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What could cause significant magnetic field shifts at home?

  1. Aug 16, 2015 #1
    Hi everyone. I have a question that I would be grateful to receive your insights on.

    In our bedroom, we have a LED strip running from a typical 12V transformer. We turn it off at night using the controller box, which is in between the LEDs and the transformer. The thing is, a couple of times per day at irregular intervals, the LEDs will light up for a fraction of a second, even as they are turned off. They also tend to create a plopping sound, and send our nearby mini fridge buzzing. Originally, I suspected voltage spikes, but putting the transformer behind voltage spike protection didn't change a thing. Then we insulated the transformer against electromagnetic influences using one of those bags computer hardware comes in, and what do you know: the flashes still happen, but they're reduced in amplitude by about two thirds.

    I haven't had physics since high school, but IIRC a sufficiently powerful shift in a magnetic field would induce a voltage over the coils in the transformer, possibly allowing it to briefly overcome the resistance that the controller box uses to stop the current when the LED device is turned off?

    My questions are as follows:
    • Is my above logic valid?
    • In a home setting in a major city, what soft of thing would cause pulses like this? I was thinking either a powerful electrical device being turned on or off in our vicinity, or the building's light net experiencing either voltage spikes or very brief blackouts in its entirety, but I'm not sure how to estimate the likelihood of these things or narrow it down further.
    • What strength would a pulse like this have to be to set off, but not apparently damage (over the course of a year) consumer electronic devices like this?
    • Any ideas for localizing the source of these (presumed) pulses, or preventing them from permeating our home?
    Thank for for your interest!
  2. jcsd
  3. Aug 16, 2015 #2


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    How does the controller box work?
    Could the mini fridge be the cause, when it switches on? Does it happen with the fridge switched off?
    I doubt any electromagnetic radiation would be strong enough to mess around with the controller box, but I don't know how that works.
  4. Aug 16, 2015 #3


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    Need to know more about the controller box. The lights won't light unless the controller is doing something. Put it in the EMI bag.
  5. Aug 17, 2015 #4
    That is a peculiar set of symptoms. I very much doubt it has anything to do with electromagnetic fluctuations in the environment setting up currents in the transformer winding. That would require, like... huge magnetic fields... Think poltergeist-effects with pots and pans flying around. Nope.

    My first suspicion is that it may a problem with the controller. Can you provided a weblink to the exact make and model?

    My second suspicion is that the motor startup current for your mini-fridge or an other appliance may be coupling through somehow and upsetting the controller electronics. It's much more likely that the mini-fridge kicking-on is affecting the LED lights, than that the LED lights are affecting the mini-fridge.

    Surge protectors only activate for major voltage spikes. They would typically ignore small voltage variations due to appliances switching on and off. And it's more likely that the startup current draw is causing the voltage from that outlet to drop momentarily, which can also upset electronics. If they are "nearby" then it's likely that they are plugged into the same circuit. Try plugging them into different circuits.

    A third, and more remote, possibility is some inductive coupling between the wires and that a small pulse is being sent to the LED strip directly. This would only happen if the mini-fridge power cord and the light power cord ran parallel and close together for some length.
  6. Aug 17, 2015 #5


    Staff: Mentor

    If I anchor my boat within 1/4 mile of the Radio Marti (Voice of America) transmitters, my LED lights do the same. It also causes trouble with FM, VHF, and HF radios and with galvanic corrosion. I also wake up speaking Spanish. :wink:

    Are you near a radio or TV transmitter?
  7. Aug 17, 2015 #6


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    Or do any of your nearby neighbors have large HAM radio antennas?
  8. Aug 18, 2015 #7
    Thank you everybody, for your insights and suggestions! Especially to Alec, that is great info.

    The controller box is one of these: http://www.dx.com/p/44-key-ir-remote-controller-for-led-light-strip-white-152672#.VdLRYm7speU. I did a reverse image search but couldn't immediately find any more thorough specifications.

    Taking a look at how the thing is set up now, it turns out my girlfriend insulated not just the LED's power supply but also the controller box at the same time. So that confounds the observation a lot, and supports those of you who said there should be something going on with the controller.

    We are nearby a pretty big antenna mast thing. Google maps puts it at a distance of approximately 420 meters (0.26 miles) from our home. I can't immediately find out what kind of signals it facilitates.

    So now the hypotheses are:
    • The mini fridge turning on is causing the LED flash when it turns on, subdivided in:
    1. By affecting the availability of power, due to them being plugged close together into the same circuit. (Doesn't explain why EM shielding reduced the flash amplitude?)
    2. By causing an electromagnetic effect of its own that affects either the controller (more likely) or transformer (less likely).
    • An environmental EM fluctuation is affecting both the fridge and the LED setup, subdivided in:
    1. The transmission mast nearby
    2. A neighbor with a HAM radio antenna
    3. Remaining unspecified sources

    1. I turned down the temperature on the fridge and got it to switch on its cooling system. The sound of this corresponded to the sound it makes when it turns on alongside the LEDs, but the characteristic accompanying 'plop' sound was absent, as was any effect on the LEDs.
    1. Remove the EMI bag from just the transformer and wait out a flash, to see whether its amplitude reduction comes from shielding the controller
    2. Turn off the fridge entirely and wait out either a flash or a period where we'll usually have seen one, to rule out the fridge hypothesis entirely
    3. Put either the LEDs or the fridge on the other circuit, to rule out the shared power source subhypothesis entirely (only if the flashes stop happening when the fridge is turned off in experiment 2)
    I'll also scout the building for radio antennas and try to find out what that mast is doing. Be back with more info soon!
  9. Aug 18, 2015 #8
    Clarification: When I referred to the "controller" I meant the control-electronics with the power supply that are responsible for receiving a signal from the remote-controller (hand-held thing) and switching the current to the LED on or off. A transformer is a lump of iron with lots of wire wrapped around it. To setup abnormal currents in the transformer component would require tremendously powerful low-frequency EMI. But much lower power signals (including fairly powerful radio waves) could tickle the power supply's control-electronics and make it do strange things, as could supply-voltage fluctuations due to appliances switching on or off.

    The remote-controller can be easily ruled out by simply putting in in a drawer. The product's name hints that it uses infrared light, not radio waves. This also means the the power supply does not have radio receiving circuitry to be swamped by nearby transmitters. But it is still quite possible that strong RF sources could affect the "thinking parts" of the power supply.

    [EDIT: Ahh, I see. The white box does not have two power-prongs sticking out of the bottom; it has a round power input connector in the side for an external DC supply.]
    Last edited: Aug 18, 2015
  10. Aug 18, 2015 #9
    Sounds to me like we mean the same thing when we refer to the controller, except that in this setup, it is a separate device from the power supply, connected between it and the LED strips. It's the white box pictured in the link; ignore the remote.
  11. Aug 18, 2015 #10


    Staff: Mentor

    I like your approach to isolate the problem. That is the essence of almost all troubleshooting.

    Hint, find the transmitting schedule for that nearby tower. If the problems stop when it is not transmitting, then you have strong evidence.

    I'll offer a guess as to the answer. The wiring segments in the house are themselves antennas. So is the ground under the house.
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