9 volt battery getting really hot! Please help.

Discussion in 'General Electronics Chat' started by marcos77, Dec 22, 2012.

  1. marcos77

    Thread Starter New Member

    Dec 22, 2012
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    Hi. Not sure if I'm posting in the right place but here goes. With Xmas around the corner I decided to visit my local Hobby store and purchased two small white LED lights to use as headlights for my kids Losi Micro remote control truck. I then stopped by Radio Shack to pickup a Push On/Off Switch, 9 Volt battery along with a 9V Battery Snap Connector. I connected everything and the lights work great! Only problem is that the battery instantly gets very hot to the touch. Something is not right. I feel like an idiot and know nothing about this. I just wanted to surprise my kid. What am I doing wrong?

    I did notice that when the switch button is pushed in the lights turn off and when the button is pushed out the lights come on. I think I have it reversed, not sure if that would make a difference. Also, on the Switch package it says, "Contacts rated 3A at 125VAC and 1A at 250VAC". I have not idea what that means. I also have all of the colored wires together. Black with black and red with red. Would posting a photo help? I really need help so that I don't have to scrap this project. Thanks
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    The switches have nothing tp do with it. It is the LEDs. You will need some kind of current limiting on the LEDs. Post the specs.

    Depending on the type of LED a 9V battery might not last very long.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    9V Cannot supply much current but it can light 5mm LED's with a 220Ω 0.25W Resistor in series with each without a problem
     
  4. marcos77

    Thread Starter New Member

    Dec 22, 2012
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    Added photo attachment. I don't have the exact specs but it's two single 3mm LEDs. Not sure what else I would need.
     
  5. marcos77

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    Dec 22, 2012
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    ok. I tried something else. This time I bypassed the on/off switch and connected the 9V battery directly to both LED wires and the battery remained cool to the touch. Red to red and black to black. Maybe I should just skip the switch but it will be a pain to remove the battery every time.
     
  6. marcos77

    Thread Starter New Member

    Dec 22, 2012
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    I'm thinking that the wires may have been touching each other on the switch causing the battery to heat up. Is that possible? Red and black
     
  7. marcos77

    Thread Starter New Member

    Dec 22, 2012
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    I used wire glue to attach the wires to the switch. I think that may have caused it to overheat. I put too much glue and I believe it spread to the other side.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    me thinks you wired the switch in parallel with the LEDs and battery instead of in series.
    Did you put both RED and BLACK wires to the switch? That is not the correct way to connect the switch.
     
  9. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    A schematic from the OP instead of a phot would have shown this.

    And "glue" is not the way to connect electrical components together.
     
  10. spinnaker

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    Oct 29, 2009
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    Not if the LEDs were lighting.
     
  11. spinnaker

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    Oct 29, 2009
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    That picture doesn't show anything except for a tangle of wires. Draw a schematic.

    You should have gotten the specs when you bought the LED. If not then that is a reason not to buy from a hobby store. Check Radio Shack, they might have them.

    Assuming a forward voltage on the LED of 2.5V @ 20ma, you will need a 330 ohm resistor in series with the led.

    [​IMG]


    There are many articles on using these LEDs for hobbies such as trains. Please google them.
     
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  12. Audioguru

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    Dec 20, 2007
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    You connected the switch parallel to the battery so the battery was shorted when the switch was pressed. I have not seen "wire glue" but if it conducts electricity and shorts both terminals of the switch then it also causes a high battery current.
    You NEVER EVER want to short a battery!

    The 3.5V white LEDs were also parallel to the 9V battery with nothing except the internal resistance of the battery to limit the resulting high current.

    High current from a little 9V battery causes it to get hot.

    Now the battery is drained so it doesn't get hot anymore and the LEDs were also killed by the high current so they will not last long.

    Find a friend, neighbour or relative who knows a little about electricity to connect the circuit correctly using 220 ohm current-limiting resistors in series with each LED.
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Especially because the LEDs were lighting (OP said lighting when the switch was OFF, and would turn off when the switch was on).
     
  14. spinnaker

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    Oct 29, 2009
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    Ahhh missed that. Well yeah that explains it and that is one messed up circuit. :)
     
  15. GopherT

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    Nov 23, 2012
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    Based on the facts that you bought your LEDs from the hobby store and they are not burned out yet, I assume your LEDs have resistors built in. If that is the case follow these instructions.

    1) Connect the red battery (+) to one switch terminal.
    3) connect other end of switch to anode of one LED (+ or red)
    4) connect cathode of LED from step 2 (- or black) to anode of second LED (+ or red)
    5) connect cathode of second LED (- or black) to battery black wire (-).

    It would be best to put all the parts in a bag, wrap it up with gift paper. Also buy a soldering pencil and a roll of solder ($10 or less total from RadioShack) and wrap that too. . Give everything to your kids for Christmas. On Christmas Day, spend an hour with them explaining to them the circuit, have them draw it out on paper then have them HELP YOU solder everything together and mount it. Even if they are 5 years old, the will understand. You could even do some "experiments" to see what happens if an LED is wire backwards, or the switch is by-passed with a jumper wire.

    If your LEDs burn out in a short time, you will need a 220 ohm resistor from RadioShack. Put it between the switch and first LED (when you rebuild the circuit because both LEDs will need to be replaced.

    Also, watch the many "how to solder" videos on YouTube with your kids. Remember to wear safety goggles when soldering and testing your circuit - hot batteries eventually pop open and over powered LEDs can pop. Good luck and make it fun. Everyone actually learns more from mistakes and "experiments".
     
  16. Audioguru

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    Dec 20, 2007
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    The photo shows that each LED has shrink-tubing with a bulge underneath (the current-limiting resistor?) and small wires protruding.
     
  17. GopherT

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    Nov 23, 2012
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    That is what i thought too.
     
  18. marcos77

    Thread Starter New Member

    Dec 22, 2012
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    ok thank you. I'm good now. I had wired it incorrectly. I followed the diagram for a basic type of switch - the On/Off switch with just 2 prongs.
     
  19. spinnaker

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    Oct 29, 2009
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    Please tell us you used a current limiting resistor too.
     
  20. GopherT

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    Nov 23, 2012
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    I don't think he needs them, the "hobby" LEDs already have a resistor attached under the heat-shrink tubing on the leads. See, OPs photo.
     
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