Lutron Diva dimmer broken

[hobbes]

Hi,

I have a Lutron dimmer that dims a 100w (4 x 25w) light fixture in a bathroom. I noticed that one of the 25w bulbs was out and that the dimmer does not dim any more. My question is can a bulb burning out cause a sufficiently high current transient / short to burn out a dimmer?

I read in this news group that bulbs blowing can be a reason that a dimmer fails. Is this true?

best, Mike.

[pheeh.zero]

Some of the clear bulbs hold the filament delicately with wires that can short together and burn the triac out.

[RBM]

It is true and happens frequently. Also fixtures with candelabra sockets often develope minor short circuits in the socket, just a momentary pop, not enough to trip the breaker, but enough to take out a dimmer

[aemeijers]

Huh. So that is maybe what happened to the dimmer in the dining 'room' area of the kitchen in my cookie cutter. It has one of those pug-ugly chandelier things that uses those damn candle-base bulbs. (as does the other big ceiling fixture, non-dimmed, also a piece of junk.) Dimmer still works as a switch, so haven't bothered to replace it yet. Been looking off and on for replacement ceiling fixtures for the kitchen, but none of them in the stores seem to have normal bulb sockets. And the current one has one neat feature- a downward-facing flood bulb in the center, to light up the table enough to read newspapers at.

aem sends....

[Chris Lewis]

According to aemeijers :

Yup. Semiconductor triacs act like _extremely_ fast fuses. The mere whiff of a short lasting a few tens of milliseconds can fry one long before a regular fuse or breaker notices anything awry.

[mm]

I always thought the phrase was plug-ugly, but your words make more sense. Anyone know more about this?

[Jeff Wisnia]

Yes, what occasionally happens when a bulb burns out is that a phenomena called a "tungsten arc" occurs. The filament break develops an arc between the broken ends which melts those ends and vaporizes some tungsten. The arc continues, melting more tungsten and shortening the remaining filament ends and the current increases as more of the filaments melt and the density of the vaporized tungsten increases.

It all happens faster than you can say Jill Robinson, usually accompanied by a bright white flash just as you "turn on the lights".

The current will sometimes surge high enough to blow a panel fuse or breaker, or as in your case, to fry the triac in a dimmer.

Good quality light bulbs used to have special thin wire "fuses" as part of their construction which were just thick enough to let the bulbs be turned on and run but would "blow out" if the bulb developed a tungsten arc. I don't know if that's still the case.

When you are replacing the dimmer, go to Rat Shack and pick yourself up an inline 3AG fuse holder and a few 2 amp 3AG fuses. Wire the fuseholder in series with the hot feed to the dimmer (it should fit inside the dimmer box) and you'll be pretty well be protected against a future burnout. You may have to replace a burned out fuse, but the dimmer should be OK.

That's just what I did with the four table lamps in our home which are fitted with "touch dimmers". After the second dimmer blew I added 2 amp fuses to all of them. I've probably replaced six fuses in the last five years, but all the dimmers are still alive and well.

HTH,

Jeff

[Chris Lewis]

According to mm :

I've normally heard "plug-ugly", but if your dog is ugly enough to serve as an example... ;-)

[Chris Lewis]

According to Jeff Wisnia :

I find it hard to imagine that a fuse would blow fast enough to protect a triac. But, if it works...

Make sure you get fast-blo.

[H]

Lutron has replaced all of the dimmer switched that I purchased (from HD) for free. In fact, they did it twice because they were apprently defective (the 2nd round of switches I got unsolicited). You may get the same courtesy by contacting them:

Mailing Address: Customer Service Lutron Electronics Company Co., Inc. 7200 Suter Road Coopersburg, PA 18036

Phone Number: 1-(888) LUTRON1

Fax Number: [phone]

E-Mail Address: E-Mail: [e-mail]

[Jeff Wisnia]

Thanks, I realized too late that I forgot to mention that.

Not to be pedagogical, but I sized the fuses for my lamps by looking up the specs of the triacs in my lamps' touch dimmers, the ones which were punching through, and found on their maximum I^2*t rating. (eye squared times tea)

Then I looked on Buss' website and found that the blowing energy (also expressed as I^2*t) of their 3AG 2A fast blow fuses was somewhat less than that of the triac, so I figured it should work.

And work it has....I use two 75 watt bulbs in a "Y" adaptor in each of those table lamps cause the two are cheaper two purchase than one 150 watter in most places, plus when one bulb dies I still can get light to see my way around from the other one, assuming it didn't expire with one of those tungsten arc blasts and take out the fuse. I think I probably have three or four "normal" bulb burnouts for every one which takes a fuse along with it.

And some people accuse me of being a geek who "gilds turds"....Wonder why that is....

Jeff

[Don Klipstein]

A bulb blowing, especially the usual burnout with a bright blue flash, can take out the dimmer.

The bright blue flash is a "burnout arc", which can briefly draw something like 100 amps or more for a few milliseconds. The dimmer may be made as cheaply as possible, and could only "usually" as opposed to really reliably survive the current surge of a burnout arc.

I have also heard of complaints of a few lightbulbs lacking fusible links in their necks. Those are supposed to blow if a burnout arc draws a really bad current surge. In extreme cases, I have heard of bulbs without fusible links failing badly with the glass bulb popping off the base. My guess is that the wires violently vaporize adjacent glue/cement due to an extreme current surge drawn by a burnout arc.

Lightbulbs of "Big 3" brands (GE, Sylvania, Philips) probably have fewer issues in this area. Store brand lightbulbs of "usual regular shape and size" and 25, 40, 60, 75 or 100 watts and same hour life expectancy figures and same lumen light output figures as "Big 3 brand" ones are "Big

3" ones with the only difference being the brand or lack thereof printed on the top of the bulb.

Lowest prices I have seen for "standard" "Big 3" lightbulbs: At Lowes.

Another idea: Use compact fluorescents and do without the dimmer. Four

7-watt spirals will outshine four 25-watt incandescents, and a 25 watt incandescent dimmed to the point of consuming 7 watts will produce about 1/4 or less the light of a 7 watt nightlight. If you never or hardly ever need less light than that and dim only for energy conservation purposes, go for compact fluorescents if you don't need dimming.

Now another idea: Compact fluorescents often do not do well in bathrooms often used for short trips - unless they are cold cathode! And cold cathode ones are dimmable. They are somewhat less efficient than the usual hot cathode ones, but still a lot more efficient than incandescents. Online lightbulb sellers sell ones up to 8 watts, which are about as bright as 25 watt incandescents. They are rated to last 25,000 hours and do not suffer extra wear from starting, and are even rated for flashing/blinking duty. What mainly tends to go wrong with those is that they fade as the phosphor gets worn out over the years, otherwise they fail from breakage or the electronics blowing from an especially bad power surge that blows electronic products.

Still another idea: If there is a need for dim light as well as bright light, the most energy-efficient option is to have separate light sources for those. (Though dimmable compact fluorescents are a close second and quite convenient.) The dim-light source could be a nightlight having a built-in switch and the traditionally incandescent bulb replaced by a 3 watt cold cathode compact fluorescent, such as the 3-watt N:Vision one available at Home Depot. If you like less light than that, LED nightlights do well there with usually around 1 watt of power consumption.

- Don Klipstein ( [e-mail])

[pheeh.zero]

I weird thing about triacs...they are opposed diacs...if you use them with a DC current...once you turn them on (gate current)...you can't turn them off. You have to open the circuit. They can be used as solid state relays. (Opposed or back-to-back is really not the right term, triacs are parallel wired with a common gate diacs.)

Hope this makes sense...I am in my 60s...and if the mind is like the body...

[M Q]

...

... Two 75 watt bulbs produces a lot less light and are a lot less efficient than one 150 watt bulb. You will pay more for the electricity:

75 watt GE "standard" 1190 lumens 150 watt GE "standard" 2850 lumens

That's 20% more light for the same power or 20% more efficient. Also, you would probably find the quality of light more desirable from the 150 watt bulb (higher color temperature).

Over the estimated 750 hour lifetime, you will use 112.5 KwH. If you are fortunate enough to pay only 10 cents per KwH, thats $22.50 of electricity.

Also note, that when you use a dimmer, although you use less power, the bulb gets much less efficient.

[Jeff Wisnia]

Points well taken. I hadn't thought that one through.

I may just buy a few 150 watt bulbs this weekend, the additional lumens will probably make it easier for my aging eyes to read stuff.

Thanks,

Jeff

[Chris Lewis]

According to :

Triacs are sorta opposed SCRs, not diacs. Diacs are two lead devices, effectively back to back zener diodes. No current until the voltage gets to the zener (diode reverse breakover) voltage. Unlike a zener, the breakover is in both directions. With zener diode, it breakovers one way, and the other way it acts as a normal diode and conducts at > .6V.

Diacs were commonly used in triac dimmer cicuits to provide firing control to the gate, but now I think they do without them.

Right - to turn of a SCR or triac, the voltage across the main terminals has to drop (close) to zero. With household AC, of course, that happens 120 times per second.

Tho, I seem to recall something violent you could do with the gate to get an SCR to shut off without zeroing the voltage. Or at least a buddy claimed it would cut off if you shorted the gate to the "nearby" main terminal.

[pheeh.zero]

Thanks for straightening me out! Of course, when you said, SCR, I went "doh!"

[bud--]

Are all dimable CFLs cold cathode?

Roughly what happens to CFL efficiency as they are dimmed?

Dimable linear tube fluorescent balasts, IIRC, have a maintained hot lead to power the filaments. What happens to efficiency as they are dimmed?

-------------- You should write a book. In effect, you probably have.

-- bud--

[bud--]

I am sincerely genuinely impressed. The application is specific to the triac and type of Buss fuse used, but has a good chance of working in general.

Nitpicking - also check the fuse voltage ratings, and fuseholder ratings.

There may be more room to install a fuse at the light fixture.

Doesn't everyone guild turds?

-- bud--

[mm]

Right, but in the dimmer, there might be room for a glass fuse without a fuseholder. Either one with pigtails (wires soldered to the ends) or small endcaps that are barely bigger than the metal ends of the glass fuses. I don't know what Jeff actually used.