# Linear alternator coil Ø50 × 10 (≈ 314 turns)

> How many turns and what size is each coil of the linear alternator?

- Category: Stirling engines › Free-piston
- Kind: Hardware
- Basis: Winding volume of one bobbin bay; turns and resistance computed in the generator for 0.30 mm wire
- Page: https://xemstudio.com/objects/linear-alternator-coil/ · JSON: https://xemstudio.com/api/geometry?object=linear-alternator-coil · Plain text: https://xemstudio.com/objects/linear-alternator-coil/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## 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.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| coil in its bay | bay volume | bobbin bay | designed | alt-coil-* |

## Sizes

| parameter | value |
|---|---|
| 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 |

## Where the files are

- NASA (NTRS, public domain): [Linear alternator design for free-piston Stirling convertors (2005)](https://ntrs.nasa.gov/search?q=20050182934) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Sunpower/NASA 80 We free-piston Stirling convertor (2002)](https://ntrs.nasa.gov/search?q=20020047256) — PDF — US Government work, public domain
- Wikipedia: [Linear alternator](https://en.wikipedia.org/wiki/Linear_alternator) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Free-piston engine](https://en.wikipedia.org/wiki/Free-piston_engine) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/linear-alternator-coil/index.json

- alt-coil-bay: [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) — 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

## How it fits

### Goes in or on
- [Linear alternator bobbin: Ø37 bore, two 10 mm bays](https://xemstudio.com/objects/linear-alternator-bobbin/): fills one 10 mm bay

### Connects to
- [Linear alternator mover: Ø35 carrier for 16 Ø10 × 3 magnets](https://xemstudio.com/objects/linear-alternator-mover/): the magnet row it sits over

## Questions

**How many turns on each linear alternator coil?**

About 314 turns of 0.30 mm wire in the Ø50 × 10 bay.

**How are the two coils connected?**

Wound in opposite directions and joined start-to-start in series: about 21.3 Ω together.

## Fits with

- [Linear alternator bobbin: Ø37 bore, two 10 mm bays](https://xemstudio.com/objects/linear-alternator-bobbin/)
- [Linear alternator mover: Ø35 carrier for 16 Ø10 × 3 magnets](https://xemstudio.com/objects/linear-alternator-mover/)
- [Linear alternator housing for Ø80 and Ø100 flexures (2 in / 3 in)](https://xemstudio.com/objects/linear-alternator-housing/)