Haltech E6K - Manual (Page 149)

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Figure E7. Illustrate constant duty against frequency
A "dumb" igniter is one that does not perform any sort of dwell control, thus input signal
directly controls switching of the coil. A constant duty cycle signal is the wrong signal to use
with this sort of igniter as it will overheat the coil at low frequencies (ie low revs), and not
allow enough charge time at high frequencies (ie high revs) Since the coil charge time
remains approximately the same regardless of frequency, it is appropriate for the ECU to
constantly charge the coil for exactly that time before firing.
The coil’s charge time can be determined from the coil -ve signal. When the coil switches on,
voltage drops to zero. As the coil charges, the voltage rises slightly, until a sharp rise where
the igniter current limits. Leaving the coil switched on any longer will not increase the energy
in the coil or of the spark. See figure E8.
When the ignition firing frequency is high, there will not be enough time to charge the coil
completely. After firing the spark, the E6K will wait for a short period, then switch the coil on
again, regaining much of the lost energy in “ringing”. This break time should normally be 1 to
1.5ms.