What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock?

Discussion in 'General Clock Discussions' started by Robert Gift, Apr 19, 2017.

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  1. Robert Gift

    Robert Gift Registered User

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    This Walmart nightlight has two flat LEDs shining up into its clear plastic diffuser.
    The diffuser easily slips off and the 2700 K light is nice for shining down onto the clock's chains, weights and pendulum.
    But there is flicker!!
    Any idea of capacitance to add to filter out the flicker?

    Thank you.
    Robert
    [​IMG]
     
  2. R. Croswell

    R. Croswell Registered User
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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Are you operating it on a dimmer switch circuit? LEDs not labeled as dimable will flicker, or the one you have may be defective.

    RC
     
  3. marylander

    marylander Registered User

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    #3 marylander, Apr 19, 2017
    Last edited: Apr 19, 2017
    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Hi Robert,

    I am not familiar to the LED flicker. Since LED is diode, which rectifier half wave. So every half wave it shine. If you reverse one of the LED polarity so each LED shine each half wave (one positive half and the other negative half wave). It will not have the flicker. What I mean is you parallel two LEDs with one LED's Anode connected to another LED's Cathode. So two LEDs are oriented in opposite direction connected in parallel. Hope this solve the flickering problem. You need to make sure both LEDs are working first. If one of the LED is not working, you only have one LED shining 50% of time.
    Ming
     
  4. Tinker Dwight

    Tinker Dwight Registered User

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    I think I understand, for the pendulum it is like
    a strobe with 120Hz flashes.
    One would have to significantly change the circuit.
    The circuit is designed to use and take advantage
    of 60Hz source. You'd need to replace the dropping
    circuit with a pure DC supply.
    If the diodes are laid out as Ming says, a capacitor would
    not be useful.
    I suspect they use a capacitor to drop the voltage of the
    AC to power the LEDs.
    Tinker Dwight
     
  5. THTanner

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    #5 THTanner, Apr 19, 2017
    Last edited: Apr 19, 2017
    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Sometimes these lights have a diode in the circuit ahead of the LEDs, some do not. If there is a diode ahead of the LEDs then reversing one will not work since 1/2 of the wave is already blocked before it gets to the LEDs. A lot of these LEDs are not designed to use 120 volts, so a bit of circuitry is included to drop the voltage. That circuitry usually includes a diode. There are LED lights where the circuitry is designed with a pass through and an inverter to provide continuous DC. It would probably be best to get one of those, although they do cost more.

    https://www.cnet.com/how-to/how-to-buy-dimmable-led-bulbs-that-wont-hum-flicker-or-buzz/

     
  6. Tinker Dwight

    Tinker Dwight Registered User

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    I'm suspecting the two diode strips are place in parallel
    with the directions reversed. A capacitor is then in series
    as a voltage dropping and current limiter.
    It then only need the three parts ( cheap ).
    Tinker Dwight
     
  7. THTanner

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    If this is true, then what is causing the flicker? Is it the capacitor?

     
  8. Tinker Dwight

    Tinker Dwight Registered User

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    The capacitor is just passing AC.
    The LEDs are each flickering at 60Hz with
    a combined 120Hz flicker.
    It would be clear on a moving pendulum.
    If it has a flicker that you can see just
    stationary looking at the light, it must
    have a poorly working regulator circuit.
    Tinker Dwight
     
  9. MartinM

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Maybe just convert whatever diode configuration it's using with a bridge array?
     
  10. Ralph

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Martin, you beat me to it. If they use a single diode in the circuit before the LED's, a bridge rectifier replacement will give them 120hz driving the LEDS.

    Ralph
     
  11. Tinker Dwight

    Tinker Dwight Registered User

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    I think we need to see how it is currently wired.
    If it is using a capacitor as a drop and current limiter,
    putting the bridge on the line will just make the
    light flash once when plugged in.
    Tinker Dwight
     
  12. David S

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Robert buy another one and take it apart so we can see it. If they are using the reactance of a series capacitor as the voltage dropping element with now smoothing then you will have a strobe effect.

    David
     
  13. novicetimekeeper

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    Re: What capacitance to filter out LED nightlight 60 Hz flicker for grandmother clock

    Isn't it easier just to buy a short length of self adhesive LED strip and use a wall wart transformer to drive it? Presumably those are already smoothed so you won't get this problem?

    Is the problem occuring because the way the supply is rectified is giving you a 60 hz flicker instead of a 120 hz flicker you get in your normal house lighting?
     
  14. Robert Gift

    Robert Gift Registered User

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    Presumably the two LEDs are connected in opposite polarity

    Thank you, All.
    Presumably the two LEDs are connected in opposite polarity. (That is the way I would do it.)
    During positive half of the AC sine wave, left LED is illuminated while right, off. During negative half of the sine wave right LED is on while left is off.
    Otherwise BOTH are ON 1/120th second and BOTH OFF for the next 1/120th second.
    I would want the capacitor to discharge in the areas of zero voltage.

    (If I could, I'd have all of our house lights be LED operating from a constantly-charging storage battery.
    Zero flicker and light during power outages. Bottom outlet receptacles and kitchen outlets would remain 120 VAC.)

    If no simple solution, I'll just leave the 5-Watt incandescent nightlight bulb in place.
     
  15. THTanner

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    Re: Presumably the two LEDs are connected in opposite polarity

    Google "flicker free screw in LED" - there are many available for different base sizes and watts made by more than one manufacturer and different color tints. I find a slightly bluish tint makes shiny brass weights and pendulums look very nice.

     
  16. Robert Gift

    Robert Gift Registered User

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    Re: Presumably the two LEDs are connected in opposite polarity

    Thank you.
    In the house we like the warm color. The yellow in the warm color brings out the brass color.

    It is unfortunate that Walmart accepted this lightnight with flicker. We already have too many things which flicker.

    (Some of our LED Christmas lights appear to be half wave emitters strobing at 60 times a second.
    I am planning to build full-wave bridge rectifiers which produce filtered DC for the outdoor and indoor lights.
    Will probably have to change some wires in the strings so sections of the strings will not be dark.)
     
  17. MartinM

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    Re: Presumably the two LEDs are connected in opposite polarity

    I must not be understanding your intent with the capacitor. This isn't half or full wave rectified DC you're looking to smooth. It's AC.
    So, (given your assumption about the current circuit, I could see you improving the dwell of one LED, but not both (with a single capacitor).
     
  18. kinsler33

    kinsler33 Registered User

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    Re: Presumably the two LEDs are connected in opposite polarity

    Historical note: The AC frequency of 60 Hz was chosen as the lowest frequency which would not cause visible flicker in an incandescent lamp. (In Europe, they lowered this to 50 Hz, which gave less voltage drop on long lines.) But I've been told that there are people who perceive 60 Hz or even 120 Hz flicker from an LED or fluorescent lamp. Dual fluorescent fixtures are arranged so that one lamp is phased 90 degrees (1/4 cycle) from the other one, which minimizes strobe effects near rotating machinery.

    If you check the label on old vacuum cleaners you'll find that they're rated for use from 25 Hz to 60 Hz. 25 Hz was used in New York City for a time, and in Niagara Falls for the first hydro-electric installations. With 25 Hz, the flicker in an incandescent is clearly visible to everyone.

    M Kinsler
     
  19. THTanner

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    Re: Presumably the two LEDs are connected in opposite polarity

    In the 70s and 80s when the first computer screens began to be used widely, there were people who would have real problems with some of the slower fly back frequencies. Some would get nasty migraines after a short time and the flicker would even trigger epileptic like seizures in others. I have a renter in one of my houses who is especially sensitive to any flicker from about 50 to 100 Hz so all fluorescent and led lights are impossible and she has to use computer screens with really high refresh cycles.

     
  20. Robert Gift

    Robert Gift Registered User

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    Re: Presumably the two LEDs are connected in opposite polarity

    How interesting!, Webster's pedestal.
    Some parts of NYC, I recall, were on DC up to the 1960s!

    In London, in my peripheral vision I could detect the 50 Hz both in Hg-vapor lamps (or were they high pressure Na?) and their TVs.

    To minimize strobing making spinning machinery wheels appear still, were fluorescent lamps in factories wired 120-degrees out-of-phase from three-phase power?

    How terrible if the 25 Hz. flicker was visible even in.candescent lamps.
    Can instruments detect any flicker from 60 Hz. AC in lower-wattage lamps? I assume the.rmal mass of heavier higher wattage filaments would reduce or prevent flicker.

    Fortunately, in our cheap Walmart "60-Watt" lamps, I cannot detect any flicker!
    On some of the bulbs I cut off the plastic top. The 9 "pin-point" LEDs are ideal for revealing detail in clock movements!
     
  21. novicetimekeeper

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    Re: Presumably the two LEDs are connected in opposite polarity

    It isn't a 50hz or 60 hz flicker in AC lamps, it is 100Hz or 120Hz. Incandescent's flicker less because they don't get a chance to cool down, however machine tools are fitted with DC lamps so that they never appear stationary to an operator through the strobe effect. The problem with LEDs is that being diodes they only react to the electron flow in one direction so it will depend on the rectification if they have a flicker.

    I demonstrate the flicker of fluorescent lights to students using the receiver of a modulated light demo, the receiver gives out a 100hz hum.
     
  22. Robert Gift

    Robert Gift Registered User

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    Re: Presumably the two LEDs are connected in opposite polarity

    Interesting about pure DC for machine tools! I suspect our "strobing" LED strings have only LEDs with no other circuitry.
    Scanning eyesight across them yields - - - - - - - - - - - indicating OFF for half each cycle = 60 illuminations/second.
    That is why I want to build a full-wave rectifier with capacitors to fill in the two zero-voltage areas each cycle.

    The Walmart nightlight is not that bad. I suspect its two LEDs are opposite polarity = but its 120 illuminations/second flicker is still noticeable
    in peripheral vision
    .
     
  23. THTanner

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    Re: Presumably the two LEDs are connected in opposite polarity

    You could also rewire the duplex that you use for the lights in the clock so that each of the receptacles is powered by a different leg of the mains, then put in two lights, one plugged into each of the receptacles. (check local building codes) ;)

     
  24. kinsler33

    kinsler33 Registered User

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    Re: Presumably the two LEDs are connected in opposite polarity

    One aspect of flicker on led or arc (fluorescent or vapor) lamps is that their minimum voltage can't be maintained over the entire ac half-cycle. Both have
    significant firing and extinguishing voltages, and so even two led's connected in anti-parallel will both be off for a significant portion of the entire ac cycle. More sophisticated circuits have a bridge rectifier plus a filter capacitor to maintain a nice dc, and there are other ways of dealing with flicker.

    M Kinsler
     
  25. Robert Gift

    Robert Gift Registered User

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    #25 Robert Gift, Apr 21, 2017
    Last edited: Apr 21, 2017
    Walmart night light ONE [O] LED!

    I have been considering making the top outlet 12VDC from a automobile battery so all lights (which I will have to alter) will be on pure DC.
    Will also operate during power outages.
    But have found no way to get cable run to the 2nd floor attic and down to the outlets. Running cables up from the unfinished basement has been easy.

    Even more fun would be to attach a coil under each end table to induce power into a coil in the base of each table lamp to charge batteries in the lamp.
    Then no wires from the lamps!

    Walmart night light circuit:
    Left plug prong - [diode] - [1/4-Watt 10,000 ohm 5% resistor] - LED[o] - switch - right prong.
    How so little flicker if half-cycle OFF period? The LED has 3 leads on each side!
    Is the solid round [o] material a phosphorescent material excited by UV from LEDs beneath?

     
  26. Tinker Dwight

    Tinker Dwight Registered User

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    Re: Walmart night light ONE [O] LED!

    Sheet-rock is temporary.
    Tinker Dwight
     
  27. kinsler33

    kinsler33 Registered User

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    Re: Walmart night light ONE [O] LED!

    That LED package likely contains a good deal of active circuit wizardry integrated right onto the chip. They may have figured out how to pulse the LED such that the flicker is minimized, though I can't think just how they'd do that.

    Yes, white LED's get their light from a dot or ring of fluorescent material that's excited by a high-power ultra-violet LED. The chip material is likely silicon carbide, a particularly sturdy semiconductor that also has the virtue of yielding high-frequency (visible blue to UV) with a minimum of trickery.

    You can certainly wire the house with 12VDC--some motor homes and boats have that arrangement, and so you'd look into those areas to find ideas and equipment. However, you might just want to install a number of stand-alone, continuously-charging emergency lights like they have in restaurants and other public venues. These could be modified/disguised/hacked to supply things like your clock lights.

    M Kinsler
     
  28. harold bain

    harold bain Forums Administrator
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    Re: Walmart night light ONE [O] LED!

    But real rocks are permanent:whistle:
     
  29. David S

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    Re: Walmart night light ONE [O] LED!

    I am not clear on your set up. But why not get some USB powered leds and power them from cheap usb chargers? Everything will be DC, low voltage and safe.

    David
     
  30. THTanner

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    Re: Walmart night light ONE [O] LED!

    Have you looked at the duplexes that have built in 5 VDC USB chargers? I am not sure how that 5 VDC is setup - it may be pulsed or continuous- but might be worth a look.

     
  31. Robert Gift

    Robert Gift Registered User

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    Re: Walmart night light ONE [O] LED!

    Good idea! They probably have good filtering if one is charging the device while using it!
    Frequently we must use cell phone or iPad while charging and never detect any hum.
    (120 VAC is already in the clock for the night light bulb.
    Filtering out the LED flicker would be so nice.)
     

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