{
 "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": "canned-linear-alternator-stator-2in",
 "name": "Linear-alternator stator that clamps round a 2 in tri-clamp tube: four coils outside the pressure wall",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "How do I take electricity out of a pressurised free-piston engine without a wire through the wall?",
 "tags": [
  "linear alternator",
  "stator",
  "coil",
  "free piston",
  "tri-clamp",
  "long earth society",
  "thermoacoustic"
 ],
 "aliases": [
  "canned linear alternator",
  "linear alternator outside the tube",
  "free piston generator stator",
  "tri clamp alternator coil"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 3,
 "url": "https://xemstudio.com/objects/canned-linear-alternator-stator-2in/",
 "sheet_txt": "https://xemstudio.com/objects/canned-linear-alternator-stator-2in/sheet.txt",
 "sheet": {
  "basis": "Coil window and pitch from the alternator design in tools/gen_ta_power.py; gap field from a magnetic-circuit estimate",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The coils sit outside the honed spool: a split bobbin clamps on the Ø50.8 tube with four 14 mm bays at the magnet rows' 32 mm pitch; the coils are wound in place, alternate hands, and joined in series; a split return-path shell (Ø66 / Ø74) clamps over them with three M4 × 16 and nuts each side. The shell has to carry the magnets' flux back; what it is made of is the builder's choice within that.",
   "The spool wall (1.40 after honing) and a 0.5 bobbin wall sit in the magnetic gap: the wall must not carry magnetic flux, or it short-circuits the magnets. In the 25 Hz field the eddy-current loss in a 1.4 mm wall is a fraction of a watt.",
   "Estimate: gap field 0.29 T (Br 1.3 T magnets, magnetic-circuit estimate with a 0.8 leakage factor), 369 turns of 0.45 mm wire per coil, Bl ≈ 79 T·m, coil resistance ≈ 31 Ω, inductance ≈ 132 mH; damping available Bl²/R ≈ 203 N·s/m. Measure Bl (EMF ÷ velocity) on the built engine; the model's power scales with it.",
   "No electrical pass-through, no wire in the gas: the generator's pressure boundary is only tri-clamp joints.",
   "Fits: bobbin bore clamps the tube (the 1 mm split is the take-up); shell bore clamps the bobbin flanges; ear holes are M4 clearance."
  ],
  "table": {
   "columns": [
    "part",
    "value"
   ],
   "rows": [
    [
     "bays",
     "4 × 14 at 32"
    ],
    [
     "coil",
     "Ø65.8 / Ø51.8"
    ],
    [
     "shell",
     "Ø74 / Ø66 × 112"
    ],
    [
     "turns per coil",
     369
    ],
    [
     "Bl",
     "≈ 79 T·m"
    ],
    [
     "coil resistance",
     "≈ 31 Ω (all four)"
    ]
   ]
  }
 },
 "sheet_text": "Linear-alternator stator that clamps round a 2 in tri-clamp tube: four coils outside the pressure wall — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/canned-linear-alternator-stator-2in/  (CC BY 4.0)\nBasis: Coil window and pitch from the alternator design in tools/gen_ta_power.py; gap field from a magnetic-circuit estimate\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The coils sit outside the honed spool: a split bobbin clamps on the Ø50.8 tube with four 14 mm bays at the magnet rows' 32 mm pitch; the coils are wound in place, alternate hands, and joined in series; a split return-path shell (Ø66 / Ø74) clamps over them with three M4 × 16 and nuts each side. The shell has to carry the magnets' flux back; what it is made of is the builder's choice within that.\n- The spool wall (1.40 after honing) and a 0.5 bobbin wall sit in the magnetic gap: the wall must not carry magnetic flux, or it short-circuits the magnets. In the 25 Hz field the eddy-current loss in a 1.4 mm wall is a fraction of a watt.\n- Estimate: gap field 0.29 T (Br 1.3 T magnets, magnetic-circuit estimate with a 0.8 leakage factor), 369 turns of 0.45 mm wire per coil, Bl ≈ 79 T·m, coil resistance ≈ 31 Ω, inductance ≈ 132 mH; damping available Bl²/R ≈ 203 N·s/m. Measure Bl (EMF ÷ velocity) on the built engine; the model's power scales with it.\n- No electrical pass-through, no wire in the gas: the generator's pressure boundary is only tri-clamp joints.\n- Fits: bobbin bore clamps the tube (the 1 mm split is the take-up); shell bore clamps the bobbin flanges; ear holes are M4 clearance.\n\npart  value\nbays  4 × 14 at 32\ncoil  Ø65.8 / Ø51.8\nshell  Ø74 / Ø66 × 112\nturns per coil  369\nBl  ≈ 79 T·m\ncoil resistance  ≈ 31 Ω (all four)\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Xem Studio: tools/gen_ta_power.py: the network model and every dimension on this page — code — CC BY 4.0 — https://xemstudio.com/\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, 3 parts): https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/index.json\nAPI: https://xemstudio.com/api/geometry?object=canned-linear-alternator-stator-2in\n",
 "sources": [
  {
   "publisher": "Xem Studio",
   "title": "tools/gen_ta_power.py: the network model and every dimension on this page",
   "url": "https://xemstudio.com/",
   "formats": [
    "code"
   ],
   "license": "CC BY 4.0",
   "license_verified": true,
   "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": [
  "free-piston-mover-2in",
  "tri-clamp-honed-cylinder-spool",
  "linear-alternator-mover",
  "list-ta-ring-3x2in"
 ],
 "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": "bobbin bore",
   "exact": "Ø50.8",
   "mates": "2 in tube outside (honed spool)",
   "fit": "clamp",
   "files": "stator-bobbin-"
  },
  {
   "feature": "bobbin flanges and dividers",
   "exact": "Ø66.0",
   "mates": "return-shell bore Ø66.0",
   "fit": "clamp",
   "files": "stator-bobbin-"
  },
  {
   "feature": "split",
   "exact": "1.0 total (0.5 per half)",
   "mates": "the other half",
   "fit": "clamp",
   "files": "all"
  },
  {
   "feature": "coil bays",
   "exact": "4 × 14 wide, Ø51.8–Ø66",
   "mates": "coils wound in place (Ø51.8 / Ø65.8 winding)",
   "fit": "designed",
   "files": "all"
  },
  {
   "feature": "coil to shell",
   "exact": "0.1 radial",
   "mates": "return-shell bore",
   "fit": "designed",
   "files": "stator-coil-"
  },
  {
   "feature": "ear holes",
   "exact": "6 × Ø4.5",
   "mates": "M4 clearance (ISO 273 medium)",
   "fit": "designed",
   "files": "stator-iron-"
  }
 ],
 "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 tube?",
   "a": "Then the only things in the pressurised gas are the moving magnets: no feedthrough to seal, and the coils are cooled by the room."
  },
  {
   "q": "How are the coils joined?",
   "a": "In series, alternate hands, because the rows under them alternate N and S: all four voltages then add."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "stator-bobbin-half-2in-112",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/stator-bobbin-half-2in-112.step",
   "stl": "https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/stator-bobbin-half-2in-112.stl",
   "note": "bobbin half (y ≥ 0.5): wall Ø50.8 / Ø51.8, end flanges and dividers to Ø66, four 14 mm coil bays at 32 pitch, 112 long"
  },
  {
   "file": "stator-coil-2in-14x7",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/stator-coil-2in-14x7.step",
   "stl": "https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/stator-coil-2in-14x7.stl",
   "note": "coil winding volume Ø65.8 / Ø51.8 × 14: about 369 turns of 0.45 mm wire"
  },
  {
   "file": "stator-iron-half-2in-112",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/stator-iron-half-2in-112.step",
   "stl": "https://xemstudio.com/files/hardware/canned-linear-alternator-stator-2in/stator-iron-half-2in-112.stl",
   "note": "return-path shell half (y ≥ 0.5) Ø74 / Ø66 × 112, ears x ±36..46 with Ø4.5 at x ±41.5, z 14, 56, 98"
  }
 ],
 "markdown": "https://xemstudio.com/objects/canned-linear-alternator-stator-2in/index.md"
}