Gee Whiz.
-----Original Message-----
From: Malcolm Stebbins [mailto:[email protected]]
Sent: Saturday, November 01, 2003 2:14 AM
To: [email protected]
Subject: Re: cs>electric recluse spider bite
Marshall, you are all over the map with your statements; but you are missing
the essential part of my message to you and the list, which is;
What you suggest is dangerous, possibly lethal.
You said you were referring to a conventional system, not a CD system. You
claimed in reply to my first response:
"Who said anything about a transistorized system? I was talking about an old
spark coil, from something like a 1960's car."
and you introduced the CD system as an aside toward the end of your original
post.
Then:
"I believe the reference indicated it was 300 or 400 volts. I was off
on the high side, . . . "
I have no idea what "reference" you refer to; all references I have
mentioned, i.e., standard texts and manuals on the "conventional" system
state 200 + volt spike on the collapse of the primary field, NOT 300 or 400.
As I took pains to emphasize, that is the voltage of the spike generated
across the primary by the collapse of a field induced by an interrupted 12
volt source, Not an interrupted 300 volt source as you suggest in
discharging 300 + volts through an 'old fashioned breaker point coil.' (My
paraphrase.)
I stated:
"You have suggested that dropping 300 volts through this conventional system
is the same as dropping 12 volts through it, and by implication that it
would be perfectly all right to inflict the consequences of this ignorant
endeavor on oneself or another human - That was what your message was
about."
To, which you replied:
"Huh, I don't follow this at all. I never said anything of the sort. "
followed by: "Both systems generate about 300 volts on the primary, a
convention system when the field collapses, and a CD ignition when the SCR
fires. The coil sees a very similar wave form with both. With a
conventional system 12 volts is applied across the coil for a period of the
dwell time of the points, and the current builds up to a point that when the
points are opened, the cap across the points drops the current in a few
micro seconds."
Disregarding some inaccuracies in your statement above, the point remains
that whatever means is used, in the automotive case you are subjecting the
coil secondary to a pulse generated by interrupting the primary's energizing
12 volts, of about 200 to 300 volts in the case of a conventional system,
and Not to the pulse which might be generated by ENERGIZING the primary with
200 to 300 volts which when interrupted would theoretically produce a
primary spike of perhaps twenty times greater magnitude. Since the
capacitor in a strobe system (as commonly recommended for the magnetic
pulser) charges to perhaps 300 volts and then dumps through the xenon
flashtube which extinguishes abruptly, thus producing an interruption which
would trigger near-instantaneous field collapse, you have suggested a mix of
two systems which could produce lethal voltages if it did not self-destruct
with even greater rapidity, which it may not.
As I implied in my first note to you, mismatches between the two systems -
for instance I'd consider the decay in current from the strobe cap over it's
discharge time vs Zsub. i of the primary in re. flashtube extinction
behavior - will "degrade" the system's response so that it may be bearable;
but then again it may not be. As I also suggested, try it!
Please forbear attempting to instruct me further in what to believe or
'think about' in relation to beginning AC theory or basic calculus. I assure
you my education goes beyond your estimate.
Malcolm
t 10:31 AM 10/30/03 -0500, you wrote:
Malcolm Stebbins wrote:
At 08:56 AM 10/27/03 -0500, you wrote:
Once again exactly what I said.
On the contrary, you said 50,000 to 100,000 secondary volts was induced by a
primary pulse of 1,000 volts, which was in turn generated by the collapse of
a field generated by virtue of a 12 volt EMF.
I admitted I was off by a factor of two or 3 on the voltage, but the
principle is still the same.
>About as "correct" as you have been so far . . . . . . in neither of these
systems has the primary field collapse generated anything like the 1,000
volt pulse you posited.
I believe the reference indicated it was 300 or 400 volts. I was off on the
high side, I never measured it, I just know from experience it kicks like
hell if you get a hold of the wire from the points when the field collapses.
There are no automotive ignition systems running 50,000 to 100,000 volts;
not only is there no need for such a dangerous level, the corona discharge
initiated by such would be extremely and rapidly destructive to the elements
of the system, make the design of a distribution system for the spark
considerably larger, more difficult and expensive, generate a great deal
more RF interference, and be an absolute bear to keep functional in damp
weather.
OK, so I am a little high on the output voltage. C
Oddly enough, the message you wrote was about the information you wrote, and
the response I gave was about your errors in that message; your reply to
that was to state that I was incorrect. On the contrary, both strictly
regarding the elements in my response and your description of the
conventional ignition system generally, it was - and is - you who are
incorrect; - get it straight!
You have suggested that dropping 300 volts through this conventional system
is the same as dropping 12 volts through it, and by implication that it
would be perfectly all right to inflict the consequences of this ignorant
endeavor on oneself or another human - That was what your message was
about.
Huh, I don't follow this at all. I never said anything of the sort.
Both systems generate about 300 volts on the primary, a convention system
when the field collapses, and a CD ignition when the SCR fires. The coil
sees a very similar wave form with both. With a conventional system 12
volts is applied across the coil for a period of the dwell time of the
points, and the current builds up to a point that when the points are
opened, the cap across the points drops the current in a few micro seconds.
This sudden collapse in the field generates about 300 volts across the
primary, which is coupled ot the secondary and produces the high voltage.
The CD ignition usually charges the capacitor through the coil during the
time between the sparks, and then when the spark is due, a SCR shorts out
the other side of the cap to ground, generating a 300 volt spike on the coil
that gets coupled to the secondary. In both cases the coil sees a 300 volt
microsecond duration spike which gets coupled to the secondary. If you
don't believe this, then get an old spark coil, and connect it to a 12 volt
battery and put a spark plug on the secondary. Then connect the battery and
you will see that you get no spark. But when you break the connection, you
will get the spark. i have done this many times.
Dynamic and static voltages for capacitors and transfomers are totally
different things. A capacitor conducts no current with DC, but will conduct
a current that is proportional to the dV/dt of the waveform for AC. An
inductor shows little resistance to DC, but will build up a current
proportional to the integral of the voltage across it, ignoring it's dc
resistance. The 300 volts in both cases is a short duration spike. Think
about it. The reference indicates that there is a 100:1 turns ratio, and it
generates about 30,000 to 50,000 volts. That means that the input MUST be
300 or more volts. 12 volts on the primary would only generate 1200 volts on
the secondary, and even that is high in a conventional system due to the
current limiting from the ballast resistor.
The only significant difference between the two is that for a conventional
system the coil is the energy storage device, and for a CD ignition the
capacitor is the energy storage device. And yes, I built a CD ignition
system from scratch back in the 60's and it worked fine on my old 1965
Impala.
A strobe works the same was as a CD ignition, but the voltages may be
somewhat higher, and the capacitor is likely larger, so the current in the
secondary may be somewhat higher.
I'd STRONGLY suggest that you try it on yourself first; perhaps the
mismatched parameters of the systems will limit the outcome to a bearable
level.
I have done this myself. In fact the first fence charger I ever made was
made this way. It had a heck of a wallop but worked for years! I used it
when at UT to keep vandals from tearing down my TV antenna I had on top of
the dorm.
Marshall
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