waiter Posted May 5, 2011 Share Posted May 5, 2011 There are several different types of level sensors used by the many RV manufactures, but my Dolphin uses a sensor called a "Capacitive Level Sensor". Basically, it uses two large metal plates on the outside of the tank. The capacitance between these plates changes as the fluid level changes. The level can then be calculated (electronically) by measuring the capacitance of the plates. OK - Enough of how it works. The "Plates" are made up of two large Aluminum foil sheets, and a wire is soldered to each of these sheets. In my case , the foil plates on the black water tank had deteriorated and were falling apart, and would not read on the monitor inside. Note how the wires are soldered to the foil sheets, also note the positioning of the old sheets. Measure the approximate size of the foil plates, mine are approximately 8x8 inches. Remove the old foil from the tank and clean the surface of the tank. it needs to be very clean so the new foil will stick to it. The foil I used is a self adhesive copper foil that's used for stained glass. It costs about $7 a sheet (12x12 sheet) and you need two sheets per tank. Google "copper foil sheet adhesive backed" to find suppliers (Your neighborhood arts and crafts store may carry it) Measure and cut the new sheets to size. (mine are 8x8 inches) NOTE - When I installed my high power inverter, I installed dedicated outlets that are powered by the inverter. I added one in the frig compartment just for these type of occasions, so I could have AC power outside without running extension cords. I plugged my soldering gun into this outlet and turned on the inverter to do this repair. Solder the wire onto each of the two new foil sheets (do this before you stick the foil on the tank, otherwise you'll melt the tank. Remove about 1/3 of the backing from the top and carefully stick the foil to the tank in the same position as the original foil was (not super critical). pull the rest of the backing off and press the foil onto the tank. go around the foil and press it firmly against the tank. I mixed up a small batch of quick set JB weld and put a dab on the wire tie things, then stick them to the foil to secure the wire bundles. Make sure the tank is full, then on the inside Tank Monitor panel, press and hold the Black tank button. Adjust the little screw (just to the left of the button) so the "Full" level just comes on. These adjustment screws are fragile so don't put to much pressure on them. When finished, paint some Rustolium on the foil to help protect it from the environment. John Mc 88 Dolphin 4 Auto Quote Link to comment Share on other sites More sharing options...
Dolphinite no longer here Posted May 5, 2011 Share Posted May 5, 2011 John, Nice work! Looks simple enough that even I might try it. John Quote Link to comment Share on other sites More sharing options...
troyrobo Posted May 5, 2011 Share Posted May 5, 2011 great job Quote Link to comment Share on other sites More sharing options...
Nam Posted May 19, 2011 Share Posted May 19, 2011 Great job there John. My Winnebago's gray water tank sensor is acting up also but I think the Winnebago uses different method...like putting several conductors at different water levels and measure conductivity in between...has anyone experienced this kind of sensor? Quote Link to comment Share on other sites More sharing options...
Gulfstream Greg Posted May 24, 2011 Share Posted May 24, 2011 Great info, thanks! Quote Link to comment Share on other sites More sharing options...
waiter Posted July 9, 2011 Author Share Posted July 9, 2011 FOLLOWUP REPORT My Black tank level quit working about 3/4 way through the Alaska trip. When I looked under the coach, I could see a wire hanging down, and concluded that the wire broke off. Today I finally climbed under the coach to fix it, and found that the copper sheets were in bad shape. This is most likely from the 1400 miles of gravel roads that beat the crap out of the them. I installed mud flaps to protect the tank drains, but I can see how gravel can kick up and hit the black tank sensors directly. I have some thin Aluminum sheet (.025) in the shop. I think I'm going to cut the sheet to size and then use contact adhesive to glue it to the tank. If I get time this weekend I'll try it. JOhn Mc 88 Dolphin 4 Auto Quote Link to comment Share on other sites More sharing options...
Lee & Joan Posted July 13, 2011 Share Posted July 13, 2011 Great Info John, Appreciate your explanation, photos, and I like knowing the "how it works" part also I had wondered how some piece of film thick metal on the outside could measure anything Variable Capacitor makes sense. Be happy the gravel did not eat off your blackwater valve... Quote Link to comment Share on other sites More sharing options...
waiter Posted July 13, 2011 Author Share Posted July 13, 2011 Be happy the gravel did not eat off your blackwater valve... That was the specific reason I installed mud flaps before the trip, to protect the black and gray tanks and plumbing. 1500 miles of gravel roads is like giant sandpaper eating away at stuff. John Mc 88 Dolphin 4 Auto Quote Link to comment Share on other sites More sharing options...
Plenfert Posted June 20, 2014 Share Posted June 20, 2014 I followed your great instructions, but I'm having an electrical problem. When I installed new copper with wire soldered, connected wires and then filled the fresh water tank full of water, the sensor panel would not adjust beyond 1/2 full. And when drained the tank down to 1/4, then to empty, the sensor did not move from 1/2. Any ideas what I did wrong? Is there anything electrical that I need to watch for or is unusual with this type of electrical current? Quote Link to comment Share on other sites More sharing options...
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