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I'm having an electrical problem the Sport 912iS engine, #441 7198, in my 2016 Tecnam Astore microlight aircraft.  The engine appears to be delivering some charge in cruise but not sufficient to supply all the 9A load and recharge the main battery. i.e Last flight, voltage read from Dynon screen: Pre-engine start 12.1V, post engine warm-up 12.5V and at cruise after 1hour flight 11.9V.

Since new the annual inspection reports show the voltage ranging between 14V - 13.1V. However, in the two years I’ve owned the aircraft I’ve never seen the voltage above 12.7V and the problem appears to be getting progressively worse. I’ve not added any addition load to the system. I've replaced the battery with a like for like HC20 Fullriver 12V 680PCA but I didn't see any improvement. I now must connect up a battery recharger after each flight.

Lanes A & B typically display 14V – 13.9V.

In Feb 2024, with the engine at 4,000rpm and all electrical loads ON, I’ve taken voltage readings at the battery terminals 12.8V, cigarette light socket (bus) 12.9V and the Dynon screen12.6V @ 9A. This would indicate that the connections are good, no dry joints, etc and that the voltage displayed on the Dynon screen is a good representation. I’ve traced the wiring and found no loose connections. Refer to the attached for voltage readings I've taken over the last year.

 I’ve been in contact with my local Rotax agent, but he is as baffled as I am. He did say he’s more familiar with carbureted 912’s than the injected electrical system and I got the impression he was too busy to spend the time investigating the problem.

Any advice on how to diagnose this problem would be most appreciated. Does this sound like a problem with the Regulator B, Alternator B or Stator B? I have access to an oscilloscope. Are you able to provide me with a procedure on how best to take the readings and what pattern and numbers I should be seeing?

10812_1_Rotax 912iS Voltage Readings.pdf (You do not have access to download this file.)
  • Re: Main Battery Low voltage

    by » 5 days ago


    Rod

    It seems a problem related to GenB. Since Lane A/B have good voltage values and both Ecus are fed by Gen A, once the engine starts GenA is in charge of all engine related loads (Ecus, fuel pumps, sensors, ignition and fuelminjection). GenB feeds the rest on the aircraft loads (Lights, Avionics, Accesories, etc)  the problem should be on Stator.B, Regulator B or the aircraft Battery. Check these 3 with an experienced Rotax service on the 912iS electrical which is not trivial.

    Maximo.


  • Re: Main Battery Low voltage

    by » 5 days ago


    Hi Maximo, thanks for your reply but I was hoping for more specific advice to narrow down the cause of the problem. The voltage was 100% normal for 6 years since new but now appears to be low. What could be the cause? I image a solid state regulator would either function or not? Same with a stator wiring, if it got mechanically damaged or burnt out it wouldn't it stop functioning completely? A progressive deterioration seems odd to me. I replaced the aircraft battery but didn't make any improvement. Any other suggestions?

    cheers

    Rod


  • Re: Main Battery Low voltage

    by » 5 days ago


    Hello Rod

    Use the maintenance manual heavy, MMH, to do the checks on the stator output wires.  This is a 3 phase system and you need to be sure each leg is working correctly.  

    Cheers


  • Re: Main Battery Low voltage

    by » 4 days ago


    Hi Maximo, thanks for your reply but I was hoping for more specific advice to narrow down the cause of the problem. The voltage was 100% normal for 6 years since new but now appears to be low. What could be the cause? I image a solid state regulator would either function or not? Same with a stator wiring,

    Unfortunately not.
     
    there are three phases either one could fully fail or partially fail. The insulation on the coils can partially break down. The rectifier can also partially fail. You could have a bad leg or earth on the RR.
     
    As others have said follow the MM process as a start.
     
    However underload partial failures that cannot be picked up static can happen. I know a guy whom built a little electrical load dyno to test for this to find failures.
     
    Regards
     
    Glenn
     
     

  • Re: Main Battery Low voltage

    by » 4 days ago


    Hi Glenn & Rotax Wizard, Thanks for your comments. MMH procedure looks to be an excellent place to start.

    cheers

    Rod


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