Re: How to calculate current to melt wire?

"Paul Hovnanian P.E." <paul@xxxxxxxxxxxxx> wrote in message news:483764C3.28C3B102@xxxxxxxxxxxxxxxx
John Larkin wrote:

On Thu, 22 May 2008 20:52:36 -0500, "Mook Johnson" <mook@xxxxxxxx>
wrote:

>
>"Michael" <nleahcim@xxxxxxxxx> wrote in message
>news:12285dfc-2e08-4c96-ac0f-fe0b3c212aa8@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> Hi there - I found an interesting failure on a PCB today. A large part
>> of one of the leads of a TO-220 was simply gone. That pin was carrying
>> a fairly high voltage and got shorted to ground.
>>
>> Does anybody know how much current it would take to blow a TO-220 pin
>> like this? Additionally, is there a rough calculation for how to find
>> out how much current would actually melt a wire in open air?
>>
>> Thanks!
>>
>> -Michael
>
>Its not just the DC current but the instintanious current that can fuse >a
>wirelink. A surprisingly small high voltage capacitance discharged >across a
>link of wire can blow it as well.
>

http://www.teledynerisi.com/products/0products_2fs_page51.asp

This uses a 1 uF cap to fire "non-primary" (ie, damned hard to fire)
explosives like

http://www.teledynerisi.com/products/0products_1ebw_page27.asp

This is a "bridge wire" detonator, just an exploding wire buried in
HE.

One of my customers is planning to use these gadgets to launch 16
starlings, in 4 groups of 4, at a couple hundred millisecond
intervals, into a running jet engine.

John

Reminds me of the story about the 'chicken cannon' used to test
airframes. Bird carcasses were loaded into this pneumatic cannon and
fired at cockpit windows, wing leading edges, etc. to certify them for
bird strike survival.

A British airframe manufacturer was provided detailed plans by a US
company to build and operate said cannon to test their assemblies. Upon
firing their first chicken into a known sound cockpit window, they were
horrified when the window was shattered and surrounding fuselage bent.
They sent detailed test procedures, results, photographs, etc. back to
the American company, seeking advice.

The Americans responded with a one sentence suggestion: "Thaw the
chicken."

--
Paul Hovnanian mailto:Paul@xxxxxxxxxxxxx
------------------------------------------------------------------
I have a truly marvellous sig which this margin is too narrow to
contain.


Mostly urban legend, according to: http://www.snopes.com/science/cannon.asp

Cheers,
John

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