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  1. #1
    Mavis's Avatar
    Mavis is online now Registered User
    Location : Looe Cornwall
    Join Date
    Mar 2006

    Default What are these???

    Referring to my earlier thread 'Electrolytic & Galvanic avtivity' on my newly aquired boat, I have these two devices:

    The red wire goes to the aternator, the black goes around the back of the engine somewhere, and the green is obviously the earth. Can anyone tell what they are or what they do. Could they some be sort of galvanic isolator or are they some sort of suppressor??? The previous owner did not know what they are.

    My engine is a Volvo 2002

  2. #2
    VicS's Avatar
    VicS is offline Registered User
    Location : Home: Kent. Boat: Chichester
    Join Date
    Jul 2002


    Capacitors fitted as suppressors.
    As sure as I can be without actually having one to look at
    Sea Wych Owners Association:

  3. #3
    lenseman's Avatar
    lenseman is offline Registered User
    Location : South East Coast - United Kingdom
    Join Date
    Jun 2006


    Quote Originally Posted by Mavis View Post
    . . . . . Can anyone tell what they are or what they do.
    Hello Mavis and welcome.

    The two cylindrical devices in your photograph look to me to be very large electrolitic capacitors. If you remove one or the other (or both) you might find a series of numbers on the side something like 4700F 250V DC (or similar)?

    That said, they are possible useless as the terminals are seriously corroded enough for me to think that they could not possibly work effectively without the terminals being cleaned and smeared with vaseline?

    You will probably find that they are acting as independant supressors and that the lead going from one of these units to the alternator goes to the large output wire from the alternator?

    You can trace where the other wire goes by using a light and a mirror but it is probably 'trying' to suppress some other dynamic unit on your new purchase?

    Looking at their state, you could probably disconnect them and remove any wiring or insulate the wires as I don't think that are doing anything at all?

    I hope this helps?
    regards David - DSW Marine Engineering

  4. #4
    Join Date
    Apr 2002


    Quote Originally Posted by VicS View Post
    Capacitors fitted as suppressors.
    As sure as I can be without actually having one to look at
    Looks like there trying to supress something Vic, but look a little on the large side. Also it looks like one could have neg to ground, the other pos to ground, so spike problem somewhere.

    Or just some odd idea by a previous owner.


  5. #5
    Join Date
    Nov 2009


    suppresors most likely, but again they look a bit on the large side. If its to address alternator whine (your engine looks to be of some vintage) I'd have thought one cap. would have done the job. Assuming the yellow is your ships ground, they could be wired back to back (both negative terminals together).
    If the black line goes to the engine block/battery negative, they may be there to supress debounce transients that can occur when disconnecting the battery leads??? (any sensitive DC equipment onboard?).

    Supressors need low impedance connections so I'd agree that they probably ain't doing their job too well whatever it may be. Would love to know where that black cable goes?

  6. #6
    Billjratt's Avatar
    Billjratt is offline Registered User
    Location : Firth of Clyde
    Join Date
    Sep 2004


    Big electrolytics by the look of them. I wonder if the previous owner had a garmin GPS that died every time the engine was started?
    Left hand down a bit.


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