I'll be installing a 912iS in my Kitfox.  I'm working on the electrical system design and have come upon a couple of questions that I can't answer, related to the engine's electrical system.  I've searched the forum and found similar questions in the past (see below), but no definitive answer has been given.


My questions:

1. Does the 912iS Generator B system have an overvoltage protection (OVP) circuit?

2. If so, at what voltage does it disconnect Generator B from the airframe bus?

3. Is the OVP set-point adjustable?  If so, how?

4. If an OVP system exists, can anyone point to a Rotax document that describes it?


Earlier forum posts:

- The only answer in this thread points to REMOS SB-013 that requires an OVP system in certain of their G3 and GX aircraft, but says nothing about Rotax-supplied components.  Did REMOS issue this SB because the engine lacks OVP and they neglected to add it in their early production aircraft?

- The first answer in this thread references the 912iS Operator's Manual.  The page number given doesn't match the current numbering in the manual, and in any case it's silent about OVP (as are all of the other manuals for this engine).

This thread discusses a design for implementing OVP, on the apparent assumption that Rotax did not include it.


Finally, the only reference I can find to a potential overvoltage condition is in the 912iS Installation Manual, in section 24-00-00, page 15 (page 61 of the PDF).  Note 5 below the table describing the pinout of Fuse box connector X3 says, "Attention: In failure conditions the output voltage [on pin 3] can exceed the specified limits."  This suggests to me that no OVP exists.

  • Re: 912iS Electrical: Overvoltage Protection

    by » 2 years ago

    To the best of my knowledge, there is NO OVP circuit.
    There MAY be an Undocumented OPV circuit within the regulators, but that is just an optimistic guess.
    I would also guess that Rotax would advertise the feature if it did exist.

    So, most likely NO!

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

    Thank you said by: Eric Page

  • Re: 912iS Electrical: Overvoltage Protection

    by » 2 years ago

    Thanks, Bill.  I agree that the regulator has no OVP feature.  This was confirmed by a teardown of the Rotax/Ducati regulator published by Gilles Thesee on his website several years ago.  It's possible that Rotax has sourced a different unit since then, but given that it's a "certified" part on some of their engines, it seems unlikely that they would change it absent a significant number of SDRs.

    I thought the most likely location for an OVP circuit would be in the Fuse box, but, as you pointed out, Rotax would describe it in the manuals if it were there...

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