DC fans are always brushless. Commutation takes place electronically. AC fans have no commutation, the torque is generated via phase shift in the motor.

With DC fans, the speed is controlled via the operating voltage or a PWM input.

SEPA plain bearing fans have a typical life expectancy (MTTF) of 210,000h and ball bearing fans of 350,000h. This value refers to continuous operation at an operating temperature of 40°C and is highly temperature-dependent.

Attention! When evaluating service life specifications, always compare the temperature specification.

Both are statistical values determined over a large number of test specimens at nominal conditions.

L10 indicates the failure probability of 10 % over “n” hours, while MTBF (Mean Time Between Failure) determines the average time between two failures, also over a large number of test specimens.

Since fans are usually not repaired, the first failure corresponds to a failure MTTF (Mean Time To Failure). The values always refer to a specific temperature. The data in the SEPA EUROPE data sheets are based on 40°C.

Hardly at all, as the bearing load is very low, almost no wear occurs. The service life is mainly determined by the ageing of the lubricant and this is independent of the speed.

No, on the contrary. Frequent switching on and off substantially increases bearing wear especially with regard to sleeve bearing systems and can also result in premature failure. We recommend switching off the fan if it is only very rarely switched on, e.g. in the event of occasional extreme temperatures.

Only partially. The values stipulated in the data sheets refer to airborne sound that is determined at a fan that has a soft suspension, free-blowing, at a distance of 1 m, taking into consideration the frequency response of the hearing sensitivity (A-evaluation) in a sound-proofed room. The conditions are completely different in the appliance. Structure-borne sound, resonances and the operating point of the fan strongly affect the actual noise development.

The noise depends to a great extent on the speed. If the speed is reduced by half, the noise drops by 10-15 dB(A)! As the speed tolerance can be up to ±15 %, a noise tolerance of ±2 dB(A) and more is not unusual. With two, slowly rotating fans that are not positioned directly next to one another, one can achieve a lower noise level than with one fan that operates at a higher speed.

The flow rate of a fan depends on the counter pressure that is produced in the appliance by the air resistance. The data sheets only contain the two extreme values, flow rate without counter pressure (free blowing) and maximum pressure (flow rate 0, closed housing). Both do not reflect actual practice. In addition one finds the curve that displays the progression between these extreme values. The typical working range of an axial fan is in the range of 20 and 30 % of the maximum pressure and must always be below the saddle that is typical for this fan design. Operation with too high counter pressure (e.g. through air intake or discharge openings that are too small) increases the noise considerably.

Yes. IP55 is realised by protective lacquering of the printed circuit board and IP68 by full encapsulation of the entire motor.   

Sleeve bearings function according to the hydrodynamic principle. Ideally, the rotating shaft floats on a film of oil. Ball bearings consist of two bearing shells in which steel balls roll in a so-called ball cage. The balls are greased and the bearing shells are sealed with two cover disks.

Currently, the MF15B05 is the smallest fan in the range, measuring only 15x15x4.5 mm.

We will be happy to send you 3D data on request.

SEPA EUROPE specialises in customised solutions. The fans can also be supplied with all commercially available connectors and with various strand lengths.

SEPA EUROPE offers a wide range of fastening options such as screws and fan sleeves. 

Chip coolers can be attached with TCT adhesive pads or HERNON heat conductive adhesive. 

Fastening with screws is also possible.

Blowers are ideally fastened with screws 

There is no arrangement that is clearly better. The position must be selected so that the air can flow optimally around the critical components that require cooling. With the suctioning position, the fan is cooled by the cooler external air which increases the life expectancy. The fan can also be positioned inside the appliance and not on the outside walls. In this case the side of the appliance exposed to overpressure must be hermetically sealed off from the underpressure side.

Both are basically output signals for monitoring the correct functioning of the fan. Malfunction results in the output signal changing which can be evaluated accordingly. The alarm output is connected with the collector of a switching transistor that switches over in the event of an
error. The output is connected with a voltage source via a series resistor (pull-up). The shift from L to H in the event of an error is standard. The tacho output provides a speed-proportional rectangular shaped output signal.

The tacho signal is used to monitor exactly the correct operation of a DC fan. While the propeller is rotating a switching transistor is activated via the rotor magnets two or three times per revolution. The tacho output is connected with a positive voltage source via a pull-up resistor. The output supplies a rectangular shaped frequency that is equivalent to 2 x or 3 x the actual speed. If the fan stops, the output signal is permanently L or H. A true speed control can be realized via the frequency of the tacho signal.

The PWM input signal modulates the voltage supply of the motor coils so that they are switched on between 30 and 100 % depending on the pulse width (= duty cycle). The clock frequency of approx. 23 kHz is outside the audible range.

What is meant here is a pulse-width modulated operating voltage. This works for most fans. However, the low voltage should not fall below 2.5V so that the motor IC is not switched off with every pulse.

The operating voltage of a DC fan can be either 5 V, 12 V, 24 V or 48 V, depending on the model. Other voltages are possible but not common. The tolerance of the supply voltage is ±10 %. When the fan starts up, a starting current of 2-3 times the nominal current is required for a short time. The power supply must be able to deliver this current. Conventional AC fans require a nominal voltage of 110 V, 230 V or 400 V and develop a speed that is proportional to the mains frequency.

Yes, if the fans are identical models. Both fans must be protected against overvoltage via parallel switched Z diodes in case a fan bocks. Both Z diodes in series must have a higher Z voltage than the voltage supply can provide. Tolerances must be given consideration:
(Z1 + Z2) * 0.95 > UN * 1.1
Example: 2 fans for 12 V at a 24V power supply, protected by 15V Z diodes:
(15+15) * 0.95 = 28.5 > 24 * 1.1 =26.4.
The upstream Z diodes must be dimensioned so that they do not become overloaded when the fan blocks.

Yes, up to 60% of the nominal voltage for 5V fans and up to 40% of the nominal voltage for 12V and 24V fans are possible. In this case, a start voltage of ≥ 85% of the nominal voltage must be applied for a short time to ensure the ramping up of fans after longer rest periods and low temperatures. The fan voltage can be easily reduced with a Z diode or a series resistor by arranging an electrolytic capacitor in parallel with the upstream component. The upstream component must be dimensioned so that it is not overloaded even when the fan is blocked.

AC fans cannot be controlled via the operating voltage, as the speed is linked to the mains frequency.

Electronically commutated AC fans with an upstream AC/DC converter are referred to as EC fans. This new generation of AC fans operate extremely efficiently, as they require considerably less electrical power compared with conventional AC fans. Further advantages are the fact that the speed is not dependent on the mains frequency and a wide-range input that is suitable for virtually all mains voltages and frequencies that exist worldwide. EC fans can be equipped with both a tacho output and a 0-10V control input