Beginners Capacitors

Discussion in 'General Electronics Chat' started by Dal1980, Aug 31, 2015.

  1. Dal1980

    Thread Starter New Member

    Aug 30, 2015
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    A long time ago at school I was taught that a capacitor was like a barrel with a hole at the bottom (+) and a hole at the top (-). Electricity would act like water and come in at the bottom (+) and begin filling the barrel until it eventually was full/charged enough to allow the flow of water/electricity to flow out the top (-).

    After reading about capacitors again it appears that this is actually the reverse of what I was taught? Only when the barrel was full does the flow stop.

    Experiment

    Battery (measuring 2.5v according to my multimetre)
    LED
    Electrolyte Capacitor 100uF (10v?)


    Attached Battery + to + leg of Cap
    - Leg of Cap to + of LED
    - Leg of LED to - Battery

    LED was lit and waited 20 or so seconds. LED has not flashed or changed at all.

    Should the capacitor not fill and stop the flow of electricity thus turning off the LED?

    capled.jpg
     
    Last edited: Aug 31, 2015
  2. Jony130

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    Feb 17, 2009
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  3. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    According to my sim. The LED will only light up for a fraction of a second and will stop after the cap is fully charged. And although a voltage remains across the LED (about 1.4V) due to it's inherent voltage drop, no current will flow through it.

    Untitled.png
     
  4. Dal1980

    Thread Starter New Member

    Aug 30, 2015
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    Left it on for a good couple of minutes... no change. The LED will not stop lighting.

    IMG_1682.JPG
     
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    According to your schematic, the capacitor is the wrong way round.

    But, it appears from the breadboard that the capacitor is short-circuited.
     
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  6. Dal1980

    Thread Starter New Member

    Aug 30, 2015
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    Ah, my mistake. I'm new to breadboard tactics. I'm running the cap in parallel with battery

    :oops::rolleyes:
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    The polarity of capacitor was wrong, it could be damaged, now it isn't damaged, because the voltage is too low and the time is not coming, but someday it will.

    The led didn't flash because the capacitor didn't discharge.
     
  8. Dal1980

    Thread Starter New Member

    Aug 30, 2015
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    Wrong way Blocco? I thought the short leg was negative... actually, forget my diagram... I'm new to them too :oops::oops:

    Oh dear, this is not going well for me :(:)
     
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  9. Dal1980

    Thread Starter New Member

    Aug 30, 2015
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    Ta-Da - It worked... I mean "I worked" lol

    IMG_1683.JPG
     
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  10. cmartinez

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    Jan 17, 2007
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    You remind me of me.... about 30 years ago! ha ha ha...
    Anyway, what were you using to power up the LED? A battery cell? if you didn't place a resistor in series in the circuit, the LED would've lighted for a few minutes and then... pooff!!
     
  11. cmartinez

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    Jan 17, 2007
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    Good lord... I placed the cap in my sim using the wrong polarity!
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Haha, glad to see I'm not the only one. Having two options causes a few errors, Murphy's law and all. When there are 3 or more options to consider (like 3-way switches), it's a miracle we ever get it right.
     
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  13. ScottWang

    Moderator

    Aug 23, 2012
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    You just take easy for your error, I involved EE close to 40 years, I still make some errors, and I will also make mistake in the feature, unless you left EE behind, otherwise you can't prevent it completely, only can be reduce.

    You just need to learn more basic theories and refresh your memory, go go go ... :)
     
  14. Dal1980

    Thread Starter New Member

    Aug 30, 2015
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    No resistors are in my circuit but had the LED lit for a good 5 minutes at least. Using 2.5v (2x AA batteries).
     
  15. cmartinez

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    Jan 17, 2007
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    Well, I'm very surprised the LED survived that long!
     
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