LED's/ dimmer question for you science guys

[edlee]

I don't understand electronics, maybe someone can explain. Flickering LED problem in 3 fixtures on one switch is resolved by installing one incandescent lamp. But it's a little more complicated than that, because the flickering is caused by a dimmer controlling a different light fixture:

In a residential kitchen/dining area we altered some lighting. 3-gang existing switch box, new wiring by others. 3 pendants over a peninsula with A19-style LED lamps on a dimmer. We swapped the dining room light fixture, which will soon have LED lamps but temporarily we installed incandescents. We installed a new LED-rated dimmer for the dining room fixture. When the dining room fixture is dimmed, the peninsula LED's start flickering. It's variable depending on where the two dimmers are set, but clearly a problem.

We replaced one pendant LED lamp with an incandescent 60A19 and all the flickering stopped.

I think it has something to do with the straight resistive load vs. harmonics created by the dimmer, but I don't really know what I'm talking about. Any ideas?

 

[GoldDigger]

The most common problem is that a two-wire dimmer module is counting on the load of the controlled devices to the neutral to provide its own current return path for the very small controller current itself.
IF the load is non-linear and therefore voltage and current dependent in its behavior as well as exibiting hysteresis in the case of an incandescent lamp. The result is that voltage builds up on the load with very low current until a threshold is reached for minimum voltage and the load fires. Then the dimmer returns to "normal"
Unless there is a weak shared neutral somewhere it does not explain the coupling between the two circuits. But noise on the hot and return lead caused by one circuit could affect the stability of the dimmer on a different circuit.

 

[edlee]

The most common problem is that a two-wire dimmer module is counting on the load of the controlled devices to the neutral to provide its own current return path for the very small controller current itself.
IF the load is non-linear and therefore voltage and current dependent in its behavior as well as exibiting hysteresis in the case of an incandescent lamp. The result is that voltage builds up on the load with very low current until a threshold is reached for minimum voltage and the load fires. Then the dimmer returns to "normal"
Unless there is a weak shared neutral somewhere it does not explain the coupling between the two circuits. But noise on the hot and return lead caused by one circuit could affect the stability of the dimmer on a different circuit.

GD, thanks for the reply. So there is hysteresis (I had to look it up) caused by the dimmer function with the non-linear LED load, which when a simple linear resistive path for the dimmer is introduced (incandescent), goes away. The hysteresis causes the flickering. Is that right?

And the interrelation between the two switching systems and lights could have something to do with neutral connections. I can look into that. It could also be "noise", which I may or may not be able to correct. Yes?

I guess my strategy will be to check all wiring and connections in the common switch box and then trying a different dimmer/lamp combination if that doesn't work.

 

[GoldDigger]

Yes. As a general rule a dimmer that has three wire connections (one to either neutral or EGC for use as the control power return path) will be less dependent on the details of the load.

Tapatalk!