The exhaust fan speed cannot be adjusted below 20%.
If I lower it by 10%, it will be adjusted back to 20%.
The cause is unknown.
From your description, it’s not yet clear whether this is expected behavior, a profile/firmware issue, or a hardware fault, so a few clarifications would really help narrow it down.
Could you please specify:
- Whether the exhaust fan issue occurs only during active prints, when the printer is idle, or in both situations?
- If the problem appears across multiple filament profiles (including untouched default ones), or only with a specific/custom profile?
- Whether changing the exhaust speed (e.g., to 40–60%) produces any audible change in airflow, or if the fan seems to run at a fixed speed regardless of the value shown in the UI?
With those details, it will be much easier to determine if we are dealing with normal profile‑driven behavior, a configuration/firmware bug, or a potential hardware problem.
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- Whether the exhaust fan issue occurs only during active prints, when the printer is idle, or in both situations?
→The same symptoms occur in all situations.
- If the problem appears across multiple filament profiles (including untouched default ones), or only with a specific/custom profile?
→Filament classification or settings are not relevant.
- Whether changing the exhaust speed (e.g., to 40–60%) produces any audible change in airflow, or if the fan seems to run at a fixed speed regardless of the value shown in the UI?
→There is no problem at all with operations above 20%, and it works well at 30%, 50%, and 100% operations.
It doesn’t appear to be a hardware issue. If it doesn’t work below 20%, it’s likely a firmware issue.
This doesn’t sound like a “failure” at all—it’s more likely intentional firmware behavior with a 20% minimum threshold.
Depending on the specific fan model used in the H2S exhaust system, there could be several technical reasons for limiting the lower speed range:
- Startup reliability: Many fans lack sufficient torque to reliably spin up from a standstill at very low PWM duty cycles (<15–20%). Laptop fans, for example, typically spin up to maximum speed first before settling to the target speed, precisely to overcome static friction and ensure reliable startup.
- Unstable operation: Some fans exhibit erratic RPM, stalling, or excessive cogging at minimal drive levels
- Bearing friction: Static friction in the bearing can exceed the electromagnetic drive force at very low speeds
Since the fan operates perfectly at 30%, 50%, and 100%, and the limitation applies universally (all profiles, idle and printing), this suggests a deliberate firmware constraint designed to ensure reliable operation across all conditions.
It’s a sensible engineering trade-off: setting a minimum threshold prevents startup failures and unstable behavior, at the cost of slightly reduced control granularity.
Unless you specifically need exhaust speeds below 20% for a particular workflow, this is likely working as designed rather than a bug.