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  1. #1
    Join Date
    Oct 2003
    Location
    west yorkshire
    Posts
    3,633

    Default Trim tab position indicator problem

    I have a set of Bennet hydraulic trim tabs, hydraulically everything seems great. They work correctly. I have separate port and starboard indicator meters at both helms, with Carling switches used as the control switches. The starboard indicator dials seems to have a mind of there own. Sometimes it reads correctly, most times it indicates fully down. Upper and lower helm indicators seem to behave in the same way.

    Almost certainly a dodgy connection somewhere, probably at the sensor. First place to check is the sensor in the hydraulic ram. Rummage around in the lazarette, hydraulic pipes all there but no wires coming through the transom. Can't see any wires on the outside of the transom. Anyone know what my indicators could be measuring?

  2. #2
    Join Date
    Apr 2011
    Location
    Boat- SoF
    Posts
    4,865

    Default Re: Trim tab position indicator problem

    There are 3 " hydraulic " pipes identical on appearance except one is a Boden cable . It's wire is attached with an adjuster on the flap .
    Obviously 2 are actually hydraulic pipe to the ram
    They all enter the boat above the WL under the platorm
    Presume the boden cable is attached to the inside of the transom to a potential ohmmeter which gives a signal to the gauge S ?
    Point is it looks like a H pipe but it's not

  3. #3
    Join Date
    Apr 2007
    Location
    midlands
    Posts
    7,188

    Default Re: Trim tab position indicator problem

    Quote Originally Posted by kashurst View Post
    I have a set of Bennet hydraulic trim tabs, hydraulically everything seems great. They work correctly. I have separate port and starboard indicator meters at both helms, with Carling switches used as the control switches. The starboard indicator dials seems to have a mind of there own. Sometimes it reads correctly, most times it indicates fully down. Upper and lower helm indicators seem to behave in the same way.

    Almost certainly a dodgy connection somewhere, probably at the sensor. First place to check is the sensor in the hydraulic ram. Rummage around in the lazarette, hydraulic pipes all there but no wires coming through the transom. Can't see any wires on the outside of the transom. Anyone know what my indicators could be measuring?
    The bennet had a potentiometer inside the ram cylinder that gives a signal as the ram rod passes over it . If it's faulty usually means a new ram .

  4. #4
    Join Date
    Apr 2005
    Location
    Warsash
    Posts
    1,051

    Default Re: Trim tab position indicator problem

    Quote Originally Posted by volvopaul View Post
    The bennet had a potentiometer inside the ram cylinder that gives a signal as the ram rod passes over it . If it's faulty usually means a new ram .
    You can buy just the Bennett upper hinge assembly from Magic Marine Ltd, which includes the potentiometer coil, and it's very easy to change this part.

  5. #5
    Join Date
    Jun 2011
    Location
    Volos-Athens
    Posts
    4,720

    Default Re: Trim tab position indicator problem

    reviving an older thread on a similar topic just to have possible solutions together...

    so bought new Bennett upper hinge assemblies for myself and a friend.
    I bought (STUPIDLY!!!) the NMEA2000 kit which only works with Lowrance displays (but that's not the point), and for him I just got normal upper hinges only.
    Have one on my desk trying to figure out how the hell this thing works.
    OK, I can see there's a coil on the hinge assembly and a metal rod that fits in it (and all together screw in the ram)

    Now, no matter what I do I only measure 240 Ohms on the two wires coming out of the sensor, no matter in or out I do, that's it. Occasionally will flash 239 Ohms for a sec and then back on 240.
    Note I'm at home so obviously I have the thing running DRY, no oil around it, could that be the problem?
    Note2 i've tried both assemblies both do the same, so cannot really be that I've got broken kit.

    any ideas?

    cheers

    V.
    Last edited by vas; 17-05-19 at 08:35. Reason: doh 240 not 140 Ohms...

  6. #6
    Join Date
    Apr 2007
    Location
    Mallorca
    Posts
    602

    Default Re: Trim tab position indicator problem

    They are inductive sensors so the resistance will not change.

  7. #7
    Join Date
    Jun 2011
    Location
    Volos-Athens
    Posts
    4,720

    Default Re: Trim tab position indicator problem

    Quote Originally Posted by aquatom View Post
    They are inductive sensors so the resistance will not change.
    I thought as much, but then it doesn't make any sense... will try with another (better) multimeter and give it 12V and measure drop or whatnot.
    BTW, 220-260 Ohms is the factory spec value for the coil.

    V.

  8. #8
    Join Date
    Oct 2007
    Location
    Belgium
    Posts
    4,781

    Default Re: Trim tab position indicator problem

    Quote Originally Posted by vas View Post
    I thought as much, but then it doesn't make any sense... will try with another (better) multimeter and give it 12V and measure drop or whatnot.
    BTW, 220-260 Ohms is the factory spec value for the coil.

    V.
    are you sure that it is not AC on the sense wires in a standard bennett system ?
    then inductive sensors make sense,

    I have such a system on the Karnic,
    tomorow we go out with her,
    I'll try to have a look, but acces to the system is very is tough...

  9. #9
    Join Date
    Oct 2007
    Location
    Belgium
    Posts
    4,781

    Default Re: Trim tab position indicator problem

    thinking about it,
    the sensor in BA is also a old Bennett system,
    its a floater with a metal shaft, gliding in a opening / coil ?
    most probably the predecessor of the more modern compact system

  10. #10
    Join Date
    Jun 2011
    Location
    Volos-Athens
    Posts
    4,720

    Default Re: Trim tab position indicator problem

    no idea Bart,

    would rather it's not AC, as how the hell am I going to produce AC Voltage to feed the thing???

    yes that's the one Bart

    https://www.hodgesmarine.com/BENNETT...p/bennmea1.htm

    cheers

    V.

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