🚀 go-pugleaf

gallant@oasys.dt.navy.mil (Robert Gallant) writes:

>Hi, I am trying to find the proper diode to combine the trigger signals
>from two ignition coils on my car.

(Diagram of std coils and diodes and description deleted)

>The voltage present at the (-) terminals should be alternating between
>0 and +14.1 volts at 300 Hz maximum.

Heh, heh, heh.  What makes you think _that_??  The turns ratio on an
ignition coil would never get you enough to put a spark across a plug
if the ratio was simply applied to 13 or 14 volts.  Nope.  The system
works by storing energy in a magnetic field in the coils, and letting
that field collapse very quickly when the points open.  When the field
collapses, the primary voltage as well as the secondary voltage goes
up a lot:  the (-) terminal can reach 300 to 400 volts -- even more
if the capacitor is too low a value.  Basically, the capacitor forms
a resonant circuit with the primary of the coil, and energy gets put
in when the points are closed.

Anyway, if you really want to do this, you could use fast, high-voltage
diodes, then be ready to accept the resulting rather high voltage
output at the diode junction, or you could put some other resonable
trigger circuit on it.  An inductive pickup is possible (on the spark
wire, like timing lights use), as is a _resistor_ from each coil to
a resistor to ground (forming a two input voltage divider), with clamp
diodes to keep the output under control.  If you use resistors, use
high enough values to not damp the coil too much:  I'd start with
something like 100kohm, 1 watt units, into about 250 ohms/volt of
desired output.  Be aware that each firing pulse may consist of several
cycles of a fairly high frequency...don't let that fool your logic.