	
		   The crossover contactor and starter contactor on firewall with 2 inch crossover connection to starter contactor. 	


   Okay



  	  Quote: 	
		  Alternator B-leads connect to crossover input and starter input lead. 	


   Okay



 

  	  Quote: 	
		   Overvoltage connections just before connection to contactors.  Any issues you can foresee? 	




   Not sure what this means . . . what hardware are

   you using for regulators . . . do they

   have ov protection built in?



 

     Bob . . .

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