ac current sensor

Discussion in 'General Electronics Chat' started by r3richard, Oct 23, 2011.

  1. r3richard

    Thread Starter New Member

    Feb 22, 2011
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    I've made a simple coil to sense current flowing to the upper and lower elements of two hot water heaters of a hydronic heating system. An led with current limiting resister lets led show when a heater element is on so I can tell if the system is keeping up with the demand or not. But, the collapsing ac when heater turns off is frying my led after a few weeks. I need a bit of guidance to add a diode or choke or what?
     
    Last edited: Oct 23, 2011
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Can you provide us with a circuit diagram?

    hgmjr
     
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Simply putting two LEDs in inverse parallel might help. LEDs normally have very limited tolerance to reverse voltage.
     
  4. r3richard

    Thread Starter New Member

    Feb 22, 2011
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    the led is a three wire red/green unit approx 20ma
     
  5. #12

    Expert

    Nov 30, 2010
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    You're letting AC voltage get on the LEDs. Several cures. Add a diode rectifier in series with each LED. Add a diode rectifier in parallel with each LED. Put 2 LEDs in parallel, but backwards to each other.
     
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  6. chrisw1990

    Active Member

    Oct 22, 2011
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    is that 3V across resistor and led or just the led?
     
  7. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    The drawing indicates ~3V across the LED.
     
  8. chrisw1990

    Active Member

    Oct 22, 2011
    543
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    that sounds a little too high to me?
    if it is 3V across the led, maybe thats whats burning the leds in addition to any potential reverse voltages
     
  9. r3richard

    Thread Starter New Member

    Feb 22, 2011
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