LED's powered by by AC draw more current

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Discussion Overview

The discussion revolves around the power consumption of an LED array powered by AC, specifically addressing the current draw and efficiency of the setup. Participants explore the implications of using capacitors and bridge rectifiers in the circuit design, as well as the potential for measuring power accurately.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • John describes his LED array setup, noting that it draws 6 watts from AC, while the expected consumption based on LED specifications suggests it should only use a little over one watt.
  • Another participant questions the method of measuring power, asking how the 6 watts were determined and suggesting that measurement techniques might be flawed.
  • John mentions using a digital power meter to measure the power, indicating that it showed accurate readings with other devices, but suspects leakage from the diode bridges may contribute to the higher power draw.
  • A participant suggests that switching to a 12 volts DC system could simplify the setup and eliminate components like capacitors and diodes, potentially allowing for clearer measurements of current draw.
  • There is a concern raised about safety when working with mains voltage and the necessity for proper insulation and mounting of components.

Areas of Agreement / Disagreement

Participants express differing views on the efficiency and measurement of the LED array's power consumption. There is no consensus on whether the current loss is acceptable or on the accuracy of the power measurement technique.

Contextual Notes

Limitations include potential inaccuracies in measurement techniques, assumptions about the efficiency of the circuit design, and the implications of using AC versus DC power for LED operation.

Who May Find This Useful

Individuals interested in LED circuit design, power measurement techniques, and the implications of using AC power for LED applications may find this discussion relevant.

John1397
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I built an array of 14 LED's the 20,000 mcd's ones maybe drawing 25 ma at 3.3 volts with each two LED's powered from 125 volts AC then to a .22 mfd capacitor in series feeding a full wave bridge rectifier so there are 7 capacitors and seven full wave bridges feeding all 14 LED's and they draw 6 watts power on AC and if you figure just the power consumption of 14 LED's at 25 ma on 3.3 volts they should only use a little over one watt is this an acceptable amount of current loss?

John
 
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John1397 said:
I built an array of 14 LED's the 20,000 mcd's ones maybe drawing 25 ma at 3.3 volts with each two LED's powered from 125 volts AC then to a .22 mfd capacitor in series feeding a full wave bridge rectifier so there are 7 capacitors and seven full wave bridges feeding all 14 LED's and they draw 6 watts power on AC and if you figure just the power consumption of 14 LED's at 25 ma on 3.3 volts they should only use a little over one watt is this an acceptable amount of current loss?
So this is a cheap and nasty method to power some LEDs for lighting, is it? Did you get the circuit from a publication, or is it your own plan?

Everything needs to be treated as though it is live at mains voltage, as indeed it only too easily can be. All wiring insulation and the LED mountings must be suitable for providing safety as though at 125VAC.

https://www.physicsforums.com/images/icons/icon2.gif How did you measure the 6 watts?
 
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I seen this searching for ways to power LED's from AC it seemed easy has no transformer which wastes current to, but I see LED lamps that have 42 LED's and only draw 3 watts. I plan to switch them all to run off 12 volts DC so this will eliminate all the capacitors and diodes then I will be able to see how much current they draw.
 
Using DC will make it simpler to measure the power, but won't much change the current the LEDs need for a particular intensity of output. You didn't answer:
How did you measure the 6 watts?
It may well be that your measurement technique is wrong.
 
Used a digital power meter even plugged in a 7 watt Christmas bulb and showed 7 watts so I know it is right seems most of the leakage is is on all these diode bridges.

John
 

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