Overheating battery on QTC torch

Discussion in 'General Electronics Chat' started by Aron0789, Feb 25, 2013.

  1. Aron0789

    Thread Starter New Member

    Feb 25, 2013
    4
    0
    Hey there,



    I have created a circuit for a torch using quantum tunneling composite (QTC) as the switching mechanism while using a thyristor as a latch switch.




    QTC is a smart material that is normally a perfect insulator but as you apply pressure it becomes a conductor.




    http://s18.postimage.org/3vdwz0ck9/SAM_0093.jpg
    This is the circuit.




    its powered by a 12V 23mA n type battery and the circuit all works fine, it switches on and off no worries.




    The issue is when the circuit is not used the battery gets really really hot and burns out with in a very short amount of time, the torch itself can be lit for over 26 hours.




    I can only think the battery is being shorted but I cannot see where, unless the thyristor is allowing current to flow through striaght to the battery.




    Can anyone spot the problem and help solve it?



    Any help or suggestions would be greatly appreciated!



    Thanks, Aron.
     
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    On the thyristor... what is the story on what looks like leftover solder or other possible shorts between the component lands ?
     
  3. Aron0789

    Thread Starter New Member

    Feb 25, 2013
    4
    0
    The soldering is fine on the thyristor, there is no bridging, the bridging on the LEDs in ok as its just the solder flowing along the track
     
  4. Aron0789

    Thread Starter New Member

    Feb 25, 2013
    4
    0
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    There is only one way a battery overheats and that is excessive current. I suspect the thyristor is not being turned off correctly or there is a current path through the parasitic diode.

    Impossible to tell until you print the schematic you are using with component values.
     
  6. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    I already made this mistake. The battery holder is cutting through the paint and shorting the battery. Put some black tape on the battery.
     
    Aron0789 likes this.
  7. Aron0789

    Thread Starter New Member

    Feb 25, 2013
    4
    0
    Sussed it!

    the battery shell is conductive, so when the circuit wasn't in use the current was flowing from the batter clips through the battery shell, causing the short.
     
  8. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    That's why you checked here...to find other people that make misteaks:D
     
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