# Build list: Linear alternator module, 2 in, closed (sealed bounce space, chargeable)

> What parts do I need to build a Linear alternator module, 2 in, closed (sealed bounce space, chargeable)?

- Category: Electronics › Generators & alternators
- Kind: List / guide
- Basis: Every part is a free STEP/STL on this site or a standard part with its own page; quantities are the full count, every screw, nut, pin, gasket and clamp.
- Page: https://xemstudio.com/objects/list-linear-alternator-module-2in-closed/ · JSON: https://xemstudio.com/api/geometry?object=list-linear-alternator-module-2in-closed · Plain text: https://xemstudio.com/objects/list-linear-alternator-module-2in-closed/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- One standard linear alternator that clamps in line on any 2 in sanitary device: a Ø48 clearance-seal piston on two spiral leaves, 40 magnets, the stator and coil outside the wall, ISO 2852 faces at both ends. Built once and moved between engines, so their power can be compared.
- Ø48 piston ±5 mm (±6 max) · moving mass 865 g · leaves 8851 N/m · Bl 28.8 N/A · coil 3.40 Ω, ≈25 mH · f₀ 16 Hz open, 19 Hz on 1 bar air, 36 Hz on 10 bar helium · 147.0 mm face to face · relief 15 bar g
- I wanted one alternator I build once and move from engine to engine: on top of a free-piston hot end, inside a thermoacoustic loop or ring, on a standing-wave engine, on anything that makes a pressure wave in a 2 in fitting. It is clamped like any sanitary fitting; nothing else holds it.
- It is the free-piston generator's alternator rearranged: the same stator, coil, magnets, leaves, half gaskets and collars, with the leaves at both ends of the magnets and nothing on the working side of the piston. The stack from face A: 42 mm bored spool (piston cup) · joint 1 with leaf 1 · 3 in bored spool (magnets inside, stator outside) · joint 2 with leaf 2 · 25.4 mm spool · face B.
- Face A takes the engine's pressure wave. Face B is the bounce space, closed by the four-port cap (fill, gauge, relief, and a plug or transducer); take the cap off and face B clamps straight onto another device, so the module can sit in the middle of a loop.
- Its own parameters, how to retune it and the measurement procedure are on the datasheet page. Leaf set A is the standard build; set B (soft leaves) and the mass discs are tuning parts.
- Charge through the fill valve slowly: the bounce space fills through the piston's clearance seal. Relief at 15 bar gauge; high-pressure bolted clamps and gaskets rated above it.

## Sizes

| subsystem | object | parts | qty | note |
|---|---|---|---|---|
|  | linear-alternator-module-spools-2in | spool-2in-42mm-bored-48.00 | 1 | face A (to the engine) and the piston's cylinder |
|  | tri-clamp-spool-bored-honed | spool-2in-3in-bored-48.00 | 1 | the alternator section: magnet carrier inside, stator outside |
|  | linear-alternator-module-spools-2in | spool-2in-25.4mm | 1 | face B end: leaf 2's hub travel |
|  | tri-clamp-flexure-leaf | leaf-2in-piston-t0.8 | 2 | choose one leaf set, A (standard 0.8): joints 1 and 2; leaf 2 turned over (opposite hand) |
|  | tri-clamp-leaf-half-gasket | leaf-half-gasket-2in-w0.45 | 4 | choose one leaf set, A (standard 0.8): two per leaf, beads outward |
|  | linear-alternator-module-tuning-2in | leaf-2in-piston-t0.5 | 2 | choose one leaf set, B (soft 0.5, tuning): joints 1 and 2 in place of the 0.8 leaves; leaf 2 turned over |
|  | tri-clamp-leaf-half-gasket | leaf-half-gasket-2in-w0.6 | 4 | choose one leaf set, B (soft 0.5, tuning): two per soft leaf, beads outward |
|  | linear-alternator-module-mover-2in | la-piston-cup-48x24 | 1 | in the 42 bored spool, crown toward face A |
|  | linear-alternator-module-mover-2in | la-tube-rod-18x14x108.15 | 1 | pressed into the cup's socket; through both leaves |
|  | linear-alternator-module-mover-2in | la-magnet-carrier-47x56 | 1 | pressed on the tube rod, centred under the stator |
|  | neodymium-disc-magnets | magnet-12x3 | 40 | 4 rows of 10 in the carrier, faces out: S, N, N, S from face A |
|  | fpse-hub-collars | fpse-collar-18x28 | 4 | either side of each leaf's hub on the tube rod |
|  | set-screws-metric | set-m3x4 | 4 | one grub per collar |
|  | fpse-linear-alternator-stator | fpse-stator-pack-43deg | 8 | round the 3 in bored spool at the magnets' centre |
|  | fpse-linear-alternator-stator | fpse-bobbin-65 | 1 | between the teeth; slid over the spool's flange first |
|  | fpse-linear-alternator-stator | fpse-coil-300t | 1 | 300 turns of 0.71 mm enamelled wire on the bobbin; the leads leave through the housing |
|  | fpse-linear-alternator-stator | fpse-stator-housing-half | 2 | clamp the packs onto the tube |
|  | socket-head-cap-screws-metric | shcs-m4x20 | 4 | stator housing ears |
|  | hex-nuts-metric | nut-m4 | 4 | stator housing ears |
|  | sanitary-high-pressure-clamp | hp-clamp-2in | 4 | bought: joints 1 and 2, face B (cap or next device) and face A (to the engine); rated above the 15 bar gauge relief setting |
|  | tri-clamp-gasket | tc-gasket-2in | 2 | Type B at face A (to the engine) and face B (under the cap); rated above the relief setting |
|  | tri-clamp-port-cap | port-cap-2in-4x-npt18 | 1 | closes face B (the bounce space): fill valve, pressure gauge, relief valve, and a plug or pressure transducer; off when face B clamps into a loop |
|  | npt-thread-envelopes | npt-1-8-male | 4 | the 1/8 NPT stems of the fill valve, gauge, relief valve and plug (bodies are the builder's choice) |
|  | linear-alternator-module-tuning-2in | la-mass-disc-41x26x4 | 4 | optional (tuning): add-on mass discs on the crown inside the cup, 0 to 4 |
|  | socket-head-cap-screws-metric | shcs-m3x20 | 3 | optional (tuning): hold 4 discs (3 × M3 × 16 for 3, × 12 for 2, × 8 for 1) |
|  | linear-alternator-module-2in-datasheet |  | 1 | load resistor: non-inductive, power rated above the expected output; value on the datasheet: bought, not drawn |
|  | linear-alternator-module-2in-datasheet |  | 1 | series capacitor: non-polar, C = 1/(ω² L) for the running frequency (datasheet), rated above the voltage across it: bought, not drawn |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Build order

1. Magnets into the carrier (rows S, N, N, S from the end that faces A), carrier pressed on the tube rod at its drawn place, tube pressed into the cup's socket. Mass discs on the crown now if the tuning needs them.
2. Coil on its bobbin over the 3 in bored spool's flange to the middle; eight stator packs round the tube at the coil; housing halves with 4 × M4 × 20. Leads out through the housing's hole.
3. 42 bored spool face A down. Mover in, crown down, until the crown is 9.00 below face A (depth gauge). Collar on the tube, half gasket (bead down), leaf 1, half gasket (bead up), the 3 in spool with its stator, collar; clamp joint 1; grubs.
4. Collar, half gasket, leaf 2 turned over, half gasket, the 25.4 spool, collar; clamp joint 2; check the crown is still at 9.00 and the mover moves freely ±6 by hand from face A.
5. Face B: Type B gasket, four-port cap, clamp; fill valve, gauge, relief valve, plug. Face A: Type B gasket and clamp onto the engine. Load resistor and capacitor on the leads before the engine runs.

All printed STLs: https://xemstudio.com/objects/list-linear-alternator-module-2in-closed/stl-list.txt

## Questions

**Why one standard unit?**

Moved between engines with the same load, it turns 'which engine is better' into a measurement: the unit's own mass, springs, losses and Bl are the same every time and are on the datasheet.

**What engines does it fit?**

Anything with a 2 in ferrule carrying a pressure wave: a free-piston Stirling hot end, a thermoacoustic loop, ring or standing-wave engine. On a ring or loop, face B clamps to the next part instead of the cap.

**What must the clamps and gaskets be rated for?**

Above the 15 bar gauge relief at their temperature. High-pressure bolted 2 in clamps are published at 1000 psi (69 bar) at 70–75 °F.

**Where is the electricity?**

Two leads from the coil outside the vessel: no wire passes the pressure boundary. Always connect the load before the engine runs.

## Fits with

- [Linear alternator module, 2 in tri-clamp: datasheet, closed and open frame (mass, stiffness, frequency, Bl, R, L, stroke, pressure) and test procedure](https://xemstudio.com/objects/linear-alternator-module-2in-datasheet/)
- [Build list: Linear alternator module, 2 in, open frame (exposed flexures)](https://xemstudio.com/objects/list-linear-alternator-module-2in-open/)
- [Linear alternator module mover: Ø48 piston cup, 40-magnet carrier and tube rod, sprung on two leaves](https://xemstudio.com/objects/linear-alternator-module-mover-2in/)
- [Linear alternator module spools: 2 in × 42 mm bored Ø48.00 and 2 in × 25.4 mm (fabrication spec)](https://xemstudio.com/objects/linear-alternator-module-spools-2in/)
- [Linear alternator module tuning parts: add-on mass discs, the soft 0.5 mm leaf and its rim shim](https://xemstudio.com/objects/linear-alternator-module-tuning-2in/)
- [Moving-magnet linear alternator stator outside a 2 in tri-clamp spool: laminated two-tooth stator, one coil](https://xemstudio.com/objects/fpse-linear-alternator-stator/)
- [Tri-clamp flexure leaf: spiral planar spring clamped in a 2 in joint like a gasket (displacer and piston)](https://xemstudio.com/objects/tri-clamp-flexure-leaf/)
- [High-pressure bolted sanitary clamp, 2 in (bought part: ratings, no drawing)](https://xemstudio.com/objects/sanitary-high-pressure-clamp/)
- [Build list: Free-piston Stirling generator, 2 in tri-clamp (pressurised, linear alternator)](https://xemstudio.com/objects/list-fpse-generator-2in/)