fuel sender

rabra
Posts: 11
Joined: Sat Mar 29, 2008 12:26 am

fuel sender

Postby rabra » Mon Sep 15, 2008 7:58 pm

hi i have a fuel sender that reads 71 omhms when empty and 1 when full, how can i generate an equation to get the dash11 to read 100 % when full and 0 % when empty? can this be done?


regards

GMS Racing
Posts: 82
Joined: Wed Nov 29, 2006 10:36 pm
Location: South Africa
Contact:

Postby GMS Racing » Tue Sep 16, 2008 11:43 am

Rabra,

Start by reading this post.

http://www.race-technology.com/forum/vi ... light=fuel

If you only have the Dash2 then you will have to find a reference voltage as the battery/alternator voltage is to variable for this purpose. You can buy a +5v reference source from R-T or from any good electronics shop.

Once you have connected the divider circuit then what I did is to completely empty the fuel tank, take a voltage reading, then add 1 litre and take reading, all the way to a full tank. Now go to "Dash2 Configuration Tool" software and click on the "Generate an equation from a table" button and enter the values obtained. Use Input X for the voltage and Input Y for the litre value.
Regards,

Gary...
Johannesburg
South Africa

rabra
Posts: 11
Joined: Sat Mar 29, 2008 12:26 am

Postby rabra » Tue Sep 16, 2008 1:09 pm

i have a dl1 aswell, i can get a 5v ref from there,where does this 5v's need to go to ?

thanks

rabra
Posts: 11
Joined: Sat Mar 29, 2008 12:26 am

Postby rabra » Tue Sep 16, 2008 1:14 pm

i only have a one wire sender?

faraday
Posts: 267
Joined: Sun Feb 25, 2007 1:18 am

Postby faraday » Tue Sep 16, 2008 2:38 pm

I assume you measured your resistances between that wire and the car chassis, i.e. ground. If the sender was not installed and the measurements were between this "output" wire and some part of the sender, that part must be grounded when the thing's in the tank.

In any case, you didn't measure a resistance with a single probe... so your sender is a two-wire thing in reality. You make it a three-wire thing with an additional resistor. Join a resistor and the "third" wire to the sender "output" wire

The reference voltage needs to be applied to the other end of the added (fixed value) resitor. The logger or dash "input" wire is connected to the sender side of this resistor, with your third wire.
If the resistor has a value of 71 Ohms, the voltage sensed by the logger (or dash) should be 2.5V when the tank is empty and 0.07V when it's full.

The added fixed resistor will divide the 5V in combination with your sender. The voltage is divided equally when the fixed resistance and the variable sender resistance are equal.

Does this make sense to you?

GMS Racing
Posts: 82
Joined: Wed Nov 29, 2006 10:36 pm
Location: South Africa
Contact:

Postby GMS Racing » Tue Sep 16, 2008 3:48 pm

Here are two wiring diagrams. The top one assumes a 2-wire fuel sender and the bottom one a 1-wire sender (the second wire is chassis). I used a 15 ohm resitor as my sender has a 15 ohm maximum resistance. You might try a 71 ohm resistor. I used a 5 watt rated resistor to be safe.

Image

I would still "map" the output voltage the way that I suggested as my sender unit was definitely not linear.
Regards,

Gary...
Johannesburg
South Africa


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