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Thread: Fuel Gauge for PA22

  1. #1
    rglake Guest

    Default Fuel Gauge for PA22

    Does anyone have a wiring diagram for the fuel gauge and sender for a PA22? I'm not sure how to connect and do not want to risk burning out the sender in the tank.
    Bob - rglake@nexicom.net

  2. #2
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    Bob
    I have never seen a owners manual for tripacer but my Colt owners manual has a wiring diagram in the section on the electrical system.

    Jim Miller

  3. #3
    rglake Guest

    Default

    Thanks Jim. My gauges have a 30 ohm resistor, mouted to the back of the gauge and connected to one of the terminals of the gauge. The other terminal of the gauge has a red tag saying connect to sender and don' connect the hot wire (+12volts) to the sender or it could be destroyed. I am exercising great caution asking for advice as I don't want to damage the sender. Any info you have would be helpful.

  4. #4
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    There are a set of gauges and a pair of senders on ebay right now if anybody is interested.
    Tom T.

  5. #5
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    Bob
    That is correct but I would look at the wiring diagram for your own confirmation. I would e-mail you a copy but don't have a scanner. I can look again at my diagram and give you a written description of how it is connected if you don't get a diagram.

    Jim Miller
    Last edited by 7083; 01-26-2007 at 05:30 PM.

  6. #6
    Wayne Guest

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    Make shure the gauge is grounded. That is important, you can burn up the gauge or sender if not.

  7. #7
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    The instrument panel gage unit gets it ground from the instrument panel it is mounted in. The sending unit is also grounded. One of the screws that mounts the unit in the tank must have a good ground back to the instrument panel.
    The panel gage is a moving vane meter movement with two coils. The resistor in the tank unit (30 ohms when full and 0 ohms when empty when read on the center terminal of the unit to ground) shunts out one coil when the tank unit is at zero ohms effectively allowing no current flow thru the full coil. Any variation between full and zero varies the current in that coil hence the magnetic attraction to the moving vane.
    When the tank is empty, no current flows thru the full coil but the other coil has full current, pulling the moving vane-needle to the empty side.

    Any bad grounds and the unit will not work properly, usually it will read erratically. With no ground it reads full and current thu the meter is about 140ma. With the lead going to the tank shorted the gage will read zero and the current thru the meter will be about 200ma. The lead going to the sender unit shorted is equal to the sending unit being on the bottom of the tank. Shorting that lead will not cause a problem other than the gage will read empty.

    There are several springs inside the gage unit to calibrate it so it will read full with 30 ohms of resistance and empty at zero ohms of resistance. If your tank unit reads 30 ohms full and zero ohms empty but the gage reads something else and all of your wiring connections are good you need to have the gage calibrated.

    Keystone Instruments, Inc. in Loch Haven 570-748-7083 can calibrate the gage and make the face look like new.

  8. #8
    Wayne Guest

    Default

    Thanks Gilbert, That was very informative. Do you remember how the voltage divider circuit works so battery voltage variations don't affect the gauge reading? I must be getting old, don't quite remember that one either.

  9. #9
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    The wire wound resistor is in series with the voltage input to the the gage. It is a 30 ohm resistor whose only function is to limit the current in gage circuit by dropping the voltage to approximately 6 volts. Piper calls it a 12 volt adapter in the electrical drawing.
    Short term voltage variations in the charging circuit are removed from the gage by the internal springs which dampen the needle movement. The system is still susceptable to voltage variations but you don't really see them due to this dampening and inherent inacuracy of the system and the bouncing around of the tank float. The spring dampening kills all of this so the needle doesn't move much except to indicate the average tank reading.

    Another way to look at: Assume the tank is half full. The voltage variation from the charging system is 0.5 volts. That is more than I usually see but I will take an extreme case. With a half full tank the variation in voltage at the gage caused by the variation in the charging system would be 0.15 volts. The variation in voltage at the gage from full to empty is 1.2 volts. Therefore the variation in gage indication caused by the charging system varying from 13 volts to 12.5 volts would be about 12%. Maybe a needle width or a little more.

    Hope this helps.

  10. #10
    rglake Guest

    Default

    Great info Gilbert. I have been able to get the gauges working now. Thanks.

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