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function of C wire on regulator

in 912 / 914 Technical Questions 9 years ago
I am designing my electrical system and wish to deviate from the Rotax schematic. I want to run the C wire directly to the essential bus, rather than connecting it at the capacitor as shown in the manual. I need to know the actual function of the C wire. I can see that it is used to power the warning lamp. Does it do anything else? I was thinking it might be the wire that is used to sense voltage. I understand it must be disconnected when the engine isn't running.

  • Re: function of C wire on regulator

    by » 9 years ago

    Hi Ken,

    I have to ask why you want to deviate? The system was setup to be very specific for its design and run parameters.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: function of C wire on regulator

    by » 9 years ago

    I want to incorporate Robert Paisley's Bus Manager, and I also want to use two batteries. Bus Manager info is here, if interested: http://flyefii.com/bus_manager/Bus_Manager_Installation_Instructions.pdf

    Can you tell me the functions of the C wire?

    Thanks,

    Ken
      
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  • Re: function of C wire on regulator

    by » 9 years ago

    C = Control. It is similar to a "field" wire in an alternator system. It tells the regulator what the bus voltage is.
      
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  • Re: function of C wire on regulator

    by » 9 years ago

    Two friends of mine that each built new kitplanes with Rotax 912ULS engines deviated from the Rotax wiring recommendations regarding the "C" wire because they installed bus manager systems. In fact the bus system supplier told them to do it. Ground taxi tests didn't show up any problem. Both of these friends of mine smoked (destroyed) their regulators on the maiden flights and had to buy new ones. They rewired according to Rotax instruction and have had no trouble since, using the same bus manager.

    I don't know enough about electrical things to tell you the details of what they did, but do know the results. I was on the ground with a handheld radio listening to "smoke in the cockpit, voltage going too high, going to land". Be extremely careful about what you do even if an "expert" tells you its ok to deviate.
      
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  • Re: function of C wire on regulator

    by » 9 years ago

    James, can you put me in touch with them? It would be good to know what they actually did. (I can't figure out how to send a private message on this forum.)
      
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