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gregxy
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Direct electrical initiation of secondary
Wikipedia lists the amount of energy to initiate PETN as
10-60mJ, not very much energy. Disposable cameras
typically contain a 100uF capacitor charged to 300V,
the equivalent of 4.5 J much more energy than is needed
if it can be delivered to the PETN.
EBW uses this type of setup, but is difficult to set up since
a very thin bridge wire is needed and the circuit design is
tricky.
Instead I decided to try converting the secondry explosive
into a resistive mass and passing the current directly through
it. If the resistance can be made on the order
of 10 ohms, most of the energy should be transrerred
to the explosive over a period of 1mS.
The electric field within the explosive will also help
sensitize it. In the best setup the explosive would not
be resistive but would enter "dielectric break down" just
below the applied voltage.
Instead of PETN I used ETN, pressed into 1/8" diameter
plastic straws. The length of the chage was about
1/2 inch). For the contacts I used a piece
of 24 guage solid speaker wire (from radio shack).
Strip off about 1/4 inch of insulation and you have two
small copper prongs about 1/16" apart which can be
inserted into the straw and pressed into the explosive.
The current flows through the explosive in this small
1/16" gap.
The power source is a disposable camera as described
above. About 10 feet of the 24 gauge speaker wire
was used to connect the camera to the device.
My first try was with powdered aluminum
to make the ETN conductive. Unfortunately my Al powder
(325mesh from Ebay) does not conduct at all even by itself
when pressed into a tube. I think my Al is mostly
Al2O3, maybe different Al powder would work better.
Next I tried powdered graphite. By itself the graphite
gives a resistance of less than 10 ohms. Mixing about
1 part graphite to 4 of ETN (by volume) the device
had a resistance of 1bout 1k. Energizing with the
camera, the device gave a loud bang. However I do not
think it was a full detonation. My first device disappeared
completely (although it did not damage the board it was
taped to). A second device just blasted a hole in
the straw and left the ETN mostly untouched.
With some refinement I think this method can be made
to work well. A metal tube to provide more confinement
would help. The loading density and amout of graphite
(or aluminum) could also be adjusted. Too little
graphite and the resistance is too high which lengthens
the pulse. Too much graphite lowers the sensitivity
of the ETN.
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The WiZard is In
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Quote: Originally posted by gregxy  |
Instead I decided to try converting the secondry explosive
into a resistive mass and passing the current directly through
it. If the resistance can be made on the order
of 10 ohms, most of the energy should be transrerred
to the explosive over a period of 1mS.
The electric field within the explosive will also help
sensitize it. In the best setup the explosive would not
be resistive but would enter "dielectric break down" just
below the applied voltage. |
----
The Telegraphic Journal and Electrical Review 1874
Change Of Resistance In High Tension Fuzes At The Moment Of Firing.
Abstract of a paper read before the Society of Telegraph Engineers.
By Major Malcolm, B.E.
The Chairman (Mr. LATIMEB CLABK) asked whether the compound in the fuse was in
the form of a powder or of a solid.
Prof. ABEL said that it consisted of a mixture of phosphide of copper and subsulphide
of copper, very specially prepared with a view to permanence, together with chlorate
of potash as the oxidising agent. These formed an explosive mixture, which served
also for conducting the current, and offered a very high resistance. The mixture was
compressed with great pressure. It was found that no great care was required in the
manufacture of fuses sufficiently sensitive to be fired by means of high tension
machines. The high tension fuses which had been more recently made for submarine
purposes were made somewhat more carefully. They were carefully compressed until
some clear resistance was obtained on the galvanometer, but the same care was not
necessary with ordinary high tension fuses.
See Spons' dictionary of engineering, civil, mechanical, military, and With Technical
Terms In French, German, Italian, And Spanish.
Edited By Oliver J Byrne, 1870
p.576
http://tinyurl.com/yfvkwgm
For details.
djh
----
"Problem is, "Thus shall not kill
whales" ranks among the top
commandments in the cannon
of political correctness. So when
the Makan Indian Nation speared
a whale off America's coast on
Monday, the environmentalists
practically choked on their granola
bars. But pity the animal lovers, for
this is no clear cut call. To the
average activist, interfering in
native American cultures is almost
as taboo as chopping down redwood
trees.
Wall Street Journal 20V99
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DougTheMapper
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Check this out:
http://www.youtube.com/watch?v=-EJ8EPgGRdg
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The WiZard is In
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| Quote: Originally posted by gregxy | Wikipedia lists the amount of energy to initiate PETN as
10-60mJ, not very much energy. Disposable cameras
typically contain a 100uF capacitor charged to 300V,
the equivalent of 4.5 J much more energy than is needed
if it can be delivered to the PETN.
|
NB - The energy sited was for static/spark ignition NOT
heat.
For a theory of spark igniiton of primary explosives see :—
Title Heuristic approach to spark initiation of reactive solids
Creator/Author Searcy, J.Q.
Publication Date 1977 Nov 01
OSTI Identifier OSTI ID: 5275524
Report Number(s) SAND-77-1649
DOE Contract Number EY-76-C-04-0789
Resource Type Technical Report
Research Org Sandia Labs., Albuquerque, N.Mex. (USA)
Format Medium: X; Size: Pages: 22
Availability Dep. NTIS, PC A02/MF A01.
A conceptual model for spark initiation of reactive solids is
proposed in this report in order to focus on an understanding of
spark initiation that can lead to the development of
more-desirable components. The proposed model is a direct
extension of a model previously developed by others for initiation
of gas phase reactions, therefore a review of earlier work is
given. In the model, energy coupling from the spark channel into
the reactive solid is modeled by a two wave structure--a shock
wave, followed by a subsonic blast wave. Detonation is initiated in
most cases if the shock wave is energetic, or a deflagration is
initiated if the shock wave is weak and the blast wave is energetic.
The division of energy between the two waves is determined by
the rise-time (or frequency) of the spark during arc development.
The amount of energy delivered into the spark channel for a given
test circuit is a function of the apparent spark resistance during
arc development, and the apparent spark resistance is influenced
by the conductive nature of the reactive solid. No new data are
presented in this report, but suggestions are made for further
work that could directly impact component design.
My copy is a poor blow back from microfiche obtained years
ago from la NTIS.
In'f anyone wanted to make/post a copy they can have (if I can find it) my MF copy.
djh
----
Heraldry—
Eleven varieties of lines, other than
straight lines, which divide the shield,
or edge our cheverons, pales, and the
like, are pictured in the heraldry books
and named as engrailed, embattled,
indented, invected, wavy or undry,
nebuly, dancetty, raguly, pontenté,
dovetailed and urdy.
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gregxy
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60mJ did seem to be very small, although it is
difficult to ignite ETN with a flame, let alone a spark,
maybe this is for dust suspended in air?
The Wikipedia article also give the initiation energy
by laser as 0.5-5.2J, which matches the energy from
the drop test 12cm*2.5Kg*9.8 = 2.9J.
Working from the physics:
The critical diameter for PETN is about 1mm,
The amount of energy to raise 1 cubic mm 1000C
(enough to insure detonation)
if the density is 1.6g/cm^3 and the specific heat
of glass (my best guess at a meterial with parameters
that are "close":
glass = 0.84 J/gK
specific heat * density * volume * dT
0.84*1.6*1e-3*1000 = 1.3J
So all these values are in the "ball park"
Now how fast must the energy be delivered:
The thermal time constant assuming the parameters
for glass and a 1mm box:
Tc = Specific heat * density * 100 * dist ^2 / thermal conductivity
Tc = 0.84 * 1.6 *100 * .1 * .1 /1.05 = 1.28 Sec
So not much heat will be lost by conduction if the
pulse is < 1mS.
To create a shock wave directly however, the energy will
need to be delivered faster than it can escape
by the shock wave. I estimate this time as
the time it takes the shock wave to cross the 1mm
volume
T = 1e-3 M / 8000 M/sec = 0.12uS
Generating a pulse this short with an energy of several J
will be difficult. (A 1uF cap charged to 2000V and < 0.1 ohm
resistance) Most of the energy will be lost on the way.
However I think a sensitive material like ETN can make
the transition to full detonation without being driven
by a full shock wave.
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quicksilver
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Be VERY careful of information in Wkipedia. Think about the elemental concept: an encyclopedia that is written by the public? Very basic concept such
as route of initiation (spark gap) vs the imposition of energy by means of contact was obviously not clearly stated. It might have been someone's cat
at 60 mj. but you know that we're not in new territory here, "Wiki" articles very frequently has this result.
Frankly; I doubt the figures to begin with. What journal article or research was the writer quoting from? (Lord only knows...)
Be really skeptical with "Wiki" information: if the writer does not have decent notes, move on.....
There IS some stuff in past threads here with some very reasonable and well documented electrical energy levels of some materials. The "exploding
bridge-wire" thread may have some factual data also. Wizard will get some solid information (as he's done for some many years now), & you know
it's solid becasue the articles are sited. I don't want simply rag on Wiki but I understand your frustration because it's become so damn popular now
people are taking for granted that it's factual. But logic tells you it couldn't be that low.
Some exists in the PATR. - Same subject. There MIGHT be some Los Alamos materiel on that subject due to it's popularity in commercial & military
applications.
[Edited on 11-10-2010 by quicksilver]
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franklyn
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Explosive molecular compounds being electrical insulators , must be considered
as such in any scheme to cause detonation by direct action of electric current.
Heterogeneous mixtures with conductive materials require a consistency comparable
to pyrotechnic mixtures serving only to increase the contact surface for reaction ,
if ignition is the intent. Whether this can result in high order explosion depends on
the explosive itself if it is a primary. Detonation of secondary explosives requires
instantaneous extreme high energy application to succeed. A conductive admixture
is essentially a resistor which by definition serves to limit current through put.
A possible approach to the problem would be to rely on an initially ignited portion
of only explosive to act as the switch in a circuit discharging a capacitor. You can
test this idea by placing a flame so that it contacts both wire leads. The sound it
makes must be of the same intensity as an explosion or the electric source / capacitor ,
cannot serve the purpose.
http://www.sciencemadness.org/talk/viewthread.php?tid=5064#p...
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gregxy
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Primary -vs- secondary is more of a contimum than a discrete state.
I don't think I could ever initiate TNT or picric acid this way but
ETN is quite sensitive. I'll try my experiment using stronger confinement
and larger capacitor and see if I can get complete initiation of the sample.
Given my 1/8" diameter sample with loose packing, it is not surprising
that it failed to go off completely.
The best setup would be to leave out the graphite and use enough
voltage to breakdown (arc thru) the ETN. The problem is that
the breakdown voltage for ETN is probably 3X higher than for air so it
is difficult to avoid arcing over the top of the sample. Plus I would need
at least 3000V instead of the 300V that the camera puts out.
Once that an insulator breaks downand the breakdown region is flooded
with ionized molecules it changes from a very high resistance to a very low one.
So the main thing that limits the current and lengthens the pulse is the
resistance and inductance of the external circuit.
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dann2
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Hello,
Quick silver wrote:
__________________________________________________
Be VERY careful of information in Wkipedia. Think about the elemental concept: an encyclopedia that is written by the public?
__________________________________________________
I'll second that!!!!!!!!!!!!!!!!!!!!!!!!!!!
Thread here:
http://www.sciencemadness.org/talk/viewthread.php?tid=13133#...
See Coopers book. http://www.megaupload.com/?d=0DIJE7NC
YOU NEED VERY VERY LOW INDUCTANCE CAPACITORS.
If setting off something like Nitro Glycerine (a secondary explosive???) then ordinary capacitors would do (so would a hammer).
If setting off PETN or RDX (the RDX must be of a particular fine crystal structure) then it won't be happening with the UTUBE stuff no matter how big
and impressive sounding/looking the capacitor is. You can have a capacitor that will blow a melon (or your hand) to Kingdom-come but it will not put
off the primary (RDX, PETN)
Dann2
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franklyn
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@ gregxy
Without stating how you arrived at those numbers I can tell it's just a wild guess.
There is no standard description for expressing breakdown values , but volts per mil
( V/mil ) is common . In the MKS system Megavolts per meter ( MV/m )/ 25.4 = ( V/mil )
Values for 2 mils and 50 microns are approximately equal.
1/8 inch ( if this is the intended gap ) is 125 mils. You need to multiply by 125 the
reference value of " dielectric strength " more commonly stated as " breakdown voltage "
for ETN. A reference value may not have been established.
On *.PDF index page 13 ( Figure 7 )
Dielectric Properties of Some Common High Explosives
http://handle.dtic.mil/100.2/AD404454
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD404454&Locatio...
Bibliography here on *.PDF index pages 66 & 67
" Static Dielectric Breakdown Studies of High Explosives " might serve your purpose
The Properties of Condensed Explosives for Electromagnetic Energy Coupling
http://handle.dtic.mil/100.2/ADA177885
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA177885&Locati...
Voltage Breakdown of Potassium Dinitrobenzofuroxan
http://handle.dtic.mil/100.2/AD747364
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD747364&Locatio...
http://www.sciencemadness.org/talk/viewthread.php?tid=1778&a...
Point here is that even if only ignited , the flame is highly conductive. As I mentioned above ,
" A possible approach to the problem would be to rely on an initially ignited portion
of only explosive to act as the switch in a circuit discharging a capacitor."
Experimental Aspects of Coupling Electrical Energy into a Dense Detonation Wave Part 1
http://handle.dtic.mil/100.2/ADA121262
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA121262&Locati...
Bibliography here at the end _
Study of Physical Chemical Transformations in Detonation Wave by Electric Conductivity Method
http://www.intdetsymp.org/detsymp2002/PaperSubmit/FinalManus...
Shock Induced Electro Conductivity in the Insensitive High Explosive TATB
http://www.intdetsymp.org/detsymp2006/downloadmanuscript.asp...
Calculation of Maximum Rate of Dielectric Heating of Explosives
http://handle.dtic.mil/100.2/ADA955144
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA955144&Locati...
I had made a brief mention about this here _
http://www.sciencemadness.org/talk/viewthread.php?tid=5064#p...
See " Sparks In Air " here
http://en.wikipedia.org/wiki/High_voltage
Some dielectric strength values charted here _
http://www.rfcafe.com/references/electrical/dielectric-const...
Physical Properties of Plastics
http://www.machinist-materials.com/comparison_table_for_plas...
Dielectric Strength of Insulating Materials
http://psyhosting.info/Ionium/Rhodium/pdf/chemical-data/diel...
Attachment: Dielectric Strength of Insulating Materials -CRC Handbook of Chemistry & Physics .pdf (876kB)
This file has been downloaded 56851 times
Related threads
http://www.sciencemadness.org/talk/viewthread.php?tid=5064
http://www.sciencemadness.org/talk/viewthread.php?tid=13719
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franklyn
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@ dann2
Available here => Pure Unobtainium
Some people believe that if you swim right after you eat a meal , you will cramp and drown.
So naturally they won't dare do so , and so the legend continues.
You will find when measuring a capacitor it will exhibit practically the same " Inductance "
as a conductor of equivalent length !
See => http://www.ivorcatt.com/2603.htm
( Self explanatory , particularly the text in red)
Next here _ http://sound.westhost.com/articles/capacitors.htm
Scroll down to 4.0 - Parasitic Inductance in Bypass Applications
and read from Figure 14 up to 4.1 - Next scroll past that and read 5.0 - ESL and ESR
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gregxy
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Thanks for all the helpful references!
Looking at Cooper's book, the description for the ebw fire set
is:
1uF, 2000-4000V, 50-100mOhm.
This is only 2 to 8 J of energy, about the same as the
disposable camera and certainly not enough to explode
a mellon!
The disposable camera has an electrolytic which probably
has ~1 ohm series resistance, about 10X too high but
still cabable of delivering 300A with short leads, which
is enough to fire a commercial EBW device,
(based on the descriptions in Coopers book)
Lead resistance is important, 20gauge speaker wire
has 20mOhm/foot, so with 100 feet you have 2ohms
and it becomes the dominant resistive factor.
Note digikey has 1uF 2000V caps with 5mOhm ESR
( part # 338-1182-ND) for $22.50, perfect for this
application.
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dann2
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Hello Grexy,
I will go back to my original shout! and say no more.
"You need very low inductance capacators"
The capacitors that you mention will NOT make RDX(correct crystal size required for reliable detonation) or PETN explode when wired up to an exploding
bridge wire.
Thats my understanding.
No amount of references or explanations from Franklin will change my understanding.
There was a large debate regarding the very rapid (rapid, photoflash Caps arentoo 'slow') discharge needed to do the job (explode RDX(correct crystal
size) or PETN).
If you get things working (making RDX or PETN explode) with the photoflash capacitor (please) come back here and report it.
Cheers,
Dann2
[Edited on 18-10-2010 by dann2]
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dann2
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Hello Folks,
I INTEND TO GET SOME!!!    (low
inductance caps)
You claim that the (small inevidable) inductance in the capacitor is not relevant?
See your post in this thread regarding A-bomb stuff, (5-7-2006)
http://www.sciencemadness.org/talk/viewthread.php?tid=5075
You state "Low inductance capacitors are also required"
and then a link to low inductance caps.
Bit of inconsistency in your argument me thinks, huh.
There is a (rather verbose at times) thread here where exploding wires are discussed:
http://www.sciencemadness.org/talk/viewthread.php?tid=12414
Custom Electronics has developed a line of standardized, low inductance capacitors for use in EFI and EBW applications.
If you Google "low inductance capacitors design ebw" some useful looking links come up.
Attached (suppressed at the time if you examine the filed date and the published date) is a patent for an 'EBW' detonator what contained no wire, just
a gap containing secondary explosive for the spark to jump accross.
Since you are using ETN (not PETN etc as I wrongly thought) the requirements of the capacitor are not so stringent since you are getting closer to
using an actual primary (as it were). Perhaps the photo flash will do the job.
Electrolytic anything will not do the job on ETN (IMO) but I could of course be wrong.
Can any good soul here come up a pspice file for examing a circuit for this type of sererio. Very high current spike 100A per micro sec), short time
intervals (micro seconds) going into a low resistence............
Dann2
Attachment: US3955505.pdf (188kB)
This file has been downloaded 514 times
[Edited on 19-10-2010 by dann2]
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Contrabasso
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With all the electric methods of firing nonel shock tube the big problem is dampness letting the HV spike run away and the actual life of the tip of
the electrodes. Usually the electrodes are made into a HV connector with some mouldings to place the nonel in the right place, but as the electrodes
wear then reliability suffers.
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dann2
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Hello,
If anyone wants to get into home brewing their own very low inductance capacitors (very fast discharge) then the community that are into Dye Lasers
may be of some use.
They use a very fast acting flash tube (contains air at low pressure, not Xenon) which needs a very fast discharging capacitor to drive it.
Link here:
http://192.197.62.35/staff/mcsele/lasers/LasersFLP.htm
Quote from page:
+_______________________________________
The flashlamp is a simple device filled with air at low pressure. A vacuum of no lower than 20 torr is needed which may be generated from an old
fridge compressor run in reverse.
The tricky part to this laser is the capacitor which stores energy to be discharged through the lamp. To make this laser work a capacitor of low
internal inductance must be used. Ordinary electrolytic capacitors will not work. Consider this screen capture of an oscilloscope trace below which
shows the current and voltage characteristics of a typical photoflash discharge through a xenon lamp. In this case the capacitor was rated at 350uF
and was connected directly to the lamp with no external inductance inserted into the circuit (However be aware that photoflash caps have a
relatively large internal inductance designed so that the impedance of the L/C circuit matches that of the lamp).
Some researchers have used extreme measures such as coaxial capacitors [2] with the flashlmp housed in the center of the capacitor disc. The
parameters of a suitable flashlamp design are covered in reference [3].
The rise time of the discharge is about 100uS and the length of the light pulse about 1.1mS. The intrinsic inductance of electrolytic capacitors will
not allow the fast discharge times required for this type of laser. Many solid-state lasers (such as the YAG, described on another page on this site)
can use a relatively slow discharge such as this but not flashlamp-pumped dye lasers. The best bet here is to either make a capacitor of foil and
plastic sheets or obtain a suitable low-inductance type. The capacitor required (as per the Amateur Scientist design) is rated at about 15 uF at 3000
Volts. Instead of a single capacitor one may use several smaller oil-filled capacitors (of about 4 uF each) in parallel. These are the type used for
high-voltage power supplies such as those used for kilowatt-plus radio transmitters.
_____________________________________________________
A Google of "low inductance capacitor for air flashtube" brings up some relevant reading.
Dann2
12AX7's original "Piffle (to photoflashes)" hold's good when trying to detonate PETN .
ETN? that's an interesting avenue.
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gregxy
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I'll do some more experiments when I get more time,
(I'm moving now so everything is in disarray).
Next time I'm going to place the ETN in an Al tube
to give better confinement and a more rigid mechanical
setup.
The analysis in Coopers book uses a lossless transmission
line model which is going to be invalid in this case. Here
both the source and the load have lower impedance (and
resistance) than the line, so the line resistance and
inductance may be the dominant factors.
I agree the 1ohm ESR in my electrolytic cap may cause problems and that caps with low resistance and inductance
would be best, but it is easiest to start with what is at hand.
[Edited on 20-10-2010 by gregxy]
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franklyn
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@ gregxy
A useful similation applet
http://www.coilgun.info/mark2/rlcsim.htm
<><><><><><><><><><><><><><><><><><><&g
t;<><><><><><><><><>
@ dann2
It is not the contradiction you imply. Reducing circuit inductance minimizes
switching jitter that delays firing until later than the exact intended moment.
32 separate charges of an implosion assembly all initiated within the same few
millionths of a second requires precise timing. An accurate switch such as a
Krytron is additionally needed to realize such timing.
Discussed in the second paragraph here _
http://www.sciencemadness.org/talk/viewthread.php?tid=12414#...
| Quote: Originally posted by dann2 | Quoted excerpts stated on that site :
http://192.197.62.35/staff/mcsele/lasers/LasersFLP.htm
" photoflash caps have a relatively large internal inductance designed "
" The intrinsic inductance of electrolytic capacitors will not allow the fast discharge times "
|
Strobe / photoflash lamps are only similar in operation to EBW's destructive
power levels which do not need controls to fire only once and turn off by
themselves forever. I don't know what power supply dye lasers require but
the references cited are 35 plus years old and very archaic for what is
presently manufactured. Capacitors whether photoflash or other do not have
inductance purposely " designed " in them , that statement indicates the
author misunderstood and is mis-stating something he read somewhere
( perhaps a cited reference ? ).
Describing a capacitor as " fast discharging " is meaningless without description
of circuit operation , like claiming a high performance car is the one that empty's
the gas tank soonest. It's evident that he is attributing to ESL
( Equivalent Series Inductance ) the characteristics produced by the ESR
( Equivalent Series Resistance ) of the electrolytics.
While perhaps knowledgeable of the needs for the laser , the gentleman is
entirely unknowledgeable about how to achieve this. " The rise time of the
discharge is about 100uS and the length of the light pulse about 1.1mS
This is far too long for a dye laser which usually requires rise times on the
order of microseconds and pulse lengths under 100uS."
" The most difficult part of building this laser was finding a capacitor which
must store over 100 J and discharge extremely quickly "
Alright , in other words he wants a short pulse.
Fair enough , I have no issue with this. An electrical engineer would address
the first need for a fast rise time by placing a metalized plastic film capacitor
of 1 or 2 uF of equal voltage in parallel with the electrolytic , which having
a very low ESR will actually discharge first providing the required fast rise.
The short duration cited requires some means of cutting off the discharge
at the end of an elapsed interval. See *.PDF index page 5 _ here _
http://www.lightingassociates.org/i/u/2127806/f/tech_sheets/...
More references below under Flashlamps and control circuits
Wave shaping at this power level requires utilizing power semiconductors
such as IGCT ( Insulated Gate Commutated Thyristor )
http://books.google.com/books?id=0_D6gfUHjcEC&pg=PA231
IGBT ( Insulated Gate Bipolar Transistor ) GTO ( Gate Turn Off Thyristor )
or ETO ( Emitter Turn Off Thyristor ) in an electronic control circuit.
http://books.google.com/books?id=0_D6gfUHjcEC&pg=PA236
Understandably the author wishes to avoid such hassle and utilize something
simpler utilizing little more than a capacitor providing the required pulse.
While this is in the realm of feasible ( cheap strobe lights function with a
simple relaxation oscillator ) the engineering to build a matched set of flashlamp
and capacitor in the specific operating range is practically in the category of
unobtainium.
IGBT GTO
http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT Kharagpur/Power Electronics/PDF/L-1(SSG)(PE) ((EE)NPTEL).pdf
Flashlamps and control circuits
http://www.htds.fr/doc/optronique/sourcesLumineuses/LampesFl...
http://sales.hamamatsu.com/assets/applications/ETD/Xe-F_TLSX...
http://members.misty.com/don/donflash.html
http://members.misty.com/don/xeguide.html
Unless indifferently manufactured , form factor and construction determine
characteristics of a capacitor. High voltage caps made by Vishay-Spraque , Cornell
Dubilier , Aerovox , and Duracap-Mallory are longish cylinders used in blasting machines
for bridge wires. An improved design is squat like a hockey puck. Updated links _
http://www.sbelectronics.com/power-ring-products
http://www.sbelectronics.com/wp-content/uploads/2009/11/PPC2...
This manufacturer assures 2 Joules per cubic centimeter , if so this may well
eclipse the aluminum electroyitic.
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dann2
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Hello,
The 'bottle neck' for getting the charge out of the capacitor in EBW applications (for PETN anyways) is the capacitor inductance. You can make the ESR
very low but the inductance will be the bottle neck that must be made low enough for the thing to work.
You need a very low inductance capacitor. Thats really all I am saying.
I presume you aggree with that as opposed to saying that the inductance of the capacitor is not really an issue?
You of course need the rest of the circuit (lines, switches etc ) up to the task.
Photoflashe Caps. will not work for PETN no matter how fancy the rest of the circuit is designed. The (homemade) caps for the Air photoflash tube are
a completely different beast than photoflashes for Xenon flash tubes (they have much lower inductance).
The discharge into Xenon flashes MUST be 'relatively' slow or the light output will NOT suit the purpose of the flash in the first place (to
illuminate the scene for a photograph).
Of course Grexy is using ETN (more sensitive) so photoflashes may work. I don't know.
It's surly a piece of piss to make a low inductance capacitor. (easy for me to say, as I will not be doing it). The end product may not be a pretty
sight and not of minimum size and weight but who cares. Just a series of flat plates and flat insulation (no 'rolled up' designs wanted!)
For PETN EBW Capacitors we will have to agree that:
"It's the inductance stupid"
I am really only echoing what 12AX7 stated in that other thread and you (Franklyn) argued and argued and argued and supplied link after link after
link to 'show' that the inductance of the capacitor did not matter. It does.
ETN is an interesting avenue and photflashes may be OK.
Dann2
[Edited on 21-10-2010 by dann2]
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Contrabasso
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Considering that every "Nonel" or Shock tube adaptor for either the Scorpion or the shrike firing machine is simple cheap and hand held, perhaps
people are complicating matters a trifle!
The Scorpion uses a internal circuit that feeds a mechanical adaptor built into a 1/4 jack plug!
Someone search Blasters supply co for the details please.
http://www.blasterstool.com/blastingnonelinitiators.aspx
http://www.blasterstool.com/combo-nonelandelectric.aspx
http://www.blasterstool.com/hr1hr2l-sbsstartertip.aspx
these adaptors wear out and must be about 50c a fire which makes the shotgun primer operated initiators simple and viable.
These both initiate the HMX in the core of shocktube reliably while the electrode tips are good but they soon wear out in real use.
[Edited on 21-10-2010 by Contrabasso]
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dann2
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Fasinating the way those tubes work. What are they coated with on the inside.
http://en.wikipedia.org/wiki/Nonel
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Contrabasso
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Apparently it's a HMX/Aluminium powder mixture at about 6g per kilometre. In the UK it's considered not explosive for storage and transport but
possession could attract the wrong kind of attention unless you have a good reason (and probably COER for HE and dets anyway) as most uses for nonel
are HE based so if you have nonel they want to know what and where and what the good reason for possession is.
If you think you are going to extract the HE I really doubt there is an economical method considering the light loading of powder
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dann2
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Hello Folks,
Having kicked the subject around for some time I have come to the conclusion that I was talking a load of codswollop (that's very accurate and
reliable information if anyone out there never hear of the word :p )
Just about any old capacitor will do so long as it can withstand a good voltage, say above 500V (the higher the better).
@Franklin
I said:
"For PETN EBW Capacitors we will have to agree that:
"It's the inductance stupid"
I am really only echoing what 12AX7 stated in that other thread and you (Franklyn) argued and argued and argued and supplied link after link after
link to 'show' that the inductance of the capacitor did not matter. It does."
You obviously did not supply ENOUGH links :p !!!!!!!!!
<b>Anyhow, I hereby retract anything I have said in the past about needing very low inductance capacitors for this job.</b>
If you are trying to make a system with the smallest possible weight/size (ie. no cables, minimal voltage on cap. etc etc etc) then capacitor
inductance will be a factor that has to be considered.
Most systems with cables are dominated by the inductance in the cables, capacitor inductance is a very small part of the total inductance of the
system.
Will post some stuff that I have been going through.
Only a very small amount of the actual charge in the firing capacitor gets to blow up the wire. Most of the charge stayes in the capacitor or just
flows as the explosion takes place into the great unknowns of the plasma. Tucker_1 (first link above) states that 98% of the Voltage is still on the
capacitor when the bridge wire explodes!
You need special 'high surface area' PETN at a density of approx. 0.88.
Perhaps thats the problem if anyone cannot get them to work.
There is an essenital read by T. J. Tucker here:
http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=AA6F4E1...
There is also another good read here:
http://www.osti.gov/bridge/purl.cover.jsp?purl=/4229184-1Ibm...
In the second document the voltage accros the exploding brige wire gets up to 10KV at 0.162 micro seconds!!
See the printout at the bottom of the document. Is this the 'freewheeling' effect of the inductance in the circuit? The capacitor is only charged to
1KV when the system is triggered.
I cobbled together the attached diagram to try and 'see' (for myself anyways) what is going on with these devices. May be useful.
Cheers,
(bear with me) Dann2
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dann2
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Double post
Waveforms from post above going out to longer times. This will never actually get to happen as the whole system has long since blown apart.
(as stated by others in threads around)
[Edited on 11-3-2011 by dann2]
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Bert
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Mood: " I think we are all going to die. I think that love is an illusion. We are flawed, my darling".
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The small nonel units don't have any output cabling to speak of, the firing electrodes are right on the box. This simplifies things- If you want a
system that can fire a remote detonator you're going to have to deal with the firing line inductance.
Nonel with shock wave in to flame output transducers is used in some display fireworks situations. Like city displays fired on building tops with
radio transmitters in the vicinity, for instance.
Rapopart’s Rules for critical commentary:
1. Attempt to re-express your target’s position so clearly, vividly and fairly that your target says: “Thanks, I wish I’d thought of putting it
that way.”
2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
Anatol Rapoport was a Russian-born American mathematical psychologist (1911-2007).
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