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Dynon D10 EMS with Erratic Tach indications

bits

Member
Please help me if you can. We installed a Dynon D10 EMS, a few years ago. It worked great until we installed new mags (Kelly’s replacing Bendix) this Spring. Now when I start the engine, my RPM indication is erratic (800 +/-300), although the engine is idling smoothly and stable. When i run up the engine and select L mag, the RPMs read erratic and higher than actual (2300 +/-600 when the actual RPMs are about 1700). When I then select R mag, the RPM indication immediately stabilizes, and becomes accurate. When I then switch back to Both, the RPM indication remains accurate and stable.

My avionics shop has spoken to Dynon tech support. They have increased the resistance in the switch P-lead lines, in 30kOhm increments, to the maximum of 150, but the problem remains. At Dynon’s suggestion, they have even tried bypassing the switch, but no improvement. They will soon remove my D10, and send it to Dynon for analysis.

I am willing to let them continue down this path, but am not all that confident that the problem resides within the D10 EMS, as it indicates accurately on the R mag switch position.

Any thoughts or suggestions would be appreciated.
 
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Based on your description it sounds like a mag circuitry problem not the EMS.

Switch the leads to the EMS and see if the problem follows the wire. IOW connect the right magneto wire to the left EMS tach input and the left magneto wire to the right EMS tach input. If the D10 indicates the problem is still with the left mag, then the EMS is at fault. If the D10 indicates the problem is now with right mag, then that mag circuitry is at fault.

This is the best way to quickly tell you if the problem is with the EMS or the mag circuitry.

:cool:
 
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Seems unlikely to be the D10, given the timing. Have you tried less resistance? If you started at 30K and kept adding and testing, I would try it at 20K. I speculate you may be muting the signal a bit too much for the D10 to read it reliably. I also suspect something may be off a bit in the new mag and it is giving a weaker electrical signal in the P lead, hence the need for less resistance.

Larry
 
Larry and Galin,
Thank you both for your thoughtful ideas. Swapping the Tach leads is exactly what I will propose to the avionics shop. Larry-your idea about reducing resistance is intriguing too. I will suggest that we, at least, re-establish a baseline by re-installing 30kOhm resistance on both of the Tach leads. I‘m clearly not an expert, but I believe there are filters available which may clean up the P lead signal from the offending mag. Thank you again for your help.

Jack
 
Try a tach gen

TACHOMETER TRANSDUCER
If you have a standard tachometer transducer (usually with a 12V output), you may simply connect its output to the RPM Left input on the EMS-D10. Ensure that you follow all recommendations given in the manual for your individual tachometer transducer.
___________________

This ACS part works great. Replaced mine from mag p-leads and resistors to this, and it is stable at all RPM ranges. You might need to reprogram the tach setting in the EMS.

https://www.aircraftspruce.com/catalog/inpages/umamagtachsend.php?clickkey=10133

Sometime replacing this is cheaper than paying a shop to troubleshoot.

Good luck.

Brian
 
Update

-Dynon analyzed my EMS, found some fault codes, replaced a circuit board, and updated the software. Reinstalled the EMS...RPM is still erratic
-Purchased MakerPlane P-Lead flyers, which promise to clean and digitize P-Lead analog signal. Installed filters...RPM is still erratic
-Grounded P-Lead shielding and installed a different mag/ignition switch...RPM is still erratic.
-Purchased and installed a new alternator...RPM is still erratic
-I will try a Tach Gen, as Pdtofly suggested.
- Any other ideas welcome
 
Check your plug wiring. A fouled plug or a loose or bad wire will give you these results.

Vern
 
Final Update

Problem Solved...Installed a UMA Magnetic Tach Sender (Tach Generator). Works perfectly. Thank you all, especially Brian (Pdtofly). 👍👍
 
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