What to learn more about fans? What is a motor? What is system impedance?
The answers to these and more can be found below.

We publish the life expectancy for all our fans. This is expressed in terms of L10 life. L10 refers to the time at which in a large population, 90% of the air moving devices will still be operative.

Airflow is the volume of air moving through a blower or duct. Units of measure are cubic feet per minute (CFM), liters per second (LPS) or cubic meters per hour (M3H).

Static pressure is the difference in air pressure between the suction side and pressure side of the blower. Unit of measure is inches of water volume (in. wc) or Pascals (Pa).

Air performance curves are graphs showing air flow characteristics: airflow (cfm) versus static pressure (in. wc) and airflow (cfm) versus blower speed (rpm).

Yes, in two planes while running.

The system operating point is the point of operation of the air mover on its air performance curve. It is described by an airflow and static pressure point. The operating point is that point on the air mover performance curve where the system resistance curve crosses the air performance curve.

System Impedance is the resistance to air flow when moving air through an airflow system. Examples: air filters, air grilles and abrupt changes in flow direction.

Fan laws are a family of mathematical relationships that allows the calculation of new operating characteristics from known system conditions.

Motor insulation systems are the materials used for wire and coil insulation and are classified according to the highest temperature at which normal service life can be expected. There are five motor temperature classifications: A (1050 C), E (1200 C), B (1300 C), F (1550 C) and H (1800 C). The maximum temperature rating is based on the temperature rise of the coil winding plus the ambient air temperature at the motor.


Yes. Most crossflow blowers can have the motor rotated in increments of 900. Motor rotation, if required, should be performed at Sofasco Industries as a value-added service.

Yes. Most models are UL and cUL recognized or CSA certified for use in the US and Canada. Please check with an Sofasco applications engineer for questions about the approval status of specific models.

In general, seventy-five (75%) percent of the rated voltage of the blower motor is required to reliably start the motor.Example: Minimum starting voltage: 111 x .75 = 86V

Yes. Sofasco (mvl) products have a three or four digit number on the lower right corner of the label on the blower housing.Examples:
029 = week 2, 1999
4999 = week 49, 1999
0500 = week 5, 2000

No. Unless the motor is specifically designed to operate at both 50/60 Hz, each motor must be evaluated for the application on a case-by-case basis.

Yes, many models are available that are manufactured to European standards with equivalent air delivery. Models that are not currently designed with European voltages can be supplied with minimum production order quantities. Most models designed for European voltages are built to VDE specifications.

A motor is a device that converts electrical energy into mechanical energy. A motor can operate on direct current (DC) or alternating current (AC) voltage supply, not both.

The single phase AC induction motor is a common design for fractional and subfractional motors. The motor consists of two basic electrical assemblies: the stator and the rotor. The stator is the primary electrical circuit that induces a current in the secondary electrical circuit, the rotor. The combined electromagnetic effect of the two circuits produces rotation of the rotor.There are two types of single phase AC induction motors commonly used for direct fan applications: shaded-pole and permanent split capacitor.

Shaded-pole motors are simple in construction and the least expensive for subfractional and fractional horsepower applications. The motors typically operate within an efficiency range of 20% to 40%. The components that make up a shaded-pole motor are the stator, the main winding (coil winding), the auxiliary winding (shading coil) and the rotor.

Permanent split capacitor motors (PSC) motors, like all capacitor motors, require an external capacitor to be connected to the motor circuit. The motor typically operates within an efficiency range of 60% to 70%. The components that make up a permanent split capacitor motor are the stator, the main winding, the auxiliary winding, the capacitor, and the rotor.

Induction motors are either asynchronous or synchronous speed motors by design. Synchronous motors operate at a constant speed with or without a load applied to the shaft. Asynchronous motors operate at a variety of speeds and are greatly affected by the load applied to the shaft.

A synchronous speed induction motor will operate at 3600 rpm for a 2-pole motor, 1800 rpm for a 4-pole motor and 1200 rpm for a 6-pole motor using 60 Hz input power.An asynchronous speed induction motor will operate at significantly lower speeds compared to synchronous motors with the same number of poles.

The speed of an AC induction motor can be changed by a number of methods. In addition to changing the design of a motor, common approaches to speed control are changing the applied voltage or changing the applied frequency.

A reduction in motor voltage can be accomplished with a resistor, variable speed AC transformer, or a solid state speed control.

This technique is not commonly used for Sofasco’s products.

A brushless DC motor is a DC motor that has commutation accomplished by electronic circuitry instead of brushes. Since there are no brushes to wear out, the brushless DC motor has a life span equal to or greater than an AC motor.

A backward curved impeller (BCI) is a centrifugal air moving device (wheel) with blades inclined in the direction opposite the direction of rotation. Such impellers can work without the aide of a specially designed scroll housing.

Yes, Sofasco manufactures a variety of fans, blowers, and motors built with materials that offer moisture and corrosion protection: plastics, coated steels, and aluminum or stainless steel alloys are used for scroll housings, impellers, and fan shafts. Moisture protected motors are built to an Internal Protection Classification of either IP44 or IP54.

The air moving industry typically rates fan life using two terms:

L10 life of the bearing and MTBF of the electronic components.L10 life is defined as the number of hours after which 10% of the fans in operation would be expected to experience bearing failure. This number is obtained using fan life test data and Weibull function statistical analysis to obtain a failure distribution prediction. Bearings usually fail because of lubricant degradation over time, which is greatly affected by the ambient temperature in which the fan is operating. This is why bearing L10 life numbers are always provided at a specific ambient temperature.

MTBF (mean time between failures) predications are based on assumed constant failure rates over the useful lifetime of electronic components like resistors, capacitors and semi-conductors. These predictions are usually based on MIL-HDBK-217 or Bellcore TR-332. Sometimes requests are made for the MTBF of the complete air mover assembly. However, because mechanical or electromechanical components like bearing and motors do not have constant failure rates over time, this would not be a valid calculation

Sofasco has fans that can be controlled by a thermistor (a device that changes resistance as temperature changes).

The vertical axis (Y axis) is pressure (inches water or pascals). The horizontal axis (X axis) is flow (CFM or M3H). The curve displays the fan delivery characteristics of specific pressure flow points.

Fans with sleeve bearings generally need to be mounted with the shaft horizontal. Exceptions can be discussed with our engineering staff. Ball bearing fans can mount in any orientation.

IP rating is an international standard for rating motors for the effects of dust.



Check the Sofasco catalog for such information.

This is a term to describe the air flow direction moving through a fan related to a common point, the fan motor supports or struts.

An external motor is a motor designed with the rotor on the outside, common construction for brushless DC motors.

The maximum voltage applied is dependent upon the product and application. Consult Sofasco application engineer for assistance.

A voltage range is the maximum and minimum voltage that can be applied to an air mover where it will operate reliably.

The pressure developed by an air moving device will change proportionally with the air density if the RPM is kept constant. An air moving device powered by an electric motor will change RPM with a change in altitude due to the change in density (less load at higher altitude). This RPM change generally will compensate for altitude changes. The exception is for AC motors that are designed to run very close to synchronous speed at sea level. These will not change the speed with altitude change and will therefore produce less pressure at high altitudes.


Concerning to choose a suitable fan for your equipment, users shall consider following objectives.

- l To optimize airflow efficiency

- l To minimize size and fit

- l To minimize acoustic disturbance

- l To minimize power consumption (if the system power supplied by battery)

- l To maximize reliability and service life

- l To justify the total cost

While making selection of the fan motor for ordinary use, the following methods are very useful.

- l To determine the amount of heat generated inside the equipment

- l To decide the permissible temperature rise inside the equipment

- l To calculate the air volume requirement from equation

- l To estimate the system impedance in the unit

- l To select the fan by performance curve shown in the catalogue or data sheet

The acoustical sound level is measured in anechoic room with background noise less than 15 dBA. The fan is hung under the hanging rod and running in free air with microphones at following three position.

One is at a distance of one meter from the right front side of the inlet.

Another one is at a distance of one meter from the center of the outlet, 45 degree left from the outlet section of the fan.The other is at a distance of one meter from the center of the outlet, 45 degree right from the outlet section of the fan.

Sound Pressure Level (SPL) is environmentally dependent and Sound Power Level (PWL) are defined as:

SPL =20 log10 P\/Pret and

PWL =10 log10 W\/Wref where,

P =Pressure

Pref =A reference pressure

W =Acoustic power of the source

Wref =An acoustic reference power

Fan noise data is usually plotted as Sound Power Level against the octave frequency bands. Following is an indication of the effect of dBA changes:

3dB Barely noticeable

5dB Noticeable

10dB Twice as loud

Noise Change:

0 to 20 dB -- Very faint

20 to 40 dB -- Faint

40 to 60 dB -- Moderate

60 to 80 dB -- Loud

80 to 100 dB -- Very loud

100 to 140 dB -- Deafening

Noise level is measured by the anechoic room. It is the sound created by airflow and normal friction from mechanical structure. Abnormal noise may come from the improper assembly, mechanical tolerance, or component failure.

We set up prototype samples for abnormal noise for every different fan model. Our quality control department check every pieces of fan according to the standard acceptable level. The QC staff are well trained and are sent to the hospital for audiology check-ups annually.

1.System Impedance -Higher airflow will create higher noise level. Likewise, the higher system impedance created by the system, the higher airflow is required in order to achieve the cooling effect. That is, users need to reduce the system impedance as low as possible in order to achieve the least noise of airflow.

2.Flow Disturbance -The turbulent air generated by the obstructions along the path of airflow will raise the system noise. Therefore, users have to avoid any obstructions in the critical inlet and outlet area as much as possible.

3.Fan Speed -As you know, a higher speed fan will generate greater noise compared to a low speed fan. Users have to try their best to choose a lower speed fan as much as possible.

4.Fan Size -A larger size fan will generate a much lower noise level then a smaller size fan does while creating the same airflow. Users shall try to use larger fan with lower speed if space is allowed.

5.Temperature Rise -Airflow is inversely proportional related to the allowable temperature increase in a system. A little change in the allowable temperature rise will lead to a significant change in the airflow requirement. If there is a little compromise to the limit imposed on allowable temperature rise, there will be a considerably less amount of airflow required. It will lead to remarkably reduction in the noise level.

6.Vibration and Resonance -<\/strong>We recommend using some soft and flexible isolator to avoid vibration transmission.

7.Voltage -The higher voltage applied to the fan; the higher vibration it will generate as will as rpm, Correspondingly, it will create a higher noise level.

8.Fan Design -Users have to choose reliable fans to avoid higher acoustic noise caused by improper mechanical and electrical design of the fan.

Different fan blade shape and the number of blades can affect both the airflow and air pressure. The more fan blades we have, the higher the air pressure we may generate. But the harder it is to maintain the plastic mold. However, special attention should be addressed to it's overall performance including balance status, noise level, and life span.

Sleeve bearing is a kind of bearing containing oil or lubricant within a friction contact when fan is rotating. The friction contact between sleeve bearing and the shaft is a face friction. The face friction will create higher noise levels and temperature. The higher the temperature caused by the friction, the greater the possibility foroil leakage. This causes the contact of the bearing to become rough and dry when the oil leaks after a certain period time. Furthermore, the uneven contact usually results in high temperature, abnormal noise and this can cause a malfunction on the fan. The lifespan ofsleeve bearing fan is approximately 20K to 30K hours or 1/2 of the lifespan of ball bearing fans.

For ball bearing fans, there are several miniature steel balls surrounding the cylinder. When the fan rotates, the balls rotate too. Compared to sleeve bearing, it is point friction and has less friction. There are no oil leakage problems so its lifespan is longer, generally 40K to 50K hours for two ball bearing fans and 30K to 40K for 1 ball / 1 sleeve fan (C).

It is a fan withrotation signal output to detect the RPM. It is called tachometer function or pulse alarm output.

Category of Bearing — Originally, spindle motor adopted ball bearing but considering the cost issue, then change to sleeve bearing and hydro bearing. The table below is the comparison of the three different types of bearing.

For ball bearing, because of processing precision and external pressure, the unregular rolling is larger, and the material is harder. It is easier to create resonance while the motor spinning at high speed.

Sleeve bearing is sintered with metal powder, the lubricant is stored among the gap of metal parts. The frication is face to face. To compare with ball bearing, the material is softer. When rpm increased, the gap between shaft and bearing will be enlarged. As well, the lubrication of the sleeve bearing will be reduced because of seal effect and shorten it's life expectancy.

For hydro bearing, the shaft and bearing will be separate by hydro oil membrane in order to maintain lubrication. The effect of lubrication is not significant if the rpm is too slow. It requires a certain operating range. Since the hydro oil membrane has the anti-vibration effect therefore the vibration can be reduced. The material is harder than sleeve bearing.

The operation theory of hydro bearing — According to the test result, obviously the hydro bearing can reach similar stability of ball bearing. For example. That is, the hydro bearing already obtains the requirement of long life expectancy for computer system, telecommunication, measurement, and medical equipments. Compare to ball bearing, hydro bearing is much competitive because of lower noise, lower cost.

Sintered hydro bearing: The progress of hydro bearing processing is owing to the development of sintering technology. Under high pressure condition, to solid metal powder to a certain shape and sintered at high temperature. Through the processing procedure, it will generate many small holes among the metal powder. The total cubic content of the hole is around 15~30% of the bearing itself. Furthermore, to fill the lubricant into the holes by vacuum©â¨ú process. Besides, there is a recycle oil storage sink design on the bearing to ensure the constant operation of the lubricant.

Even the fan is not rotating, the special design of hydro bearing can ensure the lubrication. Even at the beginning of starting, the shaft will not be dry. While the fan is at rest, the Capillarity effect will generate a lubrication membrane between shaft and bearing so that the lubricant will not leak out. When the fan starts rotating, the slight pressure difference will generate hydro wave between the gap of shaft and bearing. The rotation of the shaft will conduct the lubricant recycled on the surrounding of bearing. The hydro wave of hydro bearing will be generated at the most narrow gap between shaft and bearing (where generate the most friction). To ensure the shaft and bearing won't touch.

At the most narrow gap between shaft and bearing, where with the most lubricant pressure, the pressure will fill the lubricant into the holes among metal powder and recycle. At the same time, the lubricant will flow from where with lower pressure to high pressure (where need lubricant) to maintain the balance of lubricant. This kind of recycling will keep on certain stability.