## Another fuel gauge set up question

Red21
Posts: 11
Joined: Tue Sep 25, 2018 7:15 pm

### Another fuel gauge set up question

Hi all
A question about setting up the fuel gauge regarding out put voltages to a Dash 2 pro before I get to involved with something that may not be possible.
Without buying another 35 litres' of fuel and pouring 1L at a time, is there a way to extrapolate output voltage from the gauge sender using the 20-25L I have to hand i.e. a linear line from zero to 2.5v then the final 2.5 is self calculated.
Removal of the tank unit is not an option at present so any suggestions would be appreciated.

Rich

Red21
Posts: 11
Joined: Tue Sep 25, 2018 7:15 pm

### Re: Another fuel gauge set up question

Before sorting out my above question I need to find out why I am not getting a variation of voltage on the #5 input with a constant 5v regardless of empty or quarter filled?
The 2 wire level sender resistance ranges from 324 Ohms empty to approx 40 Ohms with 66 litres on board so I am using a 500 resister, with the ground wire to the vehicle body.
When this set up gave no variation I tried the ground to the dash ground (0v) as per basic set up & then used two 500 resister to give 1K resistance with change in the return voltage to 3.15??
On the original equipment system, the sender is directly supplied by a LCD display so is most likely to be designed to work with 5v & adding additional resisters may be affecting signal?
Is there anything regarding configuration set up I should double check that may be altering the way the dash is recognising fuel level voltage?

racetec
Posts: 224
Joined: Thu Oct 27, 2005 12:02 pm

### Re: Another fuel gauge set up question

Check out the wiring diagram for a 1 or 2 wire sensor here:

https://www.race-technology.com/wiki/in ... WireSensor

If you have additional resistors added in it WILL affect the values. If the float is connected to an existing gauge then you should be able to just tap in to the wire which is going to that gauge without adding on any extra resistors.

To confirm that the sensor is doing something sensible you could just start from an empty tank and look at the resistance change as you add fuel. Obviously depending on the exact configuration in the tank it is possible that it might not move right at the bottom or top end. You certainly can't extrapolate to get data from these things, they are often highly non-linear.

Martin

Red21
Posts: 11
Joined: Tue Sep 25, 2018 7:15 pm

### Re: Another fuel gauge set up question

I have tried the sensor combinations given in the knowledge pages, I have also filled the tank with all the fuel I had (30L) to hand and watched the sender resistance change when filling & again whilst draining.
I also know that the sender is working as the 52 mm stack gauge I've been using for the past few years and is getting replaced buy the Dash pro2 registers fuel in & out with no problems.
I understand adding extra resisters will affect voltage but I tried it to see what would happen & just in case the 500 resister was to low given the range of the sender, I haven't tried reducing the resister level yet because the chart in the knowlege page recommends a 500ohm for the given sender range, plus if I drop to far I will be using vital mA, two temps & two pressure sensors at the moment all RT supplied.

racetec
Posts: 224
Joined: Thu Oct 27, 2005 12:02 pm

### Re: Another fuel gauge set up question

If the system was working previously with whatever resistor was fitted then I would just stay with that and set up the DASH2 PRO for whatever voltages are provided by the system to the existing gauge.

Martin

Red21
Posts: 11
Joined: Tue Sep 25, 2018 7:15 pm

### Re: Another fuel gauge set up question

That would be no resister in the circuit then as the stack unit requires no resister in the external wiring & uses the vehicle body as an earth return, therefore just rely on the variable resistance of the tank unit which equals a 125mA draw at a full tank!!
Wiring wise that would be 5v down one wire to the sender & the second return directly to the signal input???

racetec
Posts: 224
Joined: Thu Oct 27, 2005 12:02 pm

### Re: Another fuel gauge set up question

That means that the Stack gauge has the resistor built in. If you are removing the Stack gauge you will need to add one externally. You will have to remove that before you do the calibration.
Disconnect Stack gauge
Do calibration.

Martin

Red21
Posts: 11
Joined: Tue Sep 25, 2018 7:15 pm

### Re: Another fuel gauge set up question

The stack unit was removed prior to installation of the dash so it has never been part of the problem.
Had another attempt at this over the weekend and after raiding an old & cheap transistor radio got a selection of resistors between 100 -150 ohms, I manged to get a voltage variation of 4v to 0.03v using the raided volume control to simulate the gauge unit.
I settle on a 120 resister as this appeared to give the best results during simulation with a max draw of 41.5mA & lowest of 8.4mA.
How ever, using this setup but now with actual gauge unit the voltage variation was only 0.32v for every 10L of fuel added.
Unfortunately I blew the fuse in the multimeter when I forgot to swap the leads from mA to volts position when re checking in & out volts so will have to continue fine tuning this weekend (I hope)
But to get a better resolution of voltage change to fluid level, is it correct to use a stablised 10v referance feed which will give a greater voltage variation & range??

racetec
Posts: 224
Joined: Thu Oct 27, 2005 12:02 pm

### Re: Another fuel gauge set up question

Yes it will give a better range with a higher voltage, but you will also be putting more power through both the sender unit in the tank and the resistor you are using.

Red21
Posts: 11
Joined: Tue Sep 25, 2018 7:15 pm

### Re: Another fuel gauge set up question

I persisted with the 5v setup & managed to get the fuel gauge to display what's in the tank with lot of trial & error when there is fuel in the tank.
The only bug is when the pump cannot pick up any fuel which I would class as empty (also my zero point for volt output) it still displays 4L but it could be the amount of fuel left which is impossible for the pump to pick up but is still float registered? If it helps any one else whilst doing the custom input, I placed the level sensor signal voltage in the input (X) column & the corresponding fuel level in litres in the output (Y) unlike the information given in the knowledge section pages.
Done a quick test tonight & wired an output from the analogue SPA boost gauge so that can be logged so hopefully just some minor tweaking & road testing left to do.