Size a magnetic coupling
The required transmission torque from load torque and safety factor, the slip power as a heat load and — for hermetically separated drives — the minimum wall thickness of the containment shell.
Size a magnetic coupling
Enter the load torque and safety factor — results appear immediately.
Load
Sizing
Preset to 2.0 — the upper, conservative end of the range “typically 1.5–2.0” given in our guides on magnetic couplings. It covers starting peaks, load fluctuations and the temperature dependence of the magnets.
Only for operation with slip. A synchronously running permanent magnet coupling has Δn = 0 — then the slip power is zero as well.
Containment shell (optional)
Only for hermetically separated applications. All three fields belong together; the minimum wall thickness follows from the boiler formula.
Formulas
T_Last = 9550 · P / n T_erf = T_Last · S P_S = T_Last · Δn / 9,55 t_min = p · D / (2 · σ_zul)
1 bar = 0.1 N/mm² · Standards for containment shells: API 685, DIN EN ISO 15783, strength verification to DIN EN 13445
What the model covers — and what it does not
What is calculated is the REQUIRED torque, never the available one. What a specific coupling actually transmits depends disproportionately on the air gap as built, so selecting the frame size remains a matter of the catalogue and of advice. Three quantities are deliberately NOT shown, because we have no sourced values for them: the eddy current losses as a number, a temperature derating curve for the magnets, and safety factors graded by application. The direction is known and stated as a note — an unsourced number would be worse here than none. The formulas come from the guides “Hysteresis coupling vs. permanent magnet coupling” and “Magnetic coupling containment shell”.
Heat is the real sizing problem
With a magnetic coupling, torque alone rarely decides the case. If it runs with slip, the entire power converted at the slip becomes heat: P_S = T · Δn / 9.55. Just 5 Nm at a slip speed of 500 rpm already produces around 262 W of continuous heat — an order of magnitude at which the frame size no longer fails on torque but on heat dissipation.
This is exactly where the two designs part ways. The permanent magnet coupling runs synchronously and without slip up to its breakaway torque — Δn = 0, so no slip heat. The hysteresis coupling may slide continuously and delivers a constant slip torque while doing so; the heat is then intentional by design and has to be dissipated. Which design fits is settled in the comparison hysteresis versus permanent magnet coupling.
The safety factor is preset to 2.0. Our guides consistently name a range of typically 1.5 to 2.0 over the operating torque; it covers starting peaks, load fluctuations and the temperature dependence of the magnets. The upper end is preset deliberately — a calculator that silently assumes the more favourable value states too small a torque, and does so unnoticed.
The containment shell: every tenth of a millimetre costs torque
In hermetically separated applications — pumps and agitators in chemicals, pharmaceuticals and food processing — a containment shell sits between the magnet halves. As a pressure-bearing part, its minimum wall thickness can be estimated from the boiler formula: t_min = p · D / (2 · σ_perm). For D = 100 mm at 16 bar and a conservative σ_perm of 100 N/mm² that comes to 0.8 mm.
Those 0.8 mm go straight into the magnetic air gap, and the transmissible torque falls disproportionately as the gap grows. That is why wall thickness is the central sizing variable: as thin as pressure and safety permit, as thick as necessary. Material, eddy current losses and media resistance are covered in the guide magnetic coupling containment shell.
Frequently asked questions
Why does the calculator not state eddy current losses in watts?
Because we have no sourced values for them per material and wall thickness. The direction is known and appears in the result: in conducting shells the losses rise with wall thickness, while ceramic and PEEK avoid them almost entirely. Stating a number we cannot substantiate would be worse than none — it would look like a calculated result and be an estimate.
And the temperature behaviour of the magnets?
That high temperature reduces the transmissible torque and in extreme cases leads to partial demagnetisation is undisputed. From which medium temperature and with which factor one has to allow for it depends on the magnet material of the specific series — there is no general derating curve. Tell us the medium temperature in your enquiry and we will check it against the material data of the series.
Which torque do I enter for a hysteresis coupling?
The one actually transmitted during slip, that is the set slip torque — not the value with the safety factor applied. This is why the calculator deliberately derives the slip power from the load torque and not from T_req: what turns into heat is what is transmitted, not the design torque.
Does the calculator tell me the frame size?
No — it gives you the target value to select against. What a specific coupling transmits depends disproportionately on the air gap as built, and that gap is shaped by shaft position, shell wall and assembly tolerances (manufacturing tolerance of the breakaway torque typically ±10–15 %). The frame size is therefore decided by the catalogue, not by the calculation alone.
Note: These calculation tools are intended for initial orientation only and do not replace a binding design by qualified personnel. All results must be verified by appropriate engineering calculations before use in safety-relevant applications. Technische Antriebselemente GmbH accepts no liability for damage arising from the use of these results.
Find the frame size for the calculated transmission torque?
The required torque and the slip power are settled — what remains open is what only the catalogue knows: the torque your frame size actually transmits at the air gap as built, the permissible continuous slip power and the choice of containment shell material. Carry your values into the enquiry and we will select the PMKC frame size with you.
Related products & guides
Hysteresis vs. permanent magnet coupling
The source of the slip power formula — with torque characteristics, overload behaviour and selection criteria for both designs.
GuideMagnetic coupling containment shell: materials & sizing
The source of the boiler formula — with material comparison, eddy current losses and the standards API 685 / DIN EN ISO 15783.
ProductPMKC magnetic couplings
Permanent magnet couplings for hermetically separated drives — series, torque ranges and containment shell selection aid.
GlossaryPermanent magnet coupling
Operating principle, breakaway torque and the influence of the air gap, in brief.
CalculatorTorque calculator
Derive torque, power and speed from one another — the step before this one when only the motor data is known.
CalculatorGearbox efficiency calculator
Loss power and energy cost of a whole drive train — where the coupling is just one link.