Weird 9V Battery heat problem

Discussion in 'The Projects Forum' started by Rob1132, Jun 7, 2011.

  1. Rob1132

    Thread Starter Member

    Nov 4, 2010
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    Ok, so I built this kit. It's very simple and I've made it before. You just have to solder wires to the geophone and plug everything in to the circuit (which is already built). This time around though, I decided to try something a little different by adding an on/off switch to the device. I bought this switch from Radioshack. I soldered a 9v battery clip to the switch and then also a wire to both the positive and negative ends. I plugged the wires into the circuit.

    When I tested it out, it worked fine at first. But then when I turned it off, I noticed the 9V battery (an Energizer; I'll get to why that matters in a second) got super hot. So I of course unplugged it. Here's where it gets really weird. I tested it again later with the battery outside of the project box I had everything in thinking maybe connections were touching. The battery was fine, but this time around I used a Duracell battery. I plugged two different Energizer batteries in then and they both got hot while the Duracell remained cool. The only thing I can think of is that the Duracell battery that was ok I had used for other devices before. Could it have worked because it's not at full power while the Energizers were right out of the box? And if that is the case, would I just have to add a resistor onto the switch to make it stay cool?
     
  2. #12

    Expert

    Nov 30, 2010
    16,278
    6,789
    Difficult to understand your words. Can you please post a drawing?
     
  3. Rob1132

    Thread Starter Member

    Nov 4, 2010
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  4. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    From your drawing it appears you have the switch connected
    between the red wire and the black wire. Is this how you have
    it connected?

    If this is how you have connected it you are shorting
    the battery. This will draw too much current for the battery
    to deliver, therefore it will get hot.

    As far as:
    My guess is the switch was actually OFF (disconnected) when the circuit was working this allowed current to flow to the device. Then when you flipped the switch, you actually turned it ON (connected), this shorted
    the battery, robbing all the current so the device/circuit turned off.

    The Duracell battery probably died quickly.

    This is all based on my interpretation of you drawing. I may be wrong.

    Do not attempt this with NiCad, NiMH, LiPo, or any other batteries for that matter. You will have a fire.
     
    Last edited: Jun 7, 2011
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    Yes, that is what it looks like you did. You should not connect the switch between the positive and negative wires. You need to connect it in series with the positive wire. What happened was that when you closed the switch, it shorted the terminals of the battery, which allowed a lot of current to flow. This is why the battery heated up.

    To fix it, cut the red wire in half and put one of the "new" ends of the red wire on one side of the switch. Then take the other "new" end and connect it to the other side of the switch. That way, when the switch is open, current can't flow at all because it is an open circuit.
    I hope this helps!
    Der Strom
     
  6. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    I'd say the others diagnosed the problem for you. A basic lesson for all folks to take away from this is: if something like a battery gets hot, you're drawing too much current from it. Look for a short or low resistance connection.
     
  7. Rob1132

    Thread Starter Member

    Nov 4, 2010
    36
    0
    Thanks for the help. I'm still pretty new at this stuff and this was the first time I tried adding a switch to something. I don't quite understand the explanations as to how to fix it still though.
     
  8. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    The black wire in your drawing should not go through the switch. It gets hooked directly from the snap to the terminal.

    The red wire goes through the switch - from the snap to one tab of the switch, and from the other tab of the switch to the terminal.

    Make sense now? If not, I can draw a diagram for you.
     
  9. Rob1132

    Thread Starter Member

    Nov 4, 2010
    36
    0
    Ok thanks, I'm pretty sure I get it now. I will try re-wiring it tomorrow.
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    The magic word is "circuit". Current will flow in a loop from high potential to low. In your case, you created a complete loop through your switch, and this was the path of least (and low) resistance. So you got a high current while the battery rapidly discharged. Lucky it wasn't a ni-cad!

    A switch should complete the loop, by being in series with the rest of the circuit, and not become its own loop by being in parallel to the power supply.
     
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    Like this:
    [​IMG]
     
    Last edited: Jun 7, 2011
  12. Rob1132

    Thread Starter Member

    Nov 4, 2010
    36
    0
    Alright, that's what I thought I had to do after reading over the explanations from everyone else. That diagram makes it very clear though. Thanks again to all who helped.
     
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