Fuel Tank Sending Unit - Experiment

[AustrianVespaGuy]

20 minutes ago, Healey3000 said:

The only issue that I can think of is that the gauge resistor value is rather low, so a lot of current will have to flow through the digipot.

I like your plan, but agree this is going to be the tricky part.  Don't digipots usually only like to see a few miliamps or so?  My best guess is that the gauge circuit probably draws about 200mA (12V/60ohms).  But why not just use a cermet pot instead? Easy to get those in 1 or 2W flavors, and yeah you need to do the trimming manually, but once you're done you shouldn't ever need to touch it again unless you change either the sender or the gauge.  Not quite as slick, but I think it'd be a much more straightforward route.  Just my 02 cents.

 

Here, something like this I think would be just about perfect:

https://www.jameco.com/z/55PR100-RJ11CP101--BI-Technologies-1-1-4-Inch-Rectangular-Cermet-Potentiometer-100-Ohms-1-Watt-10-22-Turns-Thru-Hole-Side-Adjust_2201121.html

Edited April 26, 2019 by AustrianVespaGuy
Added link

[Healey3000]

You're right that a rheostat at the gauge may do the trick.  I was thinking along the lines of having a solution that would be user-friendly for those who are not inclined to solder, etc.

 

This way, there's no guessing as to resistor values...

[AustrianVespaGuy]

Shoot, here's probably the easiest way to do it - put a pot either in-line or in parallel with the sender, then no need to pull anything other then the sender wires! Doesn't really matter whether we tweak the voltage divider at the sender or gauge end, as long as they both match up in the end. So:

 

If gauge generally reads too much fuel, pot goes in series in order to add more resistance and thus lower the needle (adjustable with pot).

 

If gauge generally reads too little fuel (like mine did), pot goes in parallel with sender wires in order to lower resistance and raise the needle (also adjustable).

 

One part, connect to too easily accessible wires, and bam, all done, just fine tune it with the adjustment screw!

 

@OP and future readers, suggest you give this trick a try and see how it works for you, kinda too easy not to!

Edited April 26, 2019 by AustrianVespaGuy

[Healey3000]

Yup, great idea!