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How do I keep a flashlight bulb from prematurely burning out when charging batteries?

Discussion in 'Electronic Basics' started by ray, Aug 6, 2003.

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  1. ray

    ray Guest

    I am building a rechargeable flashlight which uses 2 1500 mah NIMH AA
    batteries and a .78watt 2.6V 0.3A T1 bi-pin bulb, and on/off switch.
    The charging transformer output is 7.35v DC 550 mA, which plugs into
    the bootom of the flashlight via a dc jack.
    How can I wire the flashlight so that if the user turns it on while
    plugged into the charging transformer it will not cause the bulb to
    burn out from too much power. Specifically, should I put in a
    resister? If yes, How many ohms? and where in the circuit?
    My preference would be to have the flashlight bulb not come on at all
    if someone tries to turn it on when the batteries are recharging. Is
    there a way to do this easily? And if so, How?
    Any help greatly appreciated.!
  2. Dick Johnson

    Dick Johnson Guest

    Make the switch a single pole double throw type. Connect the battery to the
    bulb in one direction and to the charger in the other direction.
  3. John G

    John G Guest

    DC jacks have built in switch just for this purpose generally.
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