LED Dimmer Flickering

A/A Fuel GTX

A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
I have an issue with LED under cabinet lights flickering with a Lutron dimmer switch installed. The dimmer is LED rated but the lights flicker when on regardless of dimming level. My first thought is there is not enough of a load on the dimmer causing this issue. Any thoughts or remedies?
 
Need some more info. Could be incompatible dimmer. If you are sure the UC lights are dimmable, are they Forward Phase or Reverse Phase dimmable? Cross check that with the dimmer switch, is it a Forward or Reverse Phase dimmer? Has to match load type.

Could also be too light a load as you said. Lutron makes Phantom/Dummy Load device (LUT-LBX) or a minimum load capacitor (LUT-MLC) you could try.
 
A/A Fuel GTX said:
I have an issue with LED under cabinet lights flickering with a Lutron dimmer switch installed. ... My first thought is there is not enough of a load on the dimmer causing this issue./B]
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A/A Fuel GTX said:
Have the exact same set up on another row of lights only with more fixtures and they work and dim perfectly. The dimmer is a Lutron DVCL-153.
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That reinforces your suspicion that there's not enough load for the dimmer to work properly. You could add the minimum load capacitor mentioned by @IMFOTP above, add some additional lights, or use a dimmer that uses a neutral like the DVRP-253P (assuming you have a neutral available).
 
What’s the reason for that happening? I get the loads not enough, but why would that matter on the dimmer how come a threshold has to be achieved?

Like I have the Lutron minimum load capacitor but it doesn’t work on the Legrand dimmer. I need to use theirs so they have a different threshold that needs to be achieved. Kinda sucks, but I guess that’s the name of the game.
 
AC\DC said:
What’s the reason for that happening? I get the loads not enough, but why would that matter on the dimmer how come a threshold has to be achieved?
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The control circuitry that drives the triac in a forward phase dimmer needs to be supplied with sufficient current and voltage in order to operate. Without a neutral connection, all the dimmer has to operate with is a small fraction of the current that is flowing from it through the load. And so there is a minimum load current required in order to achieve stable operation of the control circuitry such that flickering does not occur.

LED loads are also quite nonlinear in terms of current drawn vs. voltage, and that further complicates the situation. Having a passive shunt load like a capacitor and resistor in series with each other can maintain a minimum amount of current flow over the AC cycle, and over a range of applied voltages so that the control circuitry can operate properly without flickering.
 
All right, but you’re saying without a neutral my Legrand one needs a neutral and yet it still needs one of those capacitors

I understand your second paragraph
 
AC\DC said:
All right, but you’re saying without a neutral my Legrand one needs a neutral and yet it still needs one of those capacitors
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I was just saying that a dimmer thart uses a neutral would be able to provide power to its control circuitry without having a minimum load on its output terminal. Because it has a constant L-N supply to it all of the time.

I think the design of the control circuitry in the Legrand dimmer just needs some more load current than the Lutron one does. But the 0.1A on the label of the Legrand loading device does seem a little excessive.
 
It's not IEEE standardized or anything, so how the lamp ballast handles the dimming input is not uniform.

Some dimmers for some applications are intentionally set to have a narrow variation in a firing range so that DC power supply within the lamp ballast can operate to provide a constant DC rail. Osram-Sylvania F32T8 low-pressure mercury T8 PowerSense Quicktronic is one of the finest dimming gear out there.

The relatively narrow range of dimmer wall unit ensures the ballast can operate at constant DC rail regardless of dimmer input setting. The phase angle is basically just used to produce 0-10v signal internally to control the 0-10v dimmer in the ballast. That ballast also allows 0-10v dimming. If you were to decouple the phase angle to 0-10v converter, it would just operate as a normal ballast.

That ballast maintains a flicker index from minimum to maximum at a level acceptable for video recording studio. Something that can not be said about almost all of L.E.D. type lamp ballasts.
 
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