So I tested the rectifier by the two yellow wires and the ohms measurements all seemed fine. Then I checked the AC Output and found 14.5 AC volts at 2000 rmp and than at 4000 RPM it was 20 volts. My lithium battery when started was 13.4 volts without anything on and without the engine running. When I checked the voltage at the battery after it ran for about 5 minutes it showed 13.3 volts.

So i am wondering if a lithium battery doesn't want to charge right with the rotax 912uls rectfie? Is it possible that when the input voltage coming out of the EarthX lifepo4 battery is 13.4 volts that the rectifier sees that high of voltage and doesn't kick out the proper charging voltage.

What voltage does a rotax stock stator/rectifier put out to a normal fully charged 12 volt lead acid battery?

What battery is recommended for this type of engine?
  • Re: Stator output.

    by » 5 years ago

    The nominal output of the charging system should be in the lower 14-volt range.
    This assumes the engine is in a cruise rpm range. (4000-5500rpm)
    When you start the engine you partially deplete the battery.
    If the next 5 minutes were spent idling below 3000 rpm, the generators minimal output was used powering the panel loads and very little went to recharge the battery.

    See the chart in the Installation Manual in section 24-00-00, page 8.

    Monitor the Battery Voltage and Current while the engine is running and note how it varies with RPM.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Roger james Larson

  • Re: Stator output.

    by » 5 years ago

    While the engine is running at 4000 rpm and above what should the voltage read for normal operation?

    It seems that the only voltage reading I am getting is what the battery level is at that given moment. Has anyone had luck with EarthX batteries being charged with the Rotax Stator/regulator system? Is an EarthX battery management system (BMS) a bad thing to have on a Rotax 912uls. Since that system can shut off the battery can that type of battery ruin a rectifier?

    When testing the yellow wires coming out of the Stator that plug into the rectifier, is there any advantage or disadvantage of not disconnecting them from the rectifier? So far the only test i did on them was with it plugged into the rectifier and testing by putting my meter probes into the socket along with the wire. I wonder will I get true output voltage of the stator this way or will it give me a false voltage reading being connected to the rectifier/regulator? When i tested mine this way I measured AC voltage of 14.5 volts at 2000 rpm and only 20 volts at 4000 rpm. The 20 volts sounds lower than the 30 to 40 volts that the Rotax video says i should see. Thoughts anyone?

    Thank you said by: Klaus Dorschner

  • Re: Stator output.

    by » 5 years ago

    The voltages you are reading are dependent on the electrical loads and the state of charge of the battery. I would think the 30-40 volts A/C would be a no load reading. The DC readings your getting seem fine to me.The problem I found is that after having to start the motor including warmup and taxi times the battery continues to discharge while the engine is at low rpm. Then after take off the charge system gets overloaded while trying to recharge the battery and cover the electrical loads at high rpm and sometimes over heats all the connections associated with the Rotax regulator especially the yellow A/C wires from the stator. Try to let the battery recharged before shut down and minimize any unnecessary loads until just before takeoff.
    My experience with Lithium was not good because the battery wanted to recharge (draw a lot more amps than a AGM battery) after takeoff and is what overheated my regulator and electrical connections. I went back to an Odessy PC625 AGM battery which works much better with the Rotax regulator and can take much more abuse safely. To me a lithium battery is not worth it for the the price/little bit of weight savings and danger of an inflight fire. Also on my airplane I added a B&C gear driven alternator then set the regulator 2/10's of a volt higher so that the B&C carries the load although it does not perform well at low rpm's same as the Rotax reg. Hope that helps.

    Thank you said by: Bill Hertzel, Roger james Larson

  • Re: Stator output.

    by » 5 years ago

    Yesterday I did touch and goes. Upon starting the engine i read 13.5 volts. Shortly thereafter (no additional load) at same rpm it read 13.1 volts. I brought rpm up to 4000 and read 13.4 volts. Most of my flight the only current draw was my MGL mini EFIS however the last 20 minutes I had my nav lights on and landing light which i am not sure what current draw that is. At the end of the flight i took out the battery and took it home to charge it and test the voltage. The battery was 13.1 volts. The top of the EarthX battery says 13.2 nominal volts. Does that sound like everything was working properly?

    I am so used to seeing 13.8 volts from a charging system (motorcycles, cars etc) that this all seems low to me. one of the posts said that 13.5 volts is the max the 912 puts out...is that correct?

    the plug on my rectifier looks fine. No burning and all of the wires looked seated.

  • Re: Stator output.

    by » 5 years ago

    I would contact EarthX for the charging and battery characteristics. I know that Remos Aircraft specifies a different rectifier/charger than the Rotax regulator and an over voltage protection circuit in order to use a EarthX lifepo4 battery.

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