Today I realized that our light dimmer switch, when set at the highest
point, does not seem to get the lights as bright as they had
previously been. I should point out that the power was also out a bit
today in my area.
I am suspecting that perhaps a power surge or else maybe just the age
of the switch may have caused this problem to "come to light", but I
had though that if the switch failed, the lights would simply be at
their brightest and that the dimming mechanism would not work.

I am going to replace the switch anyway, but wanted to check out if my
suspicions were correct; can the dimmer fail so as to result in a mid-
level brightness of the lights?

Thanks for any help!
Paul

On Tue, 06 Nov 2007 23:33:22 +0000, Paul Soderman wrote:

Today I realized that our light dimmer switch, when set at the highest
point, does not seem to get the lights as bright as they had previously
been. I should point out that the power was also out a bit today in my
area.
I am suspecting that perhaps a power surge or else maybe just the age of
the switch may have caused this problem to "come to light", but I had
though that if the switch failed, the lights would simply be at their
brightest and that the dimming mechanism would not work.

I am going to replace the switch anyway, but wanted to check out if my
suspicions were correct; can the dimmer fail so as to result in a mid-
level brightness of the lights?

Thanks for any help!
Paul



Dimmer switches are no more than rheostats. If carbon were to build up
on part of the switch, it may be sufficient to affect voltage. Might
cause a voltage drop.

You could test this with a volt/ohm meter.

franz frippl wrote:

Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.

You could test this with a volt/ohm meter.

In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.
There is a rheostat used in the dimmer, but it it is used
to control the triac. For a more detailed explanation:

http://home.howstuffworks.com/dimmer-switch6.htm

Paul Soderman wrote:
Today I realized that our light dimmer switch, when set at the highest
point, does not seem to get the lights as bright as they had
previously been. I should point out that the power was also out a bit
today in my area.
I am suspecting that perhaps a power surge or else maybe just the age
of the switch may have caused this problem to "come to light", but I
had though that if the switch failed, the lights would simply be at
their brightest and that the dimming mechanism would not work.

I am going to replace the switch anyway, but wanted to check out if my
suspicions were correct; can the dimmer fail so as to result in a mid-
level brightness of the lights?

Thanks for any help!
Paul


Yes, The triac (controlling device) has two "sides" that
control both the positive and negative cycle that makes up
the "AC" that lights the lamp. One side can fail, and at
the full level setting, only half the power reaches the
lamp. Just what you described. Time for a new one. You
might check how warm the dimmer is getting in normal use.
You might have more lamp watts than the dimmer is rated for
that caused the failure.

-- larry / dallas

According to lee h :
franz frippl wrote:

Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.

You could test this with a volt/ohm meter.

In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.

"More common"? Even in ye olde days, rheostat dimmers were extremely
rare, and they're now essentially non-existant.

Hint: rheostats have to dissipate a _lot_ of power, and a switch
box is not a good place to try doing that.

A rheostat capable of, say, dimming a 100W light bulb probably
wouldn't fit into a switch box, and if it did, you could use the
wall around it as a cooking surface.

Dimmers tend to fail in one of two ways:

1) Complete failure, no light at any position.
2) triac control fails, get erratic behaviour.

I suspect that the OP is simply seeing a brownout.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:
According to lee h :
franz frippl wrote:

Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.

You could test this with a volt/ohm meter.

In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.

"More common"? Even in ye olde days, rheostat dimmers were extremely
rare, and they're now essentially non-existant.

Chris, I suspect that your definition of 'ye olde' and 'many years'
is more short term than mine. The SCR which enabled solid-state
control of dimmers was not invented until the late fifties. Rheostat
dimmers and auto transformers (Variacs) were the *only* means of
dimming lights until then. So they were hardly rare. Solid state
dimmers were not commonly used in homes until the late
sixties. But, you are right about the rheostat dimmer's heat
output. Most were mounted in a box on the outside surface of
a wall, not in a switchbox.

According to lee h :
Chris Lewis wrote:
According to lee h :
franz frippl wrote:

Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.

You could test this with a volt/ohm meter.

In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.

"More common"? Even in ye olde days, rheostat dimmers were extremely
rare, and they're now essentially non-existant.

Chris, I suspect that your definition of 'ye olde' and 'many years'
is more short term than mine.

Probably not. I'm older than I look ;-)

In junior high school we had an electronics lab that a couple of us
spent time in. We did some stuff with SCRs. Triacs weren't available
then I don't think.

Actually, most of what we did was with vacuum tubes. I built a
radio telescope out of a vacuum tube IF strip out of a 50's B&W
TV set and used an oscilloscope to display the results. 150'
baseline on the antennas allowed me to do interferometry work.

Worked pretty good ;-)

The SCR which enabled solid-state
control of dimmers was not invented until the late fifties. Rheostat
dimmers and auto transformers (Variacs) were the *only* means of
dimming lights until then.

Not quite, but we'll take that as a given.

So they were hardly rare.

How many houses had any dimming whatsoever prior to SCR/triac dimmers?
How many houses had more than one? How many of these were used
in general purpose things rather than very specific (and usually
low wattage) fixtures?

I would submit that up until the late 60's, general purpose dimming
circuits were almost non-existant in residences. What dimming
circuits there were were expensive heavy-duty industrial units,
or low wattage (usually considerably less than 50W), often a part
of the fixture itself, or the cabinet it was installed in.

Solid state
dimmers were not commonly used in homes until the late
sixties. But, you are right about the rheostat dimmer's heat
output. Most were mounted in a box on the outside surface of
a wall, not in a switchbox.

And variacs are much larger & heavier. Saw a brand new one a few
days ago. 600W IIRC. It weighed about 25 pounds, and was bigger than
a regular two slice toaster. $200 IIRC. Hadn't seen one in a
very long time.

I don't think too many people had those in their house to dim
the mood lights.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

Bogus wrote:

Dimmer switches are no more than
rheostats. If carbon were to build up on
part of the switch, it may be sufficient
to affect voltage. Might cause a voltage
drop.

That information is bogus. Dimmer switches are solid state devices that
chop of part of the AC sine wave. I suppose they could fail but I have
one in a homemade electric blanket control that has been working for 25
years.


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

Chris Lewis wrote:

....
How many houses had any dimming whatsoever prior to SCR/triac dimmers?
How many houses had more than one? How many of these were used
in general purpose things rather than very specific (and usually
low wattage) fixtures?

I would submit that up until the late 60's, general purpose dimming
circuits were almost non-existant in residences. What dimming
circuits there were were expensive heavy-duty industrial units,
or low wattage (usually considerably less than 50W), often a part
of the fixture itself, or the cabinet it was installed in.
....
In 1963 my family moved into a (new) house that had a dimmer
switch for the dining room ceiling light. While it was about
the same size as today's dimmers, it was not today's 4 component
circuit. I remember looking at the schematic. There were a dozen
or more components, including a transformer. I didn't know
enough then to understand the circuit, so I can't offer more details.

Chris Lewis wrote:
In junior high school we had an electronics lab that a couple of us
spent time in. We did some stuff with SCRs. Triacs weren't available
then I don't think.

I started in ham radio in the early fifties and most everything was
homebrew or converted military. got into solid state design as an
EE in early sixties. later ttl, lsi, vlsi, computers, etc. In the fifties,
rheostat and switched resistor dimming of lights was common
in higher end housing. I installed some myself. Not exactly
complictated circuitry.


And variacs are much larger & heavier. Saw a brand new one a few
days ago. 600W IIRC. It weighed about 25 pounds, and was bigger than
a regular two slice toaster. $200 IIRC. Hadn't seen one in a
very long time.

Yes, they're still available and the Variac brand still exists. However
auto transformers are not large if only a couple hundred watts.
As I said earlier resistive type dimmers did not mount in inwall
switch boxes, but in their own enclosed panel/box on the wall
surface. (to accomodate the heat generated).

I don't think too many people had those in their house to dim
the mood lights.

No, not common, but by no means a rarity. Even nowadays with
the cheapness of triac dimmers, think about how small a percentage
are used. Especially where they'd be most useful. I'll bet they're
used in less than a few percent of homes and apartments.

I use dimmers in many switches in my house. They pay for
themselves in lower juice use and longer bulb light. I've got
some hard to reach ceiling fixtures with bulbs that have lasted
twenty years. I prefer the rotary to the lever type to slow
down that filament killing inrush and shock.

On Nov 6, 8:33 pm, Paul Soderman wrote:
Today I realized that our light dimmer switch, when set at the highest
point, does not seem to get the lights as bright as they had
previously been. I should point out that the power was also out a bit
today in my area.
I am suspecting that perhaps a power surge or else maybe just the age
of the switch may have caused this problem to "come to light", but I
had though that if the switch failed, the lights would simply be at
their brightest and that the dimming mechanism would not work.

I am going to replace the switch anyway, but wanted to check out if my
suspicions were correct; can the dimmer fail so as to result in a mid-
level brightness of the lights?

Thanks for any help!
Paul

If in doubt take dimmer out and put in a regular 50-75 cent switch,
two connections.
If it's solid state dimmer it may be making radio noise
(RFInterference) and is probably more prone to voltage hits. Keep it
simple! Haven't used a dimmer in this house for last 37 years! So
never had to replace one, have maybe replaced couple of switches in
that time period.
Like everything else, with electrcity simplest is best.

franz frippl wrote:
On Tue, 06 Nov 2007 23:33:22 +0000, Paul Soderman wrote:


Today I realized that our light dimmer switch, when set at the highest
point, does not seem to get the lights as bright as they had previously
been. I should point out that the power was also out a bit today in my
area.
I am suspecting that perhaps a power surge or else maybe just the age of
the switch may have caused this problem to "come to light", but I had
though that if the switch failed, the lights would simply be at their
brightest and that the dimming mechanism would not work.

I am going to replace the switch anyway, but wanted to check out if my
suspicions were correct; can the dimmer fail so as to result in a mid-
level brightness of the lights?

Thanks for any help!
Paul




Dimmer switches are no more than rheostats. If carbon were to build up
on part of the switch, it may be sufficient to affect voltage. Might
cause a voltage drop.

You could test this with a volt/ohm meter.

Hmmm,
You must be awake from a long snooze or?...... Now dimmers are all
electronic device whih controls conduction angle of sine wave. The
failure mode can be anything.

Chris Lewis wrote:

According to lee h :

Chris Lewis wrote:

According to lee h :

franz frippl wrote:



Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.



You could test this with a volt/ohm meter.



In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.



"More common"? Even in ye olde days, rheostat dimmers were extremely
rare, and they're now essentially non-existant.



Chris, I suspect that your definition of 'ye olde' and 'many years'
is more short term than mine.


Probably not. I'm older than I look ;-)

In junior high school we had an electronics lab that a couple of us
spent time in. We did some stuff with SCRs. Triacs weren't available
then I don't think.

Actually, most of what we did was with vacuum tubes. I built a
radio telescope out of a vacuum tube IF strip out of a 50's B&W
TV set and used an oscilloscope to display the results. 150'
baseline on the antennas allowed me to do interferometry work.

Worked pretty good ;-)


The SCR which enabled solid-state
control of dimmers was not invented until the late fifties. Rheostat
dimmers and auto transformers (Variacs) were the *only* means of
dimming lights until then.


Not quite, but we'll take that as a given.


So they were hardly rare.


How many houses had any dimming whatsoever prior to SCR/triac dimmers?
How many houses had more than one? How many of these were used
in general purpose things rather than very specific (and usually
low wattage) fixtures?

I would submit that up until the late 60's, general purpose dimming
circuits were almost non-existant in residences. What dimming
circuits there were were expensive heavy-duty industrial units,
or low wattage (usually considerably less than 50W), often a part
of the fixture itself, or the cabinet it was installed in.


Solid state
dimmers were not commonly used in homes until the late
sixties. But, you are right about the rheostat dimmer's heat
output. Most were mounted in a box on the outside surface of
a wall, not in a switchbox.


And variacs are much larger & heavier. Saw a brand new one a few
days ago. 600W IIRC. It weighed about 25 pounds, and was bigger than
a regular two slice toaster. $200 IIRC. Hadn't seen one in a
very long time.

I don't think too many people had those in their house to dim
the mood lights.
Hmmm,
You ought know then vacuum tube version of SCR, the Thyristor!
Also include Diac as well on solid state side.

M Q wrote:

Chris Lewis wrote:

...

How many houses had any dimming whatsoever prior to SCR/triac
dimmers? How many houses had more than one? How many of these were used
in general purpose things rather than very specific (and usually
low wattage) fixtures?

I would submit that up until the late 60's, general purpose dimming
circuits were almost non-existant in residences. What dimming
circuits there were were expensive heavy-duty industrial units,
or low wattage (usually considerably less than 50W), often a part
of the fixture itself, or the cabinet it was installed in.

...
In 1963 my family moved into a (new) house that had a dimmer
switch for the dining room ceiling light. While it was about
the same size as today's dimmers, it was not today's 4 component
circuit. I remember looking at the schematic. There were a dozen
or more components, including a transformer. I didn't know
enough then to understand the circuit, so I can't offer more details.

Hi,
And big heat sink?

terry wrote:

On Nov 6, 8:33 pm, Paul Soderman wrote:

Today I realized that our light dimmer switch, when set at the highest
point, does not seem to get the lights as bright as they had
previously been. I should point out that the power was also out a bit
today in my area.
I am suspecting that perhaps a power surge or else maybe just the age
of the switch may have caused this problem to "come to light", but I
had though that if the switch failed, the lights would simply be at
their brightest and that the dimming mechanism would not work.

I am going to replace the switch anyway, but wanted to check out if my
suspicions were correct; can the dimmer fail so as to result in a mid-
level brightness of the lights?

Thanks for any help!
Paul


If in doubt take dimmer out and put in a regular 50-75 cent switch,
two connections.
If it's solid state dimmer it may be making radio noise
(RFInterference) and is probably more prone to voltage hits. Keep it
simple! Haven't used a dimmer in this house for last 37 years! So
never had to replace one, have maybe replaced couple of switches in
that time period.
Like everything else, with electrcity simplest is best.

Hi,
No energy conservation?

According to M Q :

In 1963 my family moved into a (new) house that had a dimmer
switch for the dining room ceiling light. While it was about
the same size as today's dimmers, it was not today's 4 component
circuit. I remember looking at the schematic. There were a dozen
or more components, including a transformer. I didn't know
enough then to understand the circuit, so I can't offer more details.

The classic "basic" dimmer circuit published back in the late 60's and
earlier consisted of a SCR (later triac), a diac (looks like
an ordinary semiconductor small-signal diode, and my rusty
memory seems to indicate it's shown in schematics as two
paralleled back-to-back zener diodes), rheostat (variable resistor
with the knob ;-) and another resistor or two. The other components
you saw (including the transformer) were probably noise filtering
which is considered an "optional add-on".

More modern circuits do with less (or no) noise filtering, and
use a resistive network instead of a diac to trigger the triac
IIRC. SCR-based dimmers need a lot of filtering, and triac-based
dimmers need less - since modern circuits don't use SCRs, the
need for noise filtering is less.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

terry wrote:

If in doubt take dimmer out and put in a regular 50-75 cent switch,
two connections.
Keep it simple!

Use a three position switch hi-off-medium, use a 3-10Amp
rectifier diode (A15) between hi and medium terminal, line
to common terminal, lamp to hi terminal. Or add a switch
with diode in parallel, then wire switch(hi-medium) in
series with regular circuit. This used to be available as a
coin size "lamp saver" that you placed in a socket, under
the bulb. Perfect for porch & pole lights since the bulb
would last for years.

Large 20 amp diode (or one leg of bridge rectifier-1/4"
terminals) in series with low voltage lighting makes those
4/7 watt bulbs last longer than the fixture ;-)

-- larry / dallas

According to lee h :

I don't think too many people had those in their house to dim
the mood lights.

No, not common, but by no means a rarity. Even nowadays with
the cheapness of triac dimmers, think about how small a percentage
are used. Especially where they'd be most useful. I'll bet they're
used in less than a few percent of homes and apartments.

I'd think the contrary - virtually all new housing will have
at least one dimmer, and it's a very popular add-on. This
is vastly more than the old rheostat stuff. I think I'm justified
in calling something that rare "rare" ;-)

I use dimmers in many switches in my house. They pay for
themselves in lower juice use and longer bulb light. I've got
some hard to reach ceiling fixtures with bulbs that have lasted
twenty years. I prefer the rotary to the lever type to slow
down that filament killing inrush and shock.

Given that many rotaries have "full bright" and "full off"
adjacent at one end of the travel, you can't escape abrupt
on/offs with them :-(

We're switching mostly to decora-style outlets/switches, and
rotary dimmers look stupid in decora. At least slider dimmers
"slow start" better than straight switches.

Have you seen slow-start LV fixtures yet? I replaced a burned
LV supply in an Ikea track light a few months ago with a new
LV supply bought off the Internet. We liked the fixture, and
replacing the whole thing would have been difficult - discontinued
product. Not only was it higher power and smaller size, it has
slow-start - takes a bit less than 2 seconds I think to get to
full bright. _Very_ nice feature. Those bulbs should last about
forever.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

According to ---MIKE--- :

That information is bogus. Dimmer switches are solid state devices that
chop of part of the AC sine wave. I suppose they could fail but I have
one in a homemade electric blanket control that has been working for 25
years.

They most certainly can fail. Being semiconductor devices, they
can fail real fast too. An accidental short on the output side
of a dimmer that's too fast even for a breaker to notice can
fry a dimmer.

Electric blankets are nice "safe" pure resistive devices that are
relatively friendly to semiconductor dimmers. Lightbulbs are worse.
There are things that are worse still. Like motors. The motor-rated
dimmer on our ceiling fan died a few years ago (installed in 1984).

I've seen a handful of dimmers die within days of being installed,
or be dead when the circuit is first turned on. Dimmers also
occasionally die mechanically.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:
According to M Q :


In 1963 my family moved into a (new) house that had a dimmer
switch for the dining room ceiling light. While it was about
the same size as today's dimmers, it was not today's 4 component
circuit. I remember looking at the schematic. There were a dozen
or more components, including a transformer. I didn't know
enough then to understand the circuit, so I can't offer more details.


The classic "basic" dimmer circuit published back in the late 60's and
earlier consisted of a SCR (later triac), a diac (looks like
an ordinary semiconductor small-signal diode, and my rusty
memory seems to indicate it's shown in schematics as two
paralleled back-to-back zener diodes), rheostat (variable resistor
with the knob ;-) and another resistor or two. The other components
you saw (including the transformer) were probably noise filtering
which is considered an "optional add-on".

More modern circuits do with less (or no) noise filtering, and
use a resistive network instead of a diac to trigger the triac
IIRC. SCR-based dimmers need a lot of filtering, and triac-based
dimmers need less - since modern circuits don't use SCRs, the
need for noise filtering is less.
Hmmm,
Remember first ever popular transistor RCA CK722 PNP Ge junction
type? When I got one of them at such a high price and built a small
receiver with it, what an excitement. Was back in the '50s. Now I am
using florescent lights and dimmers in the house. Waiting for LED lights
to become cheap in price.
Tony, VE6CGX

According to Tony Hwang :
You ought know then vacuum tube version of SCR, the Thyristor!

A thyristor is not a vacuum tube. Thyristors are semiconductors -
"four layers of alternating N and P-type material" according to
Wikipedia. Some sources consider thyristor to be synonymous with SCR,
others have thyristor include GTOs, Triacs, SJTs, SITH and MCTs too.

Didn't have much call to play with vacuum tube switching circuits, power
or otherwise - most of my playing around with tubes was RF, with RF
mid-power amp tubes and 0D3-type regulator tubes being the more exotic
stuff.

That said, we may be getting access to a 60' radio telescope dish
to do a little serious radio astronomy. The dish steering system
is a vacuum tube and electric motor implementation of an H-bridge,
similar to that used to steer things like shipboard radars. The
modern semiconductor version is used in the small scale for hobby
robots.

This has an example circuit for the small scale: http://tinyurl.com/39xw85
Here's an IC version: http://cache.national.com/ds/LM/LMD18200.pdf

The radio telescope has vacuum tubes controlling an AC motor which in
turn generates DC for the actuator DC motors. On the order of at least
5 (and probably 10 or 20HP) apiece... [Times two for the two axis]

[The unit was designed for tracking satellites back in the 60's,
so it was designed for rather faster traverse than is necessary
for radio astronomy.]

We don't believe the vacuum tube portion will still be working
(the dish been locked for ~15-20 years), so we're thinking that
we will have to replace everything but the movement motors with
modern solid-state very high power H-bridge modules. Eg: a hundred
A at 600V or something silly like that.

Also include Diac as well on solid state side.

I've played with those (and mentioned them backthread)
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:
According to Tony Hwang :
You ought know then vacuum tube version of SCR, the Thyristor!
A thyristor is not a vacuum tube. Thyristors are semiconductors -


He meant thyratrons, I think the 2d21's were the smallest
ones and I don't remember the number of three huge ones that
controlled our Lepel 400KW 250KHz alloy bearing surface welders.

It gets hard to remember all these names when you're old
enough to remember real power control. Also, no one
mentioned carbon piles, another version of early "dimmers" ;-)

-- larry / dallas

According to larry :
Chris Lewis wrote:
According to Tony Hwang :
You ought know then vacuum tube version of SCR, the Thyristor!
A thyristor is not a vacuum tube. Thyristors are semiconductors -

He meant thyratrons, I think the 2d21's were the smallest
ones and I don't remember the number of three huge ones that
controlled our Lepel 400KW 250KHz alloy bearing surface welders.

Yeah, I figgered later he meant thyratron.

The closest I got to those (which isn't very close) is to the particle
accelerator in the basement of the University of Toronto that, if I
recall correctly, was doing pulses in the megawatts range at 400Mhz
with Klystrons.

Aside from that, my exposure to the "big" stuff was multi-kilowatt
tube transmitters.

It gets hard to remember all these names when you're old
enough to remember real power control. Also, no one
mentioned carbon piles, another version of early "dimmers" ;-)

You got that right.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.