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Electric firing system - Fireworks (again)

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by iamcat, Jun 16, 2006.

  1. iamcat

    iamcat New Member

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    Hello folks,

    I work for a fireworks supply house (we sell supplies not actual fireworks) and I’ve been tasked with trying to prototype a CDU (capacitive discharge unit) firing system (my big mouth got me the job). I know only the basic of electronics, so please excuse my ignorance. We have a vender in china who builds the systems we sell and are having a hard time explaining what we want in the new version; the language barrier and lack of examples is slowing down the final product considerably.

    After reading a similar thread on this board (http://www.electro-tech-online.com/threads/electronic-firing-system-for-fireworks.21046/) I thought I’d throw the question to you all see if I have as good luck as he did.

    What I’d like to do:
    The system need to have the ability to generate and send a short high voltage pulse (18 joules) to Ignitors in the field. The purpose of the high voltage (capacitive discharge) is that igniters are usually at the end of very long shooting wires 300-600ft of 28gauge phone wire is not uncommon. The igniters have a no fire current of 20ma and an all fire current of 2 amps. The actual resistance of an ignitor can very considerably by manufacture from .5ohms to more then 20ohms (normal is from 2-5ohms). The system will have 30 (or more) queues some containing many matches is series. Ideally the system would have 10 individual fire buttons and a multi position rotary selection switch to change between groups of queues. Safety is paramount and two actions are required to fire a match, such as keyed switch and power on/off. All circuits would need to show continuity by sending 15ma though each match to an led on the panel. Best case scenario when selecting the queue group via rotary switch a light near each fire pushbutton would light up of continuity was found. It would be great to build in some kind of short detection (a common and time consuming problem) but this may be cost prohibitive. The system should function on small (rechargeable) batteries perhaps 3 D cells (any number of standard sized batteries would likely be ok). Often in a show queues are fired in quick succession so the charging circuit for the capacitor would either need to be robust enough to charge several firing banks or quick enough to replenish them real time in a show. I should also mention we are just barely making a profit on the existing systems so adding to much extra cost would be prohibitive.

    Ok, lastly it would be awesome if there was a way to retrofit our wireless systems with capacitive discharge output as they are 5v & 18v systems and not enough energy is available to ignite fronts of 10 matches in series. It would be great to have a simple circuit that could just be connected to the firing lines to give an extra boost of energy.

    Any questions I can answer or… ?

    -Brian P
     
  2. rigdoctor99

    rigdoctor99 New Member

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    I work with black powder and set them of with a box I made that can set off 12 lines in sequence.......... I use a 12V power-pack (the type of thing you keep in the back of your car for emergancies) and pass it through a voltage multiplier. This gives me 48V for fireing the small precusion caps that in turn set off the main charge, this can be anywere from 1oz to a couple of pounds of best ICI black powder, and (touch wood) never had a miss-fire. My stuff is for medieval reanactments all over the UK, and is just a bit of added reality for the public........ But lots of fun LOL
     
  3. Oznog

    Oznog Active Member

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    An electric match doesn't use high voltage. Just low voltage DC. "capacitive discharge" is usually a term associated with a high voltage engine ignition system but it could technically apply to this DC stuff.

    It could be difficult to detect a "short" since the wire impedance of a long run of thin wire may be comparable to the ignitor's cold resistance. Actually an "open" is also quite important to detect, and finding those is easy.
     
  4. dave

    Dave New Member

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  5. iamcat

    iamcat New Member

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    Use of high voltage

    The main reason why high voltage is used is 26 gauge wires in 300+ foot lengths tend to have very high resistance limiting the power delivered. High voltage helps over come this by the loss be less apparent over a similar distance. Also keep in mind professional firing systems need to have very high reliability removing live effects that fail to fire can be very hazardous. Using a CD @ ~10j also has a nice side affect that if you have long lengths of matches in series they all fire at about the same time. Using lower voltage (say 12v) the heads need to heat and “cook off” this creates small delays that are very noticeable to the audience.

    Thanks for all your quick feedback,
    This project is not something I’d like to attempt completely on my own.
    If I can come up with a working demo, I’ll let the experts modify the design into something “useable”

    :) – thanks everyone, looking fwd to your continued comments and help.
    -Brian
     

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