How to Build a Bedini SG Motor: Complete BOM and Assembly Guide

Introduction

The Bedini SG (School Girl) motor is one of the most replicated scalar electromagnetics experiments in the research community. Originally demonstrated by John Bedini in 2004, the design uses a pulsed DC rotor to charge a secondary battery beyond the energy input. Whether you are a skeptic testing the hypothesis or a true believer refining your build, having a complete, accurate BOM is where you start.

This guide documents the canonical Bedini SG in its 1-coil form — the standard starting point for new builders. We cover every component, the winding specification, the drive circuit, and the measurement protocol you need to evaluate the build honestly.

What Is the Bedini SG Motor?

The Bedini SG is a monopole motor energizer. A rotor with permanent magnets spins past a single-wire coil. Each pass triggers a transistor, which pulses the coil and simultaneously charges a secondary battery. Bedini claimed the device operated in a radiant energy mode — drawing energy from the vacuum — producing output battery charge exceeding input power draw.

The conventional electromagnetic explanation: it is a very efficient switched reluctance motor running in a pulsed charging mode. Either way, it is a well-documented design that teaches fundamental pulse-power, coil-winding, and battery-testing skills. For scalar EM researchers, it is the canonical entry point into the Bedini corpus.

Complete Bill of Materials

The following BOM covers the canonical 1-coil SG. Quantities are for a single coil assembly. Build cost is approximately $45–$85 depending on sourcing.

Rotor

• Bicycle wheel — 20" or 26" standard spoke wheel, any condition. Thrift stores, bike shops.
• Ceramic disc magnets — 8× neodymium N52 disc, 1" diameter × 1/4" thick. Source: K&J Magnetics or Amazon. ~$12.
• Epoxy — JB Weld or equivalent 2-part epoxy for magnet bonding. ~$8.
• Plastic or wood hub block — to mount magnets evenly spaced on wheel rim. Cut from 3/4" plywood.

Coil (Trifilar Wind, the Standard)

• Coil core — 1/2" × 4" ferrite rod (Amidon R-61-050-400 or equivalent). ~$4.
• Magnet wire — 3 strands of #23 AWG magnet wire, 200 feet each. Total ~600ft. ~$18.
• Coil bobbin — wound on 1/2" PVC coupling or print a custom bobbin. ~$2.
• Tape and varnish — fiberglass tape to secure winds, polyurethane varnish to seal.

Drive Circuit

• Transistor — 2N3055 NPN power transistor × 1. TO-3 package preferred. ~$3.
• 1N4007 diode — × 1, for back-EMF clamping on the power coil side.
• 1N4148 diode — × 1, trigger circuit protection.
• Base resistor — 1kΩ 1/4W resistor × 1.
• LED — 3mm green LED as trigger indicator (optional but useful for tuning).
• Heatsink — TO-3 compatible heatsink. ~$2.

Electrical

• Primary battery — 12V sealed lead-acid (SLA), 7Ah. ~$20.
• Secondary battery — matching 12V SLA 7Ah. ~$20.
• Multimeter — any with current and voltage measurement.
• Clamp ammeter — optional but strongly recommended for accurate input current measurement.
• Hookup wire — 20 AWG stranded, assorted colors.
• Terminal blocks — for clean circuit connections.

Frame

• Wood frame — 2× 1×4 pine boards, 24" long. Mount the wheel axle with two pieces of angle iron.
• Axle hardware — wheel axle bolts, nuts, washers (reuse from bike wheel).
• Coil mount — adjustable bracket to position coil 1–3mm from rotor magnet face.

Coil Winding Specification

Trifilar configuration: three strands of #23 AWG wound simultaneously. Wind all three strands together, keeping them parallel. Do not twist.

Wind count: wind until the bobbin is full, typically 175–200 turns per strand on a standard ferrite rod with a 1.25" bobbin. Consistency matters more than hitting an exact number.

Strand identification: label each strand at both ends before winding. Color-code with tape. The three strands serve different functions: one triggers the transistor, one is the power coil, one recovers the back-EMF spike to the secondary battery.

Resistance check: each strand should measure approximately 12–16Ω on a well-wound coil at this specification.

Circuit Assembly

1. Trigger strand — connects from the coil to the base of the 2N3055 via the 1kΩ resistor. One end to battery positive through the 1N4148 diode, other end to transistor base.
2. Power coil strand — collector of the 2N3055 connects through the power coil strand to the primary battery positive. 1N4007 clamped across the coil for back-EMF protection.
3. Recovery strand — wired to the secondary battery positive through a diode. This captures the collapse spike.
4. Emitter — connect 2N3055 emitter to battery negative (shared ground for primary and secondary).

Important: primary and secondary batteries share a negative ground. The secondary positive is connected through the recovery diode. This is not optional.

Safety Notes

The Bedini SG operates at low voltages but generates significant back-EMF spikes during coil collapse — easily 150–300V transient on the recovery line. Do not touch the recovery strand or secondary battery terminals while the circuit is running without proper insulation. Use insulated test leads.

SLA batteries can vent hydrogen during charging. Run your build in a ventilated space. Do not charge SLA batteries beyond their rated voltage (13.8V float for 12V SLA).

The 2N3055 runs hot. Heatsink is not optional. Inadequate heatsinking will destroy the transistor within minutes under load.

Measurement Protocol

The canonical Bedini measurement controversy: most builders measure output charge gained by the secondary battery and compare to amp-hours drawn from the primary. This is insufficient. You must measure input power (primary battery voltage × average input current over 30-minute intervals) and output power (secondary battery voltage × current during discharge into a known resistive load). Run the build for 4 hours input, discharge the secondary into a 10Ω resistive load, measure discharge time and terminal voltage. Energy out = V² / R × time.

Most replications show 60–80% efficiency in conventional terms — which is respectable for a pulse motor but does not support overunity claims. A handful of very carefully documented builds show anomalous results. If yours does, contact us — we want the data.

What's Next

The Bedini SG is the entry point to a much larger corpus. ScalarForge's catalog includes Bedini's more complex designs — the window motor, the monopole energizer variant with multiple coils, and the G-Field Generator — with full build plans. Members also get access to our AI Invention Forge, which can synthesize hybrid device designs combining Bedini's monopole architecture with other scalar EM devices. Browse all 26 ScalarForge device build plans →