Pig Posted April 17, 2014 Share Posted April 17, 2014 Hi, Is anyone able to help? I am trying to get the voltage for the fuel sender unit in order to program my Dash 2 unit. All I can seem to find is Ohms which is approx 3 for empty and 110 for full but I don't know how to calculate the volts from this using ohms law. Is anyone able to help as this will save me pulling the unit out. Alternatively, if you have a DASH 2 file that accurately displays the fuel level then please let me know the equation. Thanks Jon Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted April 17, 2014 Share Posted April 17, 2014 Pretty sure that all you will see as the sender is resistance based, its the gauge that is powered. Quote Link to comment Share on other sites More sharing options...
Wez Posted April 17, 2014 Share Posted April 17, 2014 Been a while but I recall you have to use a pull up resistor Quote Link to comment Share on other sites More sharing options...
a98pmalcolm Posted April 18, 2014 Share Posted April 18, 2014 I have the dash2 .dat file thats its very accurate with fuel level. PM your e-mail. Quote Link to comment Share on other sites More sharing options...
Pig Posted April 18, 2014 Author Share Posted April 18, 2014 I have the dash2 .dat file thats its very accurate with fuel level. PM your e-mail. That will make my life 100 times easier. [email protected] please mate Thanks very much Quote Link to comment Share on other sites More sharing options...
Wez Posted April 18, 2014 Share Posted April 18, 2014 I have the dash2 .dat file thats its very accurate with fuel level. PM your e-mail. Wont you also need to provide the pull-up resistor size? Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted April 18, 2014 Share Posted April 18, 2014 The power goes through the Fuel Gauge (meter) and then to the Tank Sender to chassis, so the voltage at the top of the sender will vary as the fuel level varies. But without knowing the resistance of the Fuel Gauge meter, you can't work it out. However, it is unlikely to be linear, because of how the senders work (ie half a tank won't be half the full voltage) If you wanted to be really accurate, you would be best putting a multimeter at that point to read the voltage, and add a gallon at a time! Quote Link to comment Share on other sites More sharing options...
jagman Posted April 18, 2014 Share Posted April 18, 2014 Fuel gauges usually are not direct reading volt meters or ammeters , if they were , they would bounce around all the time that the fuel level moved . They employ heat : within the gauge is a bimetallic strip , this is coiled with a fine wire , the higher the fuel level the more current passes through the coil - this heats the bimetallic strip and it bends . The strip is connected to the pointer and the more it bends the higher the gauge reads . Heating and cooling of the strip takes time , so rapid changes in the current have a delayed effect and the gauge pointer remains stable. Because of this gauges tend to remain high at full / fuller readings and drop off faster at low readings ( relative) The current vs heating effect vs bimetallic strip makes exact calibration hard , again usually calibrated to zero , so you run out of fuel when empty in the tank. Some cars such as the soarer use a capacitive sensor , this uses the fuel as a dielectric in a capacitor circuit - these are very linear . How the internals of the dash 2 work - I don't know , probably a current sensing circuit internally damped , but I could be wrong Quote Link to comment Share on other sites More sharing options...
Pig Posted April 22, 2014 Author Share Posted April 22, 2014 Pretty sure that all you will see as the sender is resistance based, its the gauge that is powered. Been a while but I recall you have to use a pull up resistor I assume the stock ECU would normally hold the pull up resistor inside? I have spoken with Race Technologies who were really helpful and will look at installing a pull up resistor and going from there, that would explain why what I would expect to give an accurate reading (IMI's file) is not. Fuel gauges usually are not direct reading volt meters or ammeters , if they were , they would bounce around all the time that the fuel level moved . They employ heat : within the gauge is a bimetallic strip , this is coiled with a fine wire , the higher the fuel level the more current passes through the coil - this heats the bimetallic strip and it bends . The strip is connected to the pointer and the more it bends the higher the gauge reads . Heating and cooling of the strip takes time , so rapid changes in the current have a delayed effect and the gauge pointer remains stable. Because of this gauges tend to remain high at full / fuller readings and drop off faster at low readings ( relative) The current vs heating effect vs bimetallic strip makes exact calibration hard , again usually calibrated to zero , so you run out of fuel when empty in the tank. Some cars such as the soarer use a capacitive sensor , this uses the fuel as a dielectric in a capacitor circuit - these are very linear . How the internals of the dash 2 work - I don't know , probably a current sensing circuit internally damped , but I could be wrong Thanks Quote Link to comment Share on other sites More sharing options...
Pig Posted June 9, 2014 Author Share Posted June 9, 2014 Wont you also need to provide the pull-up resistor size? Yes you do. If anyone need the info in future, I used a 230ohm resistor and my figures for a UK spec were as follows: The stock fuel gauge showed as empty but I only managed to get 70l in so it had 10l from being totally empty. I have however, taken this figure as my 0 to allow me a little margin for error. Empty 4.3v 10l 4.08v 20l 3.84v 30 3.51v 40l 3.12v 50l 2.55v 60l 1.62v 70l full 0.63v Quote Link to comment Share on other sites More sharing options...
Wez Posted June 9, 2014 Share Posted June 9, 2014 Yes you do. If anyone need the info in future, I used a 230ohm resistor and my figures for a UK spec were as follows: The stock fuel gauge showed as empty but I only managed to get 70l in so it had 10l from being totally empty. I have however, taken this figure as my 0 to allow me a little margin for error. Empty 4.3v 10l 4.08v 20l 3.84v 30 3.51v 40l 3.12v 50l 2.55v 60l 1.62v 70l full 0.63v Now the big question, was the motor running or off Quote Link to comment Share on other sites More sharing options...
Pig Posted June 9, 2014 Author Share Posted June 9, 2014 On figured it would be silly to do it with it off unless I fancied cutting the engine to check the fuel level Quote Link to comment Share on other sites More sharing options...
Wez Posted June 9, 2014 Share Posted June 9, 2014 On figured it would be silly to do it with it off unless I fancied cutting the engine to check the fuel level Good man, not like me then Quote Link to comment Share on other sites More sharing options...
jagman Posted June 10, 2014 Share Posted June 10, 2014 Use Zener diode on the supply and it would make no difference engine on or off Quote Link to comment Share on other sites More sharing options...
Wez Posted June 10, 2014 Share Posted June 10, 2014 Use Zener diode on the supply and it would make no difference engine on or off Can you explain in more detail why, thanks The issue being the range of voltages available when the engine is on / off. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 10, 2014 Share Posted June 10, 2014 Because the voltage in a car's normal battery circuit is very different depending on whether the alternator is running or not. In the "old days" all instrument clusters had a crude voltage regulator on the back to run the instruments from a controlled voltage source. Then along came cheap Zener diodes... A Zener diode can function as a very accurate voltage regulator if its wattage rating is respected. Critical circuits run off the ECU have a very tightly controlled 5V or 12V source from the ecu itself. Quote Link to comment Share on other sites More sharing options...
Pig Posted June 10, 2014 Author Share Posted June 10, 2014 Because the voltage in a car's normal battery circuit is very different depending on whether the alternator is running or not. In the "old days" all instrument clusters had a crude voltage regulator on the back to run the instruments from a controlled voltage source. Then along came cheap Zener diodes... A Zener diode can function as a very accurate voltage regulator if its wattage rating is respected. Critical circuits run off the ECU have a very tightly controlled 5V or 12V source from the ecu itself. Would you be in agreement that it is worth fitting a Zener diode Chris? If so, is this as a direct replacement for the resistor? Quote Link to comment Share on other sites More sharing options...
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