small valves and RE: OT

Tony Duell ard at p850ug1.demon.co.uk
Wed Apr 27 17:56:46 CDT 2005


> People here play with power in the form of higher voltages, also in 
> the form of high energy.  Some of those computer supplies designed 
> to pump out dozens to sometimes  hundres of amps of power posess 
> the capability to melt off a ring (and the encircled finger), watch

Good point... Classic computer PSUs will often supply over 100A on the 5V 
line (that's only 500W, after all), and that is enough to melt jewellery, 
etc. 

High voltage, high current is, of course, the worst. A place I worked at 
had a very nice bench PSU that could output 0-300V, 0-10A (no, that's not 
a typo). It was very useful for sorting out SMPSUs, because you could set 
the current limiter low enough to prevent major damage if the chopper 
went short-circuit or whatever. But that PSU had enough power behind it 
to do serious damage to you if you weren't careful with it.

> or cause a splatter of melted metal in the eye.  Trust me, I have 
> been been to 1500volts and back due to fools around me and their
> pointing fingers. I've also seen what an 80amp regulated power

When working on high voltages, I am torn between working alone (and not 
having someone to switch the power off if I do something stupid), and 
having somebody there to turn the power off in an emergency, who is, 
alas, more than likely to be the cause of said emergency.

> I might add that something "grounded" can be more unsafe until your 
> sure there is NO POTENTIAL differences.  I got dinged in NYC one 
> fine day due to a mere 65vac differential in grounds between the

That sounds like about half mains voltage. It wasn't that one of the 
grounds was disconnected, and you got that voltage from the mains filters 
of all your hardware acting as capacitive dividers, was it?

> 12th and 14th floor.  And they couldn't understand why the RS232 
> drivers were being fried all over the place.  Seems equipment 
> ground wasn't.
> 
> Electrons are our friends, they have a dark side too.  Always play 
> nice and use proper technique.  Failure to do so really can take 
> the fun out of it.
>

I've seen the same thing said about fire (a problem if you're stuck in a 
burning building, a great help when used for heating, cooking, running 
heat engines, etc), friction (normally regarded as a waste of energy, but 
without it, screws and nails  would fall out, brakes wouldn't work, etc), 
electrcial resistance (again often thought of as a waste of energy, but 
without it, you could have no votlage differences, so electronics would 
be impossbile), etc.

-tony



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