NL-LC1 series AIO coolers’ pump speed profiles explained

Temperature monitoring and automatic safety ramp

To ensure safe operating conditions regardless of the ambient temperature and PWM input, NL-LC1 coolers feature an integrated sensor for constant liquid temperature monitoring and automatically adjust the pump speed if necessary. Below 45°C liquid temperature, the pump runs at its nominal minimum speed of 750rpm when set to 20% PWM, which enables near-silent operation in idle conditions and at low heat-loads.

In case the liquid temperature rises above 45°C, regardless of the mode selected, the allowed minimum speed of the pump automatically starts to increase and continues to increase in case the liquid temperature should keep rising. This automatic safety ramp gradually continues all the way to 55°C liquid temperature where the pump is automatically set to its maximum nominal speed of ~3400rpm, overriding any PWM input in order to protect the cooler itself from damage.

For safety reasons, PWM settings below 20% are ignored, so even if the liquid temperature is below 45°C, the pump will keep running at a nominal speed of 750rpm in order to maintain fluid circulation. If the pump detects a 0% PWM signal, it will switch to 100% speed. This is done intentionally to make sure that the pump will not run at too low speeds if it receives a corrupt PWM signal that could be interpreted as 0% PWM.

Key differences between the modes

The key difference between the three modes is how the pump responds to higher PWM settings. In Quiet mode, the maximum speed of the pump is restricted to ~2100rpm (unless the safety ramp function automatically increases RPM at >45°C liquid temperature), which ensures extremely low noise emission under normal operating conditions.

In Balanced mode, the maximum speed of the pump is limited at ~2600rpm up to 30°C liquid temperature before the control headroom starts to expand all the way to ~3400rpm at 45°C liquid temperature. This setting provides a good balance in the sense that it prevents the pump from running louder than necessary at lower liquid temperatures while offering extended performance headroom in case liquid temperatures should rise.

In Manual mode, maximum pump speed is accessible regardless of the liquid temperature, so the pump can be set to ~3400rpm even if the liquid is still at room temperature. This mode is ideal for enthusiast customers who prefer to have full control over the entire speed range and a stable PWM-to-RPM response.

Performance and noise results

Comparing the noise levels at the full nominal speed levels in each of the three modes at <30°C liquid temperatures (2100rpm / 2600rpm / 3400rpm) installed inside an Antec Flux Pro Noctua Edition chassis, the pump ran approximately 5.5dB(A) quieter in balanced mode than in manual mode. In quiet mode, the noise levels were another ~6dB(A) lower:

While sound pressure levels will vary from setup to setup due to different resonance and reflection behaviour, Quiet mode typically produces such low noise levels that the pump is difficult to pick up even from very close distances, which makes it the ideal setting for noise-sensitive users. While the difference to full speed in Manual mode is usually noticeable, Balanced mode provides a good middle ground and is highly flexible thanks to the automatic, liquid temperature-based scaling of the maximum speed.

The difference in thermal performance between the modes will largely depend on the individual setup and heat-load generated. While the difference between Quiet mode and Manual mode will usually be very small at low heat-loads such as 65 or 90W, it can be more pronounced at high heat-loads such as 200W and beyond. For reference, we have measured a difference of 2.7°C on an AMD Ryzen 7 9850X3D running at 145W, a 4°C difference on an Intel Core Ultra 5 250K Plus running at 200W and a 6°C difference on an Intel Core 7 270K Plus running at 315W:

Automatic self-bleeding

To ensure low-noise operation and consistent thermal performance, NL-LC1 coolers boost the pump to maximum speed (~3400rpm) for around 50 seconds at start-up. The reason for this is that closed-loop liquid coolers require a certain amount of air inside the loop to allow for thermal expansion and safe transport in different environmental conditions. If air bubbles get trapped inside the pump, this can lead to increased noise emission and lower thermal performance. This is where the automatic self-bleeding mechanism steps in: boosting the pump to ~3400rpm for a few seconds ensures proper bleeding and significantly reduces the risk of air bubbles being trapped in the pump.