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

"Dick M." wrote in message
news:uyk1d.36011$9Y5.17743@fed1read02...
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

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.

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.

I'm pretty sure you meant "amiss" here, not "aloof".

Dick M. wrote:
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

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.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

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

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.

--
Joseph E. Meehan

Dick M. wrote:
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

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


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

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

In article Cfp1d.37734$9Y5.14014@fed1read02, Dick M. wrote:
How could the cooling design help? The heat has to get out thru
the wallplate regardless of the cooling design.
Dick

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.

- Don Klipstein )

That's what I thought. I guess the 600-watt specification on the dimmer is
overly optimistic.
Dick


wrote:

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.

BB

Dick M. wrote:
How could the cooling design help? The heat has to get out thru
the wallplate regardless of the cooling design.
Dick

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.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"Joseph Meehan" wrote:

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

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

wrote:


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.

BB

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
--
My name is Jeff Wisnia and I approved this message....

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

Joseph Meehan wrote:

Dick M. wrote:

How could the cooling design help? The heat has to get out thru
the wallplate regardless of the cooling design.
Dick


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.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"Joseph Meehan" wrote:

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


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

--
My name is Jeff Wisnia and I approved this message....

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

In article ,
wrote:

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.

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.

There are some advanced dimmers that use pulse width modulation to
regulate instead, and they run much cooler.

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.

- Don Klipstein )