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Thread: Litium battery question

  1. #21

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    Default Re: Litium battery question

    Hello guys, You are touching on a situation that is worth exploring. I have been test running my 912ULS, B&C AVC1 regulator with an Earth X 680, and my G3X is indicting after start up 13.4 volts with a high amperage. Examples are 3400 rpms at 13.5 Volts at 15amps, or 4000 rpms at 13.8 V at 18 amps. Called and talked to Earth X, they said this was normal with an avionics load at 6-7 amps, and roughly 11 amps leftover to charge the lithium battery. Only once did my system normalize to 14.4 volts at 6 and 7 amps. This did occur at the end of one of my run sessions, however I have yet to repeat this condition. Being that I'm on the ground testing while using my header tank as a main fuel tank, I run out of gas after about 20 mins. Thinking if I run longer than 20 mins my battery will normalize. As mentioned from Earth X, lithium batteries have a very low charge resistance, therefore they command as much amperage as they can get until the battery is back to full charge. Once charged the amps should come down, and voltage should go up. Again, Earth X tells me what I am experiencing is normal.

    The million dollar question is, does anyone know the max continuous time for AC generator at full capacity? My fear is that this situation may over heat, or overtax my copper windings around the magnets and cause a total failure. On take off, I will be running at max power, then to 5500 rpms for an extended time. Should I be concerned? I do not know enough about the rotax electrical system or Earth X batteries to know any better.

    Any other thoughts from other Rotax 912 pilots using the AVC1 and Earth X Battery?

    Thank you for your comments!

    Mike
    N928M
    Mike
    West Chicago, IL
    Kitfox 5 Speedster, building
    912ULS, Airmaster 332

  2. #22
    Senior Member jiott's Avatar
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    Default Re: Litium battery question

    I'm going to give a reply that is admittedly not very expert, but I believe the Rotax generator is good for about 21 amps with no problems. The problem is much more likely to be the Ducati voltage regulator. I have heard that much over about 13 amps for a prolonged (whatever that means) period of time can overheat and damage or reduce the life of the regulator. If I were you, I would figure out a way to limit the charging amps to less than the 18 you mentioned. My 912uls system with the EarthX 680C never draws more than 10-11 amps charging and my regulator lasts a long time. Just my 2 cents.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #23
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    Default Re: Litium battery question

    Mike I have never read or seen a max alternator output time limit. 18 amps output on a good day and full power is what the stock will put out. It takes about 30 min into the flight before I will normalize my battery volts at 14.1. Edge Performance has a graph I remember seeing for the stock versus the aftermarket one they sell. I will see if I can find it. But based on your description I would have to agree that everything seems normal. You wont see 18 amps until your fully power. Just FYI I know a couple that will never see normalized voltage unless they turn off all the lights. (So they are running the alternator at max entire flight)

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    Dustin Dickerson

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  4. #24
    Senior Member Delta Whisky's Avatar
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    Default Re: Litium battery question

    Mike - here's a link to my go to page on the Rotax alternator. HTH. http://contrails.free.fr/elec_alt_rotax_en.php

  5. #25
    Senior Member Eric Page's Avatar
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    Default Re: Litium battery question

    Alternators are limited by the physics inherent in their magnetics. They are incapable of putting out more current than their design limit. If more is demanded of them, their output voltage will drop, limiting current. Unless Rotax under-specified the copper wire diameter in their alternator design, it's not a worry.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  6. #26

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    Default Re: Litium battery question

    Appreciate the feed back from everyone!

    All of your information here has been excellent!!

    The research in the Contrails article is good, most of it is above me, however the caption that talks about the tortures of the stator windings on the bench, "running at full power for weeks and the insulation still in perfect condition" gives me a lot confidence that I am in the clear that the AC power will not fail and melt down under hard operations.

    The learning curve is steep until you start communicating with other folks that have been there already. I have alot of confidence B&C has done their homework before releasing the AVC1. The lithium batteries adds a new twist to the electrical plan and it is just a matter of time before you understand what normal operations should look like. I want the first flight and beyond to be perfect, and knowing what to be look out for is essential.

    I will be doing more electrical testing this weekend with an inductance amp meter and comparing indicted volts/amps on the G3X and GEA24 engine module, to actual measurements behind the panel to ensure everything is reading correctly. Will attempt to add an extra reserve to my fuel so that I may get into that 30min recharge window and hopefully see my electrical system normalize.

    If anyone else has added input/research on this subject please share for the common wealth of knowledge!

    Thank you all!

    Mike

    Contrails caption below:

    Reassuring values

    We can rest assured, knowing that each time, the assumptions taken are very conservative.
    The heat will be better rejected by conduction through the housing of the ROTAX than by the running of our test bench, ambient air temperature might very well be below 80°C, and the insulation of the winding is not necessarily poor quality.
    NB : we observe that despite the "tortures" undergone at full power for weeks, the winding insulation still in perfect condition (Cf. fontispice).


    N928M
    Mike
    West Chicago, IL
    Kitfox 5 Speedster, building
    912ULS, Airmaster 332

  7. #27
    Senior Member
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    Default Re: Litium battery question

    So a quick question to the others running the earthX or other lithium batteries.....How long can you leave on the master switch, and avionics before the battery is depleted or the BMS turns it off?

    For example, if you turn on your master and avionics switches which turns on......Solenoid, 10" EFIS, 4" EFIS, Garmin 327, Garmin GTR 200 Radio, ADSB Echo, and IFLY GPS, all very low amperage items, how long before the BMS shuts off the Battery? I know there is a formula to figure out amp draw, but I am curious what others have experienced as far as minutes before the batt quits.
    Last edited by Jerrytex; 10-03-2022 at 03:30 PM.

  8. #28
    Senior Member PapuaPilot's Avatar
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    Default Re: Litium battery question

    I would never do this intentionally and haven't done it accidentally. I would use the formula to see what it theoretically could do.

    I estimate I can go approximately 2 hours on the EarthX 680 battery after loosing my charging system running one G3X 10" screen, com radio, transponder and a few other circuits. Lights and trim are part of my essential bus, but are intermittent loads aren't included, but are available. I bypassed my master solenoid, so the coil is not part of the load. I believe my load is between 5-6 amps when I go to my essential bus.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

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