Lutron Maestro RF2 + Birdgog Dimmable LED Rope Light = Ruh Roh

Did you call Lutron Tech support about this? I can understand the LED not dimming but I never heard that the dimmer doesn't turn off. Also the Bird Dog website says to figure 5.5w per foot. What happens when you hook up a standard bulb to the dimmer?

There can be trouble with triac based dimming or switching of some LED products which can lead to flickering, failure to turn completely off and possible failure of the LED. This includes the Lutron R4U module.

Lutron updates a list on their site of LED based light fixtures and compatibility testing of each with different Lutron dimming products. Its pretty darn handy.

jcmitch

http://www.lutron.com/CMS400/page.aspx?id=31717

is there a neutral in the box?

You could try one of those Lutron "Synthetic Minimum Loads" (LUT-LBX-CE-WH).

I bet with a little perseverence that you could come up with a solution for your special rope light. You gave up too quickly.

At the very least, you should have called Lutron Tech Support.

Edit - find out the specs on the LED driver, from Bird Dog, and then look at that Lutron LED website linked above by jcmitch.

From those model #'s, it doesn't seem like you are using the neutral. The way standard Lutron dimmers work is that they bleed a small amount of current through the dimmer to provide power for the dimmer. The dimmer expects to "see" a resistive load on its load leg. It is not seeing this load, so it bleeds power until it does. So current is hitting your LED lights even when off. Since they use so little power, they come on.

You might want to try a MRF2-6ND-120-WH which is a dimmer with a neutral. This dimmer allows the power it needs to operate to bleed back through the neutral, and not to the load.

Lutron will know more about the Bird Dog LED driver than Bird Dog.

Is there a driver involved?

Unless Bird Dog or someone else has sent Lutron their unit for testing Lutron won't have a clue.

From looking at their website, these seem to be very similar to LED Christmas lights.

That's what I'm seeing, a bunch of LEDs in series...no driver involved.

LEDs are DC and all must have some kind of driver whether built into the fixture base, the cord or remotely located. With Christmas lights you can see the driver at the beginning of the run as either a small box or cylinder. With LED rope light the driver is in the cord seen as a small box or cylinder.

LEDs are diodes, no 'driver' is required.
Have a look at some xmas lights sometime, you'll see nothing but a bunch of lEDs in series, sometimes with a current limiting resistor, mostly without.
The xmas lights with the 'driver' are multifunction.

http://www.ledropelightsandmore.com/...tructions.html

There must be an "interface" between AC voltage and the DC LEDs. Many in the industry are calling this interface a driver whether or not is is just a rectifier. I have LED Christmas lighting of different brands and have installed LED rope and they all have a lump in the cable where the rectifier/driver is. I'm not an engineer but all of the googled information shows this to be true.

Not all interfaces like being connected to a triac dimmer or switch whether they appear to work well at first or not. I'm seeing LED failures when on triac based switches with a "sense" current flowing through the LED rope lights.

Even neutral wire dimmers still let some current flow when off. To have a complete "off" you have to pull out the air gap switch at the bottom of the Lutron dimmer.

There probably should be, but the thousands of xmas lights sold every year don't have any kind of interface, and the rope light in question doesn't either.


I am an engineer and practical experience show this not to be true at all. The "lump" in the cable could simply be a fuse.

two wire triac based dimmers have a leakage current though the load, this current powers the timing circuit in the dimmer.
Dimmers with a neutral connection don't have this leakage current.

i had a similar problem with my lutron homeworks 4 setup when using led under counter lights. they were from home depot, and looked nice when on, but once off they would flicker every 5-10 seconds or so. i went back to the installer to see what was up and sure enough his demo room had crestron light modules with leds and the same thing happened. apparently, the lutron sends a very small voltage through the cable all the time to ping the keypads back and forth (or something along those lines), and would cause the led's to flicker when off. i ended up replacing them with small xenon's and they work perfectly. not the same cool light color, but they work and im happy at that.

duvetyne

The Lutron HomeWorks R4U dimming/switching module (minimum load 25 watts) and Maestro non neutral wire dimmers (minimum load 50 watts) have "sense" voltage that allow them to function. This can cause the LEDs to flicker or glow and can damage poorly designed LED systems. Using neutral wire dimmers with 10 watt minimum load and Maestro switches still have trickle current flowing to the load, according to Lutron, and may still be incompatible with LED loads not designed properly. Lutron has made their own driver that they sell to fixture manufacturers to give the best performance.

Correct me where I'm wrong. LEDs are basic semi conductor devices and require DC current to operate correctly. To use them on AC circuits will require coversion to DC by rectifier. If you look at the link I posted on the LED rope light and also click on the hi res pdf you will see that the LED rope light has a rectifier in the cord. This is a typical design for LED rope. The LEDs are arranged in sections, approximately 18" sections, in series so they don't need a transformer but still require DC current.

A Lutron rep told me that Lutron is putting a lot of effort into controlling LED lights. She said that Lutron can usually find a solution, but talking to Lutron before spec'ing the LED is a good practice.

As said, LEDs are diodes, otherwise called rectifiers. They are DC semiconductor devices, but don't have to run on already rectified DC. As diodes, they do not conduct the negative portion of an AC signal when forward polarized. They drop a specific voltage (2.5 -3 volts typically) so a bunch of them strung together as in Christmas lights would add up to the total line voltage.
I've never had one in my hands to evaluate, but also as said, the bulge in the cable could be a fuse, or a current limiting device such as a resistor, since LEDs are also spec'd with a maximum current parameters.
Because of their nature as DC devices dropping a forward voltage, conventional incandescent dimmers cannot be used unless some sort of intelligent interface is used to track the chopped AC signal from the dimmer and cleanly produce a dimming effect in the LEDs with, probably, a pulse width modulated output.
About the Triac leakage though, it was my understanding that triacs naturally have a leakage current through them that will not let them shut completely off unless there is enough of a load (low impedance). A string of LEDs is a pretty high impedance, as are two-wire electronic fluorescent dimming ballasts. Those loads are tough to shut off, and the best solution is an air-gap relay in series between the conventional dimmer output and the load.
Crestron CLX modules will shut off the LEDS and fluorescents because each dimmer output has a relay at the ass end that opens at 0% dimming. Lutron modules will do it as well, as long as only one of the four outputs is used. However, they are still all incandescent dimmers, and still will not dim LEDs [non-interfaced] correctly.
No doubt that lighting control companies can develop LED dimmers, but Luminary companies try to develop LED lamps that can be used with all that's out there now. I suppose eventually there will be convention, and incandescent lamps will go the wayside of vacuum tubes, as will their controls.
For your shut off problem, you could try wiring a small incandescent lamp in parallel with your LEDs. Maybe even a 7 Watt nightlight hidden in a closet could do the trick. Best of luck.

Yes, as mentioned in my post...it's actually sense current though.


As previously mentioned, they're diodes. Do you know what a diode does?
If you'd actually look at any of the thousands of xmas lights and ropelights sold every year, you'll see that most do not have any rectifier in them.
BTW, rectified AC is pulsating DC, still not the best supply for an LED.

Well, not really. A Half Wave forward rectified AC signal passes only the positive portion of the AC (and about -.7 volts of the negative portion). In the case of sinusoidal 60 Hz line voltage, the signal would look like the top portion of the wave, and then nothing during the negative portion, then the top portion again, and on, and on.
The signal for full wave rectification would be positive sinusoidal humps, one right after after another. In a DC power supply, full wave rectification is applied to a capacitor which charges up to the peak voltage of each hump, and then gives off the voltage as the hump tries to decay, effectively smoothing out the space between the the hump peaks for a flat DC level.

Pulsing DC is just that. It's a square wave.

Rethinking the LED string with AC applied, I can see placing a rectifier diode before the LEDs because while an LED will still drop drop its forward voltage, and not pass the negative portion, the reverse breakdown voltage parameter of LEDs is not very high. It might be advantageous the block the negative portion of the AC signal with a rectifier specified for line voltage rectification as a protection device.

Thanks for that....even though it's been a while since I got my EE degree, I still remember E101, Half/full wave linear supplies are no longer a mystery to me.



the output of a half or full wave rectifier is pulsating DC, it's not necessarily a square wave.


You seem to be forgetting that there are a bunch of them in series.

Obviously, a description of what a rectified sine wave looks like was not for you.

Yeah, what was I thinking? Ideally, a rectified AC signal is pulsating DC regardless of how analog is the response of the output. In these days of digital thinking, an elementary concept was misplaced.

I'm having a little trouble intellectualizing on the PIV issue, though. If a diode does not conduct the negative portion of the AC, how can a string be thought to divide up the total negative potential? My understanding is that once you pass the "knee" in the diodes curve, there will be conduction, but even with current limiting is it desirable to do so?

My best guess is still that the bulge in a string of Christmas lights incorporates a rectifier, probably a bridge, plus the resistor for current limiting, and possibly a fuse, though that's probably in the plug as with standard strings of LV lamps.

This type of issue might be why Crestron doesn't offer lighting devices without Neutrals..