Engine setup
- V12 60 degree even-fire
- maximum RPM is: ..... (interesting for ignition hardware peak current)
- Mounted in a boat (pro-longed high load compared to a car)
- Two spark plugs per cylinder, total 24 spark plugs (12 wasted spark coils)
- Bosch Motorsport 3x2 coilpacks (4 pcs required for one engine)
- could be driven from 6 IGBT-s (IGBT can handle the double current if dwell is set sufficiently - not too high, and peak RPM < 7000 RPM)
- Beru 3-channel ignition modules (min 10 mA drive current)
- One fuel injector per cylinder
- Siemens High-Z 9 Ohm fuel injectors
- 24-1 crank mounted trigger wheel (or 24-2 is also OK)
Due to lack of outputs I will handle the engine electrically as an inline 6 cyl.
Two injectors per injector output.
- Can one FET handle sustained high duty cycle with sufficient cooling?
- yes, 100% duty upto about 5 (or even 6A) is OK. (the FET's peak current is about 14A but we specify much lower)
- Two injectors 9 Ohm results in 4.5 Ohm @ 14 Volts = 3 Amps
- yes, 3A is no problem at all. Make sure to connect flyback wire, of course.
Driving the ignition modules
- Six outputs required - using four stepper outputs and two logic level outputs
- Drive current requirement per ignition module input is minimum 10 mA
- Driving two channels is a minumum 10x2 = 20 mA up to 40 mA.
- Can the IGBT logic driver handle this? 20mA : yes, 40mA: no (but 40mA should not be needed anyway)
- Suitable resistor values on board?. 255 Ohm is suitable to drive one module, but 120-130 Ohm needed to drive 2 modules (that still protects the i259 chip's outputs).
- I would recommend 6 IGBTs and 2 logiclevel outputs with appr 120 Ohm (=510x150-160 Ohm or so) current-limiting than it can be decided later to use logiclevel or power-outputs. It is also posssible to use 4 stepper (with module driving 8 transformers) and 4 IGBT outputs driving 4 transformers (configured in igndualout, that is perfectly valid and correct for a multispark engine like this !), either 4 driving the 4 modules individually (best setup) or possibly 2*2 connected in parallel (yes, connecting low-side switches in parallel is also safe).
- Stepper outputs are powerful, but current limiting resistors (100-200 Ohm) are recommended to protect from short circuits
Ign output concept proposal:
While using i259 with lower output protecting resistor (in the 120 Ohm range) might work (or a module that does not have stupidly low input resistance),
- Marcell would order ignout: 8 powerIGBT (0 logiclevel)
- and use stepper-A and Stepper-C outputs with 100 Ohm protection resistors for 2 or 4 external ign-driver modules (4 transformers, 8 sparkplugs),
- and 8 power-IGBT outputs for +8 transformers (+16 sparkplugs)
- igndualout is suitable for this, but it also applies to stepper ignouts, therefore (by actuating/consuming the pair of every selected output) allowing only 2 independent stepper outputs (unless firmware mod is applied)
Wasted spark groups cyls with 360 crankdegrees
Obvious, but worths to mention:
When wiring, make sure to pair cyls that are 360 crankdegrees apart (not in same phase, especially not the 2 sparkplugs of same cyl !).
Assuming an I6 with 153624 firing order (to which the big V12 is related), pairs would be:
16
52
34