🔧 Shop tool · coil
Pulse motor coil calculator
Enter wire gauge, turns, and bobbin size. Get feet of magnet wire, DC ohms, a Wheeler inductance estimate, and whether a TIP31 or a 2N3055 is the saner switch. Then open the matching long-form on YouTube.
Interactive · estimates only
Size a shop coil
Workshop starting points — not exact transcript turn counts. Tap a preset, then watch the matching long-form.
- Turns / layer
- 22
- Layers
- 5
- Finished OD
- 1.31 in
- Wire length
- 24.3 ft · 7.4 m
- One winding DCR
- 0.097 Ω
- Approx L
- 100 µH
If this coil sat on 12 V DC it would draw about >50 A. Pulses are shorter — this is a heat / switch-size check, not a running current.
This coil will heat fast if you leave the transistor on. Short pulses, air gap, and a heatsink are not optional.
Switch hint: 2N3055 or MOSFET + fat heatsink
Very low DCR — this wind slams current. Scope the switch node and do not leave it DC-on.
Next · watch the bench
DIY Low Cost Pulse Motor Build with 16AWG Coil
Starting point for a punchy drive coil. Pair it with the low-cost 16 AWG build — these turns are a shop estimate, not a transcript count.
What this calculates
Pack the enamel diameter along the bobbin to get turns per layer and layers. Mean turn length × turns is the copper footage. Resistance uses standard copper Ω/1000 ft at room temperature. Inductance uses Wheeler’s single-layer formula when the wind is one layer, and the multilayer form L(µH) = 0.8 a² N² / (6a + 9b + 10c) (a, b, c in inches) when it is not. Bifilar treats two taped wires as a wider pack and doubles the bought footage.
This is a shop helper for pulse-motor and Bedini-style coils — not a free-energy predictor and not a substitute for an LCR meter. If the coil will not physically fit, the tool says so.
Worked shop example
90 turns of 16 AWG on a 0.75 in ID bobbin, 1.25 in long, single wind: you should see on the order of tens of feet of wire, well under an ohm, and a 12 V DC current that wants a real heatsink. That is why the low-cost 16 AWG build is the preset — thick wire punches and heats. Compare with the 26 AWG 12-strand litz pickup preset if you are winding a recovery / pickup coil instead of a drive coil.
Guides that pair with this
- Best wire gauge for pulse motor coils — 16 vs 20 vs 26 AWG litz
- How to wind coils — single, bifilar, trifilar
- Which transistor — TIP31C, 2N3055, MOSFET
- How to build a pulse motor — first spin checklist
Preset videos: 16 AWG drive · 26 AWG litz pickup · 12 V coil comparison · 20 AWG bifilar
Questions
Is the inductance exact?
No. It uses Wheeler’s air-core formulas from the bobbin geometry. Real pulse-motor coils sit on plastic, wood, or ferrite-ish forms, with uneven tension. Treat µH as a ballpark, then measure DCR with a meter and watch the bench video.
Are the presets the exact turns from the videos?
No. They are workshop starting points that pair with those episodes (16 AWG drive, 26 AWG 12-strand litz pickup, 12 V comparison, 20 AWG bifilar). The videos show heat, gap, and current — not a guaranteed recipe.
Why show 12 V DC amps if the motor is pulsed?
If the transistor sticks on, that is the current the copper and the switch see. It is a fuse / heatsink check, not the running RMS. Short pulses draw less average current and still make heat.
Single vs bifilar?
Single is one drive winding. Bifilar is two wires taped and wound together (classic Bedini-style). The calculator uses twice the pack width along the bobbin and reports one conductor’s resistance.
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