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Automotive Gauge Tester

Discussion in 'General Electronics Discussion' started by gto65racer, Feb 1, 2017.

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  1. gto65racer

    gto65racer

    4
    0
    Feb 1, 2017
    I am looking for some help building a tester for automotive gauges, specifically Stewart Warner gauges. What i need is something that has 3 outputs;
    1- ground
    2- positive power
    3- ground, adjustable from 0 ohm - 240 ohm

    I need to be able to switch the positive power between 6 volt and 12 volt.

    The gauges I need to test are fuel level, 12 volt 240ohm (empty) to 33.5ohm (full) and 6 volt 100ohm (empty) to 0ohm (full)

    I hope I have described what I need well enough for someone to help me.
     
  2. Bluejets

    Bluejets

    3,974
    818
    Oct 5, 2014
    1...............For the power supply a multi output plugpack, maybe max 500mA output, then just switch between them for the required voltage.
    2.............. Wire wound pot, one shown here I think is around 2W ...500R but you can get others.
    These are 10 turn so fine adjustment possible.
    Note that if you are doing auto gauges, normally a voltage regulated supply is essential.
    In fact many auto systems run a regulated 5V supply to all their gauges.

    http://www.ebay.com.au/itm/2pcs-359...662977?hash=item2ca7233341:g:qdAAAOSwARZXlVPW
     
    Last edited by a moderator: Feb 1, 2017
  3. gto65racer

    gto65racer

    4
    0
    Feb 1, 2017
    Thanks for the help. Will that Potentiometer allow me to adjust the signal output ohms? Inorder to make the needle on the gauge move i need to be able to change the ohms. The old gauges I need to test are all 12volt and 6volt ignition power.
     
  4. Bluejets

    Bluejets

    3,974
    818
    Oct 5, 2014
    So you are going to repair gauges and yet you need to ask this question.
    I think you need to study quite a bit more before attempting any repairs.

    However, yes, this is what a pot does.
     
    Last edited by a moderator: Feb 3, 2017
  5. debe

    debe

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    64
    Oct 15, 2011
    You don't need mutch to check old automotive gauges. This is all I used when working as a mechanic in a Ford dealership. A variable resistor & an adjustable power supply. In this test its an XF Ford temperature gauge & the voltage is 8V DC for this particular instrument. The var resistor goes betwean the Sensor terminal & negative ( ground) GAUGE.1.JPG GAUGE.2.JPG GAUGE.3.JPG GAUGE.4.JPG GAUGE.5.JPG
     
  6. Proton

    Proton

    4
    2
    Sep 8, 2009
    Fyi, older analog gauges usually are 2 perpendicular windings internally. one winding has supply voltage across it, the second winding is merely shunting magnetic flux of the first by how much it is grounded out (NOT a voltage applied) to sensor terminal.

    This accomplishes: 1. No voltage/current on sensor lead (you really want that in your gas tank?) 2. stability from supply voltage... as alternator kicks in or headlamps switch on etc, should your gauges change their value? nope.
    also noteworthy - most vendors use same gauge innards and just change the dial labels. Compare degrees of sweep of the gauge needle. Many a time i'v plugged a temp gauge in place of fuel or oil ga. Quick & easy test! This is especially true for marine. Most failures are fuel senders (moving parts) re-purpose an old one for your test potentiometer! I used a universal replacement style fuel sender for most of my testing thru the years, great test tool plus i had parts "on hand" for on-site service.
    most marine are labeled with "i" for ign or batt + "S" for sender & "G"round.
    All my decades were in marine field, but, same applies to most US autos.

    Digital gauges are 5 volt. these beasts test way different. Usually same digital stream passed to all gauge's "sender" input and each gauge has unique address so swapping these as a test is inconclusive.
     
  7. gto65racer

    gto65racer

    4
    0
    Feb 1, 2017
    Thanks for the help. I am not looking to repair gauges I just want to have the ability to test them. I buy alot of used fuel gauges and I am tired of getting bad gauges.
     
  8. debe

    debe

    249
    64
    Oct 15, 2011
    Be aware some fuel gauges use a variable resistance sender But some use a sender that sends a variable voltage to the gauge.
     
  9. gto65racer

    gto65racer

    4
    0
    Feb 1, 2017
    Thanks for the info. The gauges I need to test are old Stewart Warner gauges. Any ideas on how I can build a switch in to switch from 12v to 6v?
     
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