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Thread: Low voltage LED interference

  1. #1
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    Low voltage LED interference

    Heres the setup:

    7-24v LED puck lights(WAC lighting) in kitchen on a standard single pole switch(no dimmer).

    5 watts each on a 24volt AC 60 watt dimmable (ELV) transformer

    Heres the problem:

    When the lights are on, the garage door opener will not work via remote from car, key pad at door, or button at back door. Television becomes fuzzy as well(antenna in use).

    Garage is nearby

    Transformer is mounted directly behind disposal under the sink.

    Is the disposal amplifying the interference? Can it be shielded or is it affecting the entire circuit? Would shielded low voltage wire solve this? So many questions...

  2. #2
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    Gar is the guy to ask. But I can tell you that the disposal is not "amplifying" any interference. If it were me I would just replace those junk lights and power supply with a different brand and be done with it.

    -Hal

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    181201-1934 EST

    sosuaveone:

    An LED semiconductor chip is a diode that emits light. Thus, it conducts in one direction only. So long as you do not exceed the PIV rating (Peak Inverse Voltage or breakdown) you can apply a reverse voltage and not damage the LED. No light is emitted in the reverse direction. In the forward direction a lot of current flows at a low voltage, somewhat above 1 V. So long as you do not exceed a reasonable current the chip will not be burned out. Current limiting is required. In the forward direction an LED emits light in contrast to an ordinary diode.

    What is an LED puck light? By that I mean how does it work? Is it just an LED chip or chips? Does it use resistive current limiting or something more complex?

    Note: strip LED lights are strictly DC. What does that mean? It means that the strip consists of LED chips in series with a series current limiting resistor, and many of these in parallel as the strip gets longer. A strip LED assembly may light on AC, actually it should, but will only conduct on 1/2 cycle. If AC is applied it must not exceed the PIV rating. In the forward direction the internal current limiting resistor, and the number of LED chips in series determines the design rated voltage.

    On DC a strip LED assembly is polarity sensitive? Meaning works with on polarity and not with the other.

    An LED chip with applied DC does not emit noise.

    How does the puck light compare with the strip light. I don't know. Possibly some literature will tell you. Not likely, but possibly indirectly.

    An ordinary CREE 9.5 W screw in bulb has lots of internal electronics that allows it to run from a 120 V 60 Hz sine wave, a phase shifted dimmer output, or a reduced voltage sine wave. How does the puck light compare with the CREE? I don't know. Does the CREE emit RFI? Some but not a severe amount in the AM broadcast band. It is more in the 50 kHz range. If fed from a phase shift dimmer it will make more noise in the AM range, but this is a result of the dimmer and not the LED bulb. From the dimmer noise results because of the rapid change of voltage at the turn on in the cycle. This is also true of an incandescent bulb on a phase shift dimmer.

    How can you study your LED puck problem. I suspect a battery powered AM radio can be a good detector. Pick a frequency with only a weak AM signal. Apply power to the LEDs, does the background noise increase? If so, then a useful detector.

    Apply a DC input to the puck light. Do you get noise? If so, then you have puck problems. You could use a filter at each puck, and probably solve the problem, or select a different puck.

    If no RFI with DC excitation, then your problem originates with the dimmer power supply. This requires changing to a different supply.

    If you need dimming, then there are ways that would minimize noise.

    .

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    Thanks for the response gar. Very informative and greatly appreciated.

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    Seems this problem comes up all the time. Isn't all electronic equipment sold in this country required to meet FCC requirements for maximum emission of interference? As I recall, it's part 15 and there are two classifications, Class A and Class B. Class A is residential locations and restricts the emissions the most. Class 2 is for equipment designed to operate in commercial/industrial locations and the requirements are more relaxed. There is a stipulation that if the device causes harmful interference the owner must remediate it or shut it down.

    This is why you see those ferrite choke cores on the line cords of computers and other equipment for instance.

    So what happened to LED lighting? Have we been so caught up in the feeding frenzy that we let this little requirement be ignored?

    -Hal

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    Quote Originally Posted by hbiss View Post
    Seems this problem comes up all the time. Isn't all electronic equipment sold in this country required to meet FCC requirements for maximum emission of interference? As I recall, it's part 15 and there are two classifications, Class A and Class B. Class A is residential locations and restricts the emissions the most. Class 2 is for equipment designed to operate in commercial/industrial locations and the requirements are more relaxed. There is a stipulation that if the device causes harmful interference the owner must remediate it or shut it down.

    This is why you see those ferrite choke cores on the line cords of computers and other equipment for instance.

    So what happened to LED lighting? Have we been so caught up in the feeding frenzy that we let this little requirement be ignored?

    -Hal
    It couldn’t possibly be the problem of where these devises are made, could it?
    Tom
    TBLO

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    Is LED lighting seemingly exempt?

    https://www.cableorganizer.com/image.../FCC-rules.pdf

    ETA- seems I have the classes confused. A Class A device is for use in industrial/commercial and Class B is residential.

    -Hal

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