Disconnect dead battery from circuit

Discussion in 'The Projects Forum' started by bignick270, Oct 13, 2009.

  1. bignick270

    Thread Starter Active Member

    Mar 25, 2009
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    How can I disconnect a dead rechargeable battery from a circuit to prevent leakage current from completely draining the battery therefore damaging it? It would be great to find a solution that would have a minimum increase in operating current and a minimum voltage drop from the battery supply.
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    What sort of battery?
     
  3. bignick270

    Thread Starter Active Member

    Mar 25, 2009
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    2 2500 mAh NiMH AA batteries in series
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    how much current do your circuit draw?
     
  5. bignick270

    Thread Starter Active Member

    Mar 25, 2009
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    no more than 150 mA.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Well, two AA batteries put out too little voltage to control a MOSFET gate.

    BJT's and relays would require too much current.

    Probably best to just use a simple switch to disconnect the batteries.
     
  7. bignick270

    Thread Starter Active Member

    Mar 25, 2009
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    The device is enclosed in a case and it can not be easily opened for controling a switch and it is not pratical to have a switch on the outside of the case.
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    I may be wrong here. But the some N fet from International rectifier seams to have a very precise Gate Threshold Voltage fixed at 0.7 volt. As some examples IRF7401, IRF7402,IRL3103,IRL3402,IRL3502. Maybe you can use one battery to control the V gate/source voltage
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so cut a small piece from a plastic milk jug, and insert it between the terminals of the two batteries. That will prevent any current flow from occurring.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Or use a mercury switch, turn box over & batteries are off; used sucessfully in well logging probe 1957.
     
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