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General

What is the difference between inrunner and outrunner motors? 

Simply said, inrunners have the spinning part on the inside. Outrunners spin on the outside. Inrunners are typically used in combination with gearboxes, at least for high-speed motors. Our larger machines however (diameters > 1,6m) are also inrunners and mainly applied for high torque - low rpm direct-drive applications such as wind turbines. For vehicles, inrunners have higher rpm, mostly combined with a gearbox, while outrunners are typically used for direct driven in-wheel applications. Outrunners are also very useful for aircraft and drone applications where the rotational speeds are generally lower, but the weight must be kept very low. Magnax can deliver both configurations.

 

Can the axial flux motors function as a generator too?

Yes, the Magnax machines can function as generator and motor. The machine can be used in 4-quadrants operation by using the 4-quadrant inverter of your choice. As a result, our large diameter machines are typically applied as lightweight generators for ie wind turbines. The smaller (high-speed) axial flux machines, function as e-vehicle motor combined with regenerative braking or similar purposes. 

 

Can the motors be stacked in parallel?

Yes, the machine concept is designed to connect multiple motors or generators in parallel and as such, multiply the torque and power of the generator / electric motor. This is usually done when the diameter must be kept limited. Each machine (generator or motor disc) can also be driven via a separate inverter to create a redundant solution.

 

How much acoustic noise does the machine make?

When you look at electric motor applications today; most noise is generated by the gearbox, not the electric motor. The magnax machines have a negligible noise level.

 

Which permanent magnets are used in the Magnax Axial Flux Machines?

Magnax machines use neodymium magnets, but more than 50% less magnets than traditional permanent magnet motors/generators. Even after 25 years of use, there is no measurable demagnetisation on the magnets. Some customers are afraid that the supply of the magnets becomes more difficult in the future due to the Chinese monopoly on the mining of the rare earth materials used in Neodymium magnets. However, new mines have been opened after the rare earth crisis in 2011. The problem is not that the amount of RE materials is limited because our Earth has enormous quantities of these materials available. It was the shortage of mines and the fact that most of them were located in China that resulted in the crisis. Since then, many new mines have been opened worldwide, including in countries such as Russia, Brazil, Thailand, India, Canada. What’s more, significant improvements have been made recently for the production of magnet metals which are RE free, and they will be able to meet the specs of the current magnets. More information around this subject: https://www.magnax.com/magnax-blog/permanent-magnets-china

 

 

Does Magnax provide the controllers / inverters?

Our machines stay below 1500 Hz, which means that no exotic power electronics is required. Magnax machines are designed to work with off-the-shelf inverters. Our machines can be used in 4-quadrants operation by using the 4-quadrant inverter of your choice. The only requirement is that the inverter can handle permanent magnet motors.

 

Does Magnax provide Battery packs?

No, but we are open to collaborations with battery suppliers.

 

Can field weakening be used for Magnax Axial Flux Machines?

Yes, from an electrical point of view, our axial flux machine is similar to the radial flux machine which means that also the magnetic  principles are the same. Therefore field weakening can be equally used for the Magnax axial flux machines. However, if you intent to go in much higher RPMs (> 13000 rpm), we need to make sure that specific bearings are used (which can support the high-speed operating point in the field weakening region).

 

Most Magnax high-speed motors are designed for +/-400V to +/-750V battery voltage. Can lower battery voltages be used too?

Yes, we can modify the windings and as such, reduce the voltage. This won't have much effect on the performance. However, decreasing the voltage results in an increase in current, so the inverter must be capable of coping with these higher currents.

  

 

Does Magnax deliver gearboxes too?

No, but Magnax motors can be combined or integrated with existing or new gearbox solutions on the market.

 

Can we integrate a gearbox system to provide even higher torque at lower rpm?

Yes, a (planetary) gearbox (single or multi-stage) can be combined with Magnax machines. In some cases (for larger machines and outrunner configurations), planetary gearboxes can even be integrated into the hollow axis of the Magnax motor or generator. This results in a very compact solution compared with traditional induction + gearbox systems while the efficiency remains very high. Since Magnax axial flux machines already deliver high torque at low rpm, the primary purpose is to reduce the no. of gearbox stages while keeping the weight of the total solution as low as possible. 

 

How is the cooling of the Magnax machines different compared with other axial flux machines?

Magnax machines include an in-house developed and patented cooling concept with aluminium pieces surrounding the cores. As such, the heat from the cores is extracted to the outside of the motor in a very effective way. At the outside of the motor, air cooling or water cooling can be used to remove the heat. The cooling fins or water jacket is in direct contact with the cores and proves to be extremely effective, even in hot conditions such as deserts. This cooling concept is much more effective than traditional axial flux concepts with cooling through the yoke or cooling of the cores by pushing oil through the cores generating local turbulences and air bubbles). Inside, the Magnax machines are completely filled, all air is extracted and all sensitive components, such as the cores, are completely sealed off. This gives the added advantage of excellent corrosion and vibration resistance.

 

How long can the motor run at maximum torque or power?
This varies from 5 to 20 seconds, depending on the (ambient) circumstances. The primary influence on the overloading time is the chosen cooling strategy. We can expect better overloading capacity when the motor/generator is water cooled than air cooled. Peak torque (overloading torque) is generally twice as high as the nominal (continuous) value at a given rpm.

 

Is the bearing of the machine strong enough to cope with heavy duty axial, radial and torque loads?

For normal loads, the internal bearing of the axial flux machine should be enough to cope with the forces. However, the axial flux machine is not designed to support loads from severe external forces such as turbine blades. For use cases, such as wind turbines and aircraft blades, where significant axial and bending forces are generated, a separate bearing is required.

  

What kind of cooling fluid, the Magnax axial flux motors use?

The motor itself needs a water/glycol mix for cooling (ie 10 liters/min for the 275mm version).

The motor covers that fit on the ends of the motor exist in two variants; an air-cooled, and water cooled version. Efficiency tests are done at 50°C coolant temperature in normal ambient temperature conditions.

 

How are the motors sealed?

If the motor is mounted against a flange or a motor cover is used, the rotor disk is sealed from the outside. Water cannot enter the motor this way. The junction box is also watertight (IP67). However, water or dust entering the air gap is not a significant problem since because in an axial flux design, fluids and particles are removed automatically due to the centrifugal forces (air gap is radially oriented). Secondly, thanks to our patented cooling concept, the sensitive parts (cores etc.) are completely sealed. The motor housing is made out of anodised aluminium which is effective against corrosion. 

 

How does the machine react in an overload situation?

The Magnax axial flux machine is a synchronous machine. When the torque overload surpasses 200%, the machine will ‘jump a pole’ (which is not harmful to the Magnax machine), but can cause severe shocks in the load (ie wind turbine blades). From a thermal point of view, the machine can easily cope with higher continuous loads as long as that the cooling is sufficient. For small machines, the peak torque is generally limited to 10, maximum 20 seconds. There are pt100 heat sensors built in the machines which are connected with the drive. In case of overheating, the drive will shut down the machine to prevent overheating or avoid the pole jump.

 

 

 

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Daan Moreels

Tel +32 471 78 38 04

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Magnax Axial Flux Direct Drive Generators and Motors