N45SH vs N48SH is a decision you reach once heat is already settled. Both grades hold 150°C, so you are no longer choosing for temperature — you are trading torque density against demagnetization margin, with heavy rare earth cost in the background. For EV traction motors and humanoid robot joint actuators, getting that trade right is the difference between hitting your torque-to-weight target and re-cutting the rotor.
What do the N45SH and N48SH grades mean?
The SH suffix is the key. Standard neodymium grades stop at 80°C; the H/SH/UH/EH ladder buys progressively more heat tolerance through higher intrinsic coercivity, paid for with heavy rare earth (dysprosium and terbium). N45SH and N48SH sit on the same rung — 150°C — so neither has a thermal advantage. What separates them is raw magnetic output and the coercivity margin behind it. If you are still deciding whether you even need SH, start with N42 vs N42SH for the standard-versus-SH crossover.
| Property | N45SH | N48SH |
|---|---|---|
| Max energy product (BHmax) | 43–46 MGOe | 45–49 MGOe |
| Remanence (Br) | ~1.32–1.38 T | ~1.36–1.42 T |
| Max operating temperature | 150°C | 150°C |
| Intrinsic coercivity (Hcj) | ≥20 kOe | ≥20 kOe |
| Demagnetization margin | Slightly higher | Slightly lower |
| Torque density (same volume) | Baseline | ~6–7% higher |
| Heavy rare earth content | Slightly lower | Slightly higher |
| Relative price | Baseline | Slightly higher |
How the BHmax gap becomes torque density
For motor designers, energy product tracks torque density, so the higher BHmax of N48SH is not abstract — it is a smaller, lighter, or more powerful machine. Use the toggle below to see the two ways that 6–7% shows up in a design: more torque from the same rotor, or the same torque from a smaller rotor.
Torque density: two ways to spend the 6–7%
N48SH's higher energy product becomes either more torque or a smaller motor. Pick the strategy, set your torque target.
Illustrative ~7% rule applied to your number — real gain depends on rotor topology and saturation.
That gap matters most where mass is the enemy. Modern humanoid joint actuators are built as frameless torque motors chasing high specific torque;[3] a single Tesla Optimus carries on the order of 3.5 kg of NdFeB across its 28 body actuators, with each motor holding 50–100 g.[4] At that scale, 6–7% more torque per gram of magnet is a real lever, not a rounding error. There is a second benefit too: a higher magnetic baseline lets a designer push higher peak current for short bursts — the dynamic torque a robot leg needs at foot-strike — without redesigning the rotor.
When N45SH is the smarter choice: demagnetization margin
Torque density is only half the design. Demagnetization safety tracks intrinsic coercivity and the magnetic circuit, not BHmax. The worst-case operating point is not steady-state running — it is the moment peak demagnetizing field and peak temperature land together. In an EV motor that happens during field weakening[5], when a demagnetizing current is deliberately applied to the magnets to reduce back-EMF at high speed; in a robot joint it happens at a hard impact or a fault. Drag the sliders below to push both grades to that worst case and watch which one crosses the knee first.
Worst-case operating point: which grade keeps its margin?
Second-quadrant B–H curve. Raise temperature and the demagnetizing field together — N48SH reaches its knee before N45SH.
Simplified illustration — trends only, not absolute datasheet values.
The engineer's rule of thumb: run your worst-case operating-point analysis (peak current, highest temperature, opposing field together), then spec one grade of margin above the point where the working line just clears the knee. If that clearance is thin, take N45SH; if you have room, N48SH buys torque.
Rotor topology changes the demag risk: IPM vs surface PM
This is the context that decides the grade in practice. In an interior permanent magnet (IPM) rotor, the magnets are buried in the lamination, partly screened from the demagnetizing stator field during overloads and field weakening, and protected from being flung off at high rpm. In a surface PM (SMPM) rotor, the magnets face the air gap directly and high-order stator harmonics can push the most exposed magnet corners past the knee even when the bulk of the magnet is safe. If your design is SMPM, or high pole-count with strong harmonics, the extra margin of N45SH is cheap insurance; if it is a well-screened IPM with comfortable clearance, N48SH's torque density is yours to take.
Format and tolerance: arc segments, rings, and torque ripple
A high-performance motor magnet is a geometry problem as much as a material one. Arc segments are radially magnetized for PMSM and BLDC rotors; multipole rings suit compact, high-pole-count joints. Dimensional scatter on those parts shows up directly as air-gap inconsistency and torque ripple — the cogging and vibration that becomes perceptible at the very low joint speeds of a walking robot, where stance-phase velocities drop to 1–2 rpm. Holding ±0.05 mm or tighter, and keeping batch-to-batch magnetic properties consistent, is what keeps a joint smooth.
This is also a production-scale point. A single EV drive motor can contain 1–2 kg of NdFeB; across a run, batch-to-batch consistency is not a nicety, it is what keeps your assembly line from stalling. Our DC motor magnets page covers arc-segment and ring options, and the application pages go deeper for EV motors, robotics, and industrial motors.
The heavy rare earth cost — and when to step up to UH
SH-class magnets depend on dysprosium and sometimes terbium — the heavy rare earths now under export licensing[6]. For a production program that means two things. First, price and lead time for either grade move with heavy rare earth supply, so lock specification and quantity early. Second, the cost gap between N45SH and N48SH is small enough that it rarely decides the design on its own — the torque target and the demagnetization analysis do. If your worst-case temperature genuinely exceeds 150°C, do not stretch an SH grade; move to N45UH or N48UH (180°C).
Which applications suit N45SH vs N48SH?
| Application | Priority | Recommended |
|---|---|---|
| EV traction motors, IPM rotor (compact) | Torque density | N48SH |
| Humanoid robot joint actuators | Torque-to-weight | N48SH |
| High-performance servo motors | Peak torque | N48SH |
| Surface PM rotors / strong harmonics | Coercivity margin | N45SH |
| Field-weakening / fault-prone rotors | Demag safety | N45SH |
| Wind / generator magnets | Cost & reliability | N45SH |
When you send the inquiry, have these ready
• Peak rotor temperature and worst-case operating point (peak current + opposing field together)
• Rotor topology (IPM or surface PM) and pole count — it sets your demag exposure
• Torque or torque-density target, and rotor volume / envelope
• Magnet format (arc segment, multipole ring, block), tolerance, coating, and annual volume
Specifying magnets for a hot motor?
Send your peak temperature, demag operating point, and rotor geometry. We will recommend N45SH or N48SH with the demag curve — then quote your parts.
Get a motor-grade recommendation
How to choose for your procurement spec
The decision in one line
Both hold 150°C. Pick N48SH when you need maximum torque density in a fixed rotor and your operating point has margin; pick N45SH when the rotor is exposed to field weakening or harmonics, you have room, or you want lower cost.
Compact, weight-critical hot motors — EV traction (well-screened IPM), humanoid joints, premium servos. The extra 6–7% BHmax buys torque you cannot get from geometry.
Surface PM rotors, aggressive field weakening, fault-prone circuits, or generous rotor room. Lower heavy-rare-earth cost and more coercivity safety at the same 150°C.
For SH grades especially, supplier verification is not optional. Reaching a genuine 150°C rating depends on real dysprosium content and a properly controlled microstructure — a magnet stamped N48SH but built with too little heavy rare earth can demagnetize early in service, taking the motor with it. Insist on the measured Hcj and the demagnetization curve at temperature, and ask whether the supplier runs 100% inspection on motor parts. Mainrich has supplied motor-grade magnets to names like Johnson Electric and Hitachi for over 30 years, with a 99% consistency rate across mass production.
