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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