Homestead mailing list

["Wendy" <crazygardens AT nationi.net>]

Sent this out last night, but it went to Warren instead of to the list. 
Let's try this again.
Wendy

----- Original Message ----- 
From: Wendy
To: WF Smith
Sent: Friday, November 19, 2004 11:02 PM
Subject: Re: [Homestead] Homestead tools


I'm not sure about those little "plug in" things.  When my house burned, the 
fire investigator mentioned that he had never heard of one of those things 
catching fire.  They are JUST a transformer and a little heating element. 
It is not the transformer that is the culprit in those home equipment fires. 
A transformer converts one AC voltage to another AC voltage -- either step 
up or step down.  I have designed tons of equipment with transformers.  I 
have NEVER seen a transformer catch fire all by itself (we shall ignore 
those big ones that sit on power poles -- they are a different beast in a 
different situation). When we convert AC to DC we use semi-conductor diodes 
and other components that are prone to failure such as the regulator IC and 
then there are the CMOS components that monitor the "electric eye" for the 
remote or allows the caller ID to read any call anytime.   A phenomena of 
some CMOS chips is their ability of their substrate to "fire" when they 
receive a sudden voltage spike on the input that exceeds their power supply 
voltage. This can cause the chip to throw a direct short across the power 
supply and hold it there.  A fired CMOS chip gets DANG HOT.  It will raise a 
blister on your finger by just brushing against it.  Dust and dirt in there 
can catch fire as can the lacquer coating on those cheap circuit cards. 
Fortunately, it is only the build-em-as-cheap-as-they-can crap that should 
have this problem because the more reputable CMOS manufacturers have 
internal protection to prevent substrate firing and electronic circuit cards 
used by reputable manufacturers don't use the flammable lacquer.  (However, 
if it is made in India, china, or pick your cheap-construction country 
without codes, then all bets are off.)  The rectifier diodes and regulator 
can also fail shorted, pulling excessive current.  Usually the transformer 
limits the current so that the fuse doesn't blow, and the hot stuff just 
sits there and cooks.

Well, now that I have made everyone paranoid......Have a nice evening.
Wendy



  >> Since most of this stuff is made as cheap as possible, there is not a
  lot of safety margin built in in these components, so there is a higher
  chance of a catastrophic malfunction.  Got it?

   Wendy

  Your explanation is fine. I "got it" before. I just question that they are
  the leading cause of house fires. He also blamed the little "Glade 
Plug-ins"
  and their ilk. If you knew him you could see him scrambling around his 
house
  each morning to unplug everything his wife and kids had plugged in.

  These transformers convert AC current to DC current, and by design waste a
  lot of energy as heat. It's the heat that does the trick.
  Warren