Cooling Fan In-Rush Current and how to control it with a PDM

Posted by Tony eigenseher on

In-rush current refers to the sudden surge of current that occurs when an electrical device is turned on. In the case of a cooling fan, in-rush current can occur when the fan is first powered up and the motor starts to spin.

The in-rush current for a cooling fan will depend on several factors, including the size of the fan, the voltage and current rating of the power supply, and the design of the motor. Typically, the in-rush current for a cooling fan can be several times higher than the normal operating current.

It's important to take the in-rush current into account when selecting a power supply for a cooling fan, as the power supply should be able to handle the surge in current without tripping any fuses or circuit breakers. Additionally, it's a good practice to avoid repeatedly turning the fan on and off, as this can cause wear and tear on the motor and may lead to premature failure.

The typical in-rush current for an electric radiator fan can vary depending on the fan's motor design and the power supply used. Generally, the in-rush current can be several times higher than the fan's normal operating current.

For example, a 12-volt electric radiator fan with a normal operating current of 10 amps may experience an in-rush current of 20 to 30 amps when it is first turned on. However, the actual in-rush current will depend on factors such as the fan's motor design, the size and type of the fan, and the type and rating of the power supply being used. Some fans can see peak in rush current as high as 40 - 45 amps before settling down to 10 - 12 amps.

It's important to choose a power supply that can handle the in-rush current without tripping any fuses or circuit breakers. Additionally, using a soft start circuit or an inrush current limiter can help to reduce the in-rush current and prolong the life of the fan's motor.

The method we would choose when using a PDM is to...
Soft Start: Soft starting the fan means gradually increasing the voltage to the motor over a short period of time. This can be done using a specialized controller or by adding a simple resistor in series with the power supply to limit the initial current surge in this case we have the option to choose soft start within the software( Hardwire PDM).
This is just a demonstration snippet don't use these values. 
You can see the Peak Fuse would allow the inrush to stay under the designated Limit for 500ms before tripping the fuse. In this case we enabled the soft start with a time of 1,000 ms. We can log these values or see the live output values within the software and fine tune these numbers. 
It's important to note that the solution for controlling in-rush current will depend on the specific application and the requirements of the system.
Now there is Brush VS Brushless electric fans that comes at a cost and a whole other topic to discuss.