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  1. #21
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    We've been boondocking for just a couple days until recently, so I was only filling the fresh tank (to what I thought was) 2/3 full anyway. This past week we were out for 4 days and I filled it until it overflowed, and the 'full' light never came on. I'll be interested to know if you find a broken wire, maybe mine is the same way.
    Chris, Tara, our two daughters, and our dog Slate full-timing
    2021 Imagine 2400BH
    2021 Chevrolet Tahoe

  2. #22
    Seasoned Camper more tired since retired's Avatar
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    If you think it's the sensors and you are not under warranty, check these out of Amazon


    Valterra T21301VP Horst Miracle Probe - Black Water Tanks, Pack of 4

    about $31 for the set
    2020 F-250 XLT SuperCrew 7.3L Blue Ox SwayPro, 2020 Imagine 2600RB,
    1600W Solar w/525AH LiFePO4, Victron 3000W, Road Armor w/wet bolt suspension, VisionWork Camera System, Peplink MAX BR1 Pro 5G Mobile Router,MicroAir EasyStart
    Amateur Radio Call N9XGZ FMCA#489460 Escapees SKP#166379

  3. #23
    Setting Up Camp
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    There are loads of complaints about tank level sensors in GD products, which now includes me. Our trailer is almost new, the black tank has been carefully flushed several times, and still the level never reads empty.

    As a retired electronic design engineer, I figured that I stood a shot at improving the tank sensor design. Yesterday was a rainy day so I used our down time to take down and study the level sensor electronics.

    Most conventional RV tank level sensors will use three or four probes mounted at different levels through the wall of the holding tank. When liquid rises so that it contacts a given probe, the associated electronics senses current flow through the probe and into the liquid. The displayed level is based on the highest probe that has current flow. As long as the liquid, and not gunk stuck to the side of the tank, is what conducts electricity, this system is pretty reliable because the amount of conducted electricity isn’t all that important. Either conduction to a given probe is low, meaning that the liquid level is below that probe, or it is high, meaning that the liquid level is above the probe.

    The conventional system requires three or four wires for each tank, one for each probe, and perhaps one for a common.

    This was not the case in my GD 29RS, which surprised and disappointed me. There is only one wire per tank connected to the level sensor display electronics (there must be a return as well, but this is likely shared among all tanks and may be ground or 12V) The display electronics appears to use the voltage level on the one wire from each tank as a measure of tank level.

    The implication of this is that the one probe in each tank is not a single point in the side of the tank but a long vertical shape from bottom to top of the tank. The idea would be that a higher liquid level causes more of the long probe to be in contact with the liquid, and the electrical conduction to go up. The display electronics then measures that conduction and interprets it to be a measure of tank level.

    A hybrid is also possible. A few discrete probes conventionally located in the side of the tank, but all connected together to a single wire that runs to the display panel would behave roughly similarly to one long probe.

    I have two problems with this. The biggest problem is that the exact amount of electricity conducted from the liquid to the probe depends on the contents of the liquid, especially the disolved salts. Clear clean water will have a relatively low conductivity, poop and urine is likely very high. I wouldn’t want to hang my hat on the expectation that the conductivity of everybody’s poop is the same, nor would I want to count on the amount of water flushed with pee or poop is the same. I don’t think this system stands a chance in heck of being accurate to my liking because the conductivity of the liquid can vary all over the spectrum.

    The second problem is that the one wire per tank design is analog while the three or four wires are pseudo digital. The analog approach is inherently more vulnerable to measurement errors because it relies on the amount of conduction to indicate level. The digital approach only needs to know whether a given probe is in liquid and therefore whether conduction to that probe is large or small.

    The reason for chosing a one wire per tank approach can only be to reduce cost. My trailer has four tanks and needs four wires plus a common wire. Conventional systems will need three or four wires per tank, so twelve to sixteen wires.

    This is admittedly conjecture based solely on the one wire per tank going to the display panel, and on a little reverse engineering of the display panel circuit board. I haven’t opened the belly of my trailer and looked at a tank and its sensor. However, I’ve seen enough to conclude that I will never be happy with the factory tank level sensors in my trailer. My next project when we get home will be to install a better tank level sensing system.

  4. #24
    Seasoned Camper mbergthold's Avatar
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    Quote Originally Posted by crollman View Post
    I haven’t opened the belly of my trailer and looked at a tank and its sensor. However, I’ve seen enough to conclude that I will never be happy with the factory tank level sensors in my trailer. My next project when we get home will be to install a better tank level sensing system.
    I've had that "never be happy with" realization too - a full bed advertised as a queen in a new Nash that led to an immediate trade-in, and now a growing list of items on our GD Imagine. Please post what you find when you open the belly up and what you install. I plan to reconfigure the dump system (remove the cable system and install a traditional gray to black to dump setup, with the 2nd gray dumping separately) and install toronado sprayers on all 3 tanks, so that'd be a good time to install a reliable sensor system too. Since you seem to be way more knowledgeable about electronics than I am, hopefully you can devise a way to still display the tank levels on the control panel.
    Mark and Judy
    USN/USAF family (parents and kids)
    2021 F350 Lariat Crew 4x4 SRW 7.3 Godzilla
    2021 Imagine 2500RL w/Hensley Arrow hitch

  5. #25
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    Quote Originally Posted by harryc View Post
    I just talked to my dealer and he said that all the trailers are only reading up to 2/3's. An absolutely ridiculous response. I told him about the possibility of a broken wire and he said they will look at it. Next available appointment is in June.
    Maybe time to get a new dealer with better service department. My gauges on the fresh water and forward grey tank seem to read correct but the aft grey tank only reads 3/4 full when water is backed up in the sink. Most annoying. I had the sensors replaced under warranty by a local RV repair shop that dealt directly with Grand Design Service. Fully covered but the new sensors made no difference.
    Bill & Marsha
    2020 Reflection 320 MKS
    2018 2500HD Silverado 4x4
    Not All Who Wander Are Lost

  6. #26
    Seasoned Camper
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    Quote Originally Posted by harryc View Post
    .... When I fill the FW tank to overflow it only displays 2/3...
    My gray water tank level displayed 1/2 until it reached 3/4 and above. GD technical support told me that it one of 2 things. Either the sensor has "stuff" on it, or the sensor/probe is bad. I tried the water softener and dish soap trick to try to "swish" or clean the sensor but to no avail. Brought into the dealer for warranty work. I was told about a 2 to 3-week backlog on service. This is OK with me, as our summer trips are about a month apart anyway. After about 2 weeks got a call from the dealer and was told that it was a bad probe. Covered under the warranty, but they are not sure the part will arrive in time for my trip. Not the dealer's fault, and thankfully not a major issue, but still a pain.

    I agree with other posts about all this technology and common failures on these sensors. I would gladly pay extra for quality, or give me an old fashion float gage.

    Mitch Frank
    22MLE
    Mitch and Alisa Frank
    2020 Imagine XLS 22 MLE
    2020 RAM 2500 Diesel

  7. #27
    Setting Up Camp
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    Ok. I know a little bit more.

    It looks like at some point some or many RV manufacturers switched to a one wire system. I don’t know whether this was invented by KIB or copied by them, but they seem to dominate the market.

    The KIB system connects the several tank probes together at the tank using what they call a ‘harness’. The term ‘harness’ in electronic products has usually applied to a bundle of wires neatly tied and routed together. In the KIB case it consists of four wires and a red blob. Three wires go to the tank probes and one wire goes on to the monitor display. The red blob contains a couple of resistors, one about 120k and another about 70k. The resistors isolate the probes from each other and limit the current that flows back to the monitor. The largest resistor goes to the 1/3 full probe and limits the current to a small value. The smaller resistor goes to the 2/3 full probe and limits the current to a larger value. And there is no resistor to limit the current fromthe full probe. As the liquid in the tank rises, and in a perfect world, the current to the monitor will step up from zero, to a first limited value, and then to a second limited value, and then to something high that is limited at the monitor.

    The problem I have with this is that it is especially vulnerable to leakage current flowing in contamination on the wall of the tank. The leakages at each of the three probes add. If it takes 30ua of leakage current to produce a false level reading, 10ua at each probe will be enough to cause a problem. In a comparable system using one wire per probe, the leakages don’t add, so 10ua at each probe wouldn’t be noticed.

    Furthermore, the 120k and 70k resistors in the red blob suggest that the impedance levels of the circuitry are too high. I found a study of diabetes done in 1906 that found a correlation between electrical resistance of urine and diabetes. That article talked of 45ohms of resistance measured in their apparatus as being normal for a person. The geometries aredifferent, but this is tiny compared to the 120000 and 70000 ohm resistors in the KIB harness. It doesn’t take much imagination to figure that a very thin layer of urine on the wall of a tank will have enough conductivity to muck up the KIB measurement scheme.

    I’ve seen enough. I’m going to install a SeeLevel system in my trailer. There is also a product called Tank Whisper that is worth a look, but doesn’t seem to be available. I’m not sure it is real.

  8. #28
    Seasoned Camper
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    Quote Originally Posted by crollman View Post
    I’m going to install a SeeLevel system in my trailer. .
    GREAT post and good information. I checked out a youtube or two on the SeeLevel system. Seems "simple" enough. If you do not mind, please post pics or video of the install. I think I may be doing this sooner rather than later.
    Mitch and Alisa Frank
    2020 Imagine XLS 22 MLE
    2020 RAM 2500 Diesel

  9. #29
    Seasoned Camper tjndsa's Avatar
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    I think we may have the same issue with our FW tank sensor but have had pretty good luck with the others. We do use the GEO method in our black and grey tanks. We have not had an issue getting our black tank to ready 'empty' after dumping/flushing it. With our two grey tanks, if we wait a bit after dumping them for the sensors to dry, we get a more accurate reading. Frequently, too, if we hold the sensor button down for several seconds, we can actually see the lights go out as it dries. Now, do we know for certain they are 'empty'? Not really but if no water is heard/seen dripping, etc., it's a good sign we're pretty close.

  10. #30
    Setting Up Camp
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    Quote Originally Posted by tjndsa View Post
    We do use the GEO method in our black and grey tanks.
    The GEO method also worked for us in our prior Rockwood. However a friend of mine tried it and found it made his gate valves sticky. Then I thought about it and realized that my gate valves had also gotten stiff after using it. On that trailer I replaced the gate valve rather easily because it was outside the belly. On the new trailer the gate valve is buried inside and hard to get at, so I'm not going that route.

    Our black tank sensor in the Rockwood sometimes behaved and sometimes not so much. I also noticed that letting the tanks dry helped, and that holding down the button for a while seemed to somehow improve the accuracy. In that trailer, I could look down the toilet and into the tank to see what was happening so I had an easy work around. When I look down the toilet in my new trailer I see an elbow, so that doesn't help so much. It's suddenly more important to me that I know the black tank level accurately.

    I'm getting old and cranky and no longer have patience for stuff that doesn't work right. I could get along ok using the oem sensors as lots of people do, but I just don't want the aggravation. The cost and effort of the SeeLevel is worth it to me....

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