Download Series-Parallel Circuits

Safety and Wiring Techniques in
Electrical Pyrotechnic Ignition
By Dr. James Beeghly
Additional content and formatting
by Mark S. Woodburn
Iowa Pyrotechnic Association
&
Both Members of:
The Stumptown Shooters Pyrotechnics Club
Pyrotechnics Guild International
Electrical Ignition System Elements
•
Electric match (You might call these squibs - But please DON'T)
•
Wire used to extend Shell wiring is called “Scab” or “Tramp” wire
•
From the panel or computer, there are Slats and Cables.
•
All E-Fire systems have either a Dedicated Firing Panel or a Computer.
•
The E-Matches should come out of the package "shunted" (wires twisted
together), and you should need to untwist them to insert the wires into the slat.
•
The wires should remain shunted until wired into the slat - after the Shell has
been dropped into the tube.
Simplified E-Fire System
Electric Match (from Oxral)
Electric Match Schematic
Important Match Characteristics
• No fire current:
–
Is the maximum current applied for 5 seconds that gives 0% ignitions– typically .13 to .25 amp
• All fire current:
–
Minimum current/5 seconds/100% ignition – typically .25 to .5 amp…but
You must figure in the:
• Match Resistance (of Each Match):
– Most assume 2 ohms
and
• Match Firing current (of Each Match):
– Most aim for 1 amp as the goal of whichever wiring technique you choose.
Match Safety Issues
•
Stray Current: Electrical Risks can be greatly minimized though not eliminated, by keeping
the leads shunted.
•
Electrostatic Discharge: Lightning is very risky. Moving a plastic tarp, is occasionally risky.
Static from clothing is minimally risky.
•
Generally speaking, the Colder it is, the drier the air is. Check the relative humidity often.
•
Static does better in dry air, which is why building Pyrotechnic Products is not
recommended in Non-Humidity-Controlled environments, or Naturally Non-Humid
Environments, but it can develop at any time under the right conditions. Even with 100%
Humidity.
•
Radio Waves: These pose the greatest risk is when everything is wired up. Your wiring acts
as an antenna.
http://www.hamradio-online.com/1996/feb/blasting.html.
Match Safety: Mechanical Risk
• Electrical matches are more shock and impact
sensitive than black powder. They should never
be struck or squeezed suddenly.
• They are also modestly friction sensitive. For this
reason it is doubly important that the match is
placed into and secured to the pyro device in a
way that won’t allow rubbing.
• Think of them as "strike anywhere" matches.
Connecting the Match to the Pyro Device
• One of the most dangerous parts of preparing for a show is matching.
• If the fuse ignites as the match is pushed into the fuse or lift charge…
– The lift charge will explode virtually immediately
and;
– You will have only a few seconds until the time fuse explodes the
shell.
You Increase your chances if…
•
You match shells in a relatively remote area.
–
•
NFPA Code says you MUST be a minimum of 100' from Spectators before/during or
during a Show AND stay 50' from any Fireworks Storage area with NO Smoking allowed
ever within 50'.
You limit the number of workers and number of shells in the area at one time
(2 or 3 people at a time is good).
– The are no other activities in the same area
– You shuttle boxes of shells into and out of the area on a “just in time” basis.
– You know your escape route from the building.
•
If necessary (and only if you deem it feasible), help your buddy to get out too.
You Increase your chances if…
• Never transport Matched Shells!
– (NFPA 1123 forbids this).
If using a Trailer, the proper way is:
– Move the trailer with empty racks in.
– Drop the Shells.
– Match the Shells (in the tube)
Try to be aware of what is over the Tube at all times.
–
Especially your Body parts.
Connecting the match to the Pyro Device
• Use nonferrous tools when you can to avoid generating sparks.
– Aluminum gutter nails or brass tools work well.
• Avoid removing the plastic tube around the electric match.
– Doing so significantly increases the chance of a friction ignition during insertion
(like by 10 times).
• Fasten the inserted match firmly.
– So that it does not rub against the fuse while the shell is handled.
• Match on site.
– NFPA Code and Federal Law Prohibit Transport of Matched Shells.
• Remember this should you need to Transport Live Materials BACK from a Show.
Connecting the match to the Pyro Device
Match Insertion Points
• From Ken & Bonnie Kosanke Lecture
Notes for Fireworks Display Practices,
as found in The Journal of Pyrotechnics
• The three main points to Match at
are:
• 1. End fuse
• 2. Side fuse
• 3. Lift charge
End Fuse Insertion
Side Fuse Insertion
Side Fuse Insertion
Lift Charge Insertion
(one example)
Wiring to the Slat
• The leads from electric matches should be tied to
something, typically the rack, so that the exploding shell
will not pull apart the electrical system.
• Good planning allows less use of scab wire and wiring
which in daylight, reduces tripping over wire and
simplifies troubleshooting.
• Avoid long straight runs of wire (hah) to minimize
antenna-like characteristics.
Firing Panel Safety
• Panel must be electrically isolated from AC power sources to
minimize stray currents.
• Panels designed for Outdoor uses may NOT be plugged into a
standard, wired, AC Outlet during the Display.
• EVERY Panel must require two separate actions to apply
power to a match circuit.
– (Like a Key to ARM and a button, or switch to FIRE.)
• Continuity testing must be at the lower of .05 amp or 20% of
the no-fire current.
• Computer operated panels must have a “dead man” switch
Firing Panel Safety
• Despite safety features, panels can and do malfunction.
• Despite training and experience, Operators and/or Crew can,
and do screw up.
• Do not power up a connected panel, even for circuit testing,
unless the firing area is clear.
• Disconnect the power from a panel before anyone enters the
firing area, even if you believe that all devices have been fired.
– After the Show, until the Lead Operator says so, the Crew stays out of the
Firing Area. The Public STAYS out.
Wiring Techniques
There are 3 Basic Wiring Schemes (Types).
They are:
Series
Parallel
or
Series/Parallel (Mix of both)
Series or Parallel, Which is Better?
SERIES WIRING: Delivers more current (amperage) to the match for a given voltage:
Open matches are easily found in testing
PARALLEL WIRING: Is more tolerant of variations between matches:
One bad match usually will not shut the rest down.
More commonly used, and easiest to do.
Low Voltage Systems (12 – 24 volts): Series may be a better choice if current delivery is the most limiting factor:
Note that more Voltage does NOT necessarily equal more current (Amperage).
High voltage/high energy/"CD" Systems -- capacitative (typically) delivers 300 volts or more at a higher amperage.:
Parallel may be better (or easier) to ensure that all matches fire.
Indoor (Proximate) Systems (typically driven by 110-120 volts ["Standard" AC Outlet in the US]):
Parallel is often chosen since plenty of current is available.
OHM’S law
V = voltage -- typically expressed in volts or millivolts
I = current -- typically expressed in amps or milliamps
R = resistance -- typically expressed in ohms
(”milli” as in milivolt means “one thousandth of a....”)
Reciprocal Forms of the Ohm’s Law Equation
V=I*R
I = V/R
R = V/I
WIRE RESISTANCE
CIRCUIT WIRING
Circuit: A conducting path for current from one side of a
source of voltage and current -- the positive side of a battery,
for example -- to the other -- or the negative side of the
same battery in the following example:
i. To preface the example: When apply Ohm’s law you often must think of a
large circuit as composed of several smaller (shorter) circuits, which I will
also refer to as elements making up the larger circuit just as you can think
of a large chain as made up of all the shorter links that make up that chain.
In this way you can combine series circuits or elements with
parallel circuits or elements.
Parallel Circuit
Voltage:
Each element of a parallel circuit “sees” all of
the total voltage of the circuit.
Current (I):
The entire circuit “sees" the sum total of
each device in the circuit.
Resistance:
The resistance of the total circuit is the
source voltage divided by the resistance (summed) of the
total number of devices.
Parallel Circuit
Series Circuit
Voltage:
Each element of a series circuit “sees” only a
proportional part of the total voltage of the circuit.
Current (I):
Each element “sees: all of the current that
passes through the circuit.
Resistance:
The resistance of the total circuit is the
simple sum of the the resistance of each (different) element
of the circuit
Series Circuit
Wiring in General
Parallel Circuit
Voltage:
Each element of a parallel circuit “sees” the
total voltage applied to the circuit. Since we are talking
about identical matches, the current is evenly divided
between matches.
Current:
Each element “sees" only a proportion of
the current that passes through the total circuit. Since we
are dealing with electric matches that all have the same
resistance the current through any one match is equal to
the total current through the entire circuit divided by the
number of matches.
Series-Parallel Circuits
In reality, no match circuit can be purely parallel because the wire from the
panel to the matches will always add a series resistance to the circuit. The
resulting “series-parallel” circuit can be “resolved” to a series circuit using
the preceding formula to replace each parallel wired section with an
equivalent series resistance.
Series-Parallel Circuits
Series-Parallel Circuits
Or in other words:
Series-Parallel Circuits
Series-Parallel Circuits
• The previous circuit is then analyzed as before.
• But;
• Assuming we had 100 ft of two conductor 20 gauge wire
between our 12 volt battery and the five matches,
(remember 100' out and back = 200' total of wiring and it
totals 4 ohms of resistance), then further assuming each
match now only needed one amp current to reliably fire,
would those five matches in parallel fire?
Will they Fire?
In a Parallel Circuit, the total resistance of the circuit would be 4 ohms for wire
and 0.4 ohm for the total of the matches. Twelve (volts) divided by 4.4 (amps)
equals 2.73 amp. If this current is evenly divided between five matches, each
one gets only 0.546 amps (less than 10 % over the .5 amp threshold) and firing
could be uncertain or uneven, especially with a cold battery (IE. New Years.)
What about the same setup but with the matches in series? The total resistance
would be 4 ohms (of wire) + 10 ohms (the 5 matches at 2 ohms each times 5) or
14 ohm total. The current would be 0.86 amp (12v divided by 14 ohms), which
would be “seen” by each match. This may still seem a little low, but is
approximately 60% above .5 amp each which is far more likely to fire the
matches reliably.
Series-Parallel Circuits
• This is why series circuits are usually preferred for
low voltage match circuits where the amperage is
questionable.
• The situation is different for high energy panels
and for indoor pyro and every case is unique.
• You must choose what is best for you - at that time
- and - under those circumstances.
Series-Parallel Circuits
• Modern Manufacturing Techniques are very good, and
most e-match builder's try to maintain a 2ohm/1amp
"load", but as we mentioned before, most electronic
components like resistors and e-match (they are both
rated similarly), are manufactured to a +/-10% tolerance
- meaning that any given e-match will place a 2.2 to a
1.8 ohm/1.2 to .8 amp "load range" on it's circuit.
Will they Fire?
•
For low energy systems, the pyrogen in the match usually fires before the nichrome
melts and thus all the matches in a series circuit have time to fire.
•
In some high energy systems, especially those with local firing boxes (Capacitive
discharge systems), the nichrome quickly melts, potentially breaking a series circuit
before all the matches have fired (especially if a 2.2 ohm/1.2 amp "load" is wired in
front of a 1.8 ohm/.8 amp "load" e-match).
•
For ANY wiring scheme (Series, Parallel, or Series/Parallel) and to do any of these
equations, you need to know both the Voltage and the Amperage of the Voltage Source.
On a car, deep-cycle, or marine battery for instance, the Amperage Rating is generally
found on the Identification Sticker affixed to it.
This is the CA or CCA Rating of the Battery in question.
(Hint: the CCA is the more conservative one - use it if available)
Series or Parallel?
THE BOTTOM LINE
Most panels come with instructions. Many newer systems will fire up
to 10 matches on a single Cue, even using Parallel wiring, utilizing as
little as 12 volts.
Many also "refresh" and are ready to fire another cue in as little as .01
seconds. This potentially would give you the ability to fire 1,000 Shells
Per Second, or up to 60,000 Shells Per Minute.
Talk about your huge Displays!
No matter what though, always read and follow the guidelines for
series versus parallel wiring for your particular panel, and use your best
judgement as to the choice of wiring type based on past experience and
the circumstances you have before you at the moment.
THE You
• Thank
IOWA PYROTECHNIC
ASSOCIATION