How to Use Victron Relays to Control Cooling Fans in an RV Solar System
- Big Beard Battery Team
- Apr 14
- 4 min read
Heat buildup is a common issue in RV electrical bays, especially when your inverter, solar charge controller, and other power components are working hard during the hottest parts of the day.
The good news is that if you are using Victron equipment, there are built-in ways to control cooling fans automatically. At Big Beard Battery, we help RV owners every day with smarter off-grid power setups, and this is one of those small upgrades that can make a big difference in performance and peace of mind.
If you are building or upgrading an RV solar system in Texas or anywhere across the country, here is what you need to know.
Why Cooling Matters in an RV Solar System
Your RV solar components generate heat during normal operation. Inverters can get warm while inverting or charging. Solar charge controllers heat up when solar input is coming in strong. If your system is installed in a tight compartment with limited airflow, temperatures can climb fast.
That is why adding cooling fans can be such a smart move. Better airflow can help manage heat around your inverter, charge controller, or battery compartment and keep your system operating more efficiently.
Victron Gives You Relay Options
Depending on your setup, you may be able to use relay outputs on:
a Victron solar charge controller
a Victron inverter
a Cerbo GX or other GX device
These relays let you create simple automation inside your RV solar system. When a certain condition is met, the relay closes and activates a fan through an external relay.
What NO, C, and NC Mean
NO means normally open.That means the switch stays open until a condition is met.
C means common.This is the shared terminal used in the relay connection.
NC means normally closed.That means the switch is closed by default until the condition changes.
In most fan-control applications, the setup uses NO and C. That way, the fan stays off until your chosen condition tells it to turn on.
Why You Need an External Relay
This part is important. You do not want to run fan power directly through the small dry contacts on a Victron device.
Instead, those dry contacts should be used to trigger an external relay. That external relay handles the actual fan power from your battery bank to the fan itself.
You will also need to make sure you are using the correct voltage fan for your system, whether that is 12V, 24V, or 48V.
One of the Easiest Fan Triggers: Solar Output
One of the easiest and most practical ways to set up a cooling fan is through the Victron solar charge controller.
Inside the VictronConnect app, you can go into the relay settings and choose a condition tied to power output. In simple terms, that means when your solar panels are actively bringing in power, the fan turns on.
When solar is producing, it is usually daytime. When it is daytime, it is often hotter. And if your solar controller is actively working, that is exactly when extra airflow can help.
This kind of automation means your fan can run only when it makes sense, without you needing to think about it.
Inverter relay control
Some Victron inverters, including models like the MultiPlus, offer relay options such as K1 and K2. These can be configured around conditions like:
charging activity
inverter load
temperature with the right sensor setup
This can be useful if your inverter tends to generate the most heat during bulk charging or under heavier use.
Cerbo GX relay control
If you have a Cerbo GX, you can use one of its available relays to control a fan as well. At Big Beard Battery, relay number one is often reserved for generator auto start, so relay number two is a common choice for fan control.
One nice advantage of a GX device is remote access. If your system is connected to the internet, you can manually turn that relay on or off from virtually anywhere.
That adds flexibility if you want more control over ventilation in a specific compartment or zone.
A Simple Way to Improve RV Electrical Bay Ventilation
Not every cooling solution needs to be complicated. Sometimes a basic fan setup can make a real difference, especially if you are trying to:
blow extra air across an inverter
bring fresh air into an enclosed compartment
exhaust warm air out of a cabinet or electrical bay
The key is choosing the right fan, wiring it correctly through an external relay, and using the right Victron trigger point for your setup.
Need Help Designing an RV Solar System?
At Big Beard Battery in Athens, Texas, we help RV owners design smarter off-grid systems every day. Whether you need lithium batteries, Victron components, a custom solar design, or guidance on airflow and system layout, our team is here to help.
If you are planning an RV solar upgrade and want a system that is built to perform in real-world conditions, we would love to help.
Get a free solar design:https://www.bigbeardbattery.com/solar-design
Shop batteries and learn more:https://www.bigbeardbattery.com/
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