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Venus GX tank measurement

On my boat, I have a Venus GX, and I thought it would be nifty to use it to survey the tanks (1 fuel, 2 water) as well. There are already tank meters on the tanks, which are hooked up to a shared analog gauge. I have measured the fuel tank meter, which shows 180 ohm when the tank is full. However, there is a resistor of sorts on the gauge, which shows about 150 ohm, hence the combined resistance is 82 ohm. Consequently, when hooking up the VGX to this setup, it says that the tank is about 45% full.

The obvious fix would be to disconnect the analog gauge, but I would certainly prefer to keep it as well. Is there a way to resolve this?


Thanks,


Eirik

Venus GX - VGXtank monitor
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Did you connect both the analog gauge and the venus input to one sensor output?

Yes. I hooked the wires to Venus on to the wires from the sensor to the gauge. I wanted to keep the gauge.

I am also experiencing another strange phenomenon: the tank % is changing over time, without me using or touching it. As if the resistance has changed for some reason.

I sent an answer to the post that stated tech support said it is not possible to do correctly as the input to the GX supplies its own voltage.

That said, the input to the GX is probably seeing the voltage and resitance that is across the analog gauge as well. This will basically mess up the value of the voltage across the sender. Hence no go...

I guess there is a simple solution of using a switch to switch the sensor output back and forth between the GX input and the analog gauge. You won't be able to use both indicators at the same time though.

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jgrahamca answered ·

Hey Michael

I found a device that has what you are talking about and will work. Yacht Devices YDTA-01 will work in unison with a resistive sensor and an analog gauge (has a 12 point calibration) but converts it to a NMEA 2000 protocol standard which means that using the Venus GX may be out of the question. You may have to implement a NMEA bus system if you don't have one in place. I think I may be pursing that path.

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jgrahamca answered ·

On my boat, I have a Venus GX, and I thought it would be nifty to use it to survey the tanks (1 fuel, 2 water) as well. There are already tank meters on the tanks, which are hooked up to a shared analog gauge. I have measured the fuel tank meter, which shows 180 ohm when the tank is full. However, there is a resistor of sorts on the gauge, which shows about 150 ohm, hence the combined resistance is 82 ohm. Consequently, when hooking up the VGX to this setup, it says that the tank is about 45% full.

The obvious fix would be to disconnect the analog gauge, but I would certainly prefer to keep it as well. Is there a way to resolve this?

Hi Erik,

I emailed Victron tech support and they stated that it would not work. The tank level inputs are supplied with 5 volts and the analog gauge is supplied with 12V via a bridge circuit through the ignition switch.

I am trying to do exactly the same thing ie. keep my analog gauge and and use the Venus GX to monitor the tank level. The resistor on your analog gauge is basically a matching resistor so the analog gauge can be used for varying range resistor level sensors. ie 0-180ohm or my 240 to 30ohm sensor. (This is done by using a different resistor value)

I am sure there is something out on the market that can be purchased ie an analog to digital (AD) - digital to analog (DAC) combo unit. It is just a matter of finding something as who wants to go through the hassle of building your own circuit.

I know it is possible but it may be more of a hassle then its worth.

Jason



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Hi Jason, Thanks for your answers. I had not thought of measuring if there is a voltage over the wires. Will do next time, but that will be in two weeks, unfortunately. That being said, I get the same measurements when the main switch is turned off (the Venus is powered on a completely different circuit). Hmmm.

I will, however, consider a switch, as you propose in a different post.

Cheers,

Eirik

Strange for sure Eirik! Did you try taking the lead wire off the 'S' connector of your gauge and just go direct from your sensor into the tank input of the GX?

Later

J

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Michael Riley answered ·

I have the same issue - various two tanks that are not uniform in their profile. (#1) Bottom has largest volume with four 'steps' to full with the smallest volume. As with some 'heavy truck' fuel tanks the 'steps' are built in as the treads. (#2) a variation on the above really with a sloping side to cater for the hull changes. Still trying to figure that out.

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Eirik answered ·

As an afterthought, one way to address this, as well as the issue that tanks often have various shapes, i.e. taper towards the bottom, would be to have a third way of entering tank types, where one could input the resistance for various percentages of filling, I.e in my case, a full tank would be 82 ohm, empty would be 0, and have some points in betweeen, and the VGX could calculate the level based on this. Victron, anything for you to consider?

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Exactly: a multiple point 'calibration' profile where the number of points (say up to 10) would allow a profile to be built with linear (point to point) gradients to be configured. and include any 'offset' (i.e. the area below the sensor still has fuel and you cannot always get a fuel sensor that is exactly the right length on a custom tank.