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From: (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: detonation device
Date: 24 Jan 1997 04:39:34 GMT

In article <5c8100$>, (Harry
H Conover) says:

>Gerald L. Hurst ( wrote:
>: A mechanical blasting machine generates electricity via a simple 
>: magneto or DC generator.  The electricity is preferably accumulated 
>                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
>: in a capacitor and released at the end of the stroke (plunger type)
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
>: or twist, depending on the design. 
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>In the common generator type blastic machine designs, energy accumulation
>is kinetic, not electrical.  The spinning armature accumulates energy
>from the action of the plunger or twist lever, then releases it in a
>surge when electrical contact is made a the end of the stroke. 
>No capacitor is employed, or needed.  (Examples: DuPont No. 10 Twist
>Permissible Blasting Machine; DuPont No. 50 Push Down Type Blasting
>Capacitor discharge type blasting machines came much later (Example:
>DuPond CD-12-1, et al).  In general, all of the capacitor discharge
>blasting machines appear to be associated with battery powered operation.
>In the early part of the century, capacitor technology was not 
>sufficiently advanced to provide a reliable device with sufficient
>capacity to support cost effective blasting machine applications. Thus, 
>electro-mechanical techniques were almost exclusively used. 
>Safety may have been an additional consideration in avoiding 
>capacitors in generator type blasting machines.  

You are correct that historically no capacitor was used in generator
type blasting machines.  However, I personally designed some hand-held
units which incorporated capacitors, thereby allowing the use of a
much less robust source of electricity.  That is why I said "is 
preferably accumulated."  One disadvantage of conventional twist type
generator units is that a weak wrist can allow the machine to slow
down before the circuit is closed and you can wind up with only half
your caps fired.

At the one extreme you have the homopolar generator which relies on the 
very high kinetic energy of a massive flywheel.  The other extreme is 
the piezo-electric film device which generates only minute amounts of 
electricity, which must be accumulated to fire even one cap.

We also built what I believe was the first battery-powered ten-cap unit
to employ a conventional small battery (9V).  Prior to that, the small
units had used multiple 22.5 volt batteries or the like, which were
a pain to find in the field.  Our little unit, which is still 
manufactured after nearly 30 years, puts out a 90 volt discharge.

Jerry (Ico)

Subject: Re: Fast Response Explosions
From: (Gerald L. Hurst)
Date: Nov 14 1996
Newsgroups: rec.pyrotechnics

In article <>, Isaac Bergen
<> says:

>This is my first post to your newsgoup, so please bear with me. 
>I'm a newbie to pyro, except for a little BP and firecrackers
>on arrows as a kid. My interest is in remote controlled small 
>explosions, like squibs, set off electrically via cable or
>radio. The question is, what is the fastest way (down in the 
>millisecond range) to ignite a small amount of commercial
>reloading powder or a blank shotgun shell? Can the primer
>cap be detonated electrically? I have no problem building
>anything electrical, and will consider all approaches, like
>high voltage spark, chemically coated nichrome wire, etc.

Sounds like you could use a a regular boom box (capacitor discharge
machine) firing through nichrome filaments.  No coating is necessary
if you use enough current to pop the wires.  Commercial blasting
caps use such a system and ignite their match compositions in the
1 millisecond range.  Such caps are also made without the base HE 
charges for use as squibs.  Typical firing currents are 2-10 amps
through 1.5 ohm filaments.  You can build a Boom box from Radio Shack
components but use first class high-rating switches or they will 
burn out quickly. Typically, you use two switches - one to charge the
capacitor and one to fire the charge.  They are wired such that both 
switches must be held "on" to make the shot for safety reasons. Also,
use a bleed resistor so the machine does not remain charged if you
fail to push the "fire" switch.

Jerry (Ico)

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