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Fusible Links

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Nov 28, 2007 10:48 am Post subject: Fusible Links

There are occasional questions about fusible links on the Aeroelectric.



Fusible links were common long ago, but lately engineers have eschewed them. I have seen a demo online regarding what happens when a fusible link blows--the wire inside vaporizes and the plasma arc blows through  the covering. This is not good in a bundle, or when fuel or flammables or conductive surfaces may be present. 



Usually instructions for making fusible links do include layers of  non-flammable silicone and fiber over-covering. The link covering may not be capable of enclosing the rupture arc, especially since the rupture arc may occur (probably will occur) near the ends.



So for those who have puzzled about the fusible link issue, here's my advice: Use standard fuses/breakers or whatever instead. That's my plan.



"When trouble arises and things look bad,

there is always one individual who perceives

a solution and is willing to take command.

Very often, that individual is crazy.

     --Dave Barry"

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

nuckolls.bob(at)cox.net
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Posted: Thu Nov 29, 2007 7:50 am Post subject: Fusible Links

At 10:48 AM 11/28/2007 -0800, you wrote:



 	  Quote: 	
		  



There are occasional questions about fusible links on the Aeroelectric.



Fusible links were common long ago, but lately engineers have eschewed 

them. I have seen a demo online regarding what happens when a fusible link 

blows--the wire inside vaporizes and the plasma arc blows through  the 

covering. This is not good in a bundle, or when fuel or flammables or 

conductive surfaces may be present.



Usually instructions for making fusible links do include layers 

of  non-flammable silicone and fiber over-covering. The link covering may 

not be capable of enclosing the rupture arc, especially since the rupture 

arc may occur (probably will occur) near the ends.



So for those who have puzzled about the fusible link issue, here's my 

advice: Use standard fuses/breakers or whatever instead. That's my plan.


	


   Fusible links have never been suggested as a general

   replacement for other protective devices. The instances

   where the fusible links are shown in the Z-figures

   are limited to low risk applications where the I(squared)T

   robustness of an ANL style current limiter is attractive.



   To stir breakers/fuses into the discussions about

   fusible links is to brush aside the reason the

   fusible links were suggested. They are STILL my

   best recommendation for extending the main bus

   fuse block out to the alternator field breaker

   in systems where crowbar OV protection is present

   (obviously not necessary when one chooses to use

   breakers on the main bus) AND as a b-lead protection

   for the smaller PM alternators.



   They're also okay for long service life protection

   of instrument leads off of an ammeter shunt. I think

   I've made this clear in numerous postings where a

   readers were asking about expanding on usage of

   fusible links.



   I have published instructions and offered sources

   for materials to properly craft fusible links in the

   smaller sizes appropriate to our needs.



http://www.aeroelectric.com/articles/fuselink/fuselink.html



   Also check out the writings at:



http://www.aeroelectric.com/articles/anl/anlvsjjs.html



http://www.aeroelectric.com/Reference_Docs/Misc_PDF/9021704F.pdf



   I've conducted numerous tests on the effectiveness

   of the fusible links for use as suggested. Concerns

   for "arcing" and "rupture" and "plasma blowing holes"

   are interesting and perhaps exciting to contemplate

   but the reality is quite pedestrian.



   Bob . . .

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