The VeeCU

[bvolcko38]

My secondary coils, the red ones,draw 10 amps. 5 amps each I suppose as indicated by my ammeter. But this is only if the engine is spinning. If the engine is shut down the secondary draws zero current. On initial switch on of secondary,there will be a short 10 amp surge then nothing until you turn the engine over.

[WesRagle]

Hi BIll,

That's a lot of current. There is a lot to be said for bone simple, but ...

Wes

[BRS]

Hi BIll,

That's a lot of current. There is a lot to be said for bone simple, but ...

Wes

My thoughts as well. I'm hoping that can be reduced. I'm thinking my toatal draw on a the Sportsman (SDS & avionics) is only around 17 amps.

[WesRagle]

Preliminary testing indicates that with a constant 12 mSec dwell, and 3 Ohm coils, at 14 volts, maximum possible ignition current draw will be about 3 amps at 4000 RPM (AeroVee red line). I think a good rule of thumb for fuel injectors selection is 3 to 4 GPH static flow per injector. That produces about a 25% duty cycle at cruise (one amp total). So, in cruise, current consumption will be in the neighborhood of 3.5 amps plus fuel pump. Well under 2 amps + fuel pump at idle.

Wes

[BRS]

Preliminary testing indicates ... So, in cruise, current consumption will be in the neighborhood of 3.5 amps plus fuel pump. Well under 2 amps + fuel pump at idle.

Wes

Ah, well that paints a different story. Much more manageable. Thanks for the explanation.

[WesRagle]

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 ether 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