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Light dimmer switch; can failure just cause lack of bright lights?

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Light dimmer switch; can failure just cause lack of bright lights? Paul Soderman 11-06-2007
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Posted by Chris Lewis on November 7, 2007, 5:39 pm
> Chris Lewis wrote:
> >> 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.

Posted by M Q on November 7, 2007, 9:28 pm
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.


Posted by Tony Hwang on November 8, 2007, 1:25 am
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?

Posted by Chris Lewis on November 8, 2007, 9:51 am

> 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.

Posted by Tony Hwang on November 8, 2007, 11:01 am
Chris Lewis wrote:
>
>
>>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

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