19 Jan
2010
19 Jan
'10
12:03 a.m.
Tony Duell wrote:
Off-topic, but modern consumer electronics
(particularly the cheap 'own
brands' tends to be assembled in thin sheet-metal cases with edges that
will give you a nasty-ish cut if you catch them.
I've stopped using the really cheap PC cases. The Antec 300 I'm using
now seems to have had the metal edges rolled over at least once, which
pretty much leaves it with smooth rounded edges that have the cutting
ability of a wet paper towel.
Modern components shouldn't get hot enough to burn
you :-).
Exceptions: power transistors (esp. BJTs). SCRs. Big diodes. Well, just
about anything that's handling more than about ~10W of power really...
That said an un-heatsinked 7805 running at 1A output with a 12V input
will run surprisingly hot, too, and that's only 7W. I've seen 7805s hit
the temperature threshold (where the internal limiter kicks in and tries
valiantly to stop a meltdown) and on some chips that's over 80C. Well
over enough to cause a fair amount of pain, if not an actual burn.
Glassfets are another matter.
Mmm, vacuum tubes. "After turning off main power, wait 15 minutes for
valves to cool."
And an IC that has developped internal shorts can get
hot
enough to burn you, some DRAMs were prone to this.
A few old 1k*4 SRAMs did this too. 2114 anyone?
Those things were nasty little buggers. If it wasn't a bad bit, it was a
dead bitline, address line or just a dead chip shorting the power bus.
Must be one of the least reliable SRAM chips ever made.
Yes, I was thinking of bruns from the soldering iron,
or something heated
by it Most of the time it's when I am soldering a piece of wire to a
large-ish metal object (pin of a 4mm plug) and I don't let it cool for
long enough before taking it out of the vice.
I seem to do that with startling regularity... Somehow the concept of
objects touched by soldering irons also being hot hasn't quite sunk in yet.
it), and the tiome I dropped a blob of molten solder
on my skin.
Ouch! I've done that... Hurts like hell for a good few hours (if not
days). I was trying to desolder a couple of 0805-size SMDs by putting a
solder blob on the iron. Well, the blob got too big -- I slipped, the
iron hit a metal heatsink, and the solder hit my hand. Urrrgh!
My current worst burn is from my hot-air SMD soldering workstation -- I
hit the STANDBY button, which sets the air pump to full speed and kills
the power to the heater. Problem is, it also kills the temperature
display. I figured it was probably cool, reached over it to get a roll
of equipment wire and got a hot-air burn roughly midway between my wrist
and elbow. There's still a dark red mark there, several months since.
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/