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Alternator Fuse/CB Location?

in 912 / 914 Technical Questions 6 years ago

  • Re: Alternator Fuse/CB Location?

    by » 6 years ago

    Bill attached here is a 30 amp FUSE from the same manufacturer )Littlefuse) who guarantee their product to blow in less than 10 seconds at 200%. There are other electronic fuses available to protect sensitive electronic equipment which will blow in less time.
    If you use common automotive fuses then you can expect the figures that you quote.

    My point remains - study the manufacturers data sheet of the fuse or circuit breaker that you are using and apply it correctly to your specific application.

    I have had to rewire enough amateur burned wiring jobs to recognize a fire hazard when I see one, and any fire in an aircraft is not recommended.

    Your point about ambient heat within the fuse mounting area is importantly valid. What is usually missed is the temperature cycling of the fuse as it heats and cools depending on the load and of course the vibration associated with the mounting position. These failures usually appear in older fuses as an imperceptible break in the internal fuse wire or solder points.

    Regards........Chook.
    Littelfuse_Fuse_275_Datasheet.pdf-756858.pdf (You do not have access to download this file.)
      
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  • Re: Alternator Fuse/CB Location?

    by » 6 years ago

    Chook,
    I agree that there are Normal, Fast and Slow Blow Fuses.

    Your statement of; "...a 30 amp rated fuse will blow almost immediately (within a second) if 30 amps are drawn through it", was the point of contention.
    I can only see that happening in a circuit that is monitored electronically and not with any conventional Thermal Fuse.
    Even the Ultra-Fast fuse example is only spec'd to open after >4 hours at 100% rated current.

    Sooner or later everything in the engine compartment will be subject to at least a light spray of water due to flying through a light rain, parked on a ramp during a rain shower or just accidental spray while washing the plane.
    I would not recommend mounting a common circuit breaker in the engine compartment due to the uncontrolled environmental issues.

    The key point to take away here is that the Fuse is intended to protect the Wiring.

    As an example...
    If you want to utilize a 30 amp fuse to power a panel that nominally only uses 10 amps; the wiring must still be able to carry the full 30 amps indefinitely.
    12AWG wire would be the smallest gauge recommended provided it had high temp insulation.
    10AWG would be a better choice to carry 30 amps.
    The mechanic who wires the circuit with 18AWG wire is looking for a fire.
    An 18AWG installation would be in flames at 25 amps with the 30A fuse continuing to supply full power to the fire.
    If you insist on using 18AWG, install a 10 amp fuse!

    Back when houses had screw in fuses, many a house burned down after the homeowner placed a 200A Lincoln Head Penny under the fuse because he ran out of fuses trying to figure out why the circuit kept blowing!

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

      
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  • Re: Alternator Fuse/CB Location?

    by » 6 years ago

    I'm going to return the CB's and use fuses (in the engine compartment). For the 50A I'll use: https://www.mouser.com/ProductDetail/Littelfuse/0MAX050XP?qs=sGAEpiMZZMsh2y49K8ANrXgtX8Cl56UGXbmbzcHXGtQ%3D&fbclid=IwAR05X9YBXM0dFWWu2XkvFhp9_2DAcGUwzytKGiCpl-LGlZ6Q77Vt_HE_VI4

    It's a slow blow fuse and I'll install it in this weatherproof holder: http://a.co/d/czxsbjk
      
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  • Re: Alternator Fuse/CB Location?

    by » 6 years ago

    You have chosen Well!

    Out of Curiosity, where is the 50A fuse going to be used?
    It will need at lease 8AWG, with 6AWG being preferred.

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

      
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  • Re: Alternator Fuse/CB Location?

    by » 6 years ago

    It'll be used for the 914 external alternator and will be in the engine compartment. Is that what you're asking?
    Thank you said by: Bill Hertzel
      
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