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Fuel gauge resistance range

Discussion in 'Intermediate CJ-5/6/7/8' started by Silverback UK, Aug 20, 2011.

  1. Aug 20, 2011
    Silverback UK

    Silverback UK New Member

    Devon, England UK
    Joined:
    Mar 2, 2010
    Messages:
    40
    Hi guys here's a brain melter for any electrician.

    I fitted a Moon Eyes Fuel gauge as main clock instrumentation very inaccurate / not working.

    I have worked out that the CJ5 sender unit works on a range of 10-73 Ohms whereas the gauge range is 33-240 Ohms. Is there any way of making the gauge read correctly with the current sender ?

    Jas
     
  2. Aug 23, 2011
    hudsonhawk

    hudsonhawk Well-Known Member 2020 Sponsor

    North Texas...
    Joined:
    Feb 4, 2005
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    1,922
    The only way would be to replace the trim pot on the CJ5 sendor to give you a range of 33 to 240 ohms. Or find a sender that will fit that works in that range.

    Anything else will require a knowledge of analog electronic circuits and how to build your own voltage dividers.
     
  3. Aug 23, 2011
    pete72

    pete72 Retro Aficionado

    Cumming, Georgia
    Joined:
    Feb 27, 2011
    Messages:
    158
    Thinking along the line brought up by hudsonhawk above you might try this. Add a 22 or 24 ohm resistor in series with the sender. this would give you 32 - 34 ohms at empty and 92-94 ohms full. The scale will be very compressed but will read empty when the tank is empty and that's the reading you're most interested in. Could be a quick easy and cheap solution.
     
  4. Aug 23, 2011
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Medford Mass USA
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    Aug 10, 2003
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    23,615
    You can't do it with passive components. You can put resistances in series and in parallel with the sender, but to get the values out that you need (33 empty, 240 full) requires a negative resistance (unphysical). If you want a proof, I can show you. You could do it with transistors, but it would be easier and likely cheaper just to buy the right sender or gauge.

    Or put a resistor in series like pete72 suggests, and read correctly at empty, and somewhere around 1/3 at full.
     
  5. Aug 24, 2011
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    cordele, Ga.
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    Mar 29, 2007
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    5,854
    The original jeep tank sender resistance (variable sweep) is 10 ohms FULL and 73 ohms EMPTY. Therefore you would (with 22-24 ohm) be off on the empty side. :)
     
  6. Aug 24, 2011
    72_CJ5_MUD

    72_CJ5_MUD Gunner

    now Central Florida
    Joined:
    Jan 16, 2007
    Messages:
    130
    Excellent ideas... agree... but if time should permit, Drop/pull the tank and pull the sender... reverify the wipe on the sender movable unit and we have been fortunate in past by disassembly and cleaning all but the very corroded units. And even with damage... by adding the appropriate resistance.. the dash gauge will operate as explained previous. Perhaps a friend may have a resistance decade box that will provide an opportunity to dial in different resistance settings and thus recheck different setting prior to adding a resistor... thus, by pulling the sender and keeping things simple. the face on the sender (face is the term used for the movable connection that rests against the resistor etchings as the pickup rises or falls... being an older unit... copper-oxide dust does build up and between this, moisture and more and more... well bottom line... this and that add up to alot of unneeded resistance and this is a start... we know this is just information already considered. All the best with your project... anxious to hear how things are resolved.

    There is one item a friend wanted to mention... after having pulled his sender, disassembled and cleaned everything... he had to repair his pickup and resolder the head and movable face. But the use of dia-lectric grease had resolved the intermittent reading at empty and mid-range for his particular fuel cell.

    Gunner (EE. ME)
     
  7. Sep 15, 2011
    Silverback UK

    Silverback UK New Member

    Devon, England UK
    Joined:
    Mar 2, 2010
    Messages:
    40
    Thanks for all the replies . I took the easy way out and got hold of a 10 - 73 ohms gauge . Reads spot on now . Just need to bring down the false temperature gauge reading now......
     
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