Water Tank Sensor Replacement

[Gato Gordo]

Just finished the complete level sensors last year. Contact me at jefferyalancarr@gmail.com to chat.

[ALDEBR]

My Hylas 46 #66 (Solstice) has no tank monitors.  Would love to add these to the 2 diesel and 3 water tanks.  But I need some advice about how to proceed. Will holes have to be drilled? How does one install the KUS-WEMA sensors?

[Groggo]

Hey Joel,
Yeah, access is not the issue.  The sensor comes right off (it broke off its threaded neck).  The problem is the hardened plastic that used to be the thread on the sensor is really stuck on the threads in the sensor mounting hole.  I think I'll need a heat gun to try to soften the plastic up to that I can peel it or pull it off the threads.  I'll have to rig some kind of "umbrella" catchment that I can put in the hole and then open against the bottom of the sensor attachment thread to catch the crap that may come off in pieces.

[joel]

If you remove the inspection port can you reach the sensor?  add painter's tape around the shaft, sticky side up, or maybe put a hole in a plastic cup to slide over the shaft and hold it in place while you unscrew the remains?

On a related note, I ordered KUS NMEA 2000 sensors for my water and fuel.  My B&G plotter only recognizes fuel tanks, so I have one page with the fuel tank and another with the water tanks.

[Groggo]

Back to the original question, the photo is misleading.  The original sensor was also plastic, but deteriorated so badly that it first looked like corroded metal.  Now the trick is to remove the now very hardened plastic ring from the threads on the tank, hopefully without dropping a bunch of crap into the tank.  Any ideas about removing the thread ring from the tank?

[SV True North]

To add an additional 4 tanks, you need to purchase a Victron GX Tank 140 as well.  It adds an additional 4 tanks but the measurement is either voltage or current instead of resistance as used by the cerbo inputs.  It is not difficult to convert the resistive signal from the tank senders to a voltage level for the Tank 140 with a simple voltage divider circuit by adding a specific value resistor to the wiring.

The formula to calculate the resistor value to use is Vout = Vin * (  Rtanksensor / (Rtanksender + Rpullup ))

For example the Tank 140 provides 24V on inputs 3 and 4
My tank sender measures 34 ohms when full and 240 ohms when empty
I used a 1200 ohm resistor to provide the additional resistance to bring the output voltage to be within the 0 to 5 volt range that the Tank 140 expects.

The formula above with an empty tank gives the following Vout = 24 * ( 34 / ( 34 + 1200)) which gives a Vout of 0.66 volts.
With a full tank Vout = 24 * (240 / (240 + 1200)) which gives a Vout of 4.0 volts.

This means the Tank 140 will see voltages from 0.66 to 4.0 from empty to full.  You tell the Cerbo GX the range to expect for each tank in the configuration of the tank input.

The last gotcha is that the Tank 140 does not provide power to its inputs 1 and 2.  I provided 12V using a $7 dc-dc power regulator used to power an arduino single board computer.  I had to recalculate the resistor to use on those inputs since the supply voltage was 12V instead of 24V as provided by inputs 3 and 4.

The connection to each of the Tank 140 inputs looks like

Vin

[Kevin and Gail]

Hi John,
New owner of #43 here. I've ordered the KUS sensors for fuel and water tanks along with the 7 tank analog guage. You mentioned being able to view levels digitally using the cerb gx, which would be preferable to me. In the victron gx description,  it seemed that only 4 tanks were viewable. Could you elaborate please. #43 has nmea 2000 capability so if possible,  I would rather purchase the cerb gx, connect to the backbone and cancel my analog guage order.
Thanks,
Kevin

[SV True North]

The analog gauges when turned on and a tank is selected, send a voltage over the sensor wires which mess up the reading on the Maretron.  I just disconnected the analog gauges since the tank levels are displayed on the cerbo screen along with all my electrical parameters, temperature and bilge warnings.

John

[Groggo]

That's interesting, and would explain why the corrosion.  I think the original sensor was metal also, and corroded out (though QL says they've never seen this before).  These are 91 gallon water tanks (2), and I am tempted to pull the sensor out of the other one to see if it is metal and if there is corrosion.  They sit just under the sole, so the offered explanation of (1) being immersed in salt water doesn't make sense, and (2) bimetallic corrosion from stray electrons which they say they've never seen before.  I will check the tank grounding, but it's clearly grounded.

Being able to read the tanks while filling them would be nice.  Mine are on a Maretron on the NMEA 2000, and also on a standard selectable analog.  Interestingly, they interfere.  If you choose a tank on the analog, the Maretron always shows THAT tank as completely full.

[SV True North]

I have had the sensors out of all my water and fuel tanks.  All are similar to your new plastic one but mine are all metal.  These are on the tanks of my 2006 Hylas 54 with a tank manufacture date of 2006.  I have reconnected the 8 tanks to my Victron Cerbo GX so their levels are available over NMEA 2000 to my plotter, phone and tablets.  This is much more convenient than having to go below to check levels and allows me to monitor the level at the fill pipe while filling up.

[Groggo]

Hello All,

Had a water tank sensor come loose (QL says they've never seen or heard of such a failure, blaming galvanic metal corrosion).  It appears that either QL or the tank manufacturer placed the sensor with some kind of sealant, but I can't tell how it was actually affixed to the tank.  As you can see, there appears to be some kind of corrosion or breakdown at the sensor/tank joint.  The new sensor is plastic and appears to simply screw in.  Anyone have any experience with this??