Home Forums General 107E Prefect Temperature sender not working

This topic contains 7 replies, has 3 voices, and was last updated by  brianw 1 week ago.

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  • #65952

    michaelj70
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    Club Member

    It’s not worked for a long while now – in fact since the car was taken to a garage to get going after 20 years rest. I fitted an new Anglia sender (half inch thread but with a spade connector – the original was a bullet type connector) which has a resistance of just over 1k ohm cold – still doesn’t work. It needs to get to about 25 ohms to register Normal on the temperature gauge – it doesn’t get anywhere near that so gauge continues to register cold at normal operating temperature. Would be nice to have it going again. Did the 107E have a different/unique sender with a low resistance? Any help gratefully received…. (The petrol gauge operates perfectly).

    #65958

    JAN
    Participant

    The 105E instruments were in series with a voltage stabiliser to prevent the needles fluctuating, but which also dropped the voltage to – from memory – 10V; the 107E used standard 100E instruments fed at 12V. The temperature and fuel level transmitters were therefore different and the 107E used the standard 100E temperature transmitter; all 100Es and 107Es had this which was 5/8″ thread, and none got the later 1/2″ transmitter going into a reduced sized hole.

    None of the 1/2″ transmitters I have tried work well as all are designed for use through a voltage stabiliser. With the one I’m currently using the needle rises to about half way through the COLD sector. On one occasion when the engine got very hot, it didn’t quite make it into the NORMAL sector. I’ll look tomorrow to see if I can see the colour, but that’s the best I can do for you.

    #66010

    brianw
    Participant
    Club Member

    Sounds like a small transistor circuit could be the answer. This is as near As I could find http://tickell.me.uk/magnette.org/tech-tips/maintenance/miscellaneous/516-the-temperature-gauge-problem-solving , But the magnette gauge works backwards … ..
    …. What resistance does the Prefect Gauge need for Too Hot ( call this Rh)?
    So instead..( Be warned I’m not too sure…) , connect the Gauge to the top end of R3 & the bottom transistor leg. Replace the R3 with a fixed resistor of Rh value . So now if the transistor is off the gauge reads Too Hot. Connect the R3 resistor between the top leg of the transistor where the gauge used to be & ignition 12v . You might need a higher current rated transistor & R3 & Rh resistors than those listed. Nearly any transistor will do so long as its PNP or NPN for +ve/-ve earth as in the text.
    ( I’m not sure about R1 D1 voltage regulator, seems a complication, perhaps skip that bit)

    Any School/college teaching basic electronics will have all the parts & students who could design & build such a circuit in a hour.

    #66013

    michaelj70
    Participant
    Club Member

    Thanks folks for this. I was toying over the weekend with either getting hold of a thermistor with the correct profile and strapping it into the existing sensor or digging out some transistors from my ancient electronics box. Seems as if the transistor route has worked for some so thanks for suggested values – will probably save me from blowing up the transistors! I’ll let you know how I get on……

    #66015

    JAN
    Participant

    It would be interesting indeed!

    #66016

    brianw
    Participant
    Club Member

    Hi .. The more I think the more, I am convinced the resistance/volt drop across the gauge is important. If the Gauge is too low resistance it might just deliver 12v to the Rh resistor . .& the gauge stay on hot. . Consider putting another resistor in the feed from the gauge.??

    #66141

    brianw
    Participant
    Club Member

    here is an simple on line tool that allows you to model how circuits work..

    http://www.falstad.com/circuit/circuitjs.html

    Once you get the hang of it easy to draw a circuit & see what the voltage & current are at any point . ( double click on a component to change its value & make sure wires are connected on dots) … I think it proves my simple mod of the Magnette circuit won’t work, but gives the tool for trying other options, like adding a 2nd transistor. ( eg use a potentiometer to model the Temp sender)

    #66150

    brianw
    Participant
    Club Member

    . .. One solution might be … If you have a +ve earth car, take the Magnette circuit for Negative earth. Ditch the D1 R1 as you said you don’t have voltage regulator , & swap the temperature sensor & the R2 in the circuit , connect the gauge to be “supplied” by the +12v chassis as the sensor will be.

    This txt below is the output from that falstad circuit modelling tool , if you copy all below & in that website under File “import from text” & past it into the window. The sliders on the right allow you to model the trim pots & the sensor variation.
    Need to check it it works with the full range of actual resistance from your sensor & gauge,

    $ 1 0.000005 3.9121283998153213 42 10 50
    t 192 224 256 224 0 1 -5.416899654987146 0.7506688853511829 100
    g 256 288 256 320 0
    w 256 208 256 160 1
    w 256 64 304 64 0
    R 256 64 256 16 0 0 40 12 0 0 0.5
    w 256 64 192 64 0
    w 192 288 256 288 0
    174 192 224 112 272 1 1000 0.1436 Resistance
    174 192 64 80 80 1 1000 0.33170000000000005 Resistance
    174 256 240 368 256 1 100 0.0446 Resistance
    370 416 64 256 160 1 0
    174 416 64 416 16 1 20 0.5 Resistance
    w 304 64 400 32 0
    x 448 40 526 43 4 24 Gauge\s
    x 101 41 177 44 4 24 Sensor
    x 284 329 408 332 4 24 battery\sNeg
    x 230 -7 375 -4 4 24 Chassis\sGND
    b 384 -16 566 96 0
    b 80 16 208 102 0
    x 319 217 399 220 4 15 R3\s100\sohm
    x 94 199 172 202 4 15 R2\s1K\sOhm
    p 256 160 416 160 1 0
    w 144 272 144 288 0
    w 144 288 192 288 0
    w 256 288 320 288 0
    w 320 288 320 256 0
    r 128 80 128 144 0 100
    w 128 144 192 144 0
    w 192 144 192 224 0

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