Scr capacitor circuit will not work. why?

Discussion in 'The Projects Forum' started by xpyd3r, Mar 12, 2008.

  1. xpyd3r

    Thread Starter New Member

    Jan 14, 2008
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    Okay, so im using an Scr that has its gate rated at 1 watt power dissipation and 4 amp max current. So, I have a 9 volt battery. The battery is attached to a diode, that drops ~.7 volts so I have 8.3 at a junction. One way has a 10k resistor back to ground. The other is a resistor attached to the gate of the Scr. So from what I figured, .75w ( to keep it lower than 1 watt) = 8.3 x I, so my I = .09 A. Then using that I figure that 8.3 V / .09 A = R and R = 100 ohms. It is not working so I'm stumped what I'm doing wrong. Any ideas? Please and Thanks so much guys. (and gals)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Post a schematic of what you have so far.
     
  3. xpyd3r

    Thread Starter New Member

    Jan 14, 2008
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    Okay, sorry it isn't any better, I just drew it up quick with Gimp (don't have anything better to make circuits with yet) And I think the diode is backwards, but I did switch it around both ways to make sure that wasn't the problem. So yea...
     
  4. S_lannan

    Active Member

    Jun 20, 2007
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    what is the actual purpose of this circuit?

    are you using the scr to latch

    or are you using it to rectify ac and chop the waveform?
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Do you have a common ground reference with the SCR? Simply touching the output of the circuit you have drawn to the gate of an isolated SCR will not cause it to fire. John
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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  7. xpyd3r

    Thread Starter New Member

    Jan 14, 2008
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    Thanks, and here's a full version of the circuit
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    You do not show a common ground. Is there one? John
     
  9. xpyd3r

    Thread Starter New Member

    Jan 14, 2008
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    No, thats the whole thing right there, but if it needs a common ground then how would I do this? any idea?
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    This should do it (red connection).

    Why the 10K resistor? Also, consider making the SCR on the "low side" of the solenoid. That is, put the solenoid on the positive side leading to the SCR anode.

    I am just guessing the flash battery supply is isolated from the secondary.

    John
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I have redrawn what I meant by low-side. Hope this helps.
    Please let us know whether it works. John
     
  12. xpyd3r

    Thread Starter New Member

    Jan 14, 2008
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    Yep works no problem now! Thank you so much!
     
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