For those interested -
To make the visualization a little simpler I'll try to explain, in layman
terms as I understand things, why some ignition systems were designed with
some type of ballast resistance.
When you initially crank the engine over to start it, the battery voltage
drops to around 6-7 volts because of the rather large amperage drain caused
by the starter. The ignition switch in such circuits with a ballast
resistance have an additional circuit in the "start" position that bypasses
(effectively shorts) the resistance, so now the 6 volt coil sees the
battery voltage (which is around 6 volts). In this way you receive full
spark that the coil was designed to operate at, instead of the wimpy spark
that a 12 volt coil would deliver at this cranking voltage, and at a time
when you need it most. When you let go the start position to the run
position the ignition switch, via a spring, returns to the run position
which now incorporates the resistance element (in series with the coil) to
effectively drop the 12-13 volts NOW at the battery to the nominal 6-7
volts at the coil, which is what it was designed to run at.
This the reason it's not a good idea to run a coil designed for a ballast
resistance (6 Volt) in a vehicle that was designed without a ballast
resistance circuit. In this case the coil, designed for 6 volts would see
the full 12-13 volt during normal operation, and would soon expire from
overheating.
Barry Schwartz (San Diego) bschwart@pacbell.net
72 PI, V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
|