Rookie Help (CD, BC, Other)

Discussion in 'The Projects Forum' started by Houdeani01, Sep 14, 2012.

  1. Houdeani01

    Thread Starter New Member

    Sep 14, 2012
    I am new to building more complex circuits but have been playing with the basics for a long time. I am looking for help in which route to take as far as the needs I am looking for. I am leaning towards a Boost controller, constant current driver or Capacitive discharge circuit. The issue is I am not sure what is best suited for my application.

    I am building a fireworks controller that have 45 individual firing circuits per module (building around 24 modules) each controlled a IRF540N MosFet (Pulse ratings of 100V and 100A). At each que we will be firing a electronic match which have around a 2ohm resistance rating and have 15 foot leads which and up to be around .7ohms resistance in the wire. These match should fire around 500mA but it is recommended to fire them at 1A.

    Now with all that said on each Que we could be firing one of these matches and the base system is 24V which can handle that no problem. However we sometimes want to fire upwards of 20 match in a single hit this is where the 24V falls short. I figured on 24V given the amperage and voltage I can reliably fire up to 9 match in series (Fireworks are always fired in series), what we would like is a module that can fire 20 or more match in a single Que. This means we need to be able to maintain the current of 1A or more but have a voltage much higher than the source.

    I have been looking in to Constant Current Drivers and Capacitive Discharge circuits and am not sure the best route to take. What I know I need is a high output voltage but preferable less than the rating on the Mosfets (100V) and a fast recharge rate, we are talking milliseconds. We will fire one Que after another and sometimes with less than a second between firing them and other time minuets between firing them. This immediately discounts a flash circuit of sorts because it would not recharge fast enough to fire matches that quickly.

    The other aspect is that I need the drain to be connected to the Mosfets and that needs to be the switch not the circuit to up the voltage if that makes sense? Basically when I am done I would ideal have 2 wires that have 60-100V with around 1Amp of current ready for when I switch a Mosfet on.

    I hope that helps explain it if not feel free to ask questions as I am by no means a electronics expert I just know enough to be dangerous. I know enough that once we start talking about getting over the 40V range it can potentially be deadly getting up towards the 80V range so I would like to make sure we build this correctly with help from someone who knows a lot more than me.

    Thanks in advance!
  2. chuckey

    Well-Known Member

    Jun 4, 2007
    When you fire the firework, how long does it take the fuse to take current before it blows? 1 second?, 10 seconds?, instantaneous?
    I reckon its bad practice to put all the fireworks in series, one broken connection, no show, or even worse one duff fuse, so you have to test every fuse. Or is this what you want?
    You do not say what current your power supply will supply. I would arrange your fire works in strings of 9, connect all the strings in parallel and put a very large capacitor (47,000 MFD?) across the output of the power supply to hold the voltage up while it delivers 5A for .5 seconds to blow all the fuses.
    Out of curiosity, if one fuse is fast, sets off its fire work, before the others and it then goes open circuit, what happens?
  3. Houdeani01

    Thread Starter New Member

    Sep 14, 2012
    Hello these are all very good questions and I will clear them up here sorry for leving out thes details.

    The minimum rating is 10 milliseconds but I plan on having the fire circuits open for 50 milliseconds.
    I know this sounds weird and backwards but this is what is preferred in fireworks. Without getting into the logistics basically if you are going for a certain effect you want to make sure they all go. We test for continuity on all circuits before the show and we want to know if a que is going to go in its entirety, if you wiring things in parallel you will not know if all match is good you only know one for sure is good.
    Have not picked the power supply yet so it can be what ever I want it to be. I am thinking SLA or Lipo batteries.
    Ematch are built in a way where they will fire but remain connected in a circuit. This is done with a fine trace through the head of the match. It will eventually go if you hit it a bunch of times but it is meant to hold up for a little duration to prevent against what you are referring too.

    I Hope that helps and please let me know if I left anything else out.
  4. crutschow


    Mar 14, 2008
    For 0.7Ω wire resistance to each match and 2Ω/match I calculate a required voltage of 54V to provide 1A to 20 in series. A 48V battery may be sufficient.

    48V can give a shock but it's not considered particularly dangerous, which is why the telephone service uses that voltage.
  5. Houdeani01

    Thread Starter New Member

    Sep 14, 2012
    Thanks for the input I am now considering this as a very good option. Before I was concerned on space as the box all this is going in is by no means huge and we usually use SLA batteries. However we are thinking of switching over to Lithium Polymer batters and I could run 6 11.1V batteries in series to get my desired voltage and still have lots of room in the box.

    I know LiPo's are expensive but that is only if you buy them with lots of mA hours in them which for this application is not needed. The other big cost that comes with LiPo's is the C rating which can be very low as well as we only need around an amp or 2.