Mopeka Tank Monitoring Modifications

I really like the Mopeka Propane Tank monitoring system. It’s really handy to have an idea of how much propane is left in each tank when we’re camping – especially on a trip where the temp dropped to 17 degrees.

One thing I noticed with the sensors at the tanks was that as the batteries got low, the whole system’s readings would be “off” – this lead me to take a tank for refill that was still half full, thinking it was empty.

The sensors use standard CR2032 batteries; which I seem to have a lot of thanks to various devices throughout our household. My issue wasn’t replacing the batteries, the issue was I wanted to be able to trust the system.

CR2032 batteries put out 3 volts; that’s pretty easy to replicate with some equipment. So with that, I setoff to eliminate the CR2032s from the sensors and hard-wire to the RV’s 12v DC system.

I used the following items:
Waterproof Quick Disconnects (#ad) (used 2 for this project)
Heat Shrink Splices and Ring Terminals (#ad) (had this for multiple projects)
22ga Wire (#ad) (had some already from other projects)
12v DC to 3v DC converter (#ad)
-Some 16ga “marine” wire (leftovers from other projects)
Blade Fuse Holder (#ad) (I keep a fairly good supply of these on hand for various projects)

I started off by opening the sensors much like you would do to replace the battery. On the lid to the sensor, I noticed that there was a void in the plastic sealed by a sticker. I used a razor blade to cut the sticker to the size of the void; I was expecting to have to drill a hole. This was a pleasant surprise.

There is a company that makes a CR2032 “dummy” battery with wires hanging off of it for about $15 (pack of 2). This seemed like a good solution, however I’m a bit cheap and decided to solder the wires directly to where the battery would rest. I also tied a knot in the wire I used before it passed through the opening so that it wouldn’t be the solder supporting the wire to the board. I then finished and sealed my work with a hot-glue gun. I use high-temp hot glue due to our ambient air temps out here; I don’t like risking the glue melting and running out.

When it came to running the wires to the tank location, I noticed that there were already some holes for various mounting of the propane tank holder. I enlarged one hole on each side with a stepper bit on my drill, just big enough to get the weatherproof connection through.

I then tied the step-down converter in a waterproof area to my 12v system and then used splices to connect the output of the converter to the 2 sensors.

When everything was done, I checked my gauges (both the physical gauge in the trailer and the smartphone app) and was happy to see that the tanks read their “true” value.

This modification may not be a money saver for most people, but I’m happy that I don’t have to worry about my tanks reading low just because of a low battery. My solar panels on my trailer will keep the 12v system happy, the draw from this 3v converter is minimal.

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