by WesRagle » Fri Jul 05, 2024 9:41 pm
Hi Brock,
The secondary ignition module is a low side driver that normally grounds one side of the ignition coil primary with the other side connected to 12 V. The current flow through the 3 Ohm primary is only interrupted while the magnet is aligned with the hall sensor, which fires the plugs. So, most of the time current is flowing in the primary. Bone simple but very inefficient.
The VeeCU takes over the secondary ignition driver and uses it to drive/ground a 2.5 KOhm resistor in series with the IR LED of a high speed Optocoupler which delivers the pulse to the CPU.
So, instead of driving a 3 Ohm load the secondary module is now driving a 2.5 KOhm load. That will presumably eliminate most of the secondary ignition module failures. The CPU then drives the coils, but controls dwell time, which greatly reduces the coil current consumption. This will hopefully eliminate most of the ignition coil failures.
The other failure mode of the secondary ignition system is mechanical. Some units have thrown the magnet. That failure mode is mitigated by synchronizing an alternator pole with each of the secondary ignition pulses. Should either of the secondary ignition pulses go missing (for 0.2 seconds), while the engine is running, the alternator will take over to time ignition and injection. This will not be quite as accurate as a functioning secondary so the timing is retarded by three deg. while in this mode.
Wes
Wes Ragle
Onex #89
Conventional Gear
Long Tips
Hummel 2400 w/Zenith Carb
Prince P Tip 54x50
First Flight 06/23/2020
42.8 Hrs. as of 10/30/21