{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "fpse-linear-alternator-stator",
 "name": "Moving-magnet linear alternator stator outside a 2 in tri-clamp spool: laminated two-tooth stator, one coil",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "How do I put a linear alternator outside a sealed tri-clamp tube?",
 "tags": [
  "linear alternator",
  "stator",
  "coil",
  "free piston",
  "moving magnet",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "linear alternator outside tube",
  "hermetic linear alternator stirling",
  "moving magnet linear generator stator"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 4,
 "url": "https://xemstudio.com/objects/fpse-linear-alternator-stator/",
 "sheet_txt": "https://xemstudio.com/objects/fpse-linear-alternator-stator/sheet.txt",
 "sheet": {
  "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",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "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."
  ],
  "table": {
   "columns": [
    "item",
    "value"
   ],
   "rows": [
    [
     "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"
    ]
   ]
  }
 },
 "sheet_text": "Moving-magnet linear alternator stator outside a 2 in tri-clamp spool: laminated two-tooth stator, one coil — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/fpse-linear-alternator-stator/  (CC BY 4.0)\nBasis: 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\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 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).\n- 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.\n- 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.\n- 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.\n\nitem  value\nteeth  2 × 12 wide, slot 16\npacks  8 × 43°, r 25.4–55\ncoil  300 t, 0.71 mm, 3.40 Ω\nforce constant  28.8 N/A\ninductance (est.)  25 mH\nlinear range  ±6 mm\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- 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\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/index.json\nAPI: https://xemstudio.com/api/geometry?object=fpse-linear-alternator-stator\n",
 "sources": [
  {
   "publisher": "K&J Magnetics",
   "title": "Neodymium magnet specifications: N42 Br 1.30–1.32 T, density 7.4–7.5 g/cm³",
   "url": "https://www.kjmagnetics.com/specs.asp",
   "formats": [
    "web"
   ],
   "license": "maker page; values are facts",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "fpse-power-piston",
  "tri-clamp-bored-spool",
  "linear-alternator-mover",
  "list-fpse-generator-2in"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [
  {
   "feature": "teeth",
   "exact": "r 25.4 (Ø50.8)",
   "mates": "S4 tube OD",
   "fit": "clamp",
   "files": "fpse-stator-pack"
  },
  {
   "feature": "OD",
   "exact": "Ø110",
   "mates": "housing bore",
   "fit": "clamp",
   "files": "fpse-stator-pack"
  },
  {
   "feature": "bobbin bore",
   "exact": "Ø65",
   "mates": "slips over S4's Ø64 flange (no contact)",
   "fit": "designed",
   "files": "fpse-bobbin"
  },
  {
   "feature": "ear holes",
   "exact": "2 × Ø4.5 each side",
   "mates": "M4 × 20 and nuts (ISO 273 medium)",
   "fit": "designed",
   "files": "fpse-stator-housing"
  },
  {
   "feature": "split",
   "exact": "1.0 total (0.5 per half)",
   "mates": "the other half",
   "fit": "clamp",
   "files": "fpse-stator-housing"
  },
  {
   "feature": "lead hole",
   "exact": "Ø6",
   "mates": "coil leads",
   "fit": "designed",
   "files": "fpse-stator-housing"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. Typical FDM: hole +0.0 to +0.1 mm on diameter.",
  "slide": "assembles by hand and is held by a grub, pinch or clamp: shaft in a hub, rod in a socket, spigot in a bore. Typical FDM: +0.2 mm.",
  "run": "turns or slides in use: pin in a link, rod through a guide. Typical FDM: +0.3 mm.",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. Typical FDM: +0.3 mm.",
  "clamp": "split part that closes on the mating part with screws: make it at size.",
  "designed": "a gap that is part of the design (piston fit option, displacer gap, air gap): do not change."
 },
 "faq": [
  {
   "q": "Why outside the wall?",
   "a": "No wire through the pressure boundary and no coil in the gas: the vessel stays a sealed stack of tri-clamp parts. The price is 1.4 mm more magnetic gap than an inside coil."
  },
  {
   "q": "What sets the stroke?",
   "a": "The load. The alternator's damping absorbs the engine's power; less load (higher resistance) lets the stroke grow. Keep a load connected whenever the engine is hot."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "fpse-stator-pack-43deg",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-stator-pack-43deg.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-stator-pack-43deg.stl",
   "note": "stator pack: 43° of radial laminations 0.5 thick, two teeth r 25.4–50 at |z| 8–20, yoke r 50–55; drawn as its envelope; 8 round the tube"
  },
  {
   "file": "fpse-bobbin-65",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-bobbin-65.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-bobbin-65.stl",
   "note": "bobbin Ø65 / Ø67 × 16, flanges Ø99 × 1: slips over S4's Ø64 flanges"
  },
  {
   "file": "fpse-coil-300t",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-coil-300t.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-coil-300t.stl",
   "note": "coil: 300 turns of 0.71 mm enamelled wire, the winding volume Ø67–Ø99 × 14"
  },
  {
   "file": "fpse-stator-housing-half",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-stator-housing-half.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-linear-alternator-stator/fpse-stator-housing-half.stl",
   "note": "stator housing half: shell r 55–58, end walls to r 34, ears with 2 × M4 each side, Ø6 lead hole; two halves clamp the packs onto the tube"
  }
 ],
 "markdown": "https://xemstudio.com/objects/fpse-linear-alternator-stator/index.md"
}