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Electrical Ignition System

  1. Jan 28, 2006 #1

    mrjeffy321

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    I am going to try to build an electrical ignition system similar to an Estes rocket ignition system. The idea is simple enough, just run a bunch of current through a wire until it heats up, but it gets harder if you want to do this from a safe distance away from what you are igniting or you want to do it with as few batteries to lug around as possible.

    What I has in mind was to use a 9 volt battery as the power source, which would then be connected over a length of wire to the igniter (made out of very thin nichrome wire). But I am worried about how quickly (if at all) it will take for the igniter to heat up, it would be nice if it happened rather quickly. To try to give the battery a little extra “umph”, I thought of hooking up come capacitors into the circuit to be charged up by the battery prior to the final button being pushed.
    I was wondering just how much capacitance should be needed or how effective this idea actually is?

    Below is a link to the basic circuit design,
    http://www.amazingrust.com/New/circuit.JPG
    In the diagram, I have placed two capacitors in parallel. When the circuit is armed, the capacitors will charge up, then when the button is pushed, both capacitors and the batter will all be in parallel sending current down towards the igniter (the big resistor at the end). How does 1000 microfarads sound for the capacitance, too much, not nearly enough?
    Capacitance = Charge / Voltage
    I figure at 1000 microFarads, I could store up to 9000 microCoulombs of charge each.


    Another quick question,
    Is there a way I could arrange an LED with a capacitor so that after the capacitor is charged, the LED will turn on? If I put it in series with the capacitor, while charging, the LED would fade down to nothing, I want the reverse to happen.
     
  2. jcsd
  3. Jan 29, 2006 #2

    Stingray

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    1000 uF capacitors will have a negligible effect here. They will also be charged up almost instantly, so you wouldn't have any need for an LED telling you they were ready.

    The battery itself is probably sufficient to melt the ignitor after a few seconds. If you need faster ignition, use something that can source more current. 9 V batteries are very poor in this regard, and the resistance of the ignitor is low enough that this is your limiting factor. 9 V batteries will also wear out very quickly when used this way. You'd probably get better results with a couple of AAs or Cs. Even one of these might work better than a 9 V.

    Note that I'm assuming your ignitors are similar to the Estes versions. If not, you might need to design things more carefully.
     
  4. Jan 29, 2006 #3

    mrjeffy321

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    I see.
    So is the capacitor idea even practical with any reasonable capacitance?

    My ignitors are similar to Estes ignitors.

    I suggested a volt battery because it seemed like an easy and compact way to get a pretty good voltage, but I was experimenting last night and they also seem to have a very high internal resistance compared to AA batteries. Now I will switch so using several AAs instead.
     
  5. Jan 29, 2006 #4

    Stingray

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    No. Sorry.

    Yep, that's mainly what I was getting at.
     
  6. Feb 3, 2006 #5
    have u tried a match?
     
  7. Feb 3, 2006 #6

    mrjeffy321

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    Oh, yes, in my day I have used a match or two,
    but the problem with matches is that to use them, you need to be right up next to whatever your trying to light. I can show you a video (and a scar) of an instance where if I had used a match, I would be dead, the electrical ignitor saved my life.
     
  8. Feb 4, 2006 #7
    I was being sarcastic. Should of used a wink smiley face:smile:
     
  9. Feb 4, 2006 #8

    russ_watters

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    Model rocket ignitors have a pyrotechnic substance on them that ignites the engine - it isn't the heat from the thin wire that does it.
     
  10. Feb 4, 2006 #9

    mrjeffy321

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    Yes, I had planned on adding a bit of pyrotechni material to the tip, but the heat of the wire needs to set that off.
     
  11. Feb 6, 2006 #10

    Danger

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    I haven't used real model rockets, but have played around with various things just for the sake of having handy stuff around. For ignition, I like to just use a small flashbulb with the glass cut away. It doesn't take much to set it off. (And for contact detonation, a Magicube bulb with the chemical trigger in the stem can be nice. :devil: )
     
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