Here are a few of the fundamentals that will help you understand the rest of the electrical firing section.
Fundamental Basics of Electricity
What is Voltage?
Potential Difference, more commonly known as Voltage, is the difference in electrical potential between two points. What?! Let's use an analogy of a water piping system. Lets say we have a short length of
pipe, and wanted to continously pump water from one end to the other. At first, when no water is flowing, there is no pressure difference between one end of the pipe and the other. So in order to get water
to flow, we must create a pressure "differential" between the two ends of the pipe. So, we would use a pump at one end which would raise the pressure; thus, "pushing" the water through the pipe. This is how your
garden hose works in your back yard. Electric Potential (Voltage) works in a similar fashion. The Voltage is the "water pressure" pushing the electrical current through the wire. This of course is simplified
very drastically.
What is Current? What are Amps?
Electric Current is the flow of electric charge per unit area. Amps are the units of Current. For example, you would say, the circuit is producing 5 Amps of current. Going back to our water pipe analogy,
if the "pressure" produced between the ends of the pipe is analogous to voltage, then
the flow of water (the water current) is analogous to the flow of electric charge, or current in the wire. So, to sum it all up, the voltage causes the current.
I have alot of electric matches wired into one cue. How do I know they will all fire with my system?
Well, that's a little more complicated so read on. In the physical world of electricity, there are laws that must be followed as with every branch of
physics. The most basic of these laws is known as Ohm's Law.
Ohms law in simple mathematical terms is: Voltage = Current * Resistance, or V = I*R
After a small
algebraic manipulation,
Ohm's Law becomes: I = V/R
From this equation, we can see that the amount of current through an electric match equals the voltage across the electric match
divided by the resistance of that electric match. This is important since electric matches function by electrical current flowing through them.
So to determine how many electric matches you can fire off of a single cue, you must take into account four main things.
The resistance of each electric match
The number you wish to fire
The method (series, parallel, or series-parallel) in which you wire them
The internal resistance of your firing system
To simplify matters, we shall assume it's an ideal world (it's not) and there is no internal resistance of your firing system. We shall also assume that you
are going to wire everything only in series. To not make those assumptions, the calculations are more complex, and ultimately above the scope of this tutorial.
If you are still interested in learning these more advanced ideas, order Issue 20 of the Journal of Pyrotechnics which
contains my published paper, "Maximizing the Number of Electric Matches That Can Be Fired in a Single Circuit", on the subject. There you will get
all the math, data, and experimental results you desire. Now for an example. Let's assume our electric match all-fire current (current at which all electric
matches will fire) is 1 Amp. Now let's say we have 10 electric matches. Let's also say each electric match has
a resistance of 1 Ohm (Ohms are the units of resistance, not to be confused with Ohms law). So if we tie the 10 electric matches in series, thier resistances
will add (not true if wired in parallel), thus giving us 10 ohms of resistance. So going back to Ohms law, when we plug these numbers into the equation, (24v/10ohms) we
get I = 2.4 Amps. So we will have 2.4 Amps going through each electric match. This amount of current is much more than most "all-fire current"'s given by the manufacturer
of that particular brand of electric match. Now, if we were to have 10 of the same electric matches in parallel instead of series, we would only get 0.24 Amps of current through
each electric match (math ommited due to elevated complexity). So you can fire more electric matches in series than you can in parallel. Or can you?
Believe it or not, with some more math, it can be shown (above the scope of this tutorial, once again order the journal issue mentioned above if your interested) that matches wired in
series-parellel combinations can fire more electric matches than series or parallel alone. I have fired up to 50 electric matches successfully on one 24 volt system.
This is not done very often in the world of fireworks, and applies more to ignition of a cluster of rocket engines. Click here to read more on this subject.
Is ohms law the only law we have to worry about?
No. There are a couple other important laws that govern the multiple series-parallel circuits, namely Kirchoff's Voltage and Current Laws, however they are also above the scope of this tutorial.
Look them up in a basic eletrical circuits book if you are interested.
What are the advantages/disadvantages of series-parallel wiring for multiple shots aside from the above mentioned?
Advantages:
Series
- When you check continuity, you know all matches are hooked up correctly.
- You can fire more matches on a single cue when wired in series as opposed to parallel.
Parallel
- If all matches on a single cue are not wired into the terminal properly, at least one will fire if you had continuity.
Disadvantages:
Series:
- If one match fires much quicker than the others in the chain on a multiple shot, the rest of the chain may fail to ignite.
- If something happens to the chain during the show, none of the shots on that cue will fire.
Parallel
- If only one match of a multiple shot is wired into the cue terminal correctly, you will still get "good" continuity. Ensuring that some of your shots will not fire.
Other series & parallel issues to worry about
A frequently asked question is, "What happens in a series chain if one electric match fires before the rest have time to ignite?" Nothing if you have an electric
match from a good manufacturer. If the manufacturer is not very consistant in the manufacturing of their product, they will
have significantly larger differences in the resistance of electric match. From personal experience, I have seen certain electric match brands work flawlessly, and
others fail when in series on a regular basis. So if you don't have a large number of electric matches to shoot from one cue, say five or less, then just use a parallel wiring scheme.
Just remember to double check your wiring when using parallel since one match in the terminal correctly will give you good
continuity, and not indicate any possible errors with your other shots on that cue.
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