Coil Passes in My Pulse Motor Sandbox (Magnet Induction Test)

Hook

I wanted these stationary coils to puff out a real magnetic field so every coil pass would act like a permanent magnet hitting another magnet. Here's what happened when I pulsed eight bifilar coils in series.

Watch this experiment

I spun the 6-magnet electromagnetic rotor by hand while the signal generator drove the outer 8-coil stator from 400 Hz down to 100 Hz. Voltage climbed from 12 V to 30 V and current never broke 130 mA. One coil showed north, the next showed south — all coming straight from the coils themselves.

What you'll learn

How frequency, voltage, and coil polarity affect the strength of the field on each coil pass. Why some coils flip north/south when scavenged parts have opposite winds. And what it takes to get transformer-style induction when the rotor coils fly past the energized stator coils.

From the bench

The stator coils are all bifilar. The drive half uses some 26 gauge as the smallest wire. I started at 400 Hz, walked down by 10 Hz steps, and gave the rotor a spin after each change. At 300 Hz and 20 V it pulled 50 mA. At 200 Hz it was 60 mA. Cranked voltage to 25 V at 150-200 Hz and current went to 80 mA. At 30 V it reached 130 mA and I could feel the fields getting stronger.

The test magnet showed a clear north field on one coil and south on the adjacent coil. That proved the magnetism wasn't leaking from the shaft or the rotor magnets — it was generated right in the coils by the pulsing.

How it works / what we changed

I kept the eight outer coils in series with a trigger strand ready in case I swapped the electromagnetic rotor out. The objective stayed simple: make the stationary coils develop enough magnetism on each coil pass that the rotor's permanent magnets and induction coils would react with force. Lower frequency seemed to help the field “puff out” but at 100 Hz the rotor sometimes stalled, so spacing is still an issue. On another bench I had coils literally touching with an iron-powder core — that gave me over a thousand volts on induction passes even if the current was tiny through 32 gauge wire.

Magnet induction

When one of the induction coils passes the coils that have the strong field, they should generate transformer style real quick. That's the magnet induction I'm chasing. Even if it's only 10 milliamps at a thousand volts, you can still get usable work. The primitive tool I used had to sit dead center to read the field, but the north and south poles were unmistakable. The plan is to enlarge that field so every coil pass creates a clean induction spike without needing the rotor magnets to do all the work.

Electric coil

All eight stator coils are bifilar and wired in series. The drive half includes some pretty thin 26 gauge wire. I pulsed them with the signal generator and watched the electric coil itself become a magnet. At 20-30 volts and under 130 mA we got clear north on one electric coil and south on the next. The polarity flip came from opposite winding directions on the scavenged coils. That electric coil magnetism is exactly what I need so the rotor treats the stator coils like permanent magnets during each pass.

Electric range coil top

I didn't have a real electric range coil top on the bench this time. The closest thing was the fat 32 gauge coil with iron powder core I keep mentioning from the other table. That one weighs about a pound and a half and can generate over a thousand volts DC on induction passes. You can't push much current through 32 gauge or the wire will burn up, but even a small current at high voltage can pack a punch. The electric range coil top idea is basically the same principle — a big heavy coil that can take the pulsing and still deliver strong fields on every coil pass. I'll probably swap one in next round to compare.

Builder checklist

• 6-magnet electromagnetic rotor balanced on shaft
• 8 bifilar stator coils wired in series (26-32 gauge range)
• Signal generator capable of 100-400 Hz square wave
• Adjustable DC supply 12-30 V, monitor mA
• Hand-spin or low-friction bearing for initial tests
• Small magnet or gauss tool to check north/south fields on each coil
• Trigger strand ready for future reed or hall switch
• Note winding direction on every coil to avoid unexpected polarity flips

Troubleshooting

At 100 Hz the rotor sometimes stopped — probably coil spacing or timing. If only three or four coils light up, check series wiring and connections. Fields too weak? Increase voltage but watch current on thin 26 gauge wire. Opposite north/south on adjacent coils usually means one coil is wound backwards. Primitive test tool needs to sit right in the middle of the coil to read anything useful.

Safety

Keep voltages under 30 V for these early sandbox tests. Thin 26 and 32 gauge wire heats up fast if you push too much current — stay below 150 mA until you add proper fusing. Spinning rotor by hand near strong fields can pinch fingers. Always unplug the supply before touching coils or adjusting spacing. High-voltage induction spikes (even low current) can still give a surprise shock if you touch the output leads.

FAQ

Why did one coil show north and the next south?

Scavenged coils were wound in opposite directions. The pulsing still magnetized them but the polarity flipped.

How low can you run the frequency?

I went down to 100 Hz. Below that the rotor stalled in this setup. Closer coil spacing or cores help.

Did you see over a thousand volts?

Not on this table, but the 32-gauge iron-core coil on the other bench did on similar induction passes. Current stays tiny.

Can these coil passes really replace permanent magnets?

That's the goal. If the field puffs out far enough, the rotor magnets and induction coils react to the stator coils exactly like they would to neodymium magnets.

Related on this site

• How to Build a Pulse Motor: Parts, Coil Gap, First Spin
• How to Wind Coils for a Pulse Motor (Step by Step)
• Best Wire Gauge for Pulse Motor Coils (AWG Guide)
• DIY Magnetic Induction Motor: Hobbyists in 2026
• Pulse Motor vs Bedini Motor: What's the Difference?

Watch this experiment on YouTube

• ▶ Watch full on YouTube