Re: [Phys-l] Microwave door.

[brian whatcott <betwys1@sbcglobal.net>]

On 2010, Dec 23, , at 08:24, Moses Fayngold wrote:

/snip/
>   I personally have no idea of "Why" and "How" this happened. Of course, I could
> resort to considering this as a divine message from some mysterious headquarters
> that it is time for me to switch from pure theoretical to applied physics, but I
> so far decided to keep such possibility as a last resortMeanwhile, I
> immediately called to a colleague - a professional experimental physicist with
> 30 year experience. He came over, looked at the scene and said that he has never
> encountered or heard of this kind of event. His only suggestion was that the
> cause might be a gradually  accumulated strain or stress in the microwave door,
> or explosion (rather, implosion?) of the vacuum tube in the internal magnetron.
> Neither of which explains much to me. /snip/
> On his insistence (he said there might be
> some toxic output) we wrapped the thing into a plastic bag and disposed of it,
> and now I regret this since I cannot anymore do a more thorough examination.
>   I have done some search on the Internet, but did not find anything similar
> except for SHC (spontaneous human combustion) (never before heard about that,
> either), and again, without any satisfactory explanation or even proof that all
> described cases were not some artifacts.
>   So my question to this Forum is: Has anyone any viable idea or information
> about this kind of effect? If yes, that would be a good answer to the "Why" and
> "How" question.
>
> Thanks,
>
>   Moses Fayngold,
>   NJIT
I am late into this question.
 In  financial and some political (GW?)  and criminal investigations,
 the rule of thumb is "follow the money".
In this sort of sudden failure, the ruling idea might be "follow the power".
A microwave is usually arranged on a rather straight-forward concept.
 Route line power through a switch and a rectifier diode to a capacitor
 and magnetron  (which is conceptually, another diode).

Modern microwaves often boast 1.3 KW ratings.
This amounts to an input current certainly exceeding 11 amps.


This power has to be accessible on front panel demand, so the 
possibility of
electrical breakdown is always present, even if remote.
The component best known for explosive failure is the capacitor,
 and examination  might well have shown this shell was shredded.

Another possibility is a timer failure, so that the device was running
 on an empty oven.
This would permit the glass window/reflector to be heated more than usual.
In this case, you would have expected to hear the mode-strirrer fan 
rotating.
If this fan stalls, hot spots result. This is a double failure cascade, so
 its likelihood is low.

Finally, a short developing in the wiring from the line input might provide
 a good bang before the high current fuse or breaker  blew.
 This  blown fuse would have been noted at the time however.

Brian W