I’m trying to find a solution to the problem of the water pump in my motorhome occasionally running dry without me noticing. This always happens when the water tank is empty and the pump consequently draws in air. I’m planning to use a Comworks Supersense Laser/Wireless as the water-level sensor in the tank. This sensor can be displayed via the Cerbo/Touch70.
Is there a way for the Cerbo, MultiPlus or other external components to switch the pump off when this sensor reports that the tank is empty? And then switch it back on once the tank has been filled?
Perhaps someone has already looked into this and can offer some advice.
So how is the water pump activated, how long is it supposed to run, and, above all, why does it operate unnoticed?
Based on my experience with ship operations, I can only say that all electronic level sensors produce some kind of reading when the vessel is moving or heeling—just not the correct one.
The pump is activated by a switch that turns on the power supply. When water is drawn, it switches on; when the tap is closed, it switches off again. It is relatively quiet, humming slightly in the background and easy to miss if there is any other noise around you.
If the tap is closed when the last drop of water is drawn, the pump sucks in air and continues running.
The manufacturer offers an air shut-off switch, but unfortunately not for this model, as the connections are too small.
What the standard sensors in the motorhome measure will remain their secret forever; at least, it is certainly not the current water level.
The Supersense offers a little more convenience in that respect. With a 235-litre tank, I am happy for it to shut off when there are 1–5 litres remaining; that should work.
My camper has a main switch that, of course, is very easy to forget despite the reminder sign
Idiot-proof would be foot switches that you have to keep pressed down constantly
What do you think about limiting the runtime for each activation using an Eltako multifunction relay? We don’t have a shower, so the operating time is fairly short.
Relay 1 on the Cerbo has several predefined functions, including a tank pump. I’m not sure whether that could already be used for something and linked to the fill level.
Otherwise, it should be relatively easy to build something using Node-RED.
I had also thought about NodeRed; I’ll need to look into that. I’ll install and calibrate the Supersense first, and perhaps that will already point to a solution.
Looking into the Lilie pump in a little more depth has already produced a fairly clever solution too. Lilie recommends installing the water hoses with a diameter of 12 mm, but the pump itself only has 10 mm inlet and outlet connections. So the air shut-off switch comes back into play; I had ruled it out because it only has 10 mm connections. It is wired in series with the pump’s power supply: after pumping air for 30 seconds, it interrupts the circuit via its normally closed contact, switching the pump off. To switch it back on, you install an external emergency-on button @Karl-Heinz The lockout in the event of a leak is of course excellent too. Would that also be implemented via NodeRed?
No, a simple off-delay relay; if several additional functions are required, a PLC (Siemens LOGO!) as physical decoupling from the control system and as a safety chain.
The Victron relay could, however, control the switching on of the water function (thus allowing remote shutdown).
The pressure switch and safety timer relay act directly on the pump (the safety chain, so to speak); control is handled via the Cerbo.
Thus, it is clear that if the Cerbo freezes, the safety chain is not affected.
