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I plan to implement an overvoltage protection device between the stator and regulator on my 912iS.  The installation manual says that disconnecting the regulator from the battery under load can destroy the regulator, so the overvoltage interrupt can't go in the regulator output path without risk of damage in the event of a nuisance trip.  So, I need to extend the stator harness to the overvoltage protection module, then back to the regulator.  I'll do that with matching Deutsch DTM connectors to avoid cutting any factory wires.

In the 912iS Heavy Maintenance Manual, at 74-20-00 pg. 5 (PDF page 281), an engine layout diagram shows the harness for Generator B as simply 3 wires labeled "g" (I can find no reference for what "g" means).  Section 24-20-00 shows the harness and connector in several diagrams, but nowhere is the wire cross section for the stator output shown.  None of the other 912iS manuals show these wires either.

The 912/914 Heavy Maintenance Manual has more detailed engine layout diagrams in section 74, which show the stator output as 2 wires of 1.5 sq mm cross section (~16AWG).

If Rotax had used machined pins and sockets in the Deutsch DTM connectors on the 912iS stator harness, it would be certain that they used nothing larger than 16AWG, as there are no machined contacts available in size 20 (to fit DTM housings) for wire larger than 16AWG.  However, they used stamped-and-formed contacts, and TE Connectivity Deutsch does make size 20 contacts of that type for up to 14AWG wire.  They're in the Deutsch catalog but they're very hard to get ahold of; even TEC/Deutsch has none in stock.  For this reason, it would be much easier to use 16AWG than to use 14AWG.

So, the manuals don't show the wire size, the wires that I can see are not marked, and the crimped contacts don't narrow it down.  Does anyone know for sure what wire size is used for the three stator output wires on a 912iS Generator B?  If not, can someone with access to the factory ask them?  Thanks!

  • Re: Generator B Harness Wire Size

    by » 2 years ago


    I don't really like the idea of an overvoltage cut-out between the Stator and Regulator, to me the additional failure point outweighs any potential benefit, but that's just my opinion.  Regarding your question...

    Service Bulletin SI-915i-006 / SI-912i-024 introduced a new larger connector for the 915 regulator B, which is also optional for the 912iS regulator B connector. This connector is shipped with pins that are rated for wires from 12 AWG to 10 AWG.  I installed one of these kits on a 912iS and the pins seemed to fit the wires correctly. If I remember right, the wires on the regulator side of the connector were smaller than the wires on the stator side. It may have been #12 on the stator side and #14 on the regulator side, but the pins shipped with the kit crimped down tight on both. I used the  Rotax supplied kit, and the connectors shipped had a Rotax part number on the bag, but I recognized them as Amphenol.  Specifically (and unofficially), the connectors are:

    Male Plug:  Amphenol RT06164PNHEC

    Female Connector: Amphenol RT07164PNHEC

    Male Pin: Amphenol MP10A23S (12-10 AWG)

    Female Pin: Amphenol MS10A23S (12-10 AWG)

    Note: The 12-10 AWG Pins are the only size available for this connector since it is rated for 45 Amp max current. 

    Lastly if you do decide to go with this new higher amp connector, know that the connector pins shipped with the Rotax kit have an external stop collar that is just a few thousands of an inch too big for the crimper that Rotax recommends in the service letter (at least mine did not fit).  You can easily file a bit off of the circumference of the stop collar on the pins without compromising them, but it would be better to have a crimper with the larger diameter opening.  The Rotax Bulletin calls for a DMC AF8 tool with a UH2-5 positioner, however, the 5.6mm orifice in the tool won't quite accept these pins. The DMC MH860 would fit the pins correctly but it's an expensive tool. Also, JRDTools has an AF8 style crimper that is available with slightly larger diameter opening (6.35mm) that would work well for this. That part is a JRD-FT8, still expensive, but not as bad, and a great tool to have. 


    Thank you said by: Eric Page, Paul Hamilton

  • Re: Generator B Harness Wire Size

    by » 2 years ago


    The factory has historically been reluctant to release design info.
    I am not condoning your decision to complicate the electrical system of the engine and would advise that well enough should be left alone.
    But this is Experimental aviation and we love to reverse-engineer everything. 

    The B gen is rated at 420 watts at 14.5 volts.
    That is just a hair under 29 A DC.
    The Stator is 3 phase current so dividing 29 amps by the square root of 3 yields just under 17 amps AC per phase.
    16 awg wire is rated at 18 A at 90°C according to Wikipedia.
    90°C is some mighty hot wire especially if installed in an engine compartment.
    14 awg wire is rated at  20 A at 75°C; So both wires would be candidates but as you are extending the cable length the larger cable would be the better choice.

    Take note that SB-912i-006 describes increasing the stator wire size but does not specifically state the actual size used.
    I suspect they upgraded the 16awg equivalent from the previous 912ULS design to a 14awg metric equivalent.
    So again the larger cable would be the better choice if you intend to perform this modification.
    The choice is yours.
    - - -

    The G label on the wires refers to the German word for Yellow. 
    Yellow = Gelb, hence "G".  Three Gelb-Colored wires.


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


    Thank you said by: Eric Page

  • Re: Generator B Harness Wire Size

    by » 2 years ago


    As one more data point, service instruction SI-915i-006 / SI-912i-024 instructs the installer of the new connector to set both the strip tool and the crimp tool to 12 AWG for both the Stator and Regulator side of the connector. 

    https://legacy.rotaxowner.com/si_tb_info/serviceinfo/si-912i-024.pdf


    Thank you said by: Eric Page

  • Re: Generator B Harness Wire Size

    by » 2 years ago


    Thanks very much for the replies, gents.  Lots to digest in your posts and the linked documents.  I'll have to read through it all and have a good think about it...


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