by Gary Hawkins, June 15, 2018
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Like many of you, we have found the Fan-Tastic vent installed in our Little Guy 5 Wide teardrop camper runs way too fast even on its lowest setting. Either we're forced to leave the fan off and rely on natural ventilation, or turn the fan to its lowest speed and deal with the gale blowing through the teardrop interior.
Fan-Tastic does offer a low-cost solution to reduce the vent speed based on the installation of a further resistive element to the existing three-speed resistive controller. This extra resistive element reportedly runs quite hot, requiring it to be mounted in the airflow of the fan. Thus, while the solution works, it's not very elegant.
Having done some research on the Internet, I found a much better solution was available. This involves replacing the resistive speed control unit with a PWM-based control unit (PWM stands for pulse-width modulation). Suffice it to say that a PWM controller allows the average DC voltage applied to the fan motor to be continuously varied between 0 and the nominal battery voltage. The previous resistive controller only applied DC voltages of 7, 9 and 11 V respectively for the three selectable speed settings. Since the PWM controller can produce an average DC fan voltage below 7V much lower fan speeds are possible.
The circuit diagram for single direction vent control is shown below. Basic electrical circuit knowledge, plus solder and crimping skills will be needed to complete the project.
I sourced a suitable DC PWM controller from Amazon. Since the spindle of the 10k ohm potentiometer that came with this board was too small to fit in the hole cut for the old resistive controller spindle, I also purchased from Amazon a larger potentiometer (with larger spindle) and matching knob. The replacement parts are shown below.
After removing the grill assembly from the rest of the vent, take out the old resistive controller and fuse holder (the PWM board has its own fuse). Mount the PWM controller board to the vent grill assembly by drilling a couple of holes and securing with small zip ties. Replace the 10k ohm potentiometer with the larger one, and secure the potentiometer to the grill body. Make-up suitable leads to allow connections from the PWM controller board to the On/Off switch and the vent motor. The installation of the PWM board and potentiometer on the vent grill assembly is shown below.
I decided to use the existing In/Out vent rocker switch as the On/Off switch. This saved installing a separate On/Off switch, and more importantly, ensured when the fan was switched off power was also removed from the PWM controller board. The negative result of using the existing rocker switch as the On/Off switch was losing the capability to reverse the vent airflow. Since we only ever vented out of the teardrop then this did not matter to us.
Connections were made to the fan motor and the teardrop 12V supply, and the grill assembly re-installed to the rest of the fan unit. The result was just as expected - see the short video demonstration below.
If you have any questions about the installation, please leave a comment below or use the Contact Us button. Please share this article with your teardrop friends.