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I'm building a RANS S7 with a 912IS. The project is getting close to completion and I did the first engine start about a week ago. The engine fired right up and ran great, but I had one anomaly that I'd like to ask about. 

I've got a "Start Button" momentary contact switch. Got a "start power" switch that's a regular on/off style. Also have an "Emergency Power" switch that's on/off. As I said the engine started right up, but when I turned off the "start power" switch the engine died. I found that the engine would run with the "emergency power" switch on, but if the emergency power and start power switches are off, the engine quits. My understanding is that the engine should run with the Start Power and Emergency Power switches off

I was showing almost 14 volts on the bus voltage, so I know that at least one of the alternators is working. Battery only voltage was only 12.5 before the engine start so the alternators must have been making up the difference. 

Does anyone have any ideas as to why the engine won't run with these switches off?

Jack

  • Re: 912is won't run with "start power" off

    by » one month ago


    Did you run it up to 2500 rpm for 5 seconds to get both generators online?


  • Re: 912is won't run with "start power" off

    by » one month ago


    Well, maybe not. This was a preliminary engine start in my driveway. I never ran the RPMs beyond 3000 and didn't leave it above idle much at all (trying to be a good neighbor don't you know). It's possible that it was never above 2500RPM for more than 5 seconds. 

    If it's a simple as that, I feel a little stupid for not knowing about this threshold for getting both alternators online. But I'm also relieved that it's not something more serious. 

    I'm not planning on running the engine again until the project moves to the airport and the wings are attached. I think I'll just assume that everything is Ok and not worry about further troubleshooting. That is unless someone else has input that says it's not that simple.

     

    Thanks


  • Re: 912is won't run with "start power" off

    by » one month ago


    It is NOT that simple.
    The engine will run, no matter what, as long as it has a power source, ANY Power source.
    The engine will start on either the START or the BACKUP power source, or Both. (Normally START)
    The engine will start on either Lane/Gen A or Lane/Gen B Or Both. (Normally Both)

    The engine normally Starts utilizing the B Generator initially.
    Removing START Power prematurely, before the A Gen initializes, will NOT Stop the Engine.
    It will continue to run utilizing the B Gen.  The Battery will not begin recharging, but the Engine WILL Run!

     


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Jon Tensfeldt, Jack Letts

  • Re: 912is won't run with "start power" off

    by » one month ago


    Bill

    Thanks for the reply. What you are saying makes perfect sense and is in line with what it says in the install manual. The engine will use any source of electricity to keep running. 

    That leaves the question: What's going on with my engine? Why did it shut down when I turned off Start Power? Any ideas on what I should be checking?

     

    Jack


  • Re: 912is won't run with "start power" off

    by » one month ago


    If you are seeing 14v on the Power buss immediately after starting, One or Both Gens are producing power and back-feeding through the START Power connection as expected.

    Can you provide a Photo or Diagram of how YOU Actually wired the engine?

    I suspect the problem may be in the method used to Connect the Engine and Airframe grounds together even though I can't think of a way to mess it up that would kill the engine. ???


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Jack Letts

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