FUEL GAUGE and TANK GROUNDING

Discussion in 'OnBoard Electronics & Controls' started by sebski, Nov 20, 2007.

  1. sebski
    Joined: Nov 2007
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    Location: Jersey, Channel Island

    sebski New Member

    Hello ,
    I am going to install the fuel gauge, so
    I have to install the sender inside the metal tank and
    obviously the gauge on the dash board.
    Right now I'm confused on fact that
    electric part of the sender which is connected to the 12 volts power is inside tank,
    and wires and resistor is submerged in fuel.
    It seems a little bit dodgy to me.
    And the next problem is how to ground those tanks?
    Shold I run an wire from tank to zinc anode attached to
    the outside side of the hull or to negative side of battery?

    Thank you for any help

    Sebski
     
  2. Frosty

    Frosty Previous Member

    Power goes from ign to guage--from guage to tank sender. If the sender has one terminal then the tank has to be grounded /earthed ( the tank connected to the neg side of the battery?

    If the sender has two terminals then it will probably be marked + and - and will be necessary if the tank is non metal.


    + is from the guage and - goes to neg of the battery.

    The whole circuit should be fused 1 amp will be sufficient.

    As far as grounding/ earthing the tank,-- what boat is it?
     
  3. sebski
    Joined: Nov 2007
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    Location: Jersey, Channel Island

    sebski New Member

    on the gauge, there is place to connect wires:

    GROUND
    IGNITION
    SENDER

    so I think GROUND will be just negative of the battery
    IGNITION it will be possitive wire which have power when key is on ignition position
    and SENDER where wire runs to the Sender.

    SENDER has got 2 connections,
    GROUND and SENDER,
    I assume that Ground will be negative of battery (should to be connected directly to battery or
    can I connect to GROUND on Gauge?)
    and SENDER will have wire running from "GAUGE Sender connection"

    on the manual I can read that Tanks supposed to be grounded.

    But "grounded" means that tanks I have to connect to negative side of battery or
    to zinc anode which is submerged outside the hull?

    This is PROJECT 31 boat.

    Thanks

    Sebski
     
  4. Frosty

    Frosty Previous Member

    Its probable that your guage has a ground so the light bulb works!! You can ground the tank to the guage if you want, then ground the guage to neg.
    Iether way is ok.

    If you want to ground the tank just fasten a tail from the - to one bolt of the tank sender

    Grounding to the external zincs is called bonding. To do this or not will start an argument in any pub. I would'nt ground it to the bonding system.

    Theres lots of info on the web, Youlle have to make your own mind up.

    It wont stop you launching or using the boat. You can think about it and do it later if you wish.

    If you bond the tank then the zinc is batt neg. See what I mean it gets complicated.
     
  5. sebski
    Joined: Nov 2007
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    sebski New Member

    ...
    "If you want to ground the tank just fasten a tail from the - to one bolt of the tank sender"
    ...

    Could you please explain that sentence, I am not sure that I understand that.

    Is any chance that sender will produce circuit or spark inside the tank?



    Thanks
    Sebski
     
  6. Frosty

    Frosty Previous Member

    From the neg on the tank that you are grounding to the guage or the batt, put another wire (tail) to the bolts on the sender unit,-- 2 inches.

    A spark in the tank? -- well they have been doing it like this for years --ALL cars have it this way. After the resistance of the guage the current is minute.
     
  7. Ike
    Joined: Apr 2006
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    Ike Senior Member

    Only the good Lord knows how many times I was asked this question over the last 20 years. The tank has to be grounded only if it is a metal tank. The tank sender is screwed to the tank with meatl screws. Put a ring terminal on the end of the wire and put that on one of the screws holding the sender down to the tank. Or some senders actually have terminal lug built in. This wire goes to the negative ground bus for the 12V DC system. Now the sender is grounded and the tank is grounded. Also, if you are grounding the fuel fill run the wire from the fuel fill, down the hose to the same connection on the sender.

    Second question, no the sender will not create a spark inside the tank. Even if it did it wouldn't go boom because it is too rich an environment, but all of the sensors on the market are incapable of sparking.

    Take a look at this web site http://newboatbuilders.com/pages/elect.html

    This is NOT bonding. This is grounding to the negative of the 12 v DC system. There is a difference. All grounds in the 12v DC system lead back to one point, generally the engine where the system is grounded.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The way the gauge works, is it senses the amount of ground the sender is providing the gauge to read. This way, no power is transmitted into or near the tank, neck, fill, vents, etc. There's a little coil on the sender with a moving contact, which is attached to the arm having a float on the end. This moves the contact across the coil. The sender presents the gauge with the amount of resistance the coil is providing (depending on the location of the contact). If the tank is full the contact is right at the beginning of the coil where the resistance is very low, so the gauge reads this as full tank (full ground). As the fuel level drops, the contact moves across this coil increasing resistance, which the gauge registers as less then a full tank.

    In fact, the first thing I do when accessing a fuel gauge or sender problem is ground the sender lead at the sender. If it reads full on the gauge, the sender is likely bad or has a bad connection. If the gauge reads zip, the gauge or a wiring fault needs to be addressed.

    The hot terminal on the gauge is for the light. The grounded tank is important (as Ike points out) on metal tanks. The filler should be grounded. This prevents a static spark from turning your lovely afternoon into a bad day.

    Ike, I've explained this, must be a few hundred times over the last 30+ years too.

    For what it's worth, a very large percentage of electrical issues can be sorted back to a bad ground somewhere. The marine environment is a nasty place for electrical components and connections. Once perfectly good and working circuits can take a dump with little warning. Just reseating connections can restore function (if momentary) and tell you what's really going on.
     
  9. Ike
    Joined: Apr 2006
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    Ike Senior Member

    If you buy one of the new tubular inductive guages they work even better, are more accurate and the current used is very low. How they work is thus: inside a hollow tube is a solid state electronic circuit. On the outside of the tube is a circular donut shaped coil. The elctronic circuit induces a slight current in the coil and measures its position on the tube. They are affected less by sloshing and surge in the tank and so give more accurate readings and they are a drop in replacement for the old style with a float on the end of an arm connected to a rheostat. Plus that the part actually in the tank does not have to be grounded. Only the metal plate on top of the tank must be grounded.
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Okay now you're showing off . . . :rolleyes:
     

  11. Ike
    Joined: Apr 2006
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    Ike Senior Member

    Happy Thanksgiving PAR
     
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