ok - what am i doing wrong? (fuel sender/gauge q)

the shape of the tank is far from a linear shape.  If you built your own tank, or had a round fuel cell, then it would be a lot closer.

 

I have not done any more work on this yet as my tank is still too full.  i tried to pull out my sender (removed one screw/bolt) and gas started shooting out - it's still that full.

 

i need to drive it more so i can then pull the sender out and fine tune it via the instruction in the link above.

 

stay tuned.

so i have been driving my car enough to be able to pull the sender out without it leaking gas everywhere.

 

...

 

my gauge range is 0.3 ohms to 26 ohms (full)

my sender range is 2.3 ohms to 55 ohms (full)

 

i did bend the fuel sender arm 180 degrees (snapping it off!), but after rinsing the sender and arm in water, i then re-welded it back on so that empty reads empty and full reads twice as full as the gauge will allow.

 

this brings me to my question - how do i reduce the resistance of the sender by 1/2?

 

i looked this up - thinking the answer would be fairly straight forward, but.... all i found was the stuff i slept through in Math 12: http://en.wikipedia.org/wiki/Resistor

 

can i use my Potentiometer? if so, how do i wire it up?

 

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and while i am at it (on a side note) - does anyone know about zener diodes?

http://www.autosportlabs.org/viewtopic.php?t=3752

Diode lets current flow in one direction only, zener will allow current flow in both directions if the voltage exceeds its rating. A zener rated at 5 volts will shunt excess off. An overall application for their use is prevalent in power supplies where you need a clean reference voltage.Anyway my 2 cents.

Mango, I opted out of the entire dashboard spread, instead going for three gauges visible from inside and one outside the driver's compartment. For the fuel gauge, I went with a Jeg's catalogue AutoMeter gauge and sender, about 2.25-in. across, with a black face and white lettering. The needle's orange, from the Pro-Comp series. I highly recommend them.

 

If you're sticking with what you have, you might consider adding a little more ass to the stick. If you use a metal with more resistance, a 'heavier' load, as it were, you might be able to bracket what the face reads as normal, and come out with a workable solution which won't require additional components.

 

Short of that, a wooden dowel in the car is a patent Drake answer. I did that for nearly two years.

Thanks for the ideas guys.  i have resorted to using the stick until this is all sorted.

 

i want to keep my 356-style gauge.

 

 

this looks pretty close to what i want to do:

http://www.hotrodders.com/foru...n-30-ohm-106069.html

 

and FYI - these gauges seem to match 0-30 Ohms (GM Type '64 and earlier) senders

0-30 empty-full on your gauge means it's for pre-'65 GM vehicle. I'm guessing you won't find a pre-'65 GM sender that will fit without modifying the tank, but I could be wrong.

 

To get the sender to hit 26 ohms when full, you'd need to set your potentiometer to 50 ohms. Then connect one terminal of the pot to the same terminal that the fuel sender is connected to on the back of the gauge, connect the other pot terminal to ground. You'll get skewed readings in-between but empty and full will be correct.

In general a diode is used as sort of a one-way switch. Basically, current will only really start flowing through it once the forward voltage across it has reached a certain point, e.g, 0.7 volts is common, but they can range from 0.2-4 volts. Above that voltage, the diode has very little resistance and current flows freely. If you apply that same voltage in the opposite direction across the diode, very little current leaks through, hence the one-way switch function. However, if you apply a high enough reverse voltage to it, the diode enters breakdown and once again current starts to flow through it, but obviously in the opposite direction. But this high reverse current will damage the diode.

 

A zener diode is designed so the reverse region is its primary operating zone. The reason they are used is because the transition from no current to full current is much sharper in reverse in a zener diode than the transition in the forward direction and the breakdown voltage (the turn on point) can be set very precisely (within 0.05%) and over a wide range (1.2V to 200V is common). They work very well as precision voltage regulators and surge protectors.

 

Think of a zener diode as just a more precise version of a regular diode that simply needs to be wired backwards.

Justin, I can't tell you how refreshing it is to see some no-sh*t, for real applied science on the SOC again.

 

Thanks -- and thanks for being right, not parroting someone else's 'wisdom.'

Also keep in mind that though they are similar, they aren't always a straight swap. The differences can be important depending on your actual application.

Be mindful of the wave modulation....I'm just saying.