Lycoming 6 cyl. and tacho resistors

[Battson]

Hello expert in all things Dynon,

I note the manual says my 6 cylinder Lycoming may need extra resistance to get accurate RPM readings from the P-lead tacho pickups.

Is there any downside to attaching the extra resistance now??

This is before I start the engine and check if the RPM is accurate or not. It would be a PITA to change the resistors if I could have done it up front with no possible downside.

 

[jakej]

I add them very close to the magneto switch, that way it's easier to change them IF you need to - 30kOhm has always worked for me I'd make the switch wiring long enough so that switch can be dropped down from panel without the need to disconnect them.

HTH

Jake J

 

[Dynon]

If the resistance is too low, you'll be seeing high RPM spikes as extra pulses get through. If you go too high off the bat, you can see drops to an RPM which looks too low intermittently. Most people are OK with 30K, but some mags need more to temper the voltage. We recommend starting with 30K.

 

[Battson]

Ok thanks - will do.

 

[vlittle]

I'm struggling to get the correct resistor value for my IO-540-D4A5. Initially I used 30K, but I got spurious prop overspeed alarms, so I wired in a trimmer potentiometer, accessible in flight.

I can eliminate the spurious overspeed warnings, but now I get spurious dropouts in the rpm indication at low rpms (around 1500 and below).

The sweet spot is eluding me.

I have an electronic ignition on the right, the magneto is on the left.

It would be very helpful if you could publish the input structure for the EMS standard rpm input. This will help me establish the correct resistor value (or other circuit) to minimize this problem.

Thanks, Vern

 

[Janekom]

I have used 100K on more than one RV10 with good results.