{
 "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": "linear-alternator-coil",
 "name": "Linear alternator coil Ø50 × 10 (≈ 314 turns)",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "How many turns and what size is each coil of the linear alternator?",
 "tags": [
  "linear alternator",
  "coil",
  "winding",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "linear alternator coil turns",
  "how to wind a linear alternator coil",
  "coil 314 turns 0.3 mm"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/linear-alternator-coil/",
 "sheet_txt": "https://xemstudio.com/objects/linear-alternator-coil/sheet.txt",
 "sheet": {
  "basis": "Winding volume of one bobbin bay; turns and resistance computed in the generator for 0.30 mm wire",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "One coil of the alternator, as the solid of its winding: Ø50 outside, Ø38.6 inside (the bobbin core), 10 long.",
   "About 314 turns of 0.30 mm wire fill it. Two per alternator, the second wound the opposite way; both in series come to about 21.3 Ω.",
   "At 12 Hz and 12 mm stroke the pair gives about 22.7 V peak per tesla of gap flux."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "outside",
     50
    ],
    [
     "inside",
     38.6
    ],
    [
     "length",
     10
    ],
    [
     "turns",
     "≈ 314 of 0.30 mm"
    ],
    [
     "resistance, both in series",
     "21.3 Ω"
    ],
    [
     "EMF per tesla",
     "22.73 V peak at 12 Hz, 12 mm"
    ]
   ]
  }
 },
 "sheet_text": "Linear alternator coil Ø50 × 10 (≈ 314 turns) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/linear-alternator-coil/  (CC BY 4.0)\nBasis: Winding volume of one bobbin bay; turns and resistance computed in the generator for 0.30 mm wire\nCatalog version: 2026-10-20\n\nSizes: see table below\n- One coil of the alternator, as the solid of its winding: Ø50 outside, Ø38.6 inside (the bobbin core), 10 long.\n- About 314 turns of 0.30 mm wire fill it. Two per alternator, the second wound the opposite way; both in series come to about 21.3 Ω.\n- At 12 Hz and 12 mm stroke the pair gives about 22.7 V peak per tesla of gap flux.\n\nparameter  value\noutside  50\ninside  38.6\nlength  10\nturns  ≈ 314 of 0.30 mm\nresistance, both in series  21.3 Ω\nEMF per tesla  22.73 V peak at 12 Hz, 12 mm\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- NASA (NTRS, public domain): Linear alternator design for free-piston Stirling convertors (2005) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20050182934\n- NASA (NTRS, public domain): Sunpower/NASA 80 We free-piston Stirling convertor (2002) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20020047256\n- Wikipedia: Linear alternator — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Linear_alternator\n- Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine\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, 1 parts): https://xemstudio.com/files/hardware/linear-alternator-coil/index.json\nAPI: https://xemstudio.com/api/geometry?object=linear-alternator-coil\n",
 "sources": [
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Linear alternator design for free-piston Stirling convertors (2005)",
   "url": "https://ntrs.nasa.gov/search?q=20050182934",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Sunpower/NASA 80 We free-piston Stirling convertor (2002)",
   "url": "https://ntrs.nasa.gov/search?q=20020047256",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Linear alternator",
   "url": "https://en.wikipedia.org/wiki/Linear_alternator",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Free-piston engine",
   "url": "https://en.wikipedia.org/wiki/Free-piston_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "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": [
  "linear-alternator-bobbin",
  "linear-alternator-mover",
  "linear-alternator-housing"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "linear-alternator-bobbin",
     "why": "fills one 10 mm bay"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "linear-alternator-mover",
     "why": "the magnet row it sits over"
    }
   ]
  }
 ],
 "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": "coil in its bay",
   "exact": "bay volume",
   "mates": "bobbin bay",
   "fit": "designed",
   "files": "alt-coil-"
  }
 ],
 "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": "How many turns on each linear alternator coil?",
   "a": "About 314 turns of 0.30 mm wire in the Ø50 × 10 bay."
  },
  {
   "q": "How are the two coils connected?",
   "a": "Wound in opposite directions and joined start-to-start in series: about 21.3 Ω together."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "alt-coil-bay",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-kit/alt-coil-bay.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-kit/alt-coil-bay.stl",
   "note": "coil: the winding volume of one bay, Ø50 × 10 (about 314 turns of 0.30 mm wire fill it); two per alternator, the second wound the opposite way"
  }
 ],
 "markdown": "https://xemstudio.com/objects/linear-alternator-coil/index.md"
}