For the serious overlanding enthusiast, knowing the water level of tanks on your camper is crucial: learn how to monitor your tanks.
Venus OS by Victron allows you to monitor water levels, or general liquids, in a simple and quick manner. This tutorial applies to Cerbo GX but also to Raspberry connected to Tank GX 140. Glen has four tanks, each with its own sensor connected to Tank GX 140 on Raspberry 3B+:
- Clear water main tank (original) 90L
- Additional clear water tank 47L
- Waste water tank 70L
- Thetford C200 toilet cistern 17L
Let’s take a closer look at how to monitor each tank with different sensors and set up Venus OS.
Monitor your tanks: How to
Main clear water and waste water
The sensor used is a Liquid Level Sensor Type Throw-in DC24V with 4-20mA output (TL-231).
This sensor is based on the principle that a liquid contained in a container exerts pressure proportional to its height, which determines its level.
The connection is straightforward: once a hole has been drilled in the top of the tank (the sensor is 28mm wide), the sensor is inserted and sealed with a waterproof connector, the cables are then brought into the compartment where the Tank GX 140 is installed. Power will be provided by the Tank GX 140. The connection cables are two:
- Negative: connected to ground
- Positive: sends the level signal from the sensor
Addtional clear water
The sensor used is a resistive level sensor with float from 0-190 ohms, with the sensing rod height corresponding to the 47L tank (approximately 25cm).
The sensor has an element with a variable resistance that changes its resistance based on the liquid level.
I have paired this sensor with an analog level indicator placed next to the tank itself. The power is supplied by Glen’s battery pack. The connection, as in the previous case, is straightforward: a hole is drilled into the top of the tank and the sensor is inserted and secured with screws. Connection cables are three:
- Negative: connected to ground
- Positive: connected to 12V power supply
- Signal: connected to the level monitor and Tank GX 140
Black water
The Thetford C200 toilet cassette uses a binary magnetic sensor to indicate when it’s full. One part of the sensor is fixed in the cabinet compartment, while another is installed on the float inside.
The magnetic sensor sends a negative signal (-) when the float inside the cassette reaches the full level, closing the circuit and activating the LED signaling light inside the bathroom.
To make use of this system, I used a 4-pole relay
Here are the connections:
| PIN | CONNECTION |
|---|---|
| 30 | 12V signal |
| 87 | Signal for the sensor, 12V from Tank GX 140 connection. |
| 85 | Positive power signal, 12V. |
| 86 | Negative signal from the magnetic sensor. |
Monitor your tanks: Tank GX 140
The GX Tank 140 unit is self-powered through its USB interface and does not require an external power source. It has four channels, channels 1 and 2 are externally powered, while channels 3 and 4 are internally powered at 24VCC. The connector labeled “Ext. Power” can be used to distribute power from an external source to the sensors connected on channels 1 and 2.
I have connected a grounding cable (GND) to the external power connector in order to provide power to channels 1 and 2.
| TYPE | CHANNEL | VOUT | IN | GND |
|---|---|---|---|---|
| clear 1 | 1 | – | positive | Ext. Power |
| black | 2 | – | PIN 86 | Ext. Power |
| clear 2 | 3 | – | signal | ground |
| waste | 4 | – | positive | ground |
Once the connections have been made, the sensors must be configured through the Venus OS interface:
| TYPE | SENSOR | MIN | MAX | CAPACITY |
|---|---|---|---|---|
| clear 1 | current | 0.4025 | 0.500 | 90 |
| clear 2 | voltage | 0 | 0.870 | 47 |
| waste | current | 0.4026 | 0.700 | 70 |
| black | voltage | 0 | 10 | 17 |
For the “maximum” values, some testing is required: fill the tank to its maximum capacity and check the sensor value through the graphical interface, then enter it into the corresponding configuration parameter.
Monitor your tanks: Final thoughts
In summary, having control over the state of your water tank on a camper is of utmost importance, whether you’re parked in a free campsite or at an established campsite.
Victron’s Venus OS system enables a unified central control point for immediate visualisation of the entire camper’s status, as well as setting up alarms based on critical conditions that require manual intervention, such as emptying the blackwater and greywater tanks.
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