Re: 15 hp Johnson Ignition
There are many overpriced parts in outboards but the power pack is not too bad. Note the temperature range & water resistance, the special pulse-current-proof capacitor etc.
I managed to free up a VRO alarm circuit but I failed completely scratching off the potting compound of a CD3 power pack. This stuff is simply too tough.
The 15hp CD2 has only a single trigger coil for both cylinders. Like AlTn said, a two-stroke cannot fire both cylinders at the same time (what is commonly done in two-cylinder four-strokes, the additional spark comes at the end of the exhaust stroke and is of no consequence). Charge coil and trigger coil are located on the same mounting plate and share the same flywheel magnets. So the only solution is that the trigger coil's positive pulse triggers one ignition coil and the negative one does the other. The charge coil charges the capacitor directly, probably via a bridge recitfier. Unlike in battery based CDIs a switched power supply is not needed to charge up the capacitor.
The ignition coils are ground referenced, so when using a single capacitor the SCRs can't be too. So the CD2 circuit will look similar to this:
View attachment CD2.pdf
There will be some additional filtering to the trigger pulses which is left out in my schematic.
If you get more information about the CD2/CD3 inside, please let me know.
