Connect with us

LED or CFL flickering with motion sensor in circuit

Discussion in 'Sensors and Actuators' started by Nehmo, Aug 14, 2016.

Scroll to continue with content
  1. Nehmo

    Nehmo

    7
    0
    Oct 15, 2011
    I use a motion sensor wall switch to control the bathroom light. It works fine with an incandescent bulb, and it works with some CFL bulbs and even some LED bulbs. Most bulbs of either CFL or LED cause annoying flicker. There is a difference in behavior of bulbs from the same manufacturer. That is, some bulbs don't flicker.
    I realize the motion control is working like a dimmer, and I've bought dimmer-compatible bulbs. But they still flicker.
    I know I could put a relay in the circuit to end the flickering. And I know I could go back to incandescents. I don't like either of those solutions.
    Is there some simple way to avoid flickering of an LED when using a motion sensor control?
    And what's the explanation anyway?[​IMG]
     
  2. hevans1944

    hevans1944 Hop - AC8NS

    4,471
    2,084
    Jun 21, 2012
    This is just a guess... most solid-state switches (SCRs and TRIACs) require a minimum holding current that must be in phase with the zero-crossing of the AC line voltage before the semiconductor will latch on. Most CFL and LED line-operated lamps do not draw enough current, or the current is phase-shifted with respect to the supply voltage by the internal switch-mode electronic power conversion circuits, and therefore do not remain conducting after triggering. One solution, as you mentioned, is to go back to using incandescent lamps. Perhaps just a small "night light" type of lamp connected unobtrusively in parallel with the rest of the lights will solve the problem. You might even be able to fit a 7-1/2 watt lamp inside the handy-box the motion sensor is mounted in without experiencing excessive heat rise.,, if that's enough of a resistive load to solve the problem.
     
    ORBear likes this.
  3. Sunnysky

    Sunnysky

    470
    118
    Jul 15, 2016
    This sensor triac needs more load current to sustain a holding current in all Quadrants.
    i.e. a less efficient light.

    Not all lights have PFC and this would help the triac work , maybe. (dimmable)


    try that nitelite suggestion if you have a GFCI outlet or a dummy load of 10W
     
  4. Nehmo

    Nehmo

    7
    0
    Oct 15, 2011
    The GFCI receptacle is on a separate circuit.
    Anyway, I added a 7.5 watt incandescent in parallel with the LED, and the motion detection switch works properly now.
    But I've seen available motion detector units that originally come with LED lamps. They must have a different design, or maybe they have a load built in.
     
  5. Sunnysky

    Sunnysky

    470
    118
    Jul 15, 2016
    LEDs with constant current SMPS will work while PWM types are more common in low power lamps would flicker.
     
  6. ORBear

    ORBear

    1
    0
    Feb 28, 2017
    Thanks for the insight. I am converting a number of older florescent light fixtures to LED. They are all on occupancy sensors. When I installed the LEDs they flickered when they were supposed to be off. I added a 5W night light in parallel and it solved the problem. What I don't understand is that these older occupancy sensors have a relay on the load output so I don't see why they would need any holding current!?
     
  7. Greg01

    Greg01

    1
    0
    Apr 5, 2017
    Hi,
    I have a similar problem but different!! My motion sensor switches an incandescent spot lamp. However when the spot lamp comes on, my led lights in my lounge flicker. They cease flickering when the motion switched spot lamp goes off. Replacing the led lamps with incandescent lamps fixes the problem but doesn't help with the idea of led lamps being cost savers. Can anyone help?
     
  8. Sunnysky

    Sunnysky

    470
    118
    Jul 15, 2016
    Add a 30W tungsten lamp to LED supply load to satisfy triac switch for LEDs if possible. ??
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,385
    2,772
    Jan 21, 2010
    They may have a capacitor across the relay contacts. This passes enough AC current to allow the very efficient lights to turn very slightly on.
     
  10. Sunnysky

    Sunnysky

    470
    118
    Jul 15, 2016
    If it uses a triac to create some transformerless DC voltage with a small Relay and small LED load the triac may be false triggered by dV/dT noise which must be filtered externally or internally to the triac by some means of attenuation.

    Often an Incandescent load is enough to prevent this external leakage and dV/dT noise false trigger in triacs..

    Unless a relay is latching type, they all have a holding current about 20% of activation current with normal hysteresis. That also defined by the Must latch voltage and much lower Must release voltage, but this is not relevant to your issue.
     
  11. Babbo

    Babbo

    3
    0
    Jul 5, 2017
    I have the LED-flashing-with-occupancy-sensor switch problem too. Can I install a low wattage incandescent bulb alongside two LEDs in the same fixture to solve the problem? Everyone says not to combine LEDs and incandescent bulbs.
     
  12. Babbo

    Babbo

    3
    0
    Jul 5, 2017
    Anyone?
     
  13. Alec_t

    Alec_t

    2,821
    754
    Jul 7, 2015
    Not everyone. Re-read post #8.
     
  14. Babbo

    Babbo

    3
    0
    Jul 5, 2017
    I wasn't sure if adding the incandescent to the load was exactly the same as adding it to the fixture. Thanks to all.
     
  15. AnalogKid

    AnalogKid

    2,358
    659
    Jun 10, 2015
    I strongly disagree with this suggestion. A wall box does not have many open holes because its primary job is to contain fires. I doubt there is enough room inside to add a bulb behind the sensor/switch, but if there were the bulb would fry the sensor electronics in under an hour.

    Demo: Plug a 7 W night light into a wall socket, remove any shade or cover, turn it on, and cup you hand around and over the top of the bulb so it is 1/2" away from your skin. Wait.

    ak
     
  16. hevans1944

    hevans1944 Hop - AC8NS

    4,471
    2,084
    Jun 21, 2012
    Well, I did say might... but you are right. It was a dumb suggestion to try to fit the lamp inside the handy-box. Shouldn't put anything in a handy-box that is going to intentionally generate heat. It might even be illegal to do so, in which case it was a really dumb suggestion, although I have seen (and used) a commercial light-switch dimmer that got pretty warm working with eight 60 W incandescent lamps. It was rated to handle 600 W, but it did get rather warm. So, just put the 7.5 W incandescent load somewhere conveniently in parallel with the LED load and safely in open air. Post #4 indicated this actually worked for the OP, but for some sensor/controllers it may not be enough of a load. See post #8 above.
     
  17. AnalogKid

    AnalogKid

    2,358
    659
    Jun 10, 2015
    Dimmer heating made my wife nervous until I pointed out that the front plate is the heatsink and is working to eject the heat, the components inside are rated for way higher temperatures, and the wall box is completely fireproof by law.

    ak
     
  18. hevans1944

    hevans1944 Hop - AC8NS

    4,471
    2,084
    Jun 21, 2012
    It made me nervous too, but I left it installed. This was for dimming eight (four on each side of the medicine cabinet mirror, Hollywood dressing room style), large-globe, frosted, 60 W incandescent lights. Worked pretty good for that, and at full brightness the lamps kept the bathroom nice and warrm. Expensive heat though, so I eventually replaced them with LED equivalents. Dimmer didn't work quite as well with the dimmable LEDs, but it was satisfactory, so that's the way I left it. Then we moved to Florida, where everything is electric, and lights are either curly-bulbs or LEDs. I hate curly-bulbs, so have slowly been replacing them with LEDs as soon as I can afford new ones.
     
  19. butchdon

    butchdon

    1
    0
    Jul 20, 2017
    I had a LED ceiling light I just purchased that flickered when connected to a motion sensor. I returned it and got another. Same thing. So I swapped out the MS switch for a standard single pole. works fine.

    Installed the MS switch in my kitchen. Unfortunately, the two ceiling floods are LED's, so now they flicker. There's nowhere to place a "load" incandescent bulb to cure this issue. Is there another solution? This must be happening all over the country as people convert to LED's. We love the occupancy switches.

    Someone needs to invent a 7 1/2 W wafer resistor you can place in the bulb socket.
     
  20. Tha fios agaibh

    Tha fios agaibh

    2,096
    703
    Aug 11, 2014
    Negating the efficiency of the led isn't the best solution.
    The problem with leds is they respond so quickly, the light dims to the slightest ripple of its supply. This makes a strobe effect.

    Your motion detector circuitry was likely designed for slower incandescent lamps, long before modern led lamps were available.

    They have some md devices that use a relay output. That would work. Also, I'm sure manufactures are working on a cleaner output as we speak. Perhaps a Schmidt trigger added before the triac?
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-