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ARCTIC’s new 3-phase motor explained

The Rev. 1 ARCTIC BioniX fans feature a 3-phase-motor with 6 or 9 slots and magnet rings with 8 or 12 poles, which provide high efficiency and smooth transitions between the slots and thus eliminate the vibrations from cheap fans almost entirely.

Typical DC motors have 4 stator slots and a permanent magnet with 4 poles. When the first pair of slot coils are powered up, the poles of the magnet ring align with them. At the next stage, the second pair of coils is powered and the magnet ring will turn by 90° to align the poles. While motor torque is high when the magnet ring poles are between the stator slots (45°), it drops off when the poles are aligned (90°) and only goes up again when the poles are between the next set of slots (135°). This leads to vibration and noise.

ARCTIC’s 3 phase motors have 6 or 9 stator slots and a permanent magnet ring with 8 or 12 poles.

The motor has three overlapping phases that all contribute to the overall torque. This more continuous, steady torque profile results in a smooth operating fan, a less torque-borne vibrations and a low energy consumption.

Sinusoidal versus Rectangular Drive

A conventional DC motor comes with a rectangular drive and switches the magnet field from positive to negative in an instance. This happens 4 times per rotation and leads to a jerk in the impeller as well as the frame, which can result in a humming or clicking sound – called commutation noise. Silicone vibration absorbers can reduce the commutation noise of the frame, though have no influence to the impeller since it works as a speaker.

The far advanced motor controller of ARCTIC fans drives the motor with a sinus signal. Thus the magnet field no longer switches in an instance but in a continuous way. This eliminates the commutation noise at the roots.

3-phase motor FAQ

Which advantages does a 3-phase motor have?

As already explained, the torque within the motor never drops completely. The motor is powered continuously by the overlapping phases, which helps in two ways:

  1. A lower motor temperature due to a more evenly power distribution within the motor leads to an increased lifetime of the motor.
  2. A 3-phase motor creates less vibrations, since the switching between the phases is eliminated. This mostly removes the necessity to undock the fan from other components with spacers.

Do I need Anti-Vibration Rubbers?

As mentioned above in most cases there is no need to use Anti-Vibration Rubbers when using a fan with a 3-phase motor.

Vibrations within fans are the result of oscillating torque and their rectangular drives of 1- or 2-phase motors. This causes clicking and humming sounds. Traditionally higher priced fans come with silicone or rubber vibration absorption pins which do absorb about 50% of this noise.

ARCTIC’s 3-phase motor eliminates vibration at the source, namely the drive. Due to the consistent torque and sinusoidal drive the noise from it gets eliminated by 95% and thus there is no need for further measures like silicone pins.

Should you still want an additional rubber buffering, we will of course provide you with it at your disposal. You can order the rubber buffering directly from the ARCTIC Support (eng@support.arctic.ac)

Why are the RPM above specification when using PWM?

When using PWM to control the speed of fans with a 3-phase motor, the following should be considered:

Current mainboards are developed with 1- or 2-phase motored fans in mind to measure the fan speed. As a result, the indicated RPM of ARCTIC fans with a 3-phase motor will be around 1.5x higher than the actual speed of the fan.

This has no effect in the everyday operation, the fans are not operated outside their specifications. This is simply a measurement error.

For example, if the mainboard shows a measured fan speed of 2,700 rpm for a BioniX F120 fan with a 3-phase motor, the fan actually runs at only 1,800 rpm.

Why are the BioniX louder during start-up?

BioniX Fans use a start-up controller to ensure a reliable start-up of the fans in the long run. The controller causes a slightly increased impulse when starting, which is absolutely normal. To ensure a reliable start-up of the fans in the coming years our 3-phase motors, as used in the BioniX Fans use a start-up controller. This causes a slightly increased impulse on start-up, which is absolutely normal.

The start-up controller helps to increase the lifetime significantly and is one of the reasons why we can extend the warranty to 10 years.