Quality of Swtiches used for Engine Power

Thanks for sharing this, I agree properly rated Mill Spec switches should be used.  As for the Rotax starting procedure, I would like to know the reason that both lane switches should be on before start power is applied.  I do it that way, I just don’t know why it’s better than turning the start power on first, then switching the lanes one at a time. 

After just a few Hobbs hours of operation, I had to replace a certified Cessna Split Master Switch, just like the one below. 

I have used automotive grade toggle switches for many years, without any problems. I would go so far as to suggest the Cessna switch was of inferior quality to the automotive ones.  The Cessna switch had some sort of internal resistance, causing overheating and eventual failure (luckily no fire) Anyhow the new one is functioning okay.

Perhaps the lesson is  - manufacturing faults can and do occur, certifications no guarantee of quality.

Found a photo of the cooked switch, showing overheated terminal;

I think this is the answer. When a switch closes, three phenomena occur for a few milliseconds: one mechanical (bounce) and the other two electrical (overvoltage oscilations, and small electric arcs on the contacts). When a load is connected, voltage oscillations are produced, sometimes significant. If a switch is closed without power at its terminals however, these voltage oscillations do not occur.

CASE 1 (Incorrect) we first activate the START POWER and then the LANES. In this case the ECUs will receive voltage oscillations that can influence their rapid boot process and end in an error signal.

CASE 2 (Correct) we activate the LANES first (without power) and then we give START POWER. In this case the ECUs do not receive the oscillations produced by the LAN switches but they do receive some from the Start Power switch, however, both ECUs receive them at the same time, and since the boot processes are very fast in these mission-critical computers, I understand that there are fewer failures in the boot process. In addition, there is constant communication between ECU A and ECU B, and this parallel process of giving energy to both at the same time can contribute to a better mutual starting process.

By the way, choosing a very good switch for Start Power is essential (Installation manual section 24-00-00). For example Rotax requires that Start Power switch should be 20A.

Hi Maximo

I believe you are correct.  The ECU has 2 computers and they are always looking to sync the pair.  The complete process of pairing, getting it in sync, takes just 720 degrees rotation.  2 turns of the crankshaft to calibrate crank angle and set the right injector and ignition for each cylinder.  As soon as start power to the circuit is on the fuse box powers all the sensors for cranking.  This I believe is the need for a good switch as called out in the installation manual. 

Just some background for tech peeps who might like that. 

Cheers