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L.E.D. power Consumption.

Discussion in 'General Electronics Chat' started by Glenngg, Nov 25, 2012.

  1. Glenngg

    Glenngg New Member

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  2. KJ6EAD

    KJ6EAD Member

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    The first thing to do is look for a real data sheet for the product from it's manufacturer.

    http://www.paneltronics.com/PartsComponents.asp?op=Indicator+Lights+LED+1/4+Inch

    Since they offer nothing substantial, you'd have to contact them to receive a good lie or measure a sample device.

    From what I know of these, it would have a single LED with a reverse protection diode and a limiting resistor and would pass ~15mA on every half cycle so 120 * 0.015 / 2 = 900mW. You might want to be conservative and call that 1W for energy budget calculations.

    The cost of operation on a monthly basis would depend on electric rates where installed but for example, if your rate were $0.25/kWh, it would cost $0.25 to run for 1000 hours. An average month has 730 hours. I'll leave the rest of the math to you.
     
    Last edited: Nov 27, 2012
  3. dr pepper

    dr pepper Well-Known Member

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    If you used a transformer or switcher you could reduce that even more.
    The led itself assuming its a standard green will use 15ma at 2v approx which is 30mW, a transformer supply assuming you used a 3v trans would use without losses about 45mw, you could assume alltold with losses about 100mw.
    In the uk a kw hour is 15pence and that would run this led for 10,000 hours.
    This is just a rough guide.
     
    Last edited: Nov 26, 2012
  4. dave

    Dave New Member

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  5. Glenngg

    Glenngg New Member

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    Thanks Guys: the reason I asked is I’m on a solar system with only 19Kw of battery backup and I want to put these on my 007 circulators. For the boiler. And every Watt. Is essential. But It looks like It isn’t enough to worry about. Thanks again Genngg
     
  6. RCinFLA

    RCinFLA Well-Known Member

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    A green or red LED as shown has a forward voltage of between 1.8vdc and 2.5 vdc. LED emit light on DC current. The 120vac LED likely has a capacitor ballast to provide the voltage drop from 120 VAC to 2 volts to run the LED.

    This may throw you a little but there is appearent power and true power, the ratio being the power factor of the device. The true power is in the neighborhood of 2 volts x 15 mA or 30 milliwatts. With a capacitive ballast the series cap value would need to provide 118v drop for 15 mA of average current. This is about 7870 ohms of capacitive reactance or about a 0.33 uF cap for a 60 Hz AC grid. Appearent power or V*A magnitude would be 0.015mA X 120 vac or 1.80 VA. Notice I called it VA not watts.

    Power factor would be 0.03 watts/ 1.8 VA or 0.016, which for all practical purposes is just a 0.33 uF cap put across AC line.

    Most all residential grid power meters charge for true watts with no surcharge for poor power factor. You would pay for the 30 milliwatts X time used not the 1.8 VA X time used. Some European countries are regulating power factor by putting requirements on manufacturers to produce a good power factor on some larger power draw appliances, where good is >0.9.

    A dropping resistor could be used for a ballast but this is very unlikely as the resistor would dissipate near 1.8 watts which would make such a small package get too hot.
     
    Last edited: Nov 27, 2012
  7. JimB

    JimB Super Moderator Most Helpful Member

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  8. dougy83

    dougy83 Well-Known Member

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    Judging by the small size of the case behind the LED, it's possible that they're using a resistor and running a high-output LED at e.g. 2mA - then only a standard 0.25W resistor is needed. The power consumption in this case is 0.25W.

    Another option for are Neon indicators; these use less power (e.g. 100uA or 0.012W at 120V) and are more suitable for use on mains.
     
  9. Glenngg

    Glenngg New Member

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    Wow: I asked for answers and I got them. Now you guys are making my head spin. L.O.L …I don’t understand a lot of what you guys say I’m not an electrician just a crane operator.
    I do appreciate all the help. And I do have some neon indicator bulbs from Radio Shack. http://www.radioshack.com/product/index.jsp?productId=2102793 if you think these would be better, I will be installing them in parallel strait on the circulators. Thanks again Glenngg
     
    Last edited: Nov 29, 2012

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