Tach signal with one EI and one mag

I have a question for those who run a single electronic ignition (EI) and an conventional mag: How do you pick up the tach-signal?

We have a LSE Plasma III with a mini crank sensor and one Slick mag on the left side. We plan to use the Dynon Skyview for RPM display. The first thought was to use the LSE signal for display. But I assume that the tach signal will vanish during mag check when the EI is turned off. So do we need a to install a second tach sensor (in the mag or on the mechanical tach output)? As much as I understood the Skyview has two tach signal inputs that can be used. What is the solution that you preferred?

In general, you run one tach sensor wire to each ignition. One will be primarily used until/unless it fails and then the Dynon will revert to the second. I would recommend you wire both.

Mag sensor

If you install a mag sensor in the left mag and use it you will always have an rpm indication, regardless of which system is on/off or failed. That is the way I wire them.

Vic

Good suggestions above.

If I had to pick between the two signals I'd go with the mag, to monitor the RPM drop with the EI switched off. You will see very little if any RPM drop (10-20 rpm) when you switch off the mag; you can confirm that it is operating normally by ear without having to know the actual number.

Hall effect mag sensor

I like Vic's suggestion. The mag sensor is a hall effect device that does not need the mag to be powered on to operate so you don't lose signal when doing the mag check. I ordered mine from Spruce and it works great.

I originally had the tachgen from Van's which worked well but it had to go when I added a standby alternator to the back of the engine.

Andy

Hi, CloudDancer

I have a LightSpeed Plasma II+ and a regular mag as a backup.

Dynon EMS has a Left and Right rpm input. Use the Lightspeed's digital pulse on the right, and the magneto output (via a dropdown resistor) on the left. I use a traditional ignition key switch with Both/Left/Right positions for the mag check and it works fine, just like your Cessna/Piper airplanes.

My Lightspeed fires just slightly ahead of the mag, so you'll notice very little rpm drop during your run up magneto check.

Cheers,

I had the vans tach pickup installed before I upgraded so I just used that.

Bob burns
rV-4
N82rb

Thank you for all the inputs! Using a hall effect sensor on the mag looks promising, but I have to add another sensor then .

For those who use the mag p-lead pick-ups: Do you use electrical noise cancelling devices or are you running the thing with the Dynon furnished resistors only?

So do I

Hi, CloudDancer

I have a LightSpeed Plasma II+ and a regular mag as a backup.

Dynon EMS has a Left and Right rpm input. Use the Lightspeed's digital pulse on the right, and the magneto output (via a dropdown resistor) on the left. I use a traditional ignition key switch with Both/Left/Right positions for the mag check and it works fine, just like your Cessna/Piper airplanes.

Click to expand...

No need for more sensors, RPM signal does not disappear during mag check
and in fact reflects the drop when on the mag or the EI.

I have 2 toggles switches but otherwise the same as above.
I believe the drop down resistors are provided in the Dynon EMS harware.

Ok, my situation is not exactly the same as your's as I do not have a Dynon. Regardless of the different EFIS manufacturer, I do have the same situation as you describe. The difference is that I do not have the capacity in my EFIS/engine monitor to wire a second tach lead. So, this is what I use to give me readings on single mag checks:
http://www.proptach.com/

When using an Grand Rapids Technologies EIS

The EIS has two tachometer inputs, and each input is configurable to account for the different number of pulses the EIS will see per revolution of the engine, and the voltage levels from the two different tachometer sources.

The EIS will display the tachometer reading it sees on input #1. If input #1 goes to zero (such as during a mag check) it will then use input #2.

Because of this, I prefer to wire the magneto to tachometer input number 1, as I like to keep an eye on my magneto, especially as it ages. When it get time for overhaul of the mag you might notice that the tachometer reading derived from it becomes occasionally erratic. If a magneto fails, the RPM derived from it usually is lost also.

If the electronic ignition fails, even though you are not monitoring its tach output (which may or may not reflect the failure), you will probably notice a change in the engine's behavior (power), so I don't find monitoring its tach output as useful.

When wiring the EIS tachometer input to two magnetos, I prefer that I am able to select which magneto I use as my tachometer input using an external switch. I alternate which magneto I use between flights so that I am getting some visibility into what each magneto is doing. Most people don't want to put another switch on their panel for that purpose, but I find it worth the space it requires.