Why Your Inverter Fan Keeps Running

The performance and longevity of an inverter depend on the correct loading on the AC demand-side and sufficient cooling of the internal components of the inverter. Inverters are fitted with one or more cooling fans dependent on the device’s power output.

The cooling fans on an inverter will switch on as the components in the inverter warm-up stay on for longer and increase fan speed to reduce the heat buildup in the inverter as the load demand increases. Fans running continuously signify that the device is running at maximum capacity.

Ideally, inverters should not be loaded to their maximum rated output wattage continually but should only be loaded up to 80% of the maximum operational output. Signs that the inverter is working too hard are:

  • Cooling fans running continuously
  • Cooling fans are becoming more noisy than normal
  • Inverter overload protection trips the device
  • Cooling fans could also be running continuously to compensate for insufficient cooling of the inverter due to impeded airflow via the cooling fan intakes or the ambient temperature at the installation point being too high.

Let’s look at some measures to ensure your inverters’ optimal operation and longevity.

What Is The Function Of The Inverter Fans?

Cooling fans draw cool air through air vents in the inverter housing and blow this air over the inverter components and out of exit vents. The inverter is fitted with a temperature sensor that will control the running of the cooling fans.

An electrical current flowing in a conductive wire will always experience internal resistance to flow. At the absolute zero temperature (0 K / −273.15 °C / −459.67 °F), the resistance in conductors will be at its lowest.

As the temperature increases, the vibrational movement of atoms and electrons increases, making the number of collisions that an electron is moving in the conductor more difficult. This is called resistance.

Conductors like copper have a low resistance to electron conductivity, but insulators like the plastic sleeve over the copper wire have very high resistance. Even in a good conductor like copper or silver, the flow of an electric current will cause the wire to heat up.

If too much current flows through a copper wire that is too thin to carry the current load, the copper wire will melt through due to the heat of the excessively high current. This is the principle used for making fuses and circuit breakers.

The direct current (DC) drawn from the battery bank powering an inverter is switched and modulated by a series of components, causing a massive heat buildup in the inverter. Without proper cooling, the inverter components will soon overheat and fail.

The inverter is designed with the components mounted on a large aluminum heat sink with cooling fins on the outer skin of the enclosure. The heat generated by the components is absorbed by the aluminum and dissipated to the outside air surrounding the inverter.

The higher the temperature inside the inverter, the longer and faster the cooling fans will run. If the air intake vents become blocked due to dust or dirt, the fans will run for longer as they struggle to bring down the temperature.

If there is insufficient space around the inverter for heat dissipation or insufficient airflow over and through the inverter, the cooling fans will have to work harder. Eventually, cooling fans will fail due to excessive running and cause the inverter to overheat and fail.

How To Install An Inverter For Optimal Cooling?

Inverters must be installed in a location that will allow for at least one foot of free space around the inverter housing. The space must have good air circulation and not contain heat sources such as engines, generators, or water heaters.

Follow the inverter manufacturer installation instructions as some inverters may only be installed in either a vertical or horizontal orientation. Check that the cooling fan air intake vents are clear of obstruction and will pull in cold air and allow convection to carry the heat away from the inverter.

Don’t install the inverter in a dusty area or where small fibers can be sucked into the inverter by the cooling fan intakes. The plastic blades on the cooling fan will build up an electrostatic charge and attract dust particles, making it run inefficiently.

Make sure that the inverter control panel will be visible and that you will be able to observe visual and audible alarms from the inverter. Do not install the inverter in a space where the noise from the cooling fans will be bothersome.

Monitor your inverter during the peak demand hours in your household to see how hard the fans are running and whether there are no signs of strain on the system.

See also: Solar Inverter Problems and Solutions: A Comprehensive Guide to Troubleshooting Common Issues

How To Load The Inverter For Optimal Operation?

Inverters are rated at the maximum operational output (Watt rating) and a maximum surge output. The surge output is only required by some electrical appliances such as microwave ovens, air conditioner condenser motors, hairdryer motors called inductive loads. These loads surge for a few seconds when the device is switched on.

The rated maximum operational output should never be exceeded as this may cause severe damage to the inverter. The best practice is to only load an inverter to 80% of its maximum operational watt rating.

You should identify the power demand of each appliance that you intend to run off the inverter. Place a label identifying the appliance wattage on the power cord near the plug-in connector.

Make a connection plan at the inverter indicating which appliance loads can be connected to the inverter without exceeding the 80% maximum load output. As you connect more loads to the inverter, you will hear how the cooling fans start running and run for a longer period and at higher speeds as the load increases.

As the sum of the loads approaches the maximum power output rating, the cooling fans will start running continuously and indicate that the inverter is working very hard. Disconnect some loads to get the operation load below 80%.


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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