600-watt light dimmer overheats

I have six 75-watt incandescent lights being controlled by a 600-watt rated dimmer. The dimmer is getting very hot when the lights are set to full on. Is it possible that these six lights are somehow drawing more amperes than the dimmer can safely handle? Dick
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I'd be curious if it is the only dimmer in the box ? And what make/model dimmer.
If its the only dimmer in one box, 6 standard old 75w bulbs is fine. Dimmers do get pretty hot, you say very hot which might mean something is aloof.
Some dimmers have heat sink fins on the side or cover plate to disapate heat and you derate wattage as you remove these fins. When two dimmers are mounted side by side, depending on manufactor most will derate to 500 or 450 watts max, three dimmers and the middle dimmer might only be 300w.

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I'm pretty sure you meant "amiss" here, not "aloof".
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A dimer turned wide open should not be hot. That should be it's coolest operation. The heat associated with dimmers comes from converting energy that would otherwise go to the lights to heat instead by use of resistance. There are some advanced dimmers that use pulse width modulation to regulate instead, and they run much cooler.
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That's what I thought. I guess the 600-watt specification on the dimmer is overly optimistic. Dick
A dimmer turned wide open should not be hot. That should be it's coolest operation. The heat associated with dimmers comes from converting energy that would otherwise go to the lights to heat instead by use of resistance. There are some advanced dimmers that use pulse width modulation to regulate instead, and they run much cooler.
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BinaryBillTheSailor@Sea++.com wrote:

Sorry, you're wrong about that.
You may be remembering those old theater light dimmers which were huge variable resistors, sometimes even with fan cooling to keep them from burning up.
I'd bet my virginity that there's never been a household dimmer made which will fit into a standard switch sized electrical box that doesn't use pulse width modulation.
And, those dimmers DO dissipate the most heat when they are full on, because the average current is highest then, and it's the average current times the voltage drop across the semiconductor junction(s) which produces the heat.
I did visit an old mansion (The Hammond Castle in Gloucester, Massachusetts) and seem to recall noting there was a big variac mounted on the wall which was used to dim some lights. But the place was built in the 20s, and by an inventor with electrical know-how, so that could have been just a one-of-a-kind thing, and it was hardly representative of the kind of dimmers you were describing.
HTH,
Jeff
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BinaryBillTheSailor@Sea++.com wrote:

I have never seen a dimmer like that in use in anyone's home. I once saw one in a school theater that worked that way, and it was big.

The usual household dimmers work basically that way.
The thing is that a 600 watt load draws 5 amps, and the triac (switching element that is part of the circuit that chops the AC waveform to achieve dimming) has a voltage drop of a volt or somewhat more when it is conducting. This means that with a 600 watt load, the triac produces 5 watts or somewhat more than 5 watts of heat. This is a little more heat than is produced by a typical magnetic ballast for a 15 watt fluorescent lamp.
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Dick M. wrote:

Are there any other devices other than that one dimmer in the work box?
In any case I would up the capacity of the dimmer. I don't like to run them over 50% or their rated capacity.
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This is the only dimmer switch in the box. If I get a 1000-watt dimmer, will it be less hot than the 600-watt dimmer? Is that because the components in the larger dimmer are more efficient? Dick
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Are there any other devices other than that one dimmer in the work box?
In any case I would up the capacity of the dimmer. I don't like to run them over 50% or their rated capacity.
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Dick M. wrote:

Maybe, but I believe you will find it will also have cooling integrated into the design

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How could the cooling design help? The heat has to get out thru the wallplate regardless of the cooling design. Dick
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Joseph Meehan" wrote:
Maybe, but I believe you will find it will also have cooling integrated into the design
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Most walls are hollow and heat can get out the sides of the switch box.
If your switch box has its sides covered, then I suspect this can reduce the capacity of your dimmer.
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Dick M. wrote:

I am not sure they are still making the same design dimmers that I am was thinking of. The ones I was thinking of were or are built with cooling fins on the faceplate and the even heavier duty ones took up two spaces in the work box to get more cooling fins.
It could be that they are made with more efficient electronics today. I really don't know. it has been a while since I have needed to work on such a thing.

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Joseph Meehan wrote:

The semiconductor manufacturers have been continuously improving (lowering)the "on resistance" (A parameter called Rdon) of their power switching devices, and the lower that resistance, the less heat is generated for a given average current.
Economics being what they are, the chincier manufacturers will use older lower cost semiconductors as long as they can get away with it
Short of putting on an electrical engineering hat, setting up a measuring system, and comparing different makes of dimmers, there's no practical way to tell from just the "wattage rating" exactly how hot one dimmer will run compared to another.
HTH,
Jeff
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