Re: Insteon Observations

[G. Morgan <alarmpro@xxxxxxxxxxx>]

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)

Thanks,


--

-Graham

(delete the double e's to email)