Re: Electrical Firing System
- From: David Schultz <abuse@xxxxxxxxx>
- Date: Tue, 16 May 2006 23:36:14 GMT
hhc314@xxxxxxxxx wrote:
Oz, the fact is that the firing energy capacity of an electric firing
panel isn't principally dependent on the voltage, but on the energy
storage capacity of the firing mechanism. Often a 47V system with a
large and efficient capacitor packs more punch than a multi-hundred
volt system with a puny capacitor. The firing energy punch is
universally 1/2 CV^2, no matter what. This is simply electrical
engineering and very basic physics.
You can get the desired energy discharge from a low voltage battery and
a large capacitance capacitor, or a high voltage battery and a small
capacitance capacitor. The end result is identical, excluding the
resistance of your cables. For example, I've fired Daiseyfire connected
by over 100-feet of cable using a 1.5V D-cell. Still, I prever to
shoot usiing a 90-Volt system charging a 450-Mfd capacitor. Equally, 2
12-Volt storage batteries connected in series without the energy
storing capacitor does equally well for some shooters of large
displays.
For most firing cables, typically not less than 22-gauge at distance of
300-feet or less, the difference is not very notable, although I would
not suggest trying to fire anything at this distance using a 1.5V
battery, but then only due to the resistance of your connecting cables.
You may 'cook' thing off, but none of us want to do that.
Recall that if the resitance of the cables is R (where R is the total
resistance of both the feed and return wire), then the current you're
going to push through the igniter is essential equal to V/(cable
resistance + igniter resistance). In most typical cases, 12V will be
sufficient, but 48-volts or above is generally an assured fire,
particulaly if is also includes capacitiative enery storage far beyond
the current pulse that the battery alone can provide. (The 1/2 CV^2
plus factor.)
Hope this helps.
Harry C.
Just because a higher voltage is good in some ways does not mean you can
go overboard. The biggest mess I was ever involved with was the result
of a new high voltage CD system. I forget what the voltage was but it
was substantially higher than the previous CD system. Perhaps as much as
a thousand volts but it has been a while and memory fades. I do remember
that it was greater than the 400 Volt rating of the 1N4004 diode
normally used in the distribution boxes. I asked about this and was
informed that the diodes had been replaced with higher rated devices.
The firing system was the usual multiwire with shared grounds and
distribution boxes to firing rails.
I helped set up the show and then retired to watch along with the rest
of the crowd. I noticed long pauses in the show and th row of low level effects in the front didn't go off together.
Afterwards, I found that when the pyrotechnician shooting the show was
firing the cues, sometimes nothing happened. Other times shells on other
cues went off. At the end of the show, a large percentage of the shells
hadn't fired.
The cause was likely a combination of the higher voltage, wires and/or
connectors not rated for the voltage, and the very high humidity. (There
was dew on the grass by the end of the show.) Those little electrons are
notional things and sometimes go where they want to rather than where
you want them to.
--
David W. Schultz
http://home.earthlink.net/~david.schultz/
Why am I Mr. Pink?
.
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