Adding Quiet Bottom Fans to the Victron MultiPlus-II

Steps

1. 1

   Step 1: Gathering materials and planning the build

   To start this project, I need a few specific parts and tools. I am using a 3D-print model, a buck converter to step down 48V from the battery pack to 12V, a fan controller with a temperature sensor, and two 80 mm fans.

   I can choose between cheap standard 12V fans or PWM PC fans. I chose fancy LED fans so the bottom of the MultiPlus glows blue and I can visually see when they turn on.

   • 3D-print model

   • Buck converter

   • Fan controller

   • 80 mm fans

   What I used

   Item	Amount	Notes
   3D-print model	1	free to download from the description
   Buck converter	1	steps down 48V to 12V
   Fan controller	1	includes a temperature sensor
   80 mm fans	2	LED fans with screws included

2. 2

   Step 2: Assembling the fans into the 3D-printed frame

   First, I print the 3D model that fits inside the bottom cap of the MultiPlus. I check the arrow on the side of each fan to make sure the air blows into the unit, because we want to draw cool outside air in.

   I screw the fans into the 3D-printed frame using three screws each, leaving two screw holes free so I can use those same screws later to mount the entire unit inside the MultiPlus cap.

   What I used

   Item	Amount	Notes
   3D-printed frame	1	holds two fans
   Fan screws	6 total	three per fan

3. 3

   Step 3: Modifying the fan controller for standard 12V fans

   If you use PWM fans, you can skip this step. Since I use cheap 12V fans, I need to modify the fan controller board with an extra TIP120 transistor and a 2.2 kOhm resistor to send out the proper PWM signal.

   I fold the middle pin of the transistor backward, the left pin 90 degrees to the left, and leave the right pin straight. Then I solder the resistor between the PWM output pin and the base of the transistor, and connect the power wires.

   What I used

   Item	Amount	Notes
   TIP120 transistor	1	pins bent for modification
   2.2 kOhm resistor	1	soldered to the transistor

4. 4

   Step 4: Understanding PWM power pulsing and fan handling

   PWM stands for pulse width modulation, which means the power is pulsed on and off extremely fast. If you set a PWM value of 90 percent, the power is on for 90 percent of the time and off for 10 percent. This rapid switching is why the original Victron fan makes so much noise because you hear that low frequency in the motor.

   Cheap fans handle this pulsing a lot better without making that annoying humming sound. Our modified circuit switches the fans on and off at high speed to control their speed quietly.

5. 5

   Step 5: Installing and wiring the buck converter

   I place the buck converter with the output facing left into its designated rails where it fits precisely. Then I solder the positive and negative input and output wires to the board.

   The buck converter takes 48V from the battery and converts it to a steady 12V to power the fans and the controller.

   What I used

   Item	Amount	Notes
   Buck converter	1	placed in rails
   Wire	1 set	for plus and minus connections

6. 6

   Step 6: Configuring the fan controller settings

   I connect a temporary 12V power supply to test the controller. The red dip switches allow me to adjust the minimum fan speed and temperature thresholds.

   With all dip switches off, the minimum speed is 20 percent, which keeps the fans dead silent while maintaining a light airflow. Switches 2 and 3 control the temperature range where the fans start speeding up.

   Dip Switch 2 and 3	Start Speed Temperature	Max Speed Temperature
   Both OFF	35 deg C	45 deg C
   TP1 ON	40 deg C	55 deg C
   TP2 ON	50 deg C	70 deg C
   Both ON	60 deg C	90 deg C

   What I used

   Item	Amount	Notes
   Temporary 12V power supply	1	for bench testing

7. 7

   Step 7: Setting up dip switches for a stall alarm buzzer

   Switches 4 and 5 control the stall alarm feature. If one of your fans gets blocked or stops working, a buzzer will start beeping immediately to warn you.

   To use this feature, you connect the buzzer included in your package directly to the board. I am not going to use this alarm for my setup, but the option is there if you want extra safety.

8. 8

   Step 8: Testing the temperature response

   To test the automatic response, I hold a warm soldering iron near the temperature sensor. The LED lights on the fans grow brighter as it measures higher heat, and the fans spin up to full speed.

   When I remove the heat source and the sensor cools down, the fans automatically slow back down to idle speed. This setup allows the MultiPlus to fully monitor and cool itself.

   What I used

   Item	Amount	Notes
   Soldering iron	1	used as a heat source for testing

9. 9

   Step 9: Mounting the fan assembly into the MultiPlus bottom cover

   I take the two screws we saved earlier and insert them through the bottom cap into the inner holes of the 3D-printed fan frame. Because they are neat black screws from the fan set, they do not stand out.

   The assembly is now firmly screwed into the cover without hitting any other electronics inside the MultiPlus. From the outside, the appearance does not change except for the blue LED light shining from underneath.

   What I used

   Item	Amount	Notes
   Saved fan screws	2	used to secure frame to cover

10. 10

    Step 10: Connecting the main power and finishing up

    Finally, I connect the power cable to the input of the buck converter to feed it with 48V from the system. The modification is very subtle and not directly visible from the outside unless you use LED fans.

    The MultiPlus is now continuously cooled by a gentle airflow, and the fans spin up actively when it gets warm, hopefully before the original loud fan kicks in.

    What I used

    Item	Amount	Notes
    Power cable	1	feeds 48V to the buck converter

11. 11

    Step 11: Call to action for comments and ideas

    I hope this video was useful for you and gives you a good way to keep your system cool. Please let me know what you think of this modification in the comments below.

    If you have any more ideas or suggestions, drop them in the comments too. I am happy with every remark and it makes it fun to keep making these projects for you.

12. 12

    Step 12: Takeaways

    • Adding two bottom fans helps cool the Victron MultiPlus-II quietly.

    • Using the removable bottom cover ensures the warranty is not voided.

    • A buck converter steps down 48V from the battery pack to 12V.

    • A transistor and resistor modification allows cheap 12V fans to work with PWM control.

    • Temperature thresholds can be configured using dip switches on the controller.