dimmer switch - _hot_ screws

Page 1 of 2  
I have 3 dimmers in my house that are the same model dimmer. Have them controlling ceiling lights. Two give of very minor warmth generally during operation, while one gives off so much heat that the screws holding in the face plate are almost too hot to touch.
Is this likely a bad switch? Just get a new one? Worrisome as it's housed in a plastic box, not metal.
Thanks.
bp
--
Heisenberg may have slept here.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I don't know. I would be curious though whether it gives off any heat when it's 1) almost off, very dim; and 2) fully on, max bright.
If you're going to replace it, the upscale Lutron (eg. Diva model and similar) have the advantage of being at least somewhat radio quiet; your neighbors can listen to their AM radios even if you can't for all stations, then. Most dimmers are tiny angry radio stations.
--
Ron Hardin
snipped-for-privacy@mindspring.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A thyrister device, in this case, a triac, is a silicon device. There will be a voltage drop across the device, thus heat generated proportional to the current. Since the triac is operating as a switch, triggered to turn on at different points in the AC waveform on each half cycle, depending on the control dial position, the heat produced will be proportional to the dial setting. However, if the triac has a slow rise time, it may not behave this way. John

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yeah! I hate those damned dimmer switches. They interfere BIG TIME with AM radio reception. We seldom watch TV, but do listen to AM radio quite a lot. I think the FCA should ban the damned dimmers.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Maybe the screws are getting VERY hot, because the OP is using a plastic coverplate. The plastic is insulating the entire dimmer faceplate, so the only way the heat can now escape is via the 2 metal screws, effectively concentrating a possible 6 sq. in. of heat sink into 2 tiny dots.
I'd change to a metal switchplate if at all possible.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@aol.com (HA HA Budys Here) wrote:

To replace the in-wall box would require tearing into the drywall which I'd rather not do. This switch/light assembly has been in place for a number of years.
bp
--
Heisenberg may have slept here.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No, what I'm saying is, the faceplate over the dimmer - if it's plastic, change it to metal.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
031108 0129 - Blake Patterson wrote:

The Triac -- the semiconductor device in the dimmer that does all the work -- is fastened to the metal strap of the dimmer for heat sink function. It is obvious that the dimmer is at its maximum with the lights on full bright. If you turn the lights on the dimmer on dim, the heat should diminish. Maybe you should consider getting a new dimmer with a higher wattage rating.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Isn't that backwards? When the lights are full bright, the dimmer is doing nothing and the triac should be completely bypassed. At the very least, it's doing no work whatsoever.
When dimmed, the dimmer the lights, and the higher the total wattage, the more work the triac is doing and therefore, the hotter it gets.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
full power dissipation occurs when the triac is full on (full brightness). The triac has only 2 states (on and off) and dimming is controlled by where in the AC cycle it turns on. Compare the wattages of the bulbs on the 3 dimmers, the warmer dimmer should have the higher wattage bulb.

work
It
bright.
it's
more
rating.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Go back and read the OP. Only one of three dimmers is running hot.
The OP says that the SCREWS are too hot to touch. What do you suppose the temperature of the plate that the device is using as a heat sink would be in that case? The maximum dissipation of triac should never get that high. The current flow may be at a maximum, but the "on" voltage drop should never get very high. Typically it should only be around 2 volts.
If the dimmer has a switch position at the end of its range that bypasses the triac it should not get hot at all.
At an rate, I would replace that dimmer as it is certainly not acting normal.
Also see > http://www.americanmicrosemi.com/tutorials/triac.htm
Charlie
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
indago wrote:

Hi, Maybe that one is at ~max load. I'd replace it with higher Wattage rated one. I had to do that with my Chandelier dimmer. Tony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Add up all the wattages from the lamps that are controlled by the dimmer that is getting hot. Next, remove the face plate of the dimmer an see what the maximum wattage is (typ. 600w). If you are exceeding the maximum wattage, you should reduce the lamp wattage by replacing the bulbs with that of a lower wattage.
Also, you may find the wattage below the capacity of the dimmer. It is normal for them to be quite warm when there are several hundred watts of load. John

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article

It is a 600W max Lutron dimmer. This one, of the three I mention having in the house, has by far the greatest load on it. There is another one where the screws are slightly warm and it has 180W total on it. This one has between 400 and 500W on it. It is also in a PLASTIC phone-style box in the wall, not metal, oddly. Bad construction, clearly. So the box itself is not helping as a heatsink. The screws are quite hot (not too hot too touch, really, after more experimenting), but the plastic faceplate on the dimmer switch just feels warm.
Can't decide if this is a problemed switch or if I should leave it as normal.
bp
--
Heisenberg may have slept here.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

There is nothing wrong with plastic boxes. they are the normal now. Metal is not being used as much
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It would have been easier if you just *accurately* posted the "problem", that is, "dimmer switch - _WARM_ screws" instead of "dimmer switch - _hot_ screws".
There are enough real problems in homes without you going around exaggerating your symptoms, and berating long accepted, standard construction techniques which clearly you have not a clue about...

Not really, and certianly not "clearly bad construction." Most boxes installed since the early 60's in homes are either composite or plastic. The dimmer is UL listed and rated for your load, and there should be no danger whatsoever with such a typical, standard arrangement.

And it shouldn't. Even if it were metal, the dimmer would not get a UL listing if it required a metal box, or purposefully dissapated heat into the box itself. That would eventually damage all the wires contained therein. The dimmer is *supposed to* dissapate heat through the face, not into the box.

OK then, just warm, correct? Perfectly normal operating parameters.

Normal.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It does not sound like a problem. 400-500W on a 600W dimmer would result in warm operation. You could consider going for a higher rated dimmer if you like, but you will find that it will also get warm. If I had to replace the dimmer, I would go for a more heavy duty one.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Warm is normal. The screws on a 600W dimmer go right into the heat sink of the dimmer, so warm screws would be normal. And if the dimmer is running too warm, just wait a while and the triac will short out and you will have only an on-off switch with NO dimming. The next step up from the 600W in-box dimmers is a dimmer with higher wattage ratings, but the 1000W dimmers have external heat sinks. If you can manage with the 600W dimmer (for how many years?) with it not going bad, just stick with it. It should be noted that the higher wattage dimmers will dissapate the same power, but with their better heat sinking, their temperature will be some lower. But they are not as pretty, since the heat sinking is external. --Phil
Blake Patterson wrote:

--
Phil Munro Dept of Electrical & Computer Engin
mailto: snipped-for-privacy@cc.ysu.edu Youngstown State University
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
There's a lot of quasi technical discussion about triac/ thyristor theory going on here that does not explain the excessive heat. The whole idea behind using a solid state switch is that it is a low loss ( and so low heat ) device.
Now then if the screws are too hot to touch, consider how hot the plate that they are screwed into must be. And that is inside the wall!
Since you reported that it controls a ceiling light and I assume we are not talking about a chandelier or other multi- bulb arrangement, I would replace that dimmer in a heart beat.
Charlie

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You left out a few important facts. First, are they all handling the same load (total wattage?) Are they all set to the same brightness? Are they are rated the same and the same brand/model.
As suggested, I suggest you get a heavier duty unit to replace the one that is getting hot.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.