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Fuel Gauge

Discussion in 'XJ Modifications' started by goser, Sep 23, 2008.

  1. goser

    goser Member

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    I'm about to fit up a 750 tank on my 650, and am thinking of building a fuel gauge since the new tank has a sending unit. I was thinking of building the battery voltage meter as described in the XJ CD, and hooking it up in series with the sending unit. As the resistance changes from the sending unit, the voltage at the battery meter would change, thus providing a gauge. Since I'm dealing with flammables here, is there any reason why this wouldn't work?
     
    goser, Sep 23, 2008
    #1
  2. kd5uzz

    kd5uzz Member

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    First off, I want to do the same thing. Is there any way you could send me a few pics?

    Below you will find my response to this
    http://xjbikes.com/Forums/viewtopic/t=12474.html
    thread.

    It is untested, but even after re-reading it just now it still seems plausable.

    Let me know how it goes/if you need help!

    There is a device called a wheatstone bridge (http://www.hobbyprojects.com/dc_theory/ ... ridge.html).

    I'll skip over the why, and jump right to the what its good for.

    Lets say you put your sending unit in place of R4, and have the correct value for R2 (Fig2). (and the same values for R1 and R3)

    When the resistance of the sending unit (R4 from now on) is the same as R2 the voltage between points 'a' and 'b' will be 0volts.

    The greater the difference between R2 and R4 the greater the voltage between A and B.

    If there is enough of a voltage difference you could actually light an LED.

    If that LED was part of an optoisolater then you could use the other side of the optoisolator to switch a light.

    It may be easier to put another variable resistor in place of R2 so you could fine tune the 'low' level.

    Keep in mind that if the inbalance between R2 and R4 is one way then the voltage between A and B will be positive, if it is in the other direction it will be negative. You could also use a volt meter in place of a dummy light and you would get a gas gauge.

    You would need to measure the resistance of the sending unit to choose the correct value of R2. You would need to think about the voltage swings involved. If you need more help send me a PM and we can continue this over email. I've been thinking for awhile about a gas gauge for my '82 Maxim, and I think this could be the way.

    I'm in a similar situation, I'm going to change my handlebars and gauges out and will be making a new 'dashboard'. I wonder if your type of sending unit would work in my Maxim.
     
    kd5uzz, Sep 26, 2008
    #2

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