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Mod #67: Holding Tank Monitor System

Posted By ModMyRV On January 12, 2009 @ 3:03 pm In featured, plumbing | 29 Comments

Why is it that the simplest solutions often go undiscovered? Take for example holding tank monitors. They are notoriously inaccurate and mostly useless at giving the discriminating RVer the comforting feeling of knowing just how much holding tank capacity or fresh water he has left. Now you might argue that most RV manufacturers try to control cost by using cheap parts, but a tank monitor is a no-brainer, something that for a few extra bucks can make most RVers in to happy campers.

Mod Difficulty:

So what makes these so called tank monitors so inaccurate? Most RVs come with a monitoring system that can be best described as “idiot lights”. You press a button on the monitor and a number of little lights come on indicating the levels of liquid in your tanks, 2 lights equals 1/3 full, 3 lights equals 2/3 full, 4 equals full. 1 light equals empty. Or does it? This is the frustrating part. As simple as these monitors are, they aren’t telling the full picture.

Most tank monitoring systems today consist of a bank of sensors mounted through the side of a holding tank at the Empty, 1/3, 2/3, and Full positions. Whenever the fluid inside the tank contacts these sensors a light will light up indicating just how full that tank is. These sensors are the same as used on fresh water, gray water, and black water holding tanks. The problem is that these they are susceptible to fouling. Various tricks range from dumping water softener or other chemicals into the tanks to dumping bags of crushed ice into the tank and then driving around to knock the crud off of the sensors.

Even when the sensors are clean, they still don’t give really accurate readings. If you have a gray water tank that is filled to around 60%, your monitor lights will indicate that it is only 1/3 full because the water level has not yet reached the 2/3 sensor. Conversely, your fresh water may be between 34% and 65% full and it will indicate 1/3 on your monitor display. As soon as you run a quart of water through the faucet, that light may read empty, even if you were at the 34% level. Or it will still read 1/3 if you were at a higher level. You just don’t know exactly what you have.

Fortunately there is a relatively simple solution. SeeLevel makes a variety of monitoring systems suitable for almost any RV, from tent trailer to luxury diesel pusher. These monitoring systems work completely different from the standard fare. Rather than using through-the-tank sensors, the SeeLevel sensors are mounted on a flexible “electronic strip” that adheres to the outside of the holding tank. They can never be fouled or contaminated as they never see the inside of the tank. Well it sees it but only though some magic radar system.

From the outside of the tank, the sensors determine the tanks level by the density difference of the liquid as measured between all the sensors on the strip. So it is highly accurate and virtually foolproof. And instead of LED lights, the monitor displays the tanks levels using a percentage, which is arguably easier to interpret than some fraction.

Installation is much easier than understanding how the sensors work. There are basically two ways to install the SeeLevel monitoring system. The first method is to use the existing tank sensor wires by relocating the wires from the old sensors to the new sensor strips, and then replacing the existing monitoring panel with the new SeeLevel display. The second method is to start from scratch and run new wires. If you opt for the second method, consider where you will mount the display and how you will route the new wiring.

The easiest way to do this mod is to reuse the existing sensor wiring. This is what most folks choose as it gets you quickly to holding tank level measuring capacity nirvana. Start by locating where you want to mount the display. Depending on where the existing level monitor is, you may be able to directly replace it. But some installations require some trimming to accommodate the SeeLevel display, as the display unit has to be recessed in to the hole to flush mount it. Follow the recommendations in the installation manual to determine the size hole required and cut to fit.

Remove the current monitor and detach wiring, paying careful attention to which wires came from where. Most wiring is color coded but you never know. You can mark them with a piece of masking tape wrapped around the wire with the location written on the tape. Keep the wiring hanging out of the hole and carefully cut the hole to the appropriate size. The SeeLevel comes with a pigtail connector that makes it very easy to connect the factory sensor wiring to the display. Connect the factory wiring to pigtail first following the wiring table in the directions. Then connect the pigtail to the display. Slip the display in to the hole and secure.

The next step is to mount the sensors and connect them to the factory level sensor wiring. Find a flat vertical area on the side of your holding tanks to fit the sensor strips. This could be a bit of a challenge depending on where your holding tanks are located. Motorhomes tend to provide the easiest access to the holding tanks as they are usually just behind a bay door next to the holding tank controls and valves. For travel trailers and fifth wheels, you may have to remove the sheeting covering your holding tanks to gain access. Some trailers have them, some don’t. Just an FYI.

Be sure the area you selected for the sensor strip on the side of the tank is large enough so the whole width of the sender is in contact with the side of the tank, all the way from the top to the bottom of the tank. Make sure that any metal is at least an inch away from the sender. Clean the area well so that there is no dust, grease, oil, water, etc., that would prevent the adhesive on the sender from sticking. Now here is the cool part. If the sensor strip is too long for the height of your tank, you can cut them. What? Yup. The strips are designed to be cut to length to a minimum height of 6″. The sender ends should be 1/4″ to 3/4″ away from the top and bottom of the tank, to allow for the thickness of the tank top and bottom and any bows in them.

Now peel the adhesive backing from the sensor strip, square up the strip with the top and bottom of the tank, and stick on. As with the display wiring, the sensor wiring is really easy. Simply disconnect the sensor wires from the factory sensors and connect them to the corresponding sensor strip wiring, following the instructions. Splicing connectors are provided in the kit to make the job simple. Repeat this for the other sensor strips. Now all that’s left is to calibrate the display and your done.

Einstein once said that things should be made a simple as possible but not any simpler. Knowing your tanks levels to the highest accuracy possible is now simple. Does that make you as smart as Einstein? You be the judge.

TipThere are many models of the SeeLevel monitoring system. Only the most basic model installation was described in this mod. Other models add battery voltage, indoor temperature, water pump switches, water heater pilot light indicators, etc., and various combinations of these features. And they are still just as simple to install.
TipYou can install more than one display unit using the same sensors. A convenient location is near the holding tank valves. If you have an enclosed water bay or a way to waterproof the display panel, adding a second display can help you know when your tanks are empty at the dump station without leaving the comfort of the sewer drain hole.

ModMyRV recommends these parts for this mod (may differ from what is described in the mod):
Tank Monitor System - Monitors up to four tanks from one convenient location

General Reference

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