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It's not depicted on the wiring diagram, the manual just says use a "suitable" one.

Edit: it appears that there is no breaker for the generator, just a relay to protect the fuel pump and an 80 amp braker/fuse on the main battery line, the superseded diagram had a 25 amp braker.

I still don't know if I should just follow the diagram exactly or put a braker in.

If anyone has any sample wiring diagrams for your 914 install I would love to see them.

  • Re: What size circuit breaker for generator / sample wiring diagrams

    by » 4 months ago


    If you look at the wiring diagram in the 914 installation manual, section 24-00-00 page 3, there is no fuse or breaker shown between the internal generator and the main power bus.  It’s reasonable not to have a fuse in this location because the current of the internal generator is self limited to 22 amps.  There is however a relay that connects the generator to the power bus only when battery voltage is present.  This is important because the battery needs to be disconnected from the voltage regulator when the engine is not running to avoid discharging the battery over time.  Simply put, when the master switch is closed, the alternator relay also closes.  

    However, section 24-00-00 page 9, says that the rectifier/regulator must be protected by a suitable slow blow fuse. I find this unclear, but I believe they are referring to the fuse between the battery and power bus, which would also protect the regulator from a shorted battery as long as the rectifier is connected downstream of this fuse, as in the Rotax diagram.  Hopefully someone will correct me if I’m wrong. 

    If you also have the optional external generator, there is a 50 amp breaker between the output of that device and the main power bus.  


  • Re: What size circuit breaker for generator / sample wiring diagrams

    by » 4 months ago


    I'm confused, with the master off, the battery contactor would disconnect, so wouldn't the alternator not be able to drain the battery?

    Edit - I see this note

    "During engine stop break circuit between battery and terminal C to avoid discharge

    of battery!"

    So maybe the relay is set up such that power from the generator closes the relay and connects it to the main bus?

     

     


  • Re: What size circuit breaker for generator / sample wiring diagrams

    by » 4 months ago


    If you look at the separate publication Installation Manual for 914 it shows quite clearly a 30 amp fuse in the rectifier/regulator circuit for the engine generator. It also shows that for an external alternator a 50 amp fuse is required. Regarding the fuel pumps you must wire each pump to separate circuits.  In my installation one fuel pump is wired in the aircraft normal system, the other is direct wired to the battery, both with separate switches.  Check the Installation Manual publication. 


  • Re: What size circuit breaker for generator / sample wiring diagrams

    by » 4 months ago


    I can't seem to find the manual you are referring to John, I have the MMH-914 (heavy mx) and the IM-914 (instillation).

    In that manual the diagram doesn't seem to show a breaker

    regulator wiring diagram


  • Re: What size circuit breaker for generator / sample wiring diagrams

    by » 4 months ago


    OK. You are correct.  This diagram is different from my (older) version. Don’t know why it has changed?  My older diagram doesn’t have the relay in the line from the rectifier, just a 30 amp fuse which works well.  Apologies for the confusion.  Maybe someone with a later 914 and different wiring can help with your question.


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