If I understand this system correctly the EDIS is capable of running without the ECU/Megajolt and will fire at 10 degrees BTC. If one were to position the pickup so that corresponds with 25 degrees BTDC on our engines failure of the Megajolt in cruise is almost a non event.
Kirk (see earlier, this thread) is planning to install his #2 ignition without a Megajolt box, EDIS module only, thus fixed timing at 25 degrees via offsetting the pickup 15 degrees.
One Megajolt is also capable of firing multiple EDIS units. So it is reasonable to build a dual ignition system with one Megajolt and two EDIS units? It may actually be preferable to reduce programming requirements etc.
The programming requirements are nil. The ignition maps are created offline. With two maps stored on your laptop, plug in, open one at a time in the Megajolt software, and flash each with two keystrokes. For the second ignition, just move the RJ11 plug from #1 to #2 and repeat.
Presumably the EDIS is a CD ignition, and would compare to the PMAG in terms of spark energy and duration?
As Larry noted, the EDIS system is inductive, not CDI. Spark characteristics will be very similar to a P-mag,
because a P-mag uses the same Ford coil. To clarify; there are two Ford coils, early and late model. The early model incorporates positive plug wire retention. The late model has a flat bottom, so mounting is simplified (like on a P-mag body), and it has taller towers. Choose your preference; there doesn't seem to be any practical difference in output or reliability. Other coils seem to work fine too. Select one without internal switching.
Energy, duration, and claims of increased HP are mostly BS.
Has anyone measured the current requirements of the system to size an appropriate backup battery?
An English builder did so as part of his LAA approval, and reported 1.05 amps at 14.4 supply voltage at 2750 rpm. You can read about his work in the August 2011 LAA magazine. Kirk and I made local measurements on the lathe, but I seem to have misplaced the notes.
I've flown one EDIS paired with a Slick for a year. It has been trouble-free, so now I'm installing a second EDIS. The battery for #2 is a Motobatt MB3U AGM rated at 3.8Ah, charged via a Schottky. Both the PC925 main and the little MB3U are located in the cool space behind the baggage compartment. Power feeds are battery direct via fusible links for circuit protection, independent of the aircraft system. KIS is good.
Diagram (updated 2018):
So far, the only potential issue I've seen has to do with timing at cranking speeds. The system fires before TDC, so users with low inertia propellers could conceivably get kickback. It doesn't seem to be a problem with a metal Hartzell. Exactly how far before TDC may depend on EDIS module part number. We've measured as little at 2 degrees at very low RPM, and nobody has ever reported more than 10. It ramps up as RPM rises, transitioning to the mapped values at about 500 RPM.
Early P-mags had the same problem, since corrected with software. The EDIS doesn't seem to offer a software-based approach to retarding the spark at cranking speeds (no Megajolt control below 500 RPM), so the only way to do it is with a mechanical offset, which I flew most of last year. To fire ATDC during cranking with the EDIS, I retarded the trigger wheel 10 degrees, and uploaded a map with all values advanced 10 degrees. The result is a very soft start, almost like a turbine spooling up, in particular hot starts using the "slowly advance the mixture knob" method.