Voron CPAP Fan Mod — High-Flow Part Cooling Guide

Cooling Mod Speed Printing V2.4 Trident

If you've pushed your Voron past 200 mm/s, you've hit the wall: your part cooling fan simply can't keep up. The standard 5015 blower fan used in the Stealthburner reaches its aerodynamic limit around 15-18 CFM, which is fine for 80-120 mm/s printing. But when you're chasing 300 mm/s with a 0.6mm nozzle, you need serious airflow. Enter the CPAP fan mod — a repurposed medical Continuous Positive Airway Pressure blower that delivers 40-60 CFM of directed cooling through a custom duct.

Last updated: May 2025. This guide covers everything you need to know about the Voron CPAP fan mod: why it's useful, what parts you need, step-by-step installation, China-direct pricing, difficulty level, and compatibility with all major Voron models.

What Is the CPAP Fan Mod?

The CPAP fan mod replaces the standard 5015 or 4020 part cooling fan on your Voron's toolhead with a high-pressure medical blower originally designed for CPAP machines. These blowers (typically manufactured by companies like ResMed, Philips, or generic Chinese OEMs) are designed to run continuously for thousands of hours, produce minimal noise, and deliver high static pressure — exactly what you need for effective part cooling at high flow rates.

The most common CPAP blower used in the Voron community is the generic 24V DC CPAP blower (often labelled as a "CPAP motor" or "high-flow blower" on AliExpress). These are paired with a custom 3D-printed duct that mounts to the toolhead and directs airflow precisely at the nozzle tip from two or more angles. The result is a dramatic improvement in part cooling capacity — typically 3-4x the airflow of a standard 5015 fan.

Why Is This Mod Useful?

Part cooling is the single biggest bottleneck when printing at high speeds. Here's why the CPAP mod matters:

• Eliminates bridging limits: With 40+ CFM of directed airflow, you can bridge across 200mm gaps without sagging. Standard 5015 fans struggle beyond 80mm bridges.
• Crisper overhangs: At 300 mm/s with a 0.6mm nozzle, molten plastic needs aggressive cooling to solidify before the next layer. The CPAP blower delivers enough air to keep overhangs at 65°+ looking clean.
• Faster layer times for small parts: Small, detailed parts (like Voron printed parts themselves) print faster because you can reduce your minimum layer time — the part cools almost instantly.
• Better PLA and PETG printing: Vorons are ABS/ASA machines by design, but many builders also print PLA and PETG. These materials need aggressive cooling that stock Voron fans struggle to provide at speed.
• Quieter operation: Surprisingly, a properly ducted CPAP blower is often quieter than a 5015 fan running at 100%. The blower moves more air at lower RPM, producing a lower-frequency hum rather than the whine of a small fan.

Parts Needed

Optional: A buck converter ($3-5) if you want to run the blower at lower voltages for reduced noise. Some builders also add a 47-100µF capacitor across the blower terminals to smooth out PWM ripple.

Assembly and Installation Steps

Step 1: Print the Duct and Mounting Hardware

Download the STL files from the Voron User Mods repository or a community-maintained GitHub repo. The most popular designs are the "CPAP for Stealthburner" by hartk1213 and the "Dual 5015 to CPAP Adapter" from the Voron Discord. Print all parts in ABS or ASA at 0.2mm layer height, 4 perimeters, 40% infill. The duct must be dimensionally stable — PLA will deform in an enclosure at 50-60°C.

Step 2: Prepare the CPAP Blower

Remove any plastic housing from the CPAP blower if it came pre-packaged. Most generic units ship as bare blowers. Solder 18AWG silicone wires to the positive and negative terminals. Use heat shrink tubing on each connection. If your blower has a third wire (tachometer/speed sensor), leave it disconnected — it's not used in this application.

Step 3: Wire the MOSFET Module

Connect the MOSFET module as follows:

• MOSFET "Signal" pin to your mainboard's fan header (e.g., FAN0 on Octopus or SKR boards)
• MOSFET "VCC" pin to 24V power supply positive
• MOSFET "GND" pin to 24V power supply negative (common ground with mainboard)
• MOSFET output to CPAP blower positive and negative

Important: Never connect the CPAP blower directly to your mainboard's fan header. The 3-6A draw will blow the onboard MOSFET. Always use an external MOSFET module rated for 30A+.

Step 4: Mount the Duct to the Toolhead

Remove your existing 5015 or 4020 fan from the Stealthburner or toolhead. Mount the printed CPAP duct in its place using the original M3 screws. The duct should align so that the air outlet points directly at the nozzle tip, typically at a 30-45° angle. Some designs use two outlets for symmetrical cooling.

Step 5: Connect the Blower to the Duct

Use the PTFE tube adapter to connect the blower outlet to the duct inlet. A 50mm ID silicone tube works best — it's flexible enough to route through the cable chain or along the z-axis cable management. Secure with zip ties or worm-drive clamps. Make sure the tube doesn't kink or pinch during toolhead movement.

Step 6: Configure Klipper

Add or modify the following in your printer.cfg:

[fan]
pin: PA8  # Your fan header pin
max_power: 1.0
shutdown_speed: 0.0
cycle_time: 0.010  # 10ms cycle for MOSFET
hardware_pwm: False
kick_start_time: 0.100  # Helps blower start from 0%

Tune your PWM frequency if the blower hums at certain speeds. Most CPAP blowers run best at 100-200Hz PWM. You can adjust the cycle_time parameter (set to 0.005-0.010 for 100-200Hz).

Difficulty Level: Medium

The CPAP fan mod requires basic soldering skills, some wiring experience (MOSFET integration), and the ability to print ABS parts. If you've built a Voron from a kit, you have all the skills needed. Expect 2-3 hours for the full installation, including Klipper configuration and tuning.

Compatibility with Voron Models

Before vs After Benefits

The real-world difference is dramatic. With a CPAP mod, you can print PLA at 250 mm/s with a 0.6mm nozzle and get better overhang quality than a stock Voron at 100 mm/s. Printed parts come out noticeably crisper, with sharper corners and less stringing. The one trade-off is power consumption — the CPAP blower draws significantly more power at full speed, so make sure your 24V power supply has headroom.

Common Issues and Troubleshooting

Blower won't start at low PWM

CPAP blowers need a "kick start" pulse to overcome static friction. Set kick_start_time: 0.200 in your Klipper fan config. If it still won't start, increase the minimum fan speed to 15-20% in your slicer's start g-code.

Blower hums or vibrates

Try different PWM frequencies. CPAP blowers typically run best at 200-500Hz. Adjust the cycle_time parameter in Klipper (cycle_time = 1/frequency). For 200Hz, set cycle_time: 0.005.

Duct gets hot inside enclosure

Make sure your duct is printed in ABS or ASA. PLA will soften at 50-60°C enclosure temperatures. If you're printing at high chamber temperatures (70°C+ for polycarbonate), consider using polycarbonate or ASA for the duct.