Part of DIY Wind Turbine
Permanent magnets are the heart of any wind turbine generator — they create the magnetic field that converts mechanical rotation into electricity.
Permanent Magnets
Why Permanent Magnets Matter
Without permanent magnets, your wind turbine is just a spinning stick. The magnets mounted on the rotor disc create a sweeping magnetic field that passes over your stator coils, inducing voltage through electromagnetic induction. The stronger your magnets, the more electricity you produce at any given speed — which means your turbine starts generating useful power in lighter winds.
In a post-collapse scenario, you will not be manufacturing magnets. Every magnet you use will be salvaged, so knowing where to find them, how to handle them, and how to arrange them correctly is the difference between a working generator and a decorative lawn ornament.
Magnet Types and Grades
Not all magnets are created equal. The three types you will encounter in salvage are:
| Type | Strength | Temperature Limit | Where Found |
|---|---|---|---|
| Neodymium (NdFeB) | Strongest — 10x ferrite | 80-200°C depending on grade | Hard drives, headphones, motors |
| Ferrite (Ceramic) | Weak but stable | 300°C+ | Speakers, cheap motors, fridge magnets |
| Alnico | Moderate, easily demagnetized | 540°C | Old guitar pickups, vintage meters |
Neodymium is what you want. A single neodymium magnet the size of a coin produces more flux than a ferrite magnet the size of your fist. For wind turbines, this means a lighter rotor, less starting torque needed, and more power output.
Understanding Magnet Grades
Neodymium magnets are graded by their maximum energy product. The number after “N” tells you the strength:
- N35 — Entry level, common in cheap electronics. Adequate for small turbines.
- N42 — Good balance of strength and availability. Found in quality speakers and motors.
- N52 — Maximum commercial grade. Found in high-end hard drives and precision motors.
Grade Matters Less Than Size
An N35 magnet that is 50mm x 25mm x 10mm will outperform an N52 magnet that is 20mm x 10mm x 5mm. Total flux depends on both grade AND volume. Prioritize finding large magnets over hunting for the highest grade.
The letter suffix indicates temperature rating: N (80°C), M (100°C), H (120°C), SH (150°C), UH (180°C), EH (200°C). For wind turbines, standard N-grade is fine — your generator should never reach 80°C unless something is very wrong.
Salvage Sources
Finding strong magnets requires knowing where to look. Here is a ranked list by magnet quality and ease of extraction:
Tier 1: Best Sources
Hard disk drives — Every HDD contains two arc-shaped neodymium magnets (typically N48-N52) mounted on steel brackets inside the voice coil actuator. A single 3.5” drive yields two magnets roughly 40mm x 15mm x 3mm. Collect 20-30 drives and you have enough for a small turbine. Remove magnets by clamping the bracket in a vise and prying with a flathead screwdriver.
Brushless DC motors — Found in power tools (drills, saws), electric bikes, scooters, and servo motors. These contain arc-shaped neodymium magnets glued to the rotor. Heat the rotor to 150°C with a torch to soften the adhesive, then pry magnets free.
Speakers and subwoofers — Large speakers (8” and up) contain ring magnets. PA speakers and car subwoofers have the strongest ones. Most are ferrite, but high-end models use neodymium. Even ferrite speaker magnets work if you collect enough of them.
Tier 2: Good Sources
MRI machines — If you find a hospital or medical facility, an MRI scanner contains the most powerful magnets on Earth (1.5-3 Tesla superconducting magnets). However, these are electromagnets, not permanent magnets, and are useless without power. The accessory equipment may contain useful neodymium magnets though.
Electric vehicle motors — Tesla, Prius, and other EV motors contain large neodymium arc segments. A single Prius motor yields enough magnets for a 1-2 kW turbine.
Wind turbines and alternators — Salvaging magnets from existing generators is circular but valid. Car alternators use electromagnets (not useful), but permanent magnet alternators from boats and small wind turbines are excellent sources.
Avoid Microwave Oven Magnets
Microwave magnetrons contain ceramic magnets that are ring-shaped and brittle. They are ferrite, relatively weak, and often crack during extraction. Not worth the effort when hard drives are everywhere.
Rotor Disc Layout
The magnets mount on a steel disc (the rotor) that spins with the turbine blades. The arrangement follows strict rules:
Alternating Poles
Magnets must alternate between North-facing-out and South-facing-out around the disc. If you have 12 magnets, the pattern is N-S-N-S-N-S-N-S-N-S-N-S. This creates alternating magnetic fields that induce AC voltage in the stator coils.
Spacing
All magnets must be evenly spaced around the disc. For 12 magnets on a 300mm diameter disc, that is 30 degrees apart. Use a protractor or divide the circumference into equal segments with a compass.
| Number of Magnets | Degrees Between | Best Paired With |
|---|---|---|
| 8 | 45° | 6 coils (single phase) or 9 coils (3-phase) |
| 12 | 30° | 9 coils (3-phase) — most common DIY setup |
| 16 | 22.5° | 12 coils (3-phase) |
| 20 | 18° | 15 coils (3-phase) |
The Classic Ratio
For three-phase generators, use a 4:3 ratio of magnets to coils. 12 magnets with 9 coils is the most proven DIY configuration. Each phase gets 3 coils, and the geometry ensures smooth power output with minimal cogging.
Dual Rotor Configuration
Most DIY turbines use two rotor discs with the stator sandwiched between them. The magnets on the front and back discs must be aligned so that a North on one disc faces a South on the other disc directly across the air gap. This concentrates the magnetic flux through the coils.
Mark your discs with alignment lines before mounting magnets. Getting this wrong halves your output.
Safe Handling
Neodymium Magnets Can Cause Serious Injury
Two magnets snapping together can crush fingers, pinch skin hard enough to draw blood, and shatter into razor-sharp fragments. A stack of large magnets can break bones. Never let children handle them, and always work with gloves and eye protection.
Handling Rules
- Separate magnets with spacers. Keep wooden or cardboard spacers between magnets during storage and transport.
- Slide, don’t pull. To separate two stuck magnets, slide them apart sideways rather than pulling straight apart.
- Keep away from electronics. Neodymium magnets will erase hard drives, destroy credit cards, and damage screens from 15cm away.
- Work on a wooden surface. Steel workbenches will grab magnets and make positioning impossible.
- One at a time. Never carry a handful of loose magnets. They will slam together violently.
Mounting Magnets to the Rotor
Epoxy Method
- Mark magnet positions on the steel rotor disc using a template.
- Rough up both the magnet face and disc surface with sandpaper (80 grit).
- Clean both surfaces with acetone or alcohol.
- Mix two-part epoxy (JB Weld or marine epoxy — avoid 5-minute epoxy, it is too brittle).
- Apply a thin, even layer to both the magnet and the disc.
- Place the magnet and press firmly. The magnet will self-center on the steel disc due to magnetic attraction.
- Allow 24 hours full cure before handling.
Mechanical Retention
Epoxy alone can fail under vibration and heat cycling. Add mechanical retention:
- Lip ring: A thin steel ring around the outer edge of the disc that overlaps the magnet edges by 2-3mm.
- Individual tabs: Small steel tabs tack-welded or bolted next to each magnet.
- Fiberglass wrap: After epoxy cures, wrap the entire magnet face with a layer of fiberglass cloth and resin.
A Magnet Flying Off at Speed Can Kill
At 500 RPM, a 50-gram magnet launches with the energy of a bullet. Mechanical retention is not optional — it is a safety requirement. If you cannot add retention, limit your turbine RPM with furling or braking.
Matching Magnets to Coils
The number of magnet poles must match your coil configuration for the generator to work. The key relationship:
- Electrical frequency (Hz) = (RPM x Number of pole pairs) / 60
- Pole pairs = Number of magnets / 2
For a 12-magnet rotor spinning at 300 RPM: (300 x 6) / 60 = 30 Hz. This produces 30 cycles per second of AC output. After rectification, this becomes DC for battery charging.
For battery charging (12V or 24V systems), you want the generator to reach charging voltage at relatively low RPM (200-400). This means either more magnets, more coil turns, or stronger magnets. See Coil Winding for calculating the coil side of this equation.
Common Mistakes
| Mistake | Cause | Fix |
|---|---|---|
| Magnets mounted with same pole facing out | Didn’t mark polarity before mounting | Use a compass or known magnet to test every magnet BEFORE epoxying |
| Generator produces no voltage | Front and back rotor magnets not aligned (N to N instead of N to S) | Mark alignment lines on both discs, verify with a thin piece of steel that bridges both discs |
| Uneven voltage output | Magnets not evenly spaced | Use a printed or drawn template with precise angular divisions |
| Magnet shattered during handling | Two magnets snapped together | Always use spacers, slide apart sideways, wear eye protection |
| Epoxy failed, magnet flew off | Used wrong epoxy or didn’t prep surfaces | Use structural epoxy (not superglue), sand both surfaces, add mechanical retention |
| Low power output despite strong magnets | Air gap too large between rotor and stator | Minimize gap to 1-2mm per side. Thinner stator = more power |
Key Takeaways
- Neodymium magnets from hard drives are the most accessible high-strength source — collect 20-30 drives for a small turbine
- Magnets must alternate N-S-N-S around the rotor disc with perfectly even spacing
- The classic DIY setup is 12 magnets with 9 coils in a 4:3 ratio for three-phase output
- Always add mechanical retention beyond epoxy — a loose magnet at speed is lethal
- Dual rotor discs must have opposite poles facing each other across the air gap
- Handle neodymium magnets with extreme care — they can crush fingers and shatter explosively
- Match magnet count to coil count using the 4:3 ratio, and verify charging voltage is reached at your expected RPM range