Fw: [Homestead] Homestead tools
crazygardens at nationi.net
Sat Nov 20 11:52:08 EST 2004
Sent this out last night, but it went to Warren instead of to the list.
Let's try this again.
----- Original Message -----
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.
>> 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?
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
and their ilk. If you knew him you could see him scrambling around his
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.
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