AA batteries hot with LED strips

Discussion in 'General Electronics Chat' started by Gr1m3eaper, Jul 21, 2014.

  1. Gr1m3eaper

    Thread Starter New Member

    Jul 21, 2014
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    Hey guys. I found an instructable for a lamp and instead of using a normal household light globe ive decided to use LED strips that ive previously used for a computer mod. Theyre 12V and ive wired them up to a 8x AA battery holder with a switch. Wired them up and they work fine but when i turned them off i went to go do something else and came back a few minutes later, the AA batteries were quite hot. What causes this? Have i wired them up wrong? Should i have used a resistor somewhere? Dont have much electronics experience so not sure if theyre in serial or parallel. Cheers for the help guys :)
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    LED strips which have powerful LEDs use a LOT of power. Your long-suffering batteries have to provide that, and in doing so the current through their internal resistance generates heat.
    The LED strip, if rated for 12V, probably already has a resistor built-in. An external resistor could be used in series with such a strip to reduce the LED current (hence battery heating but also light output).
     
  3. Gr1m3eaper

    Thread Starter New Member

    Jul 21, 2014
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    would the quality of the batteries have something to do with the heat? i just bought cheap ones instead of good quality just to test. also how much current would it draw? im using 4 strips with 3 LED's per strip
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Poor quality batteries might have a higher internal resistance than top quality ones. As for current draw, what is the rating of the strip or LED? Can you upload, or post a link to, its type number or specification/datasheet?
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Were the batteries hot before you turned them off? Slight possibility that SW was wired wrong, shorting battery when off.
     
  6. Gr1m3eaper

    Thread Starter New Member

    Jul 21, 2014
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  7. Gr1m3eaper

    Thread Starter New Member

    Jul 21, 2014
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    <a href="http://tinypic.com?ref=vgqttv" target="_blank"><img src="http://i57.tinypic.com/vgqttv.jpg" border="0" alt="Image and video hosting by TinyPic"></a>

    [​IMG]
     
    Last edited by a moderator: Jul 21, 2014
  8. Gr1m3eaper

    Thread Starter New Member

    Jul 21, 2014
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    gahh its not letting me upload images. i think theyre just generic LED strips. i see no marking on them just DC12V and little markings on what i assume are the resistors. no the batteries werent hot before i turned them off. i wired it all up, glue the LED strips in place, inserted the batteries to make sure they worked, turned it off left the room for a few minutes. When i came back the batteries were quite hot. I am using really cheap batteries as they were all i could buy at the time.
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    As Bernard guessed, you wired the switch wrong and you are shorting the battery.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Can't tell from the pic how the '151' resistors (150 Ohm) are wired, but if each LED is in series with a respective resistor then your four LED strips will dissipate in total about 12 x 12 x (12-3.5)/151 = 8.1 Watts. Your batteries would have to provide ~0.67A. No big surprise they got hot! If they're wired differently the wattage could be less; but then I don't see why each group of 3 LEDs would need 3 resistors.
     
    Last edited: Jul 22, 2014
  11. BobTPH

    Active Member

    Jun 5, 2013
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    Except that they get hot when the strips are turned OFF. Agree with Bernard, and MrChips, the switch is shorting the batteries.

    Bob
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    Cheap crappy batteries might not even contain enough energy to get hot.

    IIRC - anything over about 5W is pushing your luck with AA size batteries.
     
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