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Thread: Capacitor Wiring

  1. #21
    Senior Member Esser's Avatar
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    Default Re: Capacitor Wiring

    I’m sure you’ve noticed with all my questions I’m new at this stuff. Apparently from what I gather it’s mostly there to take out alternator noise. It makes me wonder if I really need two capacitors for two alternators...
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  2. #22
    Senior Member Dave S's Avatar
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    Default Re: Capacitor Wiring

    Josh,

    FWIW - I am running both alternators (Not fuel injected - just two alternators on two separate systems with a cross tie) and do not have a separate cap for the belt drive alternator - no problem with alternator noise.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #23
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    Default Re: Capacitor Wiring

    Good to know Dave, just interested to hear why you went with no capacitor an the external alt when Rotax recommends it? Did you know of other people having success too? I may go this route...
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  4. #24
    Senior Member Dave S's Avatar
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    Default Re: Capacitor Wiring

    Josh,

    I don't recall seeing any requirement for a capacitor on the belt drive alternator at the time I bought the unit.

    Also remember that this was quite a few years ago (2006 or there abouts) and I believe the EFI rotax engine was still a gleam in the eye of some Rotax engineer - I do not have an EFI or turbo engine - just the garden variety ULS with a need for more juice than the little integral alternator could provide.

    My electrical system has two separate busses/batteries/alternators with a cross tie if one or the other fails. All my essential stuff including radios is on the integral alternator and all the high draw stuff like position lights and strobes, etc is on the belt drive alternator.

    Just a wild elbow guess; but, I wonder if the cap for the belt drive alternator was added at a later date????? Maybe there is now a reason for it?

    Not aware of anyone else with this setup.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  5. #25
    Senior Member Esser's Avatar
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    Default Re: Capacitor Wiring

    It’s on page 47 of my 914 installation manual. I’ll poke around. I don’t know why one couldn’t do the job for both if it wasn’t a competely separate system
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  6. #26
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    Default Re: Capacitor Wiring

    Quote Originally Posted by jrevens View Post
    I found out that Silent Hektik recommends even higher ... 33,000 uf? My capacitor is “beefier” than the original at a 50v rating, but still 22,000 uf. There may be some potential benefit to a higher micro farad rating, with no real downside. It’s still unclear to me what the capacitor actually does in this circuit. I’ve read some descriptions of that which are obviously incorrect. When I take the time to find out for sure I’ll post it on this forum. Of course there are people participating here who can probably tell all of us the real facts already.
    This is kind of an older post, I found it when I was looking for some info on the 912 wireing. A while back I picked up a 912 engine that had some ignition problems. I'm building a stand where I can run the engine and sort out the ignition issues before I get around to mounting it on the plane that I'm rebuilding. Also, I want to get it running and sorted out before it gets to cold up here in Mn. With having to build the panel and other things on the plane, if I wait till that's done, it will be well into winter, (maybe next summer :-) I guess my question is: should I worry about having a capacitor wired in for what I'm trying to do at this point? Or does the capacitor mainly filter out noise in the system, but doesn't really effect the charging system? Basicly, I don't want to burn out the alternator or regulator. Thanks, JImChuk

  7. #27
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    Default Re: Capacitor Wiring

    I was digging through the installation manual today, and it had a circle around the capacitor and it said optional. So I guess I should be able to run the engine for a little bit with out it. JImChuk

  8. #28
    Senior Member Av8r_Sed's Avatar
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    Default Re: Capacitor Wiring

    Do you need a charging system for an engine on a test stand? The ignition system should be independent of the charging system. Might simplify things a little unless you’re trying to test the charging system as well.
    -- Paul S
    Model III SN910
    582 IVO Med

  9. #29
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    Default Re: Capacitor Wiring

    I'm not sure. Would it hurt the alternator to be producing power if it can't go anywhere? I had just figured to temporarily wire things up and run it so I could tell if things were sorted out with the ignition or what ever it took to get it there. The last thing I am is an electrician.... :-) Any help is appreciated. JImChuk

  10. #30
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    Default Re: Capacitor Wiring

    Shouldn’t be a problem to leave unwired, but I’ve never done it myself.
    -- Paul S
    Model III SN910
    582 IVO Med

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