Riddle me this

[Dennis Alwon]

The other day I got a call from my brother in Texas who just had 3 Minkaire fans installed. Interesting string of events happened. Firstly I will say that candelabra based CFL light bulbs were used in the light kit.

The wall switch is one of those electonic switches that has a glide switch on the bottom which turns off all controls.

As we all know there always seems to be some leakage of current that is present on the load side of a dimmer. Why????

This is what happened. When the switch is turned off with the glide switch no problems are present, however if you just turn the light (dimmer) switch off the cfl flicker just a bit and can only be detected at night when it is dark.

There are 3 or 4 bulbs on the fixture and if one bulb is changed to an incandescent the flickering stops.

So my question is threefold:

Why is there a leakage?? when the dimmer is off?
Why is there flickering on the CFL?
Why does an incandescent stop the flickering?

 

[kwired]

My guess is not leakage of the switch, but maybe a capacitive charge. I think I have seen this before with ordinary switches.

 

[Dennis Alwon]

My guess is not leakage of the switch, but maybe a capacitive charge. I think I have seen this before with ordinary switches.

Wasn't sure what to call it so I choose "leakage" but I don't see how it is possible with a standard switch. I have only seen it with dimmer switches or electronic switches. I know that the switch is causing this but was curious as to the "why"? It has something to do with Triac circuitry in the dimmer , I believe.

 

[kwired]

The question is does the dimmer have an "off" position that opens the circuit, if not then triacs will have leakage current. An incandescent lamp will have low enough resistance to drop any voltage to nearly zero. This has been an issue with things like PLC's with triac outputs for a long time and bleed resistors or other additional load is the solution.

I don't know much about the anatomy of typical CFL's I am guessing the ballasts are becoming more solid state if they are not already entirely solid state.

 

[Dennis Alwon]

The question is does the dimmer have an "off" position that opens the circuit, if not then triacs will have leakage current.

Well if an incandescent is in the dimmer works just fine. If you want the light off you just push the button quickly and it's off. If you maintain pressure on the button the light will dim to what may look like off then it will start to brighten. It will do this till you let go of the button. Again push and release and supposedly the switch is off. Standard dimmers with an off switch also tend to have this voltage when the switch is off. Not sure why, if the switch is off, there is still this voltage present.

 

[ELA]

Dennis,
This was talked about here:
http://forums.mikeholt.com/showpost.php?p=1125616&postcount=14

and in a few other threads.

Solid state relays often have a snubber connected to protect them and it leaks a small current. This current then slowly charges up the input capacitor of the CFL until it is a high enough voltage to fire the bulb.
The cap discharges once again slowly from the small leakage current and repeats this cycle.

 

[kwired]

does it eventually stop the flickering or whatever it is doing? If so I would still guess some capacitive charge that finally gets discharged. Put some resistive load in the circuit and it discharges rapidly.

I still think I have seen this before on a regular wall switch and it did lessen and quit after a while. It was in my own house noticed it in the bathroom in middle of night. May have to try to make it happen again tonight. The flicker was not very bright so you need very dark and your eyes need adjusted to darkness or you may not see it.

 

[Dennis Alwon]

Not very bright but will continue all night if left with the glide switch on.

 

[RICK NAPIER]

I was at a presentation by a CFL distributer where they acknowledged this problem and spoke of rows of CFL lights with one incadescent hidden to correct this problem.

 

[Dennis Alwon]

Thanks for the responses. Here is the entire thread that ELA linked to.