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Strange electrical anomaly — Parallax Forums

Strange electrical anomaly

xanaduxanadu Posts: 3,347
edited 2013-07-09 07:26 in General Discussion
This isn't one of those gag LED won't shut off type videos, it's 100% legit. Maybe someone it used to seeing this, I really don't know but thought I'd share it and feedback is always most appreciated.

A friend of mine asked if I could custom wire LED strips into display cases. I decided to solder them in place. When I touched the soldering iron tip to the positive (+12v) of the LED strip and put my finger on the resistor a few LEDs would glow. Maybe more of a flicker. My soldering iron's tip is earth grounded. I checked the soldering station and it is isolated with infinite resistance across the tip and the AC side with a dead short from the tip to ground.

Pretty freaky, there's an electrician coming to check it out. I couldn't measure any AC or DC between myself and that third prong but the LED had no problems showing it...

[video=youtube_share;dkZ-GjmX7As]

Comments

  • CuriousOneCuriousOne Posts: 931
    edited 2013-07-08 00:17
    Check this out, same "feature" but without the soldering iron even :)

    http://www.youtube.com/watch?v=IelSPYNaVcw
  • Mike GreenMike Green Posts: 23,101
    edited 2013-07-08 06:46
    There are all kinds of sources of small amounts of electrical power around. Remember that an LED is a diode, so you could be supplying a small amount of AC with the soldering iron providing earth ground. Try the same experiment in different places. You'll find that it works in some areas and not in others. The source is likely induced current from the power wiring in the area. It doesn't take much to make an LED flicker. There's even a measurable voltage between parts of your body, like top of head to foot, even in the absence of power wiring. Remember that the ground wire may travel some distance from the circuit breaker panel to the socket where the soldering iron is plugged in. All of that wire is subject to having voltage induced in it (mostly magnetically) from other wiring. If there's a radio transmitter nearby (or even at a little distance if it's high power), your ground wiring may be acting as an antenna.
  • davejamesdavejames Posts: 4,047
    edited 2013-07-08 09:32
    xanadu wrote: »
    Maybe more of a flicker.

    Can you guesstimate the rate of "flicker"? 60 FPS maybe?
  • skylightskylight Posts: 1,915
    edited 2013-07-08 10:17
    Nice guy as you sound, I hope you don't mind if I don't shake hands :lol:
    Seriously though, you can see how much electricity you have in you if you touch a finger on a probe tip on a scope
  • ercoerco Posts: 20,256
    edited 2013-07-08 10:24
    Stray fields? I had a similar weird experience when I remodeled my kitchen in my 1958 ungrounded, raised foundation house. I was installing ceiling flourescent lights (with a dropped ceiling & translucent panels). My installation was a frustrating, infinite DO loop:

    DO
    TEST LIGHTS ON FLOOR
    IF WORK THEN INSTALL IN CEILING
    INSTALL: TEST LIGHTS ON CEILING
    IF WORK THEN BEER
    TAKE LIGHTS DOWN
    LOOP
    BEER: 'never got here

    Long story short, the lights worked perfectly on the floor, but not on the ceiling. Turns out they needed to be grounded. But even ungrounded, they worked on the floor since they were relatively close to the ground/earth and the "field" made the connection. Quite maddening until I figured it out. Fortunately, in the kitchen, there was a nice new shiny copper cold water line handy to ground the lights, which quickly solved the problem. Eventually, I had that beer.
  • xanaduxanadu Posts: 3,347
    edited 2013-07-08 15:20
    Thanks guys. I assumed that if it were a good earth ground that the electricity wouldn't be trying to go through me. Oh well, hopefully the electrician doesn't charge them too much. I guess LEDs are a lot more sensitive than I had thought. Also, yes the flicker appeared to be like some kind of induced 60hz AC.
  • xanaduxanadu Posts: 3,347
    edited 2013-07-08 22:51
    I'm no electrician but I'm pretty sure this is not right:

    IMG_1924.jpg


    I soldered the rest of the strips in anyway:

    IMG_1925.jpg


    The "designer" will be affixing the strips. Not my design, just the guy with the soldering iron...
    IMG_1924.jpg
    1024 x 768 - 110K
    IMG_1925.jpg
    1024 x 768 - 54K
  • lanternfishlanternfish Posts: 366
    edited 2013-07-09 02:11
    I showed the top pic to an electrician friend. I can't repeat what he said so to paraphrase "that doesn't look good and probably needs r inspection".
  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2013-07-09 05:30
    This reminded me of this article: http://www.evilmadscientist.com/2007/cooking-hot-dogs-via-electrocution/
    Apparently if you stick LED's in an electrocuted hotdog they light up, regardless of positioning or polarity. The article doesn't explain how this happens, though.
  • HarbingerHarbinger Posts: 7
    edited 2013-07-09 06:58
    xanadu wrote: »
    I'm no electrician but I'm pretty sure this is not right:

    IMG_1924.jpg


    I soldered the rest of the strips in anyway:

    IMG_1925.jpg


    The "designer" will be affixing the strips. Not my design, just the guy with the soldering iron...

    Nothing looks bad to me but im not an electrician. Seems to be wirenuts in a grounded junction box looks fine. Your lights looks good by the way.
  • CircuitsoftCircuitsoft Posts: 1,166
    edited 2013-07-09 07:26
    xanadu wrote: »
    I'm no electrician but I'm pretty sure this is not right:

    IMG_1924.jpg
    You're correct - black is the "hot" line, and should not be connected to ground or using the ground wire.
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