Repair Black Holding Tank Level Sensor

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 8×8 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 (12×12 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 8×8 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