Most explanations of a wind turbine stop at the blades. But the blades only decide how much energy is available — what happens to it is decided by the generator, and specifically by how its magnets are arranged. This is a look inside the permanent magnet generator that TESUP builds for the Atlas and Magnum, and at the one property that decides whether a turbine turns in light wind or just stands there.
What is a permanent magnet generator?
A permanent magnet generator produces electricity using fixed magnets rather than electromagnets that must first be energised. Because the magnetic field is always present, the machine generates from the very first rotation and needs no excitation current, no slip rings and no external power to get started.
TESUP's generator is a 24-pole permanent magnet machine using NdFeB N42 (neodymium-iron-boron) magnets, each 60 × 25 × 5 mm, nickel-coated and bread-shaped. There are 24 of them, 180 cm³ of magnet in total, turning inside a stator measuring 16 cm × 12 cm.
Why 24 poles, and why no gearbox?
Pole count sets the relationship between rotational speed and output frequency. A generator with few poles has to spin fast to be useful, which is why many turbines put a gearbox between the rotor and the generator. A gearbox is also the component most likely to fail, the one that needs oil changes, and the one that makes noise.
Twenty-four poles produce usable voltage at low rotational speed, so the rotor can drive the generator directly. No gearbox means no gear oil, no gear wear, and one fewer thing that can seize on a roof in February.
What is cogging torque?
Cogging torque is the resistance you feel when you turn a permanent magnet motor by hand — that notchy, step-by-step reluctance, as though the shaft wants to settle into fixed positions. It is caused by the magnets attracting toward the steel teeth of the stator. Each tooth is a preferred parking spot, and the rotor has to be pushed out of it.
In a fan or a power tool, cogging is a minor annoyance. In a small wind turbine it is the single most important obstacle to low-wind performance, because cogging torque is a fixed threshold that the wind must overcome before anything turns at all. Below it, output is not small — it is zero.
This is why cut-in wind speed matters so much more than rated power for a domestic turbine. Rated power describes a windy day. Cut-in speed describes every other day.
How does skewing the magnets reduce cogging torque?
If every magnet sits exactly parallel to the stator teeth, all 24 poles reach their attraction peak at the same instant. Those peaks add together, and the result is a strong, notchy pulse the wind has to break through on every step.
Skewing means mounting the magnets at a slight angle to the axis of rotation, so that each magnet engages a stator tooth progressively rather than all at once. The peaks no longer coincide — they spread out and partially cancel. The total torque the generator produces is unchanged; what disappears is the ripple.
TESUP uses skewed magnet mounting for exactly this reason. Lower cogging torque means a lower breakaway threshold, and a lower breakaway threshold is what allows the Atlas to self-start at 2 m/s with its low-wind blade set — roughly one third the cut-in speed of a typical horizontal-axis turbine.
Skewing is not free: it slightly reduces peak flux linkage, so a skewed machine gives up a little top-end output in exchange for starting earlier. For a domestic turbine, where light wind is the common condition and storms are rare, that is the right trade to make.
Why does a turbine that makes about 1 kW use a 15 kW motor?
Because a generator's rating is a thermal limit, not a promise of output. The 15 kW continuous rating is what the machine can sustain indefinitely without overheating, and it is set by three things: the Class 200 °C enamelled wire insulation (IEC 60317-13 GR 2, the same grade used in industrial servomotors and EV drivetrains), the 4 kg of copper winding acting as thermal mass, and passive cooling through the housing.
At the Atlas's typical output of around 1 kW, the motor is running at under 7% of its continuous rating. It runs cold. Copper losses rise with the square of current, so a machine operating far below its limit wastes very little as heat — and heat is what ages insulation and eventually ends a motor's life.
The 22 kW peak figure is the short-term overload capacity for gusts. It is bounded by two physical limits: the demagnetisation threshold of the N42 magnets, and saturation of the stator iron.
Why tooling is what actually decides cogging torque
Skewing only cancels cogging torque if every magnet sits exactly where the design says it should. The cancellation is a geometric effect: 24 magnets, each offset by a precise angle, so their attraction peaks fall out of step with one another. If the seats those magnets sit in vary from one rotor to the next, the skew angle varies with them — the peaks drift back into alignment, cogging rises, and the wind speed needed to break the rotor free rises with it.
That is why ±0.05 mm across all machined components is not a boast on a spec sheet. It is the tolerance the physics requires. A rotor built to loose tolerances can carry exactly the same magnets, the same pole count and the same copper, and still start later in the wind.
Holding that tolerance on one prototype is straightforward. Holding it on every unit, for years, is a tooling problem — which is why this arrived at our facility:
A press tool like this is not bought for speed, though it is faster. It is bought for repeatability. The first rotor formed on it and the ten-thousandth come out of the same steel, located by the same pillars, to the same dimensions. That is the only way a tolerance figure means anything once you are building at volume rather than one at a time.
It also means one more component that no longer depends on somebody else's quality control. Our European facilities already produce over 270 components in-house — generators, electronic cards, blades and mounting hardware. Every tool that lands makes that list one item longer.
Where the energy actually comes from
The power available in wind follows:
P = ½ · ρ · A · V³ · Cp · η
Where ρ is air density, A is swept area, V is wind speed, Cp is the power coefficient and η is electrical efficiency. The Atlas rotor sweeps 1.035 m² (1030 mm diameter × 1005 mm height), reaches a Cp of 0.28 in good wind, and converts at 92% electrical efficiency.
The term that dominates is V³. Wind speed is cubed, so a site with 30% more wind yields roughly double the energy, not 30% more. This is why mast height and siting change results more than any specification on this page — and why an honest answer to "how much will I get?" always begins with a question about your location rather than a number.
Full generator specification
| Parameter | Value |
|---|---|
| Generator type | 24-pole permanent magnet, direct drive (no gearbox) |
| Magnets | NdFeB N42, 60 × 25 × 5 mm, nickel-coated, bread-shape |
| Magnet volume | 24 magnets · 180 cm³ total |
| Magnet mounting | Skewed — minimises cogging torque |
| Stator | 16 cm × 12 cm · 2.4 L |
| Winding | 4 kg pure copper · 90 turns per stator slot |
| Wire insulation | Class 200 °C enamelled, IEC 60317-13 GR 2 · CE / UL |
| Machining tolerance | ±0.05 mm across all machined components |
| Rotor | 1030 mm diameter × 1005 mm height · 1.035 m² swept area |
| Cut-in wind speed | 2 m/s with the low-wind blade set |
| Power coefficient (Cp) | 0.28 in good wind |
| Electrical efficiency | 92% |
| Motor rating | 15 kW continuous · 22 kW peak |
What this does and does not tell you
Every figure above is a property of the machine, and machine properties are the part we control. Cogging torque, pole count, magnet grade, insulation class and machining tolerance are the same in every unit we ship.
Annual energy yield is not. That depends on your wind, and published yield for the Atlas spans 180–2,900 kWh per year precisely because the range between a sheltered suburban garden and an exposed coastal site is that wide. Tell us your location and mast height and we will give you a realistic range rather than a best case.