Jon;
The AC component is from undamped ringing in the LC circuit
(inductance-capacitance) of the secondary & the reflected primary (coupled
across the coil).
In the old Kettering ignition system, the "condenser" that was connected
across the points was actually a resistor in series with a capacitor. This
is why you were always warned not to substitute a "radio type" capacitor
across the points. The series RC provided a measure of damping on the plug
HV waveform. If anyone doubts the effectiveness of damping, just pull your
condenser off your points.
Without a conventional points ignition, the only way to achieve damping is
to insert a resistance in the secondary HV circuit. Radio noise suppression
is a worthwhile side benefit. "Gap" plugs were a way that manufacturers came
up with to increase the rise time of the HV across the gap in the cylinder.
A small gap inside the body of the plug prevented the voltage from firing
the cylinder until the voltage had increased above a minimum that caused the
internal gap to break down. Once ionized, the internal gap's voltage drop
was minimal.
Bendix published a good manual on ignition system waveforms when they built
their aircraft ignition analyzer scopes years ago.
Regards, Neil
-----Original Message-----
From: Jon Wennerberg [mailto:jonw@up.net]
Sent: Friday, March 29, 2002 6:31 AM
To: 'Thomas E. Bryant'; 'Doug Anderson'
Cc: land-speed@autox.team.net
Subject: RE: secondary resistance Q for Tom Bryant, Neil Albaugh, &
others interested
How's a dc pulse turn into ac at the other end of a transformer? I thought
that the field was established from the primary pulse, which is a shot of
dc, which field collapses as that primary pulse ends, and the collapse
across the secondary windings creates a (high) voltage pulse in those
windings. I thought the collapse made a pulse that rises to a high value
and then returns to zero. Didn't know it bounced all the way back through a
high negative value.
PS: This statement is based on points-and-coil or a magneto -- not an
electronic-al system that might use AC for higher efficiency. Did I miss
something one day at school?
Jon E. Wennerberg
Seldom Seen Slim Land Speed Racing
#436 M/PS/G 1340 CC
2001: 200.471 mph - 2002 GOAL: 220.554++mph
Marquette, Michigan 49855
(That's Way Up North)
Original included:
<<<
Secondary voltage is AC current, which means it cycles between negative
and positive.
Tom, Redding CA - #216 D/GCC>>>
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