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22 microF Capacitor

in 912 / 914 Technical Questions 6 years ago

  • Re: 22 microF Capacitor

    by » 6 years ago

    ... The capacitors shown in the manual are also connected before the fuses for the generator and alternator. Does that mean that it is better to have the two capacitors connected in case one of the fuses blows, (same effect as opening the alternator switch for the associated regulator?...


    Yes! The Caps are properly a part of the regulators.
    The physical size of 22,000uF Caps makes it impractical to install them internal to the regulators so they are spec'd to be installed externally of the Regulators.

    Two Regulators means Two Capacitors installed just after each Regulator and before any Fuses or Switches.

    The failure mode of Capacitors is quite docile.
    They pop their End-Cap, Smoke a lot and bubble out their guts.
    Other than the mess and nasty smell, the fire hazard is nearly non-existent.

    The failure rate of Capacitors is extremely low.
    I worked in Electronics for 45 years and while I have replaced dozens of blown caps you need to consider that I saw hundreds more every a week that were just fine.
    The average person may not see a blown cap in his lifetime.
    Fusing a Cap is not useful because they do not tend to fail to a short that would blow a fuse.

    Note that the End-Cap opposite the wires/terminals has "X" or "Y" creases in the cap.
    This is to cause the End-Cap to split open if it ever builds up internal pressure as it fails.
    You can add inspecting the opposite end of the Caps to your annual inspection.
    If the Cap shows any sign of bulging, it is starting to fail.
    Replace it before blows out its guts.

    If you want to add a little overkill, instead of going with a larger capacitor, select one with a higher voltage rating.
    15v Caps running at the 14-volt system voltage would be just asking for a failure.
    A 25-volt rating would be the bare minimum.
    50v or 63v rated Caps should make you sleep well at night.

    Never install underrated Caps.
    Even grossly Overrated Caps will do no harm.
    100,000uf, 100 Volt Caps would work just as well as the smaller ones.
    There would be little advantage in the massive Caps.
    They might cost a fortune, Weight a Pound each, and be the size of Quart Cans of Oil, But they would work just fine.

    Note:
    The Capacitor size is 22,000uF NOT 22uF.
    22K = 22 Kilo (Thousand) uF (Micro Farads)
    Expect It to be about 1.25" in diameter and 2.5" Long.
    A good hand full.

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

    Thank you said by: Alan. Hunter, RotaxOwner Admin
      
    Report

  • Re: 22 microF Capacitor

    by » 6 years ago

    For everyone that only has One Capacitor installed near the battery...

    Why does it work???

    Remember that the Caps are only used when the ALT switches are OFF with the engine is running.
    You normally turn ON the ALT Switches and the Master Switch before engine start.
    The Switches remain ON for the entire flight and are only turned OFF after engine shutdown.
    The Alternators remained connected to the Battery at all times.
    So, You have never made use of the Capacitor at any time. It might as well not be there at all.

    Do you Need the Capacitor in the event of an Alternator Failure? Probably Not!
    The Capacitor is Only Needed to stabilize a Good working Regulator that is disconnected from the Power Bus.
    Have you ever turned OFF the ALT Switches of a Fully Functioning Alternator in Flight? Probably Not.
    If you turned OFF the ALT switch and the Cap was not properly connected to the regulator, would it cause any damage? Maybe, Maybe Not!

    The capacitor is just an inexpensive insurance policy that you may never cash in.

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

    Thank you said by: Alan. Hunter, Henri monnin
      
    Report
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