Re: Exploding wire (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 21 Nov 2006 20:07:30 -0800
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>, hvlist <hvlist@xxxxxxxxxx>
Subject: Re: Exploding wire (fwd)

At 07:07 PM 11/21/2006, High Voltage list wrote:
>Original poster: Steven Roys <sroys@xxxxxxxxxx>
>
>
>
>---------- Forwarded message ----------
>Date: Mon, 20 Nov 2006 18:17:48 -0800
>From: Jim Mora <jmora@xxxxxxxxxxx>
>To: 'High Voltage list' <hvlist@xxxxxxxxxx>
>Subject: Exploding wire
>
>Hello All,
>
>
>
>I just bought 1400ft of .008, 32AWG piano wire. My Capacitor charge will be
>14.3uf @ 40KV, I could do up to 50KV but the history of the Geek Mighty Caps
>is unknown. How many feet can I blow of this wire? Surely this would be more
>spectacular then a copper wire. Am I in the right ballpark for gauge? I
>would like to reach 8 feet ~ 2.5 Meters. The caps are rated at near 9KJ at
>full charge.


No problem with your 8 feet.

You want to do a couple quick calculations to see if its inductance 
(about 2.5 uH) or resistance (measure it, or look it up.. but steel 
varies lot) that's going to determine the current.

You can do a RLC circuit calculation (almost certainly, you can 
ignore the R) to figure out how long it will take to reach peak 
current.  To get an explosion, you have to heat the wire to iron's 
boiling point (i.e. vaporize it) before it has a chance to move.  The 
energy to boil it is something you can calculate from the mass  (200 
kJ/kg to melt.. and you need a bit of a margin above that.. your 9kJ 
should be sufficient).

But really, the way to find out is to try it.  Get that bang stick 
out, make sure you're shielded from shrapnel, and poke at it.  You'll 
know if it exploded, as opposed to melted with a bang.

As a comparison, I was able to explode a couple meters of AWG 30 wire 
(copper and aluminum) with 14 uF at 20kV, with a pretty lashed up 
rig: A couple meters of welding cable to one end of the test section, 
another meter or so of wire to the bang stick.

Start at low voltage and bring it up in steps.  You'll rapidly get a 
feel for the various energy/rate phenomena.. You start with fairly 
pedestrian "fuse melting", then go to a "break into glowing segments 
that burn", to "flash", to a distinct "bang".

>
>
>Thanks,
>
>Jim Mora
>
>
>
>The shot from Downunder of an "iron" wire blow was wild! I'll start assembly
>of the discharge apparatus after I get done batting down the hatches as our
>rains approach soon; and, I work mostly outside since my one car garage is
>full!