Re: Insteon Observations

[Victor Roberts <xxx@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 15 Dec 2006 18:59:20 -0600, G. Morgan
<alarmpro@xxxxxxxxxxx> wrote:

>On Fri, 15 Dec 2006 18:04:57 -0500, Marc_F_Hult
><MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>On Fri, 15 Dec 2006 22:27:03 GMT, nobody@xxxxxxxxxxxx (Dave Houston) wrote in
>>message  <45831e9f.29307109@xxxxxxxxxxxxx>:
>>
>>>"Dennis Brothers" <brothers@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>>
>>>>Hard to imagine how a defective LampLinc could damage an ordinary 100W
>>>>incandescent bulb.  On the other hand, it's easy to see how a current surge
>>>>as the bulb dies (typically accompanied by a blue flash) could damage a
>>>>triac.
>>>>
>>>
>>>Why would there be a surge when the (resistive) circuit opens? The inrush
>>>current when a cold incandescent is turned on is significantly higher than
>>>after the filament heats up. If the filament is thin in a spot, the normal
>>>inrush current causes it to break.
>>
>>Dave,
>>
>>When a tungsten filament fails, a "tungsten arc" can occur through vaporized
>>tungsten connecting the ends of the foreshortened filament. There is a
>>positive feedback in this effect, so as more tungsten is consumed to support
>>the arc, the current path through the remaining filament becomes shorter, and
>>the current increases causes more vaporization. This can result in the bright
>>flash that is sometimes seen when a filaments fails.
>>
>>This is a well-known phenomenon. Some lamps have fuses built into the base to
>>provide some measure of protection. One of the functions of the RC snubber
>>circuit across a TRIAC is to protect the TRIAC gates from inductive spike
>>during filament failure that can damage the TRIAC. This is also a problem with
>>IGBT and MOSFETs used in reverse phase dimmers.
>
>Marc,
>
>So the net effect is indeed a current surge while the light bulb
>filament is breaking apart?
>
>(x-posted to sci.engr.lighting,alt.engineering.electrical,sci.physics)

Yes.

--
Vic Roberts
http://www.RobertsResearchInc.com
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