From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: 12 Volt, Strobe Project (Coil Powered)
Date: Sat, 09 Nov 2002 19:10:54 GMT
NNTP-Posting-Date: Sat, 09 Nov 2002 11:10:54 PST
John Jardine wrote:
> Neat strobe circuit!. Nice departure from the usual, lethal rectified mains
I always find statements like the second sentence above a bit puzzling.
I will try to explain. The strobe in question is said to consume about
12 joules per second (1 amp at 12 volts). I'm guessing that the flashes
are about 1 joule each (more or less) limiting the device to about 12
flashes per second more or less. Perfectly good for some purposes but
not useful for others. For example, if 200 flashes per second are
required, the minimum input power is 200 joules per second or about 12
volts at 17 amps. A nicely designed lethal mains power supply is very
attractive don't you think?
What is a "lethal voltage?" It is winter. I routinely (many times per
day) get a shock in the 15,000 to 30,000 volt range. I do not keel over
and die on the spot (not often anyway). The other guy in the lab can
hear it across the room and shouts "gotcha" while I curse the furniture
for the 20th time that day. When I was married, I used my ring to catch
the arcs because that way, I could not feel them. It does seem like
30,000 volts is not itself dangerous.
A few hundred volts has a worse reputation than some high voltages. Why
is this? I know the reason. Voltage has little to do with electrocution.
It is current and the path it takes that is important. Hence the ancient
advice to keep one hand in a pocket while working with high voltage.
The fact is that shocks from 100 volts to several hundred thousand volts
(lightening) are survivable for various reasons. To understand why
voltage is irrelevant, you have to understand the physiology of electric
shock. The one caveat here is that in the 100 to perhaps 500 volt range,
the muscular spasms can make it impossible to let go of the terminal or
Tektronics published an excellent safety bulletin in the early 1960's
explaining the main issues in electrocution. Voltage is a factor by
ohm's law but current is by far the most important factor.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org