Linear alternator module, 2 in tri-clamp: datasheet, closed and open frame (mass, stiffness, frequency, Bl, R, L, stroke, pressure) and test procedure — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/linear-alternator-module-2in-datasheet/ (CC BY 4.0) Basis: My analysis of the module (tools/gen_la_module.py) at the drawn geometry; the stator and leaf models of the free-piston generator (tools/gen_fpse_gen.py) Catalog version: 2026-10-20 Sizes: see table below - Built once and moved from engine to engine: the same mover, leaves, magnets and coil every time, so the difference in electricity is the difference in the engines. Its own numbers are below; the numbers marked model are my estimates from the drawings and cited methods, and the tests in the procedure check each of them on the built unit. - Two versions share the face-A spool, the mover, the leaves, the magnets and the whole stator. Closed: the leaves sit in spool-to-spool joints and face B is closed by the four-port cap, a sealed bounce space you can charge; use it on charged engines, in thermoacoustic loops and rings, and in line with face B on another device. Open frame: the leaves sit on an open frame clamped on the face-A spool, the back of the piston is at the room's pressure; use it on unpressurised desk and demo engines at 1 bar, for quick swaps, and when you want to see and retune the leaves. - Leaves that fit both: leaf-2in-piston-t0.8 and the soft leaf-2in-piston-t0.5 (Ø64 rim, Ø18 hub). In the closed module, and in any 2 in spool-to-spool joint, the rim goes between two half gaskets (0.45 webs beside a 0.8 leaf, 0.6 beside a 0.5); in the open frame it sits in a Ø64 × 0.8 seat under a clamp ring, on a 0.3 rim shim if it is a 0.5 leaf. Both mounts clamp the rim inside r 23.75, so stiffness and stress are the same. - Method. Mass from the CAD volumes; leaf stiffness and stress from a 3D Euler-Bernoulli frame model of the spiral arms (rim clamped, hub rigid); bounce spring γ p A²/V (adiabatic); force constant, coil resistance and inductance from the free-piston generator's magnetic-circuit estimate of the same stator and magnets; side pull from the same estimate against the leaves' radial stiffness as a 2 × 2 lateral / tilt stiffness matrix. Linear free-piston dynamics as in Redlich & Berchowitz; Sunpower's convertors (NASA reports) are the reference for clearance-seal pistons on spiral flexures with a moving-magnet alternator. - Electrical model of the module: an EMF E = Bl·v in series with R = 3.40 Ω and L ≈ 25 mH. A series capacitor C = 1/(ω² L) cancels L at the running frequency (20 Hz 2500 µF, 30 Hz 1111 µF, 40 Hz 625 µF, 50 Hz 400 µF, 60 Hz 278 µF, 80 Hz 156 µF); rated above the voltage across it. - Example (model): helium 10 bar behind the piston, 35.8 Hz, ±5 mm: EMF 32.4 V peak; into 6.8 Ω with the series capacitor, 34.2 W in the load and 17.1 W in the coil, if the engine supplies that much. - Measurement procedure (each engine the same way): - 1. Check the unit alone (once, and after any change). Ohmmeter on the coil leads: R_c. LCR meter at the running frequency: L. Face A up and open, depth gauge on the crown: 9.00 mm below face A when centred. Turn it face A down: the mover sags by m·g/k; pass DC current through the coil until it is back at 9.00: Bl = m·g / I (m the moving mass, g 9.81 m/s²). - 2. Resonance and damping (motoring test). Closed: face B on its cap, the charge you will test at, face A closed with a plain end cap and gasket. Open frame: face A open to the room (the leaves-only resonance) or on a plain end cap (leaves plus the trapped face-A volume). Drive the coil from an audio amplifier through a 1 Ω sense resistor and sweep the frequency: the current dips at the resonance f₀ (the EMF opposes the drive). Stop the drive and record the coil voltage as it rings down: the decay rate σ (1/s, from successive peaks) gives the open-circuit mechanical damping c_m = 2·m·σ. Repeat with one mass disc fitted: m = m_disc / ((f₀/f₁)² − 1) and k = m (2π f₀)², a check of the published mass and stiffness. - 3. On the engine. Clamp face A to the engine (Type B gasket and clamp; high-pressure clamp on a charged engine). Closed: face B on its cap at the engine's charge, or face B into the loop. Open frame: nothing to charge; keep fingers and loose wires off the exposed leaves while it runs. Connect a non-inductive load resistor R_L (power rated above the expected output) in series with the capacitor C for the expected frequency. Never run with the coil open: the load is what holds the stroke. - 4. Read a true-RMS voltmeter across R_L and the frequency f. Load power P = V_rms² / R_L. Current I_rms = V_rms / R_L. - 5. Stroke check. EMF E_rms = I_rms · |R_c + R_L + j(ωL − 1/(ωC))| (= I_rms (R_c + R_L) with C tuned); amplitude X = √2 · E_rms / (Bl · ω), ω = 2π f. Keep X at or below 6 mm: if it is above, lower R_L (more load, shorter stroke) or reduce the heat. - 6. Power the engine delivered to the piston: P_engine = P + I_rms² R_c + ½ c_m ω² X² (load, coil, and the unit's own mechanical loss from step 2 at the same charge and frequency). Compare engines at the same X, the same charge and gas, and say which numbers were measured. - Geometry, closed: a stack of three plain 2 in spools (42 bored, 3 in bored, 25.4) with leaves 1 and 2 clamped in the two inner joints; nothing of it lies beyond face A or face B, so either face clamps on any 2 in ferrule. - Geometry, open frame: the 42 bored spool, then the open frame on its second ferrule: frame base, leaf 1, a clamp ring on 10 mm posts, the stator sleeve with the stator, a top plate on 5 mm posts, the leaf-2 seat ring, leaf 2 and a clamp ring; 167.7 mm from face A to the top ring. Only face A is a clamp face. parameter closed (sealed bounce space) open frame (back open to the room) basis use it on charged engines (mean pressure above 1 bar), thermoacoustic loops and rings, in line with face B on another device unpressurised engines at 1 bar (desk and demo engines), quick swaps, watching and retuning the leaves design build 42 bored · leaf 1 in a spool joint · 3 in bored spool with the stator · leaf 2 in a spool joint · 25.4 spool · four-port cap 42 bored spool · open frame (base, leaf seats, clamp rings, stator sleeve, posts) with both leaves exposed drawn geometry back of the piston sealed bounce space, 156.9 cm³ at mid-stroke, chargeable through the cap open to the room: 1492 mm² side opening (piston 1810 mm²) drawn geometry moving mass, standard build 865 g 899 g (longer tube rod) model: CAD volumes × 7.9 g/cm³ (assumed) and 7.5 g/cm³ magnets; weigh the mover add-on mass disc 24.1 g each, up to 4 same model: CAD volume × 7.9 g/cm³ leaves leaf-2in-piston-t0.8 (set A) or t0.5 (set B), rim between two half gaskets the same leaves, rim in a Ø64 × 0.8 seat under a clamp ring (0.3 shim under a 0.5 leaf) drawn geometry; both mounts clamp the rim inside r 23.75 leaf axial stiffness (0.8) 4426 N/m per leaf, 8851 N/m for the two same model: 3D frame of the spiral arms, E 200 GPa (assumed) leaf axial stiffness (0.5, soft) 1135 N/m per leaf, 2269 N/m for the two same model, as above leaf radial stiffness (0.8) 189 kN/m per leaf same model, as above natural frequency, leaves only 16.1 Hz (soft 8.2) 15.8 Hz (soft 8.0) f = √(k/m)/2π gas spring on the back of the piston, γ p A²/V 2.96 / 29.2 / 34.8 kN/m (air 1 bar / air 10 bar / helium 10 bar) none adiabatic gas spring; model natural frequency with the gas 18.6 / 33.4 / 35.8 Hz (bounce space at air 1 bar / air 10 bar / helium 10 bar) leaves plus the engine's own gas on face A at 1 bar air: V_e 50 cm³ 22.6 Hz, V_e 100 cm³ 19.5 Hz, V_e 200 cm³ 17.7 Hz, V_e 400 cm³ 16.8 Hz k_e = γ p A²/V_e added to the leaves; model (an engine's own volume and its power set the running frequency) force constant Bl (= EMF constant, V·s/m) 28.8 N/A same model: magnetic-circuit estimate of the generator's stator (N42 Br 1.31 T, 75 % linkage assumed); the open frame keeps the same Ø48 / Ø50.8 gap; check by the DC lift test coil resistance 3.40 Ω at 20 °C, 300 turns of 0.71 mm same model: wire length × IEC 60028 resistivity; measure with an ohmmeter coil inductance about 25 mH same estimate (gap reluctance + 30 % slot leakage); measure with an LCR meter at the running frequency EMF 0.181 V peak per mm of amplitude per Hz same E = Bl·ω·X short-circuit damping Bl²/R 244 N·s/m same model stroke ±5 mm design, ±6 mm maximum; first contact −7.05 (crown to the face-A gasket lip) / +7.10 (cup rim to leaf 1's half gasket) ±5 / ±6 mm; first contact −7.05 (crown to the face-A gasket lip) / +7.05 (cup rim to the Type B gasket lip at the frame base) drawn geometry; ±6 is the stator's linear range (half a tooth) swept volume at ±6 21.7 cm³ (piston area 1810 mm²) same drawn geometry leaf bending stress 148 MPa at ±5, 177 MPa at ±6 (0.8); 114 MPa at ±6 (0.5) same model, as the stiffness side pull of the stator on the mover 55 kN/m negative radial stiffness against 379 kN/m from the two leaves 77.9 mm apart: held on the axis in shift and tilt: yes (soft leaves yes) same side pull; leaves 93.0 mm apart: held on the axis in shift and tilt: yes (soft leaves yes) model: the generator's side-pull estimate; 2 × 2 lateral / tilt stiffness matrix positive definite pressure mean up to 10 bar in these numbers; relief 15 bar gauge; hoop stress at relief 27.5 MPa (1.40 bored wall); 4.0 kN on each joint 1 bar: the back of the piston is at the room's pressure; face A on an engine at 1 bar mean (standard clamp, Type B gasket) design; clamps and gaskets rated above the pressure they see at their temperature length (face A to the far end, mid-stroke) 147.0 mm to face B; 166.7 mm to the top of the four-port cap 167.7 mm to the upper clamp ring; the tube rod's end 169.7 (+6 at full stroke) drawn geometry Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - Xem Studio: tools/gen_la_module.py: the module's geometry, masses, bounce volume, natural frequencies and every number on these pages — code — CC BY 4.0 — https://xemstudio.com/ - Xem Studio: tools/gen_fpse_gen.py: the free-piston generator whose stator, magnets, leaves and collars this module reuses; its leaf frame model and magnetic-circuit estimate — code — CC BY 4.0 — https://xemstudio.com/ - Proc. IMechE Part A: Redlich & Berchowitz (1985), Linear dynamics of free-piston Stirling engines — PDF — journal; method cited [verify license at link] — https://journals.sagepub.com/doi/pdf/10.1243/PIME_PROC_1985_199_025_02 - NASA (NTRS, public domain): Wood, Gedeon et al.: Sunpower free-piston convertors on planar spiral flexure bearings (Advanced Stirling Convertor: moving magnet linear alternator, flexure-supported clearance-seal piston) — PDF — US Government work, public domain — https://ntrs.nasa.gov/api/citations/20080047351/downloads/20080047351.pdf - NASA (NTRS, public domain): Geng, Mason, Dyson & Penswick (2008): Sunpower EG-1000, 1.1 kWe, 50 Hz, 3.0 MPa helium, 550 / 50 °C — PDF — US Government work, public domain — https://ntrs.nasa.gov/api/citations/20080033114/downloads/20080033114.pdf - 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 - IEC: IEC 60028 international standard of resistance (1.7241 × 10⁻⁸ Ω·m at 20 °C, the conductor value used for the coil); IEC 60317 enamelled round winding wire (0.71 mm nominal conductor) — standard — values are facts [verify license at link] — https://webstore.iec.ch/publication/1167 Xem Studio scan: not needed; this is a published standard. The sheet is the geometry. API: https://xemstudio.com/api/geometry?object=linear-alternator-module-2in-datasheet