Micro Autonomations LLC – Fan Controller v3
3
Document Rev 1.0
Theory of Operation
The v3 controller has been designed to work in a variety of different systems. It can work with any
standalone temperature sensor, or it may piggyback off any 0-5v EFI temperature sensor. The controller
is able to detect and operate properly with both positive and negative going temperature sensors.
During programming, the controller detects whether the EFI or standalone temperature sensor input is
active. The controller is then able to use this information to aid in detecting various error modes.
During normal operation, the controller reads the current temperature at a rate of once a second. It
then checks several different factors in determining whether to turn the fan on or off, or what speed to
command the fan to operate at. The fan can operate at any speed between 25% and 90%.
After programming, the controller contains two temperature points: the turn on temperature, where
the fan will turn on to 25% speed, and the 75% temperature, where the fan will operate at 75% speed.
In the figure below, the controller has been programmed with pre-set temperature range #1, with a turn
on temperature of 170°F, and a 75% temperature of 185°F. As the engine temperature rises and
reaches the turn on point, the fan will turn on to 25%. As the engine temperature continues to rise, fan
speed will increase linearly until it reaches 75% speed at 185°. If the engine temperature still continues
to rise, fan speed will continue to increase until it reaches its full speed of 90% at 190°.
Figure 1 – Fan speed vs. Engine Temperature
As the engine temperature decreases, fan speed will also decrease, eventually reaching the 25% turn on
temperature. If the engine temperature continues to decrease below the turn on temperature, it will
maintain 25% fan speed until the engine temperature has dropped approximately 3-5°F below the turn
on temperature. Once the engine temperature is below this hysteresis point, the fan will turn off and
await the need to turn on again.
