Fuel Gauge converted to Volt Meter

[BobK]

Hey, I do my best work when I am asleep!

Bob

 

[Arouse1973]

Below is from the people who make my cluster (Acewell model number 2853). NOTE: as mentioned, I do NOT have a sensor/sender in my tank. The lack of sensor in tank is why I'm looking to re-purpose that part of my gauge cluster. The motorcycle is 12V.

The Acewell meters that include a fuel gauge have LED 7 bars. The output of the sender determines how many bars are displayed, as follows:

Fuel Gauge display
Bars displayed..... Sener Resistance (ohms)
7..... 0-10Ω
6..... 11-20Ω
5..... 21-35Ω
4..... 36-45Ω
3..... 46-60Ω
2..... 61-75Ω
1..... 76-90Ω
1 flashing..... 91-100Ω

Ok good. The cluster manufacture must know how to convert this in their equipment. So they must have a resistor inside that convert the current going through the sensor resistances to a voltage that they can measure. Are you able to reproduce these resistance with a POT and measure the voltage produced for each step? Even if they are measuring the current they will need to do this with a resistor.
Adam

 

[Arouse1973]

Hey, I do my best work when I am asleep!

Bob

Me too, my misses says I run the marathon some nights in bed, you wouldn't think so looking at me
Adam

 

[Arouse1973]

Below is from the people who make my cluster (Acewell model number 2853). NOTE: as mentioned, I do NOT have a sensor/sender in my tank. The lack of sensor in tank is why I'm looking to re-purpose that part of my gauge cluster. The motorcycle is 12V.

The Acewell meters that include a fuel gauge have LED 7 bars. The output of the sender determines how many bars are displayed, as follows:

Fuel Gauge display
Bars displayed..... Sener Resistance (ohms)
7..... 0-10Ω
6..... 11-20Ω
5..... 21-35Ω
4..... 36-45Ω
3..... 46-60Ω
2..... 61-75Ω
1..... 76-90Ω
1 flashing..... 91-100Ω

This is what I mean, the bottom resistors are fixed and represent the input resistance of the cluster, but there will be only one in the real unit. I have shown it like this so we can see the difference between them. I just chose 100R of the top of my head it will most likely be different. For the top resistors, I have gone in the middle of the ranges of the fuel gage sensor's output.
Adam

 

[Arouse1973]

Thinking about it now. To maintain accurate readings with battery level variations they probably have a constant current output from the cluster. does the cluster have it's own dedicated power wire for a sender unit?
Adam

 

[sabre170]

Thinking about it now. To maintain accurate readings with battery level variations they probably have a constant current output from the cluster. does the cluster have it's own dedicated power wire for a sender unit?
Adam

Nope.....there is only one wire that connects the cluster to the sender unit. The Cluster could be called a "passive" gauge in that it only receives a signal. No signal or power is sent TO the sender FROM the cluster. The sender unit rather is directly wired into bike power. I"m guessing it is standard to have a 12V +/- 2 volt tolerance.

 

[Arouse1973]

Ok so it might have internal supply. Connect say 50R to the sensor input and 0V.Measure the voltage then do the same with the resistor connected to 12V, then repeat with half the value of resistance, this will tell you if its a current source . We need to quantify the voltages that make the unit read the different value. This way we can fool it into thinking it has a sender attached.
Adam

 

[sabre170]

Here is what I am thinking would do the trick. The arrows represent some voltage triggered device....not sure what would work in my case though. If the voltage is less than the number by the arrow, the "device" would be closed. When the voltage is equal to or greater than the labeled voltage, the device would open. In doing so, if I have 13.5V, my cluster would only "see" the 5ohm resister (full tank). If I was at 11.1 V, it would see 40ohms (half tank). And if seeing 9.75V, it would "see" 100ohms (empty).

Is my theory flawed? If not, what "device" would work best in the case of the arrow....CMOS? MOSFET?

 

[Arouse1973]

Cant see how that will work. Your input is what is changing its not constant. Also your resistors are shorted.
Adam

 

[BobK]

I think you should determine how the meter responds to a voltage. I assume that if you put 12V on it, you will get full. What happens at lower voltages, with no resistor.

Bob