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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 12, 2007, 11:06 am
> Chris Lewis wrote:
> >>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.

Posted by ---MIKE--- on November 7, 2007, 6:31 pm
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=B0 15' N - Elevation 1580')


Posted by Chris Lewis on November 8, 2007, 10:08 am

> 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.

Posted by Tony Hwang on November 8, 2007, 1:19 am
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.

Posted by larry on November 6, 2007, 10:52 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
>

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

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