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FUSIBLE LINKS & CURRENT LIMITERS

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Apr 22, 2022 8:49 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

Hi Bob,



 Currently studying fusible links.  It's straight forward circuit protection but I'm confused about an example in your book.  The third paragraph of Note 4 on page Z7 references fusible links in the shunts on figure Z14, and the fusible lengths are clearly shown in the diagram.  However, in the 5th paragraph you reference the fusible-link in the AUX alternator B-lead feed but I don't see any such link in the diagram.  I do see what appears to be a fuse labeled MAX30 at the aux batt contactor.  Is this the fusible link?



   While the MAX30 is fusible circuit protection it is not, by definition,

   a fusible link. It is a member of a robust MAX family of plastic

   fuses. 



 Note 10 says alternator B-lead protection is best done with current limiters.  Is there any difference between a current limiter and a fusible link?



   Only in their general time-to-function characteristics.

   Fusible links are generally rather slow to operate and

   are intended to stand off effects of a 'hard' (typically

   battery driven) faults. They are quite robust and unlike

   fuses, are not vulnerable to thermal "hammering".



   Yes, a MAX30 fuse is shown in the b-lead of a 20A alternator

   (de-rated by 30% or so). Fusible links are generally

   preferred in this application. Stone simple, low parts

   count, spliced into the feeder with reliability exceeded

   only by the wire itself. But de-rated fuse serves the

   same design goal even tho clumsy to implement

   compared to the fusible link.



 And finally, help me understand the fusible link between the buss and master switch in Z11, but there is no fusible link in this circuit in Z12.



   Are you talking about the link protecting the feeder

   out to the alternator field circuit breaker? There's

   a link in that feeder for both drawings.



 A lot to absorb, trying to understand as best I can.  Thanks again.



   No problem.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Apr 23, 2022 11:41 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

At 06:25 PM 4/22/2022, you wrote:

  	  Quote: 	
		  Thanks Bob.  Appreciate the explanations.  I suspected the fusible link is used due to it being

 more resilient or as you say slower to operate. 	


  In general, fuses and circuit breakers are more sensitive to

  moderate overload and will operate in seconds to tens of seconds.



  Current limiters (ANL, ANN, MAN, etc) look like fuses but thermally

  tailored to withstand high transient loads. They are generally used

  to protect feeders to downstream protection like fuses and/or

  circuit breakers where you don't want the upstream protection

  to operate because of a hard fault on one of the individually

  protected, downstream feeders. Fusible links fall into that

  same category of protection.



 

  	  Quote: 	
		  And you answered my follow up question before I could ask it.

 If a slow operating device is preferred, why not use a slow blow fuse? 	


  That's essentially what a current limiter is . . . it's

  a fuse with a 2 to 3 times overhead for operating current

  and a much longer thermal time constant.



  	  Quote: 	
		  Fusible link easy to install compared to the clumsy fuse.  Duly noted. 	


  Yup. You can now buy fusible link wire in the automotive

  parts stores . . . ordinary copper wire insulated with

  Hypalon or similar insulation resistant to toxic destruction

  due to melting wire within. Neat stuff. 



  https://tinyurl.com/yy7xy8wd



  	  Quote: 	
		  But in diagram Z12 I still don't see a fusible link in the circuit that feeds the alternator field.  What am I missing?  I see a 5A field breaker at the main power buss.  From there a 20AWG wire feeds tab 5 of the master switch.  From tab 4 of the master switch a 20AWG wire feeds pin 6 of the B and C LR-3 controller.  A 20AWG wire from pin 4 of the controller feeds the alternator field.  I don't see a fusible link in this circuit as I do in diagram Z11.  The system in Z11 uses fuses and Z12 used CB's.  Does this make any difference? 	


  Here are the relevant excerpts from Z-11 and Z-12. There's

  a fusible link upstream of alternator field breakers

  in both diagrams. Z-11 is an older drawing that suggests

  a '4AWG-smaller', DIY fusible link while Z-12

  suggests commercial-off-the-shelf, fusible link wire.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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johnbright

Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA

Posted: Sat Apr 23, 2022 2:59 pm Post subject: Re: FUSIBLE LINKS & CURRENT LIMITERS

 	  nuckolls.bob(at)aeroelect wrote: 	
		  Hi Bob,



 ... help me understand the fusible link between the buss and master switch in Z11, but there is no fusible link in this circuit in Z12. 	




The latest Z12 rev N shows a fuse link for the feeder from main bus to field CB. The previous rev M which is in the latest AeroElectric Connection book rev 12B shows the field CB directly on the bus. Fuseblock or busbar and CBs (acres of breakers)... it's a culture war and Bob in in the fuseblock camp. I'm guessing the older Z12 reflects a production aircraft.



Find the latest Z templates in the Adobe folder at http://www.aeroelectric.com/PPS/

[/quote]

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

rv8iator

Joined: 11 Apr 2006
Posts: 145
Location: Newberg, OR

Posted: Sat Apr 23, 2022 5:23 pm Post subject: FUSIBLE LINKS & CURRENT LIMITERS

 	  Quote: 	
		  Bob et al...



	




Is thereÂ  a min/max length for fusibleÂ links?Â  Â WithÂ either fusibleÂ link wire or

fabricated using the method described in "The Connection"?

...chrisÂ 

 	  Quote: 	
		   	  Quote: 	
		  	


 Â In general, fuses and circuit breakers are more sensitive to

 Â moderate overload and will operate in seconds to tens of seconds

 Â That's essentially what a current limiter is . . . it's

 Â a fuse with a 2 to 3 times overhead for operating current

 Â and a much longer thermal time constant.



  	  Quote: 	
		  Fusible link easy to install compared to the clumsy fuse.Â  Duly noted. 	


 Â Here are the relevant excerpts from Z-11 and Z-12. There's

 Â a fusible link upstream of alternator field breakers

 Â in both diagrams. Z-11 is an older drawing that suggests

 Â a '4AWG-smaller', DIY fusible link while Z-12

 Â suggests commercial-off-the-shelf, fusible link wire.



 

 

 Â  Bob . . .



 Â  Un impeachable logic: George Carlin asked, "If black boxes

 Â  survive crashes, why don't they make the whole airplane

 Â  out of that stuff?"

_________________
C. Stone (RV8iator)

johnbright

Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA

Posted: Sat Apr 23, 2022 6:47 pm Post subject: Re: FUSIBLE LINKS & CURRENT LIMITERS

 	  rv8iator wrote: 	
		   Is there a min/max length for fusibleÂ links?Â WithÂ either fusibleÂ link wire or fabricated using the method described in "The Connection"?



...chrisÂ  	




Note 4 says 4 to 6" and  http://www.aeroelectric.com/articles/fuselink/fuselink.html says 5 to 6".

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Apr 24, 2022 7:31 pm Post subject: FUSIBLE LINKS & CURRENT LIMITERS

At 09:47 PM 4/23/2022, you wrote:

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



 

 rv8iator wrote:

 >  Is there a min/max length for fusibleÂ links?Â WithÂ either fusibleÂ link wire or fabricated using the method described in "The Connection"?

 > 

 > ...chrisÂ 



 

 Note 4 says 4 to 6" and   http://www.aeroelectric.com/articles/fuselink/fuselink.html says 5 to 6".

 	


    There is no 'maximum' length . . . i.e. no limits

    other than what you'd put on a wire of that same

    gage.  The minimum is not terribly critical but

    we do want to exploit the tendency for a fusing

    conductor to open up pretty close to the center.



    The time it takes is somewhat related to length.

    Current generated heat along the conductor's length

    propagates outward and longitudinally with the

    center being most remote from heat-sinking

    qualities of the ends. You can take a clue from

    the pre-assembled fusible links found in

    car parts stores. I would judge the assembly

    shown to be on the order of 9" long. I don't

    think I've ever seen one on a car less than

    6".



    I think a longer link may open faster. Somewhere

    around here I've got a test fixture I built up

    to demonstrate and measure fusible link

    performance . . . may dig that up and finish

    the experiment.



    I saw a builder's contactors installation

    wherein he used fusible link wire to make

    a connection between the power posts on two

    contactors . . . no splice to extending

    wire.



 



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 25, 2022 5:10 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

At 08:22 PM 4/23/2022, you wrote:



  	  Quote: 	
		    Bob et al...

  

 Is there a min/max length for fusible links? With either fusible link wire or



 fabricated using the method described in "The Connection"? 	


   The DIY fusible link was suggested about 20 years

   ago when I was looking for a cleaner way to protect

   ammeter shut instrument wires. BePiCesMo guys used

   to favor a dual, glass cartridge fuse holder mounted

   right at the shunt. Pieces of 4AWG smaller wire

   under fiberglass seemed much neater.



   Mind you, fusible links were already widely used

   in the automotive world at this time but the bulk

   wire was not readily obtainable nor had the idea

   germinated in the aviation community for replacing

   current limiters with specialty wire.



   Fusible link wire has an interesting history. Waayy

   back when, the electric locomotive industry was

   looking for an insulation that minimized the

   toxicity of smoke should a faulted wire burn.

   Persons working in closed environments with very

   high current wiring were at risk. Railroad and

   mine locomotives (and I suspect submarines) were

   prime markets for such a material.



   I think it was DuPont that came up with a material

   called "Hypalon" which has now has many competing

   products. The smoke produced was more to the liking

   of the Marlboro Man than the death row executioner.



   We are now favored with a host of suppliers for

   application specific fusible link wire. The

   ability to eliminate the mechanically bulky

   current limiters and certain fuses is attractive;

   much simpler than the original DIY techniques

   offered some years ago.



   Keep in mind that fusible links (beefy and slow)

   are NOT one-for-one replacements for fuses (agile

   and fast). They are attractive alternatives to

   current limiters.

   

   I poked around on Youtube for examples of 

   fusible link replacement and did see one

   example of very short (3" or so) factory

   installed fusible links albeit poorly. The

   Youtube author was replacing links where

   joints had become intermittent due to

   corrosion (!!!!). In our world, fusible link

   installations should offer no greater risk

   of failure than an equivalent hunk of quality

   wire. The reason for having to make that

   video was, in my not so humble opinion,

   unforgivable. Just because the product sails

   under the flag of a respected brand does not

   automatically insure good craftsmanship.



   As an aside, be wary of well meaning youtuber's

   work product. I've gleaned many useful

   insights from the works of DIY video producers.

   I've also observed astounding ignorance of

   the physics for the processes being demonstrated.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Mon Apr 25, 2022 6:07 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

Â 

 	  Quote: 	
		  

 Â Â  I saw a builder's contactors installation

 Â Â  wherein he used fusible link wire to make

 Â Â  a connection between the power posts on two

 Â Â  contactors . . . no splice to extending

 Â Â  wire.



 



 

 Â  Bob . . .



	
Guilty.Â 

The top pair of contactors control the B-leads of two internally regulated alternators; the blue wires are fusible links to protect the red B-lead wires seen leaving the contactors.

Without a long drawn-out explanation, the reason one is on the 'hot' side of the master is that the plane has a fully electricallyÂ dependent engine; I wanted access to an alternator even if the master contactor failed. (Engine bus primary feeder is also fed from the hot side.)

Charlie

Firewall_contactors_(med).jpg

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_________________
Charlie

rv8iator

Joined: 11 Apr 2006
Posts: 145
Location: Newberg, OR

Posted: Mon Apr 25, 2022 6:12 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

Bob et al...Â 



I garner from your explanation that a fusible link of any length will perform as intended. (To open a circuit).

But the longer length will open near the center due to localized thermal characteristics.Â 

Is there a downside to a shorter length other than it may burn through near to or at the connection to

the feeder?Â  Thus we want to avoid this condition?

Just trying to better understandÂ the preferredÂ opening mode.

If the feeder connection is robust then the fusible link will open somewhere along its length

as its resistanceÂ is greater than that of the feeder.Â  Regardless of length.Â Â 

It seems what we strive to avoid is heating and degradation of the feeder wire

and/or connection during the over-current event?

Your expertise, experimentation and sharing of knowledge is very much appreciated !

Chris

Â 

Â 

Â 



 	  Quote: 	
		  

  	  Quote: 	
		    Bob et al...

  

 Is there a min/max length for fusible links? With either fusible link wire or



 fabricated using the method described in "The Connection"? 	


 Â  The DIY fusible link was suggested about 20 years

 Â  ago when I was looking for a cleaner way to protect

 Â  ammeter shut instrument wires. BePiCesMo guys used

 Â  to favor a dual, glass cartridge fuse holder mounted

 Â  right at the shunt. Pieces of 4AWG smaller wire

 Â  under fiberglass seemed much neater.



 Â  Mind you, fusible links were already widely used

 Â  in the automotive world at this time but the bulk

 Â  wire was not readily obtainable nor had the idea

 Â  germinated in the aviation community for replacing

 Â  current limiters with specialty wire.



 Â  Fusible link wire has an interesting history. Waayy

 Â  back when, the electric locomotive industry was

 Â  looking for an insulation that minimized the

 Â  toxicity of smoke should a faulted wire burn.

 Â  Persons working in closed environments with very

 Â  high current wiring were at risk. Railroad and

 Â  mine locomotives (and I suspect submarines) were

 Â  prime markets for such a material.



 Â  I think it was DuPont that came up with a material

 Â  called "Hypalon" which has now has many competing

 Â  products. The smoke produced was more to the liking

 Â  of the Marlboro Man than the death row executioner.



 Â  We are now favored with a host of suppliers for

 Â  application specific fusible link wire. The

 Â  ability to eliminate the mechanically bulky

 Â  current limiters and certain fuses is attractive;

 Â  much simpler than the original DIY techniques

 Â  offered some years ago.



 Â  Keep in mind that fusible links (beefy and slow)

 Â  are NOT one-for-one replacements for fuses (agile

 Â  and fast). They are attractive alternatives to

 Â  current limiters.

 Â  

 Â  I poked around on Youtube for examples of 

 Â  fusible link replacement and did see one

 Â  example of very short (3" or so) factory

 Â  installed fusible links albeit poorly. The

 Â  Youtube author was replacing links where

 Â  joints had become intermittent due to

 Â  corrosion (!!!!). In our world, fusible link

 Â  installations should offer no greater risk

 Â  of failure than an equivalent hunk of quality

 Â  wire. The reason for having to make that

 Â  video was, in my not so humble opinion,

 Â  unforgivable. Just because the product sails

 Â  under the flag of a respected brand does not

 Â  automatically insure good craftsmanship.



 Â  As an aside, be wary of well meaning youtuber's

 Â  work product. I've gleaned many useful

 Â  insights from the works of DIY video producers.

 Â  I've also observed astounding ignorance of

 Â  the physics for the processes being demonstrated.



 

 Â  Bob . . .



 Â  Un impeachable logic: George Carlin asked, "If black boxes

 Â  survive crashes, why don't they make the whole airplane

 Â  out of that stuff?"

_________________
C. Stone (RV8iator)

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 25, 2022 7:02 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

 	  Quote: 	
		  Is there a downside to a shorter length other than it may burn through near to or at the connection to

 the feeder?  Thus we want to avoid this condition?

 Just trying to better understand the preferred opening mode. 	


    I'd like to believe that the manufacturer

    of that automobile with 3" links tested their

    design decision. Intuitively, one must believe

    that the 'short' hunk of 4-AWG-Smaller wire is

    a dominating weak-link that will indeed open

    faster than the protected feeder.  



  	  Quote: 	
		  If the feeder connection is robust then the fusible link will open somewhere along its length

 as its resistance is greater than that of the feeder. Regardless of length. 

 It seems what we strive to avoid is heating and degradation of the feeder wire

 and/or connection during the over-current event? 	


   Agreed.  I've got a couple of 100AH batteries

   on my maintainer bench for a neighbor. One

   of these would offer a really good energy source

   for a fusible link demonstration/experiment. I'll

   poke around and see if I can find all the 'stuff'

   to lash this up.



  	  Quote: 	
		  Your expertise, experimentation and sharing of knowledge is very much appreciated ! 	


   Thank you.



   If one strives to advance the state of the

   art and science, knowledge must be quantified,

   shared, debated, refined and demonstrated. Lacking

   any of these endeavors, the value of that

   knowledge is diminished if not extinguished.

   I've observed comments about the 'experimental'

   nature of our work-product . . . "isn't that

   a dangerous hobby?" they ask.



   To the contrary, the advancement of every

   art is a study in properties of materials,

   management of energy and refinement of

   process . . . experimentation is the very

   essence of that last quality.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

rv8iator

Joined: 11 Apr 2006
Posts: 145
Location: Newberg, OR

Posted: Mon Apr 25, 2022 9:16 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

 	  Quote: 	
		  Looking forward to the result of your efforts in better understanding the properties of these devices

Â 

	
Â ...Live to learn.Â  Learning is a lifelong endeavor.Â  Knowledge is a social construct.Â 

 	  Quote: 	
		  

	
Wisdom is gained by the application of curiosity, judgement and reflection...



Chris

 	  Quote: 	
		  

 Â  To the contrary, the advancement of every

 Â  art is a study in properties of materials,

 Â  management of energy and refinement of

 Â  process . . . experimentation is the very

 Â  essence of that last quality.



 

 Â  Bob . . .



 Â  Un impeachable logic: George Carlin asked, "If black boxes

 Â  survive crashes, why don't they make the whole airplane

 Â  out of that stuff?"

_________________
C. Stone (RV8iator)

fasilpereira

Joined: 17 Jul 2011
Posts: 86
Location: Brazil

Posted: Mon Apr 25, 2022 11:33 am Post subject: Re: FUSIBLE LINKS & CURRENT LIMITERS

Regarding those Fusible Link Wires, is there any source for a 24 AWG version of it? I could only find it on 20AWG and up (or down?  ) gauges.



I was looking insterested in installing it on the shunt sense wires, but I think that using 16 AWG (20AWG minus 4AWG) an overkill...



Thank you,



Fabricio

_________________
Fabricio Pereira
Engineer / Pilot

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 26, 2022 10:22 am Post subject: FUSIBLE LINKS & CURRENT LIMITERS

At 02:33 PM 4/25/2022, you wrote:

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



 Regarding those Fusible Link Wires, is there any source for a 24 AWG version of it? I could only find it on 20AWG and up (or down?  ) gauges.



 I was looking insterested in installing it on the shunt sense wires, but I think that using 16 AWG (20AWG minus 4AWG) an overkill... 	


  Agreed. No commercial fusible link wire smaller than 20 that

  I know of. Make yours out of 22AWG and cover in two layers

  of heat shrink.  I'll test that configuration along with

  the COTS wires . . . but I'm confident the work-around

  will be fine.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

Eric Page

Joined: 15 Feb 2017
Posts: 245

Posted: Tue Apr 26, 2022 12:57 pm Post subject: Re: FUSIBLE LINKS & CURRENT LIMITERS

For DIY fusible link wire, you might want some high temperature silicone impregnated fiberglass sleeve.  It's available in several diameters as small as 3/16" from a U.S. seller...



http://www.ebay.com/itm/194849574612



...or as small as 1mm if you don't mind ordering from China and waiting awhile:



http://www.ebay.com/itm/224016110766



For all eBay results use the search terms, "silicone fiberglass wire (sleeve,tube) -hose" (without quotes).

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