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 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

[WesRagle]

Hi Guys,

After about two months of waiting I finally received the prototype boards for the VeeCU. I've been working on a Bearhawk project and have a couple of more days before reaching a stopping point. I can then start bringing the board up.



Very exciting time for me. Been a long time coming. We went over the design several times before committing to spending the money for the prototype boards. However, there is always a chance that the board will be DOA. So send out good vibes.

Thanks,

Wes

[Bryan Cotton]

Wes, that looks awesome!

[WesRagle]

Thanks Bryan,

I hope it works as good as it looks.

Wes

[WesRagle]

Hi Guys,

A little more on the project.

The worst case scenario when receiving a new board is this: You hook up the programmer/debugger and power the board and nothing happens. The board just sits there looking at you looking at it. So, I just couldn't resist powering the board and attempting a program download so I would know whether or not I had a good starting point for porting the software from the breadboard to the prototype.



Success!!

The CPU and Engine Control IC are very low power devices which makes the power supply design easy.

The front end of the power supply consists of a high voltage schottky diode for reverse voltage protection, a 24 V transient voltage suppressor, and a small inductor to filter high frequency noise.

The front end feeds four linear regulators. One to power the analog circuitry, one to power the MAP sensor, one to power the CAN bus, and one to serve as the pre-regulator for the MPU power regulator. The large number of regulators is all about fault tolerance.

These regulators are pretty trick.

Wide Input Voltage Range: 4.5V to 55V- Up to 70V transient- Under Voltage Lock Out (UVLO): 2.7V typical
Extended Operating Temperature Range: -40°C to +150°C
Low Dropout
Rated for continuous short to ground (MAP Power Fault)

Anyway, the power supervisor monitors the output of MPU pre-regulator. When the output of the pre-regulator drops to approx 4.7 volts the MPU is reset. So, the 3.3 V MPU regulator never drops out of regulation before the MPU resets. The MPU will never see an unstable voltage.

I did a quick check of the reset voltage. It was somewhere below 5.5 Volts. I wanted it to be below 6 volts so I'm happy with that.

I'll go away for a while now for the rather lengthy process of porting the software.

Thanks for listening to me ramble.

Wes