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My breadboard RC circuit not working

Discussion in 'General Electronics Discussion' started by NuLED, Jun 22, 2013.

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  1. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    OK back to hands on experimentation.

    I rigged this up to understand how the RC time constant works.

    With no power to the relay, the right side LED lights up.

    The RELAY here will break that connection when the relay is powered. And when it does the other LED (left side) lights up. And it also breaks the circuit to the relay, so it resets.

    I put a capacitor in to slow it down a bit, and it works. I measured maximum voltage across the capacitor.

    8.44 volts MAX on the capacitor during these cycles.

    HOWEVER when I add in a resistor to slow down the recharge rate of the capacitor, it does not work. The max voltage I get across the capacitor is a mere 0.328 volts and it does not go higher. The larger the resistor, the less voltage stored by the capacitor. The relay NEVER cycles.

    I am not sure where I wired this wrongly.

    ???

    (Photos show set-up with resistor, and then a couple of shots with no resistor but just a wire directly to power, and there you can see the voltage gets up to 8.44v)
     

    Attached Files:

  2. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    1000 uF capacitor.
     
  3. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    I want to do more experimentation and connect just a capacitor with resistor, directly (no relay, no LED, etc). And measure the voltage as it accumulates across the capacitor.

    But what happens to the capacitor at maximum charge? It won't explode or anything right? Assuming polarity is correct. The 1000 uF capacitor I have says 25V and my battery 8xAA is max 12V.

    (What would be the max voltage on the capacitor?)

    OK to experiment?
     
  4. davenn

    davenn Moderator

    13,596
    1,875
    Sep 5, 2009
    can you draw and post an actual circuit diag of your setup, just makes it a little easier to visualise :)

    Dave
     
  5. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    Yikes. OK but please answer my last query first, because that could mean I have the confidence to go ahead and experiment without worrying I am going to spray capacitor bits all over my desktop. I can just connect them in series with the 12V right?

    (I will have to take some time to draw the schematic properly :)
     
  6. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    12V battery -> Resistor -> Capacitor -> Ground

    Then measure voltage across Capacitor as it accumulates. Is good?
     
  7. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    Ha! Okay, I took a leap and connected it all up, and put a plastic "shield" over it. I used one of those mutual fund reports to protect my desk (which is about the only thing they are good for these days, hahaha).

    Well, now I know these things don't blow up and it stabilized at around the voltage going into the circuit.

    So, off for more experimentation. I will see if I can debug what's wrong with the breadboard.
     

    Attached Files:

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