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Infra red illuminator

Discussion in 'The Projects Forum' started by mouth_, Aug 23, 2011.

  1. mouth_

    Thread Starter New Member

    Aug 23, 2011
    Hi, i have an infra red illuminator that runs off a mains adapter providing it with 12V 500mA and i would like to run it off batteries instead. I have a 12V 1300mAh battery to supply it, how do i work out the resistance i need to add in to make this work?
  2. elec_mech

    Senior Member

    Nov 12, 2008
    Hi mouth_,

    You don't need a resistor. Your illuminator should only pull the current it needs. Most mains AC to DC adapters are cheap and provide anywhere from 12V to 18V depending on the load. The illuminator already has whatever current-limiting resistors it needs. Since you are replacing said adapter with a battery of the same voltage, you can hook it up directly.

    If the battery is fully charged and the illuminator really needs 500mA, then you'll get a little over 2 hours of operation before the battery needs to be recharged.
  3. wayneh


    Sep 9, 2010
    If you want to convince yourself, measure the voltage seen by your light under load. I'll bet the adapter is supplying more voltage under load than the unloaded voltage of the battery.
  4. someonesdad

    Senior Member

    Jul 7, 2009
    Warning: you should research the amount of charge you should take out of your battery before you recharge it. Don't blindly assume the amp*hr rating of the battery means that's what you can take. Discharging a battery too deeply can shorten its life.