RPM Signal for CSU Prop

Jeff Blakeslee wrote:

John Flemming,
The tach input for a G3X system connects to a Garmin GEA-24 (engine information module) and then is transmitted to the EFIS over the Garmin CAN bus. Specifically, the wire you are looking for should be connected to pin 8 of the J243 connector on the GEA-24.  At the point where the tach (+) pulse wire connects to the GEA-24, Garmin wants a diode, zener diode and a 300 ohm resistor to stabilize the circuit.  This is shown in the Rotax sensor interconnect examples in the G3X installation manual.

I think there is a good chance that connecting the CSU to the tach wire (before it reaches the diodes/resistor at the GEA-24) would not affect the tach function on your EFIS.  I would call Garmin Aviation support and tell them what you want to do, if they don’t know they will find the answer for you.  You can also email them at g3xpert@garmin.com.  Also, the manufacturer of the CSU controller must know the answer to this.  There is only one tach coil on the 912, so they must run into this every day. Their controller needs a tach signal, and they can’t expect you to disconnect your tachometer to do so.  

Thanks man. 

We’ve put an email into to DUC and am waiting for a reply.  Hopefully they will come back with a solution, but yes, I will send an email into Garmin support tomorrow.  They are really good to deal with.  

Cheers

John. 

UPDATE!!

So... after hunting around for an answer, I managed to get hold of a Rotax tech, and he advised me that you can pair up another tach from the one pickup coil.  It is just a pulse as the motor spins, and so having a couple of instruments listening to that pulse, will not matter, and they will all get the same pulse.

So once the prop was installed and the idle and static speeds set, I connected the instrument's RPM In, and confirmed that the reading was the same.  Idle and Static all checked out.  HAPPY!

Long story short of it, the new DUC prop is on the machine, configured and is running beautifully.  Great climb performance, and runs good.

It will take some getting use to in order to find the sweet spot, but so far - Happy!

Anyways... Just thought I would let you all know.

Cheers

J