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How can I ignite these three rocket igniters?

  1. Jul 18, 2009 #1
    First off, let me say that what I am working on has taken me a few days to get to work and I just cant figure it out. It is really frustrating so any help is really appreciated.

    I have three igniters. They are connected to a circuit. Once a switch is turned to "on" the three igniters are supposed to ignite.

    This is the diagram
    l.jpg

    I am using two nine volt batteries each charged at 9.50 volts. Now, if I remove the igniters from the diagram and test the voltage of each side of the wire, the voltage reads about 9.50 volts at all locations. Now, when I attach the igniters to these wires, and to a test ignition, only one of the igniters ignite. the batteries are connected in parallel, and the igniters are connected in parallel also.
     
  2. jcsd
  3. Jul 18, 2009 #2

    negitron

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    I thought your batteries were to be in series, for a nominal 18 V.
     
  4. Jul 18, 2009 #3
    They were in series but then I removed them in parallel. This is because when I tested the circuit with the batteries in parallel only one igniter ignited.

    Also, as takled about in my previous post, the voltages near the igniters were rapidly jumping from one voltage to another. I found out this is because of the clips I was using. Apparantly, they cant be used in this sort of project.
     
  5. Jul 18, 2009 #4

    negitron

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    Try using something other than 9 V batteries. Those small rectangular batteries have a very high internal resistance and cannot supply a large current--typically less than an amp, because they are comprised of 6 smaller 1.5 V cells (usually AAAA-size) in series. I would suggest a small 12 V lead-acid gel cell, such as used for alarm systems, UPS units and emergency lighting since these have a much smaller internal resistance and can supply several tens of amps easily.
     
  6. Jul 18, 2009 #5
    Ok now where can I buy this item? It needs to be inside of my rocket which means that it neeeds to be light.
     
  7. Jul 18, 2009 #6
    Ok. Now I need to buy this item from radio shack because that is the only hardware store in my area. The problem is that I cannot find this item that they sell.
     
  8. Jul 18, 2009 #7

    negitron

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    I thought the battery was 200 feet away?
     
  9. Jul 18, 2009 #8
    No. That is a different circuit. i already figured out how to launch the rocket frmo 200 feet away using one car battery. Once the rocket is in the sky, another circuit will be turned to on which will ignite a different part of the rocket in the sky.

    That is what I am trying to figure out. I am trying to figure out how to launch these three igniters.
    Thanks
     
  10. Jul 18, 2009 #9

    negitron

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    Ahh. In that case, use lithium cells. They are very light and can source a lot of current.
     
  11. Jul 18, 2009 #10
    Ok. I looked into these batteries. It appears that their voltages are about 3 volts. I have found that the igniters need atleast 9 volts to ignite. I have found this through trial and error. Do you think we will definitly be able to know what batteries my circuit needs if we had detailed information about the voltage and amperage required to ignite the igniters?

    It seems like getting those batteries will just lead to more trial and error.
     
  12. Jul 18, 2009 #11
    Also, I would suggest putting the ignighters in series. This would ensure that they all light and at the same time.

    Also, Unless I'm mistaken, I believe you can buy model rocket motors with an ejection charge that also lights the next stage.
     
  13. Jul 18, 2009 #12
    I understand that the ejection charge can do that but the ejection charge in this design is beign used for other applications. Therefore, I need to use a battery to ignite tthe followign stage.

    Why exactly does putting the batteries in series ensure that they all light at the same time?
     
  14. Jul 18, 2009 #13
    Not only the batteries, but put the ingighters in series. Actually, I'm rethinking that now.
     
  15. Jul 18, 2009 #14

    negitron

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    No, don't do that. What will happen inevitably is that one will fire and fuse open first, leaving the rest on an open circuit and unable to fire. Like those annoying Christmas tree lights. One goes out and the entire string is dead.
     
  16. Jul 18, 2009 #15
    That's right. I see it now. Once again comes the glorious lesson of being wrong.

    You do want the batteries in series though. Double the voltage, double the curent.

    v=ir

    i = v/r
     
  17. Jul 18, 2009 #16

    negitron

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    Almost. You do double the open-circuit voltage, but remember that you're also putting the batteries' internal resistances in series so your actual load voltage and current will be somewhat less than doubled because your load resistance in series with the battery internal resistance act as a voltage divider.
     
  18. Jul 18, 2009 #17
    Ok. Now you are saying that I should put these two 9 volt batteries in series? Also, after looking through my notes, I found that if I have two batteries charged at 10 volts in parallel in the circuit, then all igniters ignite simultaneously.

    Now, if I were to use these lithium cells, it appears that the voltage will be three volts which my understanding shows is just too low. The only problem is I cannot charge my batteries up to 10 volts and have them stay at that voltage.

    Any ideas?
     
  19. Jul 18, 2009 #18
    Bad advice. More likely is a parallel wiring results in a fuse close of one of the igniters pulling all the amps leaving not enough for the rest of the igniters. There is a reason the law required series wiring of the blasting caps in the mine. Setting off twenty shots at a time in the mine required the caps to be wired in series. One check for continuity ensures that all caps are made up. The blaster charged a large capacitor to ensure a large amperage flowed thru the series circuit igniting all the shots. Wiring in parallel would require the testing of each circuit for continuity. Series wiring ensures that all are in the circuit. If one is not made up, then none will go off. Parallel wiring may result in only one shot going off because the rest are not making a circuit. Not good when men will have to load out the shot material with maybe several live sticks of Tovex in the gob.

    Wire the blasting caps or igniters in series and use a car battery for your three rocket igniters. Test for continuity with a high impedance quality meter such as a Fluke 77 or find a galvanometer. Illegal to use the Fluke in the mine. Only the galvanometer.

    The following link mentions the advantages of series wiring and the disadvantages of parallel wiring of your igniters. The problems generally manifest on larger numbers of igniters but it helps to understand what is going on and get it right the first time.
    http://www.pyromate.com/Basics-of-Electrical-Firing.htm
     
    Last edited: Jul 18, 2009
  20. Jul 18, 2009 #19
    Ok. Now there is a problem I can see with this. Say that I use the igniters in series. If the circuit is turned to on, I can see the first igniter in the series to ignite first. Then, I can see this igniter becoming burnt out which will then ruin the continuity of the circuit. Thsi will then cause the other two igniters to not igntie. If this hapens, then I am in trouble. These three igniters need to ignite simultaneously. That is why I chose to use a parallel circuit.

    let me know what you think.
     
  21. Jul 18, 2009 #20
    Read the link. Much better and more authoritative than this old retired coal miner. Your picture of the chain of events in the series setup is eliminated by having enough amps available at your blaster. The one in the mine was pretty heavy and it took about 15 seconds for the capacitor to come up enough to light the ready light. For your rocket motors I think a 12 volt car battery will be enough. You're not trying to set off 20 shots at a time and some of those shots might have three or more sticks of Tovex. Just pretend that what you are doing can be so unforgiving that you can't take chances.

    How would you test your parallel circuit? Series is simple. Check the two wires you hook to your blaster or battery and in a series an open on any igniter will be revealed. Not so on a parallel arrangement. http://www.pyromate.com/Basics-of-Electrical-Firing.htm" [Broken] Also refresh the page as I have altered my previous post somewhat.
     
    Last edited by a moderator: May 4, 2017
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