igniter?

Discussion in 'The Projects Forum' started by braeden, Feb 6, 2008.

  1. braeden

    Thread Starter Member

    Feb 6, 2008
    17
    0
    hi im a noob just getting into electronics as a hobby and decided to make my first project and igniter.

    heres the plans i drew up:

    [​IMG]
    sorry bought the bad drawing. still trying to find a program to let me draw up good plans on a mac.

    i need to know if:

    1. i should put a resister by the led's.
    2. school confused me with the dman which wya current flows. so which way should i be putting the resistors etc.
    3. i can put up to probably about 4 batteries which are 1.2v and 3A each. is that enough
    4. will nichrome work with that low of a voltage? or should i use a small coiled spring.


    thanx for everyones help.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    1. Absolutely put a resistor in series with each LED. This will limit the current flowing through the LED, and prevent the LED from being damaged. In order to know what resistor to use, we'll need to know the current limit of the LEDs. Do you have that number available to you?

    2. Electrons flow from - to +. "Current" has two definitions. See here: http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

    3. Batteries in series add voltage. Batteries in parallel add current.

    4. How thick is your nichrome wire and how long is it? Back when I was an avid model rocketeer, we used 12V sources for our igniters. That was back before hard drives, though.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Braeden!

    I'm a "rocketman" too ;)

    Yes, you will need resistors for the LEDs.

    Resistors don't care which way current flows through them. LEDs will only light if the current is passed through them in the correct direction.

    6V @ 3A should be reasonably sufficient to light off small-gauge Nichrome wire.
    Wrapping thin-gauge Nichrome wire in a small coil will concentrate the heat at one point. 12V will make ignition more reliable.

    Have you ever seen the movie, "October Sky"? If not, you should.

    I'll help you with this.
     
  4. braeden

    Thread Starter Member

    Feb 6, 2008
    17
    0
    awesome thankyou very much. october sky is a great movie.
     
  5. braeden

    Thread Starter Member

    Feb 6, 2008
    17
    0
    not sure bout my nichrome. ive got the right led's and resistors for the leds coming in the mail. i was planning on building it all in a little notebook HD case thats just holds AA's and about 4 of them so thats why i havent been going for something bigger.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    There are at least a dozen different kinds of conventional LEDs. Then there are the super-bright ones and other special ones. Do you know which kind you ordered? Can you provide a link for who sold them to you?

    On the igniters themselves, did you get your own nichrome from an industrial supplier, or does it come from Estes or Centauri or one of their competitors?
     
  7. braeden

    Thread Starter Member

    Feb 6, 2008
    17
    0
    thanx but i used an online calculator to calculate the resistor needed. may have to adjust depending on the batts i put in but i think its all good. havent got my nichrome yet. i still have to find somewhere to order it from in small quantities.
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The following link lists current needed through a nichrome wire of given size to achieve a given temperature. It also lists resistance per linear foot for different sizes. Ohms Law and a little algebra should offer up a solution.

    http://www.heatersplus.com/nichrome.htm
     
  9. braeden

    Thread Starter Member

    Feb 6, 2008
    17
    0
    wow. long list of confusing info.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Braden,
    You've posted a question, and received a LOT of responses.

    Give it a day or so, and let the comments fall where they may.

    Meanwhile, your original schematic does not provide for a removeable "key" that those tasked with launch platform duties must return before the igniter can be enabled. A simple toggle switch is NOT a suitable substitution, and could lead to accidents.
     
  11. braeden

    Thread Starter Member

    Feb 6, 2008
    17
    0
    ok. ya i thought a key may be good though i dismissed the idea because i have no experience with them. ill do some researching.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    A key doesn't have to be complicated. You could simply use a 1/8" or 1/4" mono phono jack and plug with a shorting wire. Tie a long red ribbon or red piece of fabric to the phono plug so it's easier to find if dropped.

    Nobody approaches the launch pad unless they have the key with them.

    I've attached a variation on your schematic.

    When the key is inserted, the "armed" LED will turn on, and the piezo buzzer will sound continuously as a warning. If the igniter is connected or alligator clips are shorted together, the "IGNITER CONNECTED" LED will turn on. Pressing the "Launch" button will cause the "IGNITER CONNECTED" LED to turn off, and apply full battery current to the igniter.

    For the piezo buzzer, I suggest this one: http://www.radioshack.com/product/i...iezo+buzzer&kw=piezo+buzzer&parentPage=search

    As for the nichrome wire, use very small gauge. 28 gauge should work OK. Use a very small drill bit, and wrap a couple of turns of the wire around the shank of the bit to make a nice compact coil, sort of like the spring on a safety pin - only much smaller. Carefully insert the coil into the nozzle of the engine, spreading the ends of the wire apart. Use a bit of flame-retardant wadding to hold the wire in place.

    As far as the alligator clips - there are some different schools of thought. When I bought my first Estes launcher in the early 1960s, it had this type of clips:
    [​IMG]
    Above is Radio Shack item#270-373, http://www.radioshack.com/product/i...kw=test+clips&kw=test+clips&parentPage=search

    These were kind of a pain in the neck, because they were either always slipping off, or shorting out against each other. Instead, consider this type:

    [​IMG]
    Above is Radio Shack item# 270-378, http://www.radioshack.com/product/i...kw=test+clips&kw=test+clips&parentPage=search

    The disadvantage here is that the insulation will rapidly get burned up, but it should last for several launches before needing replacement. The teeth seemed to stay on the nichrome wire much better.
     
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