Am I doing this wrong?

Discussion in 'General Electronics Chat' started by antaine1916, Dec 24, 2013.

  1. antaine1916

    Thread Starter New Member

    Dec 24, 2013
    Let me preface this by saying I'm an extreme newbie. I've wired eight models before this one, but I have either been following LED kits or told my local store what I wanted to do and had them hand me what I needed for the circuit.

    So, I've parallel-wired a set of four LEDs into the roof/ceiling of a model I've built. I assembled the circuit that I've drawn in the picture (except that I have the resistor on the positive lead and not the negative). The LEDs came in a kit that had resistors rated for certain voltages. I'm using an A23, 12v Energizer. I've used the same LED kit in other models with no problem (sometimes even with 5 LEDs).

    This one seems to drain the battery exceptionally fast, even when the LEDs are not on. I put a fresh battery in the model last night, switched it on for thirty seconds to test it. Today, I switched it on to admire my work and the LEDs were very dim. Tonight, the battery is dead. The whole thing has been switched off pretty much the entire time. That's the second battery this setup seems to have killed in as many days, with it "off" almost the entire time.

    Now, my configuration is a little different from my other models, largely dictated by the layout of this particular model. I've checked to see that none of my joints accidentally touch, and I have no loose solders (a fresh battery shows nice and bright, but I hesitate to leave it in there because I have no spares and I'd have to take it out of another model).

    It was my understanding that the order of the elements doesn't actually matter...have I unwittingly done something wrong, causing the battery to drain even when the Leds are not on?
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    Your toggle switch is in the wrong position. Actually, when it is in the off position, the LEDs will light. But when it is in the on position, you have almost a direct short across the battery. I say almost because the resistor is in series with the current flow but certainly will allow to much current to flow draining your battery fast. I leave the calculation of the actual current draw as an exercise. The toggle switch should be placed in series in one of the wires leading from the battery.
  3. ronv

    AAC Fanatic!

    Nov 12, 2008
    The switch needs to be in series with the resistor. As it is now when you throw the switch it shorts out the battery (through the resistor). The leds go out but the battery is still draining. I'm thinking your leds have built in resistors???
  4. antaine1916

    Thread Starter New Member

    Dec 24, 2013
    Thanks. I had a feeling it was something like that, but I thought it just broke the circuit and thus it didn't really matter. A lot of what I read backed that up.

    I appreciate the quick reply.

    My switches are really tiny and they're not marked on or off...I only know which way is which when the lights go on (or off).
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
    You can make the most efficient use of the battery by putting the LED's in series.

    Check the voltage across 1 LED using a series 1k ohm resistor.
    (Voltage drop changes depending on the LED color)

    For example, if the voltage drop across 1 LED is 2.1 volts then for 4 in series it would be 8.4 volts. Then calculate your series resistor from there..
    Last edited: Dec 24, 2013