Effi­cient cooling of hot spots made easy

Modern elec­tronic compo­nents and assem­blies make it possible to achieve a high power density together with a compact design. As a result, more heat does however have to be dissi­pated from both CPUs and power elec­tronics. Conven­tional cooling concepts with moderate amounts of air require large heat sinks in such situ­a­tions and would coun­teract the desired minia­tur­i­sa­tion effect. Active cooling with effi­cient high-perfor­mance fans offers a better alter­na­tive for high-perfor­mance cooling in data processing systems, inverters and laser devices for example. With an edge length of just 40 mm, such fans convey a powerful flow of air to the hot spot. The high-speed, turbu­lent flow dissi­pates heat exactly where it is needed, saving valu­able instal­la­tion space. Intel­li­gent elec­tronic fan control constantly ensures optimum power adjust­ment and pinpointed vari­a­tion of the air volume in line with require­ments. This reduces both energy consump­tion and oper­ating noise.
High power combined with a compact design offers a variety of advan­tages: Users benefit from greater effec­tive power, whilst minia­tur­i­sa­tion conserves both resources and the envi­ron­ment. This applies not only to computers and control elec­tronics but also to power compo­nents such as tran­sis­tors, thyris­tors or diodes in frequency converters, welding appli­ances or inverters. Increased power and minia­tur­i­sa­tion are however unfor­tu­nately also accom­pa­nied by greater losses in each compo­nent. New cooling concepts are called for. Which is why the ebm-papst fan special­ists from St. Georgen in the Black Forest devel­oped a fan to suit the demands of modern high-perfor­mance elec­tronics. The cata­logue of require­ments included compact dimen­sions, a very high air conduc­tion rate and pres­sure increase to be able to provide a suffi­cient volume of cooling air for even tightly packed compo­nents (Figure 1). At the same time the aim was to design a fan which would set new stan­dards in terms of effi­ciency and vari­ability. This was achieved by devel­oping special control elec­tronics with opti­mised actu­a­tion and a connec­tion for external commu­ni­ca­tion to permit demand-based air volume control.

Figure 2: The complex control board is fully inte­grated into the fan housing

Compact fan full of exper­tise

With regard to conveying a certain air flow per unit of time, a small cross-section produces a much higher flow velocity than a larger one. In addi­tion, the infeed of energy is required to move gas mole­cules – a func­tion performed by the blades of the fan rotors. Simi­larly to a large propeller on an aircraft, a large impeller conveys a large volume at moderate speed and air velocity. By contrast, a higher blade speed and opti­mised inlet/outlet geom­etry are neces­sary for a small fan to convey the same volume of air per unit of time. With a high speed and high air jet velocity, a small, ideally designed rotor can there­fore achieve the air perfor­mance level of a large fan rotor. The diffi­cult aspect is the optimum inter­ac­tion of all compo­nents. This was where our devel­op­ment experts in the Black Forest were able to draw on their decades of expe­ri­ence.
Two criteria there­fore had to be consid­ered for the compact fans with an edge length of 40 x 40 mm and flow rates of nearly 40m³/h: an aero­dy­nam­i­cally opti­mised design for the rotor and housing and a suffi­ciently powerful drive system. Ideally, a balance should be achieved between the demands for a high speed in terms of aero­dy­namics and in rela­tion to the elec­tric drive: Smaller elec­tric motors draw their power from a high speed with a rela­tively moderate torque. In several stages, the powerful external rotor motor of the fan was ideally adapted to the opti­mised aero­dy­namic compo­nents. This was so successful that the new fan, designed with the stan­dard 40 x 40 x 28 mm dimen­sions, now attains virtu­ally twice the power of its prede­cessor.

Air conduc­tion “On Demand”

Intel­li­gent control of the drive system and thus of the air volume must also be possible. For this purpose, the elec­tron­i­cally commu­tated motor is regu­lated by way of complex control elec­tronics (Figure 2). This permits not only econom­ical, in other words power-saving oper­a­tion, but also pinpointed air conduc­tion: For instance, the air flow is reduced if a CPU or diode laser is in idle mode, whereas accord­ingly more cooling air is conveyed if the amount of heat to be dissi­pated increases under load. In addi­tion to lowering the power require­ment and noise level, this also extends the service life of the upstream filters for example. All-in-all, the built-in intel­li­gence of the fan dras­ti­cally cuts the oper­ating costs of the cooling system. Special func­tions such as a speed signal, a Go/NoGo alarm, an external temper­a­ture sensor, a PWM control input and protec­tion against mois­ture or even salt spray fog extend the range of possible appli­ca­tions beyond the bounds of switch cabi­nets or computer centres right through to tough indus­trial envi­ron­ments.

Figure 3: A small fan with a lot to offer – as the air perfor­mance diagram shows!

In prac­tice

The fans in the 420J series are designed and manu­fac­tured to ebm-papst “Green­Tech” envi­ron­mental stan­dards. They have extremely compact dimen­sions of 40 x 40 x 28 mm. Two versions are avail­able with 12 or 24 VDC nominal voltage. Depending on the model the air flow is between 24 and 38 m³/h with a pres­sure increase of up to 500 pascal and a power consump­tion of 2.5 or 7,1 W (Figure 3). The fan is quieter than the old version, with a reduc­tion in sound power level of between 2 and 5 dB(A) depending on the oper­ating point. The small fan weighs only 45 g, as the housing and impeller are made of light, vibra­tion-damping GRP (glass fibre-rein­forced plastic) such as PBT (poly­buty­lene tereph­tha­late) or PA (polyamide). The fan is suit­able for use over a broad temper­a­ture range between -20 and +70 °C. At full load, power consump­tion is around 70% lower than that of its prede­cessor. The improved motor effi­ciency level also has a posi­tive effect in terms of bearing heat gener­a­tion. Years of oper­a­tion at a nominal speed of up to 17,200 rpm are thus no problem. The service life (L10) values based on ebm-papst’s strin­gent in-house stan­dard are very high: 75,000 or 32,500 hours for the M-version of the fan at 40°C or 70°C respec­tively. Employing the usual L10IPC method, the life expectancy of an M-version at 40 °C is around 127,500 hours.
The robust plas­tics can with­stand even tough envi­ron­mental condi­tions. An extra-robust version of the fans is also avail­able to provide a broader range of appli­ca­tions extending to indus­trial equip­ment and mobile units. In this case the elec­tronics board is encap­su­lated in polyurethane and the stator is provided with a protec­tive coating for example. This enables the fan to pass the salt spray mist test, qual­i­fying it for use in the tough envi­ron­ment of converters or diode welding systems.