Capacitive Discharge Circuit

Discussion in 'The Projects Forum' started by FX GUY, Sep 6, 2009.

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  1. FX GUY

    Thread Starter New Member

    Sep 6, 2009
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    I'm looking to build two different circuits to interface into the same device Circuit #1 will be the primary circuit and Circuit #2 will be a safety Circuit.

    I'm a licensed Special Effects Operator and I'm looking to build a simple controller.

    The controller will be used to fire pyrotechnic devices on long runs of zip lines. The controller is hooked up to leads coming from a pyrotechnic device. The controller is armed and a momentary switch (Charging Switch) is pressed to charge the Int. capacitor once charged an LED lights. A second momentary switch is depressed and the capacitor is discharged into the leads attached to the pyrotechnic device.

    Circuit #1- I need to be able to charge a 300vdc or so capacitor from a 9 volt battery and be able to tell that it is charged- charge time 2-3 seconds. Then be able to push a momentary switch that will discharge the capacitor into two terminals. Now if after the capacitor is charged and the momentary switch is not depressed that within X time the capacitor will full discharge on its own through a resistor array. The momentary switch must utilize a switching MOSFET to interface with Circuit #2

    Now for the hard part.... or fun depending how you look at it!

    Circuit #2- Without using a PIC, I would like to be able to build a circuit that will test for resistance and if the resistance is above 400 ohms will turn off the above circuit. I thought that an op-amp-comparator could be used for this circuit.

    The reason behind Circuit # 2. This is a safety, so the controller can not be accidently discharged when some might be holding the leads. I know the human body has roughly 1500 ohms so I figured anything above 400 ohms would indicate a problem.

    Ok done, any ideas I know that there is allot here but any ideas are very much welcome.
    To make it worse I would like to build using the least possible components.

    Thanks
    FX Guy
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Isnt this equipment available commercially? What value of cap? How many parellel devices are connected to "Blaster". An SCR makes a good switch, never welded switch contacts when using SCR to carry the current. ' Would use 4 AAs C or Ds. or is size critical. Are silver oxide batteries still required for continuity checking?
     
  3. FX GUY

    Thread Starter New Member

    Sep 6, 2009
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    Isn't this equipment available commercially? Yes but not for what I'm building. This will be used for theatrical effects where talent is armed and charged before going on stage and then fires his own device. If he doesn't fire within 20 sec. the cap has discharged enough so it doesn't have the ability to fire.

    At close to What value of cap? 160mFd, 330v

    How many parellel devices are connected to "Blaster"? Could be 1-50 depending on what application at that time.

    Would use 4 AAs C or Ds. or is size critical. Size is critcal 9 volt would be ideal for hand held device or to be built into a prop or talents wardrobe.

    Are silver oxide batteries still required for continuity checking? This is not being used for Blasting. Silver Oxides batteries are being phased out little by little. Blasting Galvanometers used Silver Oxide for quite a bit but now are going to other power sources. Continuity circuits are required to produce no more than 25 milliamps or 10% of the rated no-fire current for the device.
     
    Last edited: Sep 7, 2009
  4. Bernard

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    Ckt # 2, outline. Continuity check. When 9V switched on, 5mA flows thru firing ckt & squib; if less than 400 Ω,output of comparator is lo, turning on P CH MOSFET; charging switch then enabled. When firing sw pushed 160μF cap discharges into firing ckt, diode blocks reverse flow, .1 cap supresses leakage spikes. Found article on flyback converter: http://www.dos4ever.com/flyback/flyback.html
     
  5. Bernard

    AAC Fanatic!

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    Link broken, will try again:
     
  6. FX GUY

    Thread Starter New Member

    Sep 6, 2009
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    Thanks Bernard. I will experiment with this circuit and post some results when I get a chance.
     
  7. Bernard

    AAC Fanatic!

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    A few items that you might check from www.goldmine-elec.com ,G13596 photoflash cap; G16376, G16054,small strobe circuit boards; G16821, ferrite high voltage inverter transformer.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Heres another possibility, Strobe kit working from 9V battery, 40 flashes/min. It should take care of high V needed at a reasonably fast recharge rate. Also from The Electronic Goldmine @ about US $18. Remaining control ckt about worked out.
     
  9. Bernard

    AAC Fanatic!

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    Small change to ckt 2, Replace squib with 400 Ω, adjust 5k pot from minimum resistance untill output of comparator goes low, ,then replace pot with fixed resistor, about 1.44k.One V ref used for both ckts, LM 336,2.5V or zener. For hi V of 250V ,R2 should be about 220k with 2.5V ref. When charge reaches 250V , green LED lights. Oops , need small addition , add 4.7k from VR to Q2-B neg input[ not labled] , then connect Q2-A out to Q2-B neg. This shuts off +9V . Darn, another correction, Ckt 2 +9 should come from power SW not charge sw. With power off to Hi V will slowly drop ,turning off green lamp, restarting +9V. So as long as charge sw is held down , green will blink. When time X expires, 555-2 sec one-shot will dump HV cap.
     
  10. Bobby

    New Member

    May 20, 2009
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    Hi I have looked at your project, and it is essentially identical to one that I need to knock together for a disposable 'explosive 'blaster'. I need to trigger a detonator or shock cord, initiating the main explosive detonation. This is in a mining application. I know that the normal 'blaster' is commercially available. We have plenty of them but they are expensive and not disposable. I will use a PIC to do the count-down, etc, but would rather not have to re-invent the wheel as far as the capacitor discharge circuitry goes, if someone has a good circuit. How did your's function in the end., and if really well can I peep at your circuit. ? I would appreciate that.

    My e-mail in case you need it is <snip>
     
    Last edited by a moderator: Jan 27, 2010
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    Sorry - violates Rule 2
     
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