New Classic Finds and etc. (Long)

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon Jan 26 17:32:13 2004

> Wrong... I'll give you an example which ANYONE and EVERYONE working
> with electricity should know, and if they don't they SHOULD NOT work on
> anything even remotely related to electricity until they do know it.
>
> You know that it's the current of the electricity is what will kill
> you right? You could have thousands of volts running through your body

First fundamental error : 'volts' do no run through anything. A voltage
is measured across something. Currents run through things.

> and still live. How is this possible, you might ask? Well if the the
> current (power) is below .5 mA then it should not cause a problem. Ask

OK, IIRC, the short circuit current of an alkaline (Duracell-like) D cell
is about 6A. Care to explain to me why you are not instantly killed by
this current if you touch the ends of such a cell (To the rest of you, _I_
know the answer, OK...)

Similarlly I would be _very_ wary of touching the output of a power
supply that could continuously supply 1kV at 0.4mA. I would guess it
would quite happily supply 0.5mA for long enough to kill me!
 
> any electricity teacher "At what point will electricity kill a human
> being?" and their response will be something along the lines of
> "Anything at or above .5 mA will (more than likely) kill a human being."
> Of course there have been cases that said otherwise but this is the
> majority case. Same thing applies to delicate electronics... apply more
> amps then it's rated to handle and it's fried. Just last week I fried a

You know, I have a PSU on my bench that will supply up to 8A continously.
I have _never_ fried anything by using it, unless I cranked the voltage
up too high. The fact that it _can_ supply 8A doesn't mean it's going to
do so if given a single 7400 as a load.

Similarly, I just said that the short-circuit current of a D cell was
about 6A. A typical torch (flashlight to you) might have a bulb that
draws 300mA in it. Why doesn't this burn out instantly at switch-on?
 
> 2.4GHz wireless phone by applying a power supply that had exactly
> the rated voltge but was 1A instead of the required 800mA. I smelled
> smoke not long after plugging it in. All this in a unit that worked
> properly with the right PSU just 2 weeks before... the original PSU
> being lost. Need I sa!

OK. Did you check if the adapter needed was AC or DC? If the latter, was
the polarity correct. There are many reasons why the wrong adapter may do
damageg, but having it capable of safely supplying 1A rather than 0.8A is
not one of them!

> y any
> more? Current is everything... voltage is nothing.
>
> Lyos Gemini Norezel
>
> BTW- goto the nearest high school and ask the electricity teacher
> about this... see what he say... then compare it to what I said.
> Remarkably like, eh? LOL

At least in the UK, schoolteachers are not a reliable source of
information. People who have been doing electrical and electronic
engineering for 30 years or more tend to be. And there are plenty of such
people on this list.

-tony
Received on Mon Jan 26 2004 - 17:32:13 GMT