Moving-magnet linear alternator stator outside a 2 in tri-clamp spool: laminated two-tooth stator, one coil — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/fpse-linear-alternator-stator/  (CC BY 4.0)
Basis: Two-tooth moving-magnet topology (flux through the coil reverses as the magnet rows pass under the teeth); magnetic-circuit estimate with the magnets' published remanence; coil numbers from the winding window
Catalog version: 2026-10-20

Sizes: see table below
- The coil and its iron never touch the gas: they sit round the bored spool's 1.40 wall, which is not magnetic for this to work. Eight packs of radial laminations form two teeth on the tube and a yoke outside the coil; the flux from the S N N S magnet rows closes through one tooth, the yoke and the other, and reverses through the coil as the piston moves ±6 (the linear range: half a tooth).
- Estimate: gap flux density 0.42 T (magnets 1.31 T, 63 % of the carrier covered, 1.9 mm magnetic gap), 75 % of it linking the coil; dΦ/dx 0.096 Wb/m; with 300 turns of 0.71 mm wire: force constant 28.8 N/A (V·s/m), coil 3.40 Ω, inductance about 25 mH.
- At the design point (10 bar helium, ±5.0 mm, 45.1 Hz) it gives 40.8 V peak open circuit and 43.2 W into 11.5 Ω through a 500 µF series capacitor that cancels the coil's inductance (20 V peak across it). The load is the stroke control: never run it open-circuit.
- The flux in the laminations reverses at the running frequency: the plates must be thin and insulated from each other (drawn as 0.5 mm, as the pack envelope). The coil slides over S4's flange before the stack is clamped; the housing halves clamp the packs onto the tube with 4 × M4 × 20; the leads leave through the housing's hole between two packs.

item  value
teeth  2 × 12 wide, slot 16
packs  8 × 43°, r 25.4–55
coil  300 t, 0.71 mm, 3.40 Ω
force constant  28.8 N/A
inductance (est.)  25 mH
linear range  ±6 mm

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- K&J Magnetics: Neodymium magnet specifications: N42 Br 1.30–1.32 T, density 7.4–7.5 g/cm³ — web — maker page; values are facts [verify license at link] — https://www.kjmagnetics.com/specs.asp
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/index.json
API: https://xemstudio.com/api/geometry?object=fpse-linear-alternator-stator