Permanent magnet motor
Use the calculator first, then read the evidence layer. This single canonical page answers the 1.25 motor magnets alias without publishing a duplicate route.
Evidence reviewed: June 5, 2026
Alias
merged
Default OD
31.75 mm
Primary risk
heat
The visual shows a 14-pole screening layout around a 31.75 mm rotor. It is an explanatory model, not a universal magnet SKU.
Result feedback
Deterministic screenEmpty state: defaults are loaded
Run the screen to turn the default 1.25 inch rotor assumption into a magnet pitch, target arc width, thermal margin, and next action.
Pole pitch
7.12 mm
Target arc
5.13 mm
Thermal margin
60 degC
Confidence
Medium
Next action
Use the calculator, then request an RFQ review if the magnet grade, magnetization direction, or original rotor drawing is unknown.
Request magnet reviewLimit: this is a screening tool, not a finite-element magnetic model. It does not infer magnet thickness, skew, adhesive chemistry, air gap, or rotor balance.
Evidence gaps closed
The calculator gives the first answer, then this table shows which evidence gaps matter before a size clue becomes a purchase or production decision.
| Gap found | Why it mattered | Information added |
|---|---|---|
| Size-only replacement logic | The baseline page explained that 31.75 mm is only a clue, but it did not show why no public table can safely map the phrase to one SKU. | Added explicit public-evidence gap and a decision boundary: require original drawing, pole count, magnetization direction, grade, coating, and post-repair electrical tests. |
| Material risk evidence | The first version relied heavily on vendor grade guides and did not separate material property screening from motor qualification. | Added IEC 60404-5 measurement context and clearer language that BH curves at operating temperature are needed for production decisions. |
| Supply-chain risk | The page covered heat and demagnetization but underplayed procurement exposure for Dy/Tb-bearing high-coercivity NdFeB grades. | Added DOE, IEA, and USGS 2026 evidence on NdFeB supply-chain concentration, rare-earth value exposure, and heavy rare-earth import reliance. |
| Rotor assembly risk | Balance was listed as a risk, but the page did not connect loose magnet replacement to recognized rotor balancing practice. | Added ISO 21940 context and an action boundary: balance the assembled rotor and ask for balance/runout data when replacing a rotor assembly. |
Report summary
The immediate question is usually size-driven, but the decision depends on grade, heat, magnetic circuit, and assembly risk. These conclusions are tied to the tool assumptions and source table below.
80-220 degC
Standard N grades are commonly screened around 80 degC, while higher-coercivity suffixes such as SH, UH, EH, and AH extend the published service-temperature range.
Evidence: K&J Magnetics specifications and temperature guide
31.75 mm
A search for 1.25 motor magnets usually points to rotor outside diameter or magnet size. Pole count, arc length, thickness, magnetization direction, and grade still decide compatibility.
Evidence: Dimensional conversion plus replacement-magnet workflow
60-84%
The calculator flags very narrow or very wide magnet arcs before a full magnetic circuit review. No IEC, ISO, or public motor OEM table was found that turns this band into a universal design rule.
Evidence: Internal engineering screen; public evidence is insufficient
95%
IEA analysis published in 2026 says permanent magnets account for around 95% of total rare-earth consumption by value, so replacement decisions should treat grade availability and sourcing resilience as real risks.
Evidence: IEA Rare Earth Elements report, 2026
N/A
Motor magnets are application-specific. Public magnet grade tables help with material risk, but the final rotor bill of materials must come from the original drawing or reverse engineering.
Evidence: Public evidence is insufficient for a universal SKU match
Evidence and material choices
The ranges below are source-backed where public data exists. They are screening ranges, not a replacement for motor-specific BH curves, FEA, and thermal validation.
| Material | Strength clue | Service clue | Best fit | Caution |
|---|---|---|---|---|
| NdFeB N35-N52 | 30-52 MGOe | 80-220 degC by grade family | Compact, high torque-density rotors | Heat, corrosion, and demagnetization curve must be checked |
| NdFeB SH / UH / EH / AH | Lower max grade options at higher coercivity | 150-220 degC typical screening range | Hot rotors, high current spikes, enclosed motors | Higher cost and availability limits |
| SmCo | Lower than top NdFeB, strong thermal stability | Often selected above NdFeB comfort zone | Aerospace, vacuum, medical, and high-temperature axes | Brittle and costlier than common NdFeB |
| Ferrite | About 1.05-3.5 MGOe | High temperature tolerance but low energy density | Large low-cost motors with space for more magnet volume | Usually not a drop-in substitute for compact NdFeB rotors |
Standards boundary
The tool is intentionally narrow. These standards and records define the next evidence layer when a result affects production, high speed, safety, or warranty exposure.
| Reference | Applies to | Decision use | Limit |
|---|---|---|---|
| IEC 60404-5:2015 | Measurement of permanent magnet magnetic flux density, magnetic polarization, and field strength | Ask suppliers for BH or demagnetization curves measured at the relevant operating temperature before approving a production substitute. | It characterizes magnetic material behavior; it does not certify that a repaired rotor will meet torque ripple, balance, or thermal limits. |
| ISO 21940 rotor balancing family | Mechanical vibration and rotor balancing practice, including balance quality and verification concepts | Treat loose magnet repair as an assembled-rotor problem; request residual unbalance, runout, retention, and speed-rating evidence. | A balance grade is not a magnetic-fit result and does not prove the substitute magnet grade or pole layout is correct. |
| OEM motor drawing / reverse engineering record | Motor-specific geometry, material, coating, adhesive, magnetization, skew, and inspection requirements | Use the calculator result only to prepare questions; approve the part only after the motor-specific record closes the unknowns. | No reliable public data was found for a universal table that resolves every 1.25 motor magnets query. |
Inputs: 31.75 mm OD, 14 poles, N42SH, 90 degC rotor estimate
Result: Use as an RFQ starting point. Confirm magnet thickness, radial magnetization, adhesive, and balance before ordering.
Inputs: 31.75 mm OD, 10 poles, standard N42, 105 degC rotor estimate
Result: Reject standard N grade from the screen. Move to higher coercivity NdFeB or SmCo and request a demag curve.
Inputs: Diameter known, pole count unknown, original magnets cracked
Result: Do not infer a replacement from size only. Count poles, identify magnetization direction, and test no-load current after repair.
Inputs: CAD stackup and thermal model available
Result: Treat the page tool as a procurement checklist, then run the motor-specific electromagnetic and thermal model.
| Risk | Impact | Mitigation |
|---|---|---|
| Demagnetization after overload | Lower torque, higher current, unstable control | Keep hot-spot temperature below grade limit with margin and ask for BH curves. |
| Wrong magnetization direction | Motor may not start, torque ripple rises, hall timing appears wrong | Confirm radial, diametric, axial, or multipole magnetization before purchase. |
| Corrosion or plating damage | NdFeB swells, cracks, or loses coating bond in humid service | Specify coating, adhesive compatibility, and environmental exposure. |
| Rotor imbalance | Bearing damage, vibration, air-gap rub, and noise | Balance the rotor assembly after magnet replacement, not loose magnets only. |
| False SKU equivalence | A same-size magnet changes back EMF and current draw | Measure no-load current, back EMF, and temperature after any substitution. |
| Heavy rare-earth sourcing shock | High-temperature NdFeB grades become expensive or unavailable | Qualify alternate coercivity grades, SmCo fallback, or a thermal redesign before production release. |
Supply risk
Thermal fixes are not only magnetic decisions. High-coercivity NdFeB grades can depend on rare-earth inputs with concentrated supply chains, so a production buyer should qualify alternates before a repair-size decision becomes a production dependency.
| Factor | Evidence added | Buyer impact |
|---|---|---|
| High-coercivity NdFeB grades | DOE notes NdFeB magnets use Nd/Pr and often Dy/Tb for performance; rare-earth metal inputs can account for over 90% of material cost. | An SH/UH/EH/AH upgrade may solve heat risk but can increase price, lead time, and sourcing exposure. |
| Magnet rare-earth demand | IEA 2026 reports permanent magnets account for around 95% of rare-earth consumption by value and are strategically important for EVs, wind, industrial motors, AI data centres, aerospace, and defence. | For production programs, qualify alternate grades or suppliers before the first production run instead of waiting for a shortage. |
| Heavy rare-earth dependence | USGS Mineral Commodity Summaries 2026 reports 100% U.S. net import reliance for heavy rare-earth compounds and metals, and notes April 2025 Chinese export controls on dysprosium and terbium among others. | Hot motor programs should separate thermal design margin from geopolitical availability; both can block a replacement plan. |
| Recycling and secondary supply | IEA 2026 estimates recycling could lower primary rare-earth supply needs by up to 35% by 2050, but current secondary supply is mostly manufacturing scrap. | Recycled content can be part of a sourcing strategy, but it is not a near-term guarantee for small replacement quantities. |
Comparison
The page is meant to drive a next action. Use this table to decide whether to buy loose magnets, replace the rotor, commission a custom rotor, or change architecture.
| Option | Best for | Weakness | Action |
|---|---|---|---|
| Buy loose 1.25 motor magnets | Low-risk repair experiments | Size match can still fail electrically or thermally | Require grade, coating, magnetization, and tolerance data |
| Replace full rotor assembly | Servo axes where balance and air gap matter | Higher part cost and possible supplier lock-in | Ask for balance grade, runout, and traceable BOM |
| Commission custom PM rotor | OEM torque-density, noise, or heat targets | Needs drawings, samples, and engineering time | Share duty cycle, rotor OD/ID, pole count, and cooling path |
| Switch motor architecture | Severe heat, cost, or rare-earth supply constraints | Controller and mechanical redesign may be required | Compare PM, induction, ferrite PM, and reluctance options |
Sources and uncertainty
Published magnet tables are useful for screening grade and temperature risk. They do not replace the original motor drawing, measured rotor temperature, and supplier demagnetization curve.
| Source | Used for | Link |
|---|---|---|
| K&J Magnetics neodymium specifications | NdFeB grade families, maximum operating temperature ranges | Source |
| K&J Magnetics temperature guide | Why maximum operating temperature is a guideline and depends on shape and magnetic circuit | Source |
| K&J Magnetics neodymium vs ceramic comparison | BH(max), coercive force, MaxOpTemp, Curie temperature contrast | Source |
| e-Magnets UK NdFeB grade guide | Grade suffix as intrinsic coercivity signal and application-dependence warning | Source |
| Published PM machine demagnetization study | Engineering context for comparing NdFeB and ferrite permanent magnets under thermal and current stress | Source |
| DOE Rare Earth Permanent Magnets supply chain assessment | NdFeB supply-chain segments, Dy/Tb material exposure, and rare-earth material cost concentration | Source |
| IEA Rare Earth Elements report | 2026 market context for permanent magnets, rare-earth value exposure, EV motor demand, and recycling limits | Source |
| USGS Mineral Commodity Summaries 2026: Rare Earths | 2026 U.S. rare-earth production, imports, stockpile context, and heavy rare-earth reliance | Source |
| IEC 60404-5:2015 magnetic materials standard page | Boundary between screening data and formal permanent-magnet property measurement | Source |
| ISO 21940 rotor balancing family | Boundary between loose magnet fit and assembled rotor balance verification | Source |
Open evidence gap: no public source can map every 1.25 motor magnets query to one universal magnet part number. Treat size-only matches as low-confidence until the full rotor specification is known. Source review updated June 5, 2026.
FAQ
These answers focus on actions and boundaries rather than glossary definitions.
Not reliably. 1.25 usually describes a dimension, often 1.25 inch or 31.75 mm, but a replacement still needs pole count, arc width, thickness, grade, coating, tolerance, and magnetization direction.
Only after checking heat and control behavior. N52 can raise flux, but it may also change back EMF, current draw, cogging, and demagnetization margin.
No reliable public data was found for a universal 1.25 motor magnets part table. Public sources support material screening, supply-chain risk, and measurement standards, but not a motor-specific rotor bill of materials.
Permanent magnet strength and coercivity fall as temperature rises. A same-size magnet can be acceptable cold and fail after overload or enclosed operation.
Do not order from diameter alone. Use magnetic viewing film, a compass pass, hall signal mapping, or the original motor documentation to count magnetic poles.
No. SmCo is useful for high-temperature or harsh environments, but it costs more, is brittle, and may not deliver the same compact torque density as NdFeB in cooler applications.
Usually not as a drop-in part. Ferrite has much lower energy density, so the rotor may need more magnet volume and a redesigned magnetic circuit.
The suffix indicates higher intrinsic coercivity and is commonly associated with a higher service-temperature rating than a plain N grade.
Rotor magnets normally need spacing, adhesive clearance, manufacturable segments, and flux-shaping tradeoffs. Full coverage can raise leakage, assembly risk, or cogging depending on design.
No. Thickness depends on the air gap, back iron, saturation, target torque, and demagnetization curve. The page only screens pitch, arc, and thermal risk.
Higher-coercivity NdFeB grades may depend on dysprosium or terbium additions. DOE, IEA, and USGS sources show those materials are economically and geopolitically exposed, so production programs should qualify alternatives early.
Ask for grade, coating, magnetization direction, dimensional tolerance, BH or demagnetization curve at operating temperature, adhesive compatibility, traceability, and whether final rotor balance is included.
Document the original rotor, preserve one intact magnet if possible, measure polarity and dimensions, then test no-load current and temperature after repair.
Use it for intake and sanity checks only. Production design needs electromagnetic simulation, thermal validation, tolerance stackup, rotor retention, and end-of-line testing.
The query is an alias inside the permanent magnet motor intent cluster. A single canonical page avoids duplicate thin pages while still answering the specific 1.25 motor magnets question.
This page intentionally keeps 1.25 motor magnets as an anchor inside the canonical permanent magnet motor URL instead of publishing a separate alias route.
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