Re: Monitor Discharging

Well, if I remember right (and I was never good at this) Joules are the same
thing as watt-seconds which should be capacitance times the square of the
voltage. So if you have 20,000 volts and 2000 pF of capacitance you have .8
joules. That just doesn't seem right, does it?

John Robertson wrote:

> Fair enough caution. Great respect for the safety flag raided here, thanks
> Joel!
>
> Now the question is: How much current can a picture tube hold. I suspect it
> is not many Joules, after all it is a very simple capacitor, but until I
> (or someone else) can find this info out, then it certainly is wise to be
> very cautious. Certainly if the HV supply is running it is very dangerous
> as they put out a few microamps...
>
> And, of course, the point of entry into the body would have a bearing of
> the potential <grin> lethality...picture tubes tend to discharge across an
> arm or two...One thing I was taught (and should ALWAYS mention) is to use
> the RIGHT arm for probing circuits, as the path to ground through the feet
> is a bit further from the heart on the right side...
>
> Perhaps someone with a capacitance meter could put it across a fully
> discharged picture tube and that would give us a capacitance value, then
> the number of Joules could be worked out for 20KV.
>
> "let's be careful out there"
>
> John :-#)#
>
> At 03:36 PM 12/9/1999 -0500, you wrote:
> >John, (and everyone else)
> >
> >
> > >This person (todd1814) has NO idea what he is talking about. First, the
> > >charge on a monitor is NOT lethal (no current) as it is a static electric
> > >charge. It certainly will give you a healthy shock and that is dangerous
> > >because you might drop the picture tube (a bomb!), but otherwise not a
> > >serious (life threatening) situation. I have accidently discharged a few
> > >monitors through my arms over the years and no ill effects (I think ;-).
> >
> >
> > >critiques welcome!
> >
> >I know that we all know that we must pay attention when discharging tubes.
> >This is nothing new to anyone on vector list, I'm sure. However, John's
> >comment above made me pause because it is strikingly inaccurate. The fact
> >that the charge in a monitor is a "static electric" charge has nothing to do
> >with how lethal it is. (Lightning strikes, anyone?) I design
> >defibrillators that use precisely this principal to deliver a shock to a
> >fibrillating heart. We charge a large capacitor up to 2300v and when we
> >"discharge" the capacitor, we deliver 200J into the patient. This can be
> >quite lethal if delivered during a T wave segment. We must discharge at
> >precisely the right time so that the discharge doesn't kill the patient.
> >
> >Joel-
> >
> >
> >
> >
> >
>
> John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
> Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
> http://www.flippers.com
> "Old pinballers never die, they just flip out."

--
Windows:
32 bit graphical interface for a
16 bit patch for an
8 bit operating system written for a
4 bit processor by a
2 bit company that can't stand
1 bit of competition.