Quote:
Originally Posted by
mathewst
voltage doesnt change.
resistence however yes.
Empty tank is 140 and Full tank 20 ohms. (greenwhite and black wires)
These are readings without bike started.
What is a problem though, when I start the bike, theres some potential messing things up and I cant read resistance well anymore. (even polarity of the multimeter changes reading) I dont get this. I should maybe try with cables directly at the tank.
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Are you using the old feed from the dash, or have you using a fresh 12V supply to the tank sender and for the testing?
One thing you can do to help get a broader range of voltages produced by the potentiometer (sender) and make them easier to detect is to wire in a second resistor in series with the pot, but connect the gauge (voltmeter) between the new resistor and the pot to take your readings. An additional 100ohm resistor should give you 2V when the pot is giving 20ohms and 7V when its giving 140ohms.
Here's the circuit:
You can experiment with different resistors to get the voltage readings you want/need. All you need to know is the formula:
V(in) = V(out)x(R2/R1+R2) [where R2 is the pot and R1 is the series resistor]
This setup is known as a voltage divider network. Haven't got time to explain it now, but
this site explains the theory in simple terms.