Using Pancake Coil in My Latest Pulse Motor Run – What the Numbers Show

Hook

I’m back in the workshop using pancake coil on the same pulse motor setup from the live stream. This time everything is closed-loop on one battery and I’m hunting for the sweet spot between 75kHz and 111kHz to see how close we can get to unity.

Watch this experiment

I hooked the pancake coil to the signal generator, ran the output through a cap bank, then fed that DC to the motor. At the same time I watched input voltage, output voltage, and the amp reading coming off the motor before it dumps back into the battery.

What you'll learn

You’ll see how output voltage climbs as we drop frequency, what milliamp numbers we actually hit, why the rotor speeds up even when the meters look weird, and the tiny machining issue with the spherical magnet pocket.

From the bench

Started at 12.40V on the battery. Signal generator set first around 111kHz plus a little offset. The red LEDs on the circuit were blinking so we knew power was moving. The DC output off the cap bank (AC side of the pancake coil) started at 6.92V. That’s a long way from the 12V input so I began sweeping the frequency downward.

At 100kHz we were already at 7.32V. Dropped to 90kHz and the output kept climbing. Hit a plateau, then at 85kHz we sat at 8V. Kept going down to 80kHz (8.5V) and finally settled around 75kHz where we saw almost 9V and the highest amp output.

How it works / what we changed

The pancake coil is being pulsed on the AC side. That energy gets rectified to DC, feeds the motor, and the motor output is measured before dumping back to the battery. I moved the multimeter to the collector-emitter of the transistor to try catching real input current, but it’s still tricky to know exactly how much is being spent versus what the coil is returning.

house neodymium 1

The 3D-printed rotor part is supposed to house neodymium 1 spherical magnet. Right now the pocket is off by about 0.03mm so the fit is tighter than I want. I need a little clearance so the magnet can move a tiny bit but still stay centered.

neodymium 1. 1.26-in

The design calls for a neodymium 1. 1.26-in spherical magnet at N52 strength. The printed cavity is just a hair too small, maybe 0.03mm short, so the magnet doesn’t sit with the exact play I was after. It still works but I’ll open it up on the next print.

neodymium 26

I didn’t install a neodymium 26 style magnet in this test; the rotor uses the spherical 1.26-in N52 instead. The 26AWG wire showed up in a different pickup coil video but isn’t part of this pancake coil run.

Builder checklist

• Pancake coil connected to signal generator on AC side
• Cap bank rectifying to DC for motor power
• Multimeter across transistor collector-emitter for input current attempt
• Rotor pocket checked for 1.26-in spherical magnet fit
• Frequency swept from 111kHz down to 75kHz while watching output
• Battery voltage monitored (started 12.40V, ended 12.37V)
• Output stabilized near 8.9V and 159-215mA depending on exact frequency

Troubleshooting

Output voltage plateaus and won’t climb further? Drop frequency another 5-10kHz and watch both volt and amp meters. If amps start dropping while voltage rises you may be past the peak. Rotor speed increasing but input voltage sagging? That usually means we’re still spending more than we recover. Hard to read exact input current? Try placing the meter right at the transistor like I did; the reading is cleaner there than at the battery leads.

Safety

Keep an eye on battery voltage so you don’t run it too low. The coil stayed cool but always feel it after a long run. Magnets are strong N52; mind your fingers around the rotor. Signal generator and transistor can get warm; nothing scary here but don’t leave it unattended for hours.

FAQ

Did you reach over unity? Not yet. We got close on the output side (almost 9V at 160mA) but input draw is still higher than the return.

What frequency worked best? 75kHz gave the highest stable output current around 159-160mA and nearly 9V.

Why is the magnet pocket too tight? The printed cavity is 0.03mm undersized for the 1.26-in sphere. Easy fix on the next print.

Will a bigger magnet help? I only tested the spherical N52; the video with 26AWG pickup coils used different magnets and that’s a separate build.

Related on this site

• How to Build a Pulse Motor: Parts, Coil Gap, First Spin
• Best Neodymium Magnets for Pulse Motor Rotors
• Pulse Motor Rotor Design: Magnets, Materials and Balance
• How to Wind Coils for a Pulse Motor (Step by Step)
• Pulse Motor vs Bedini Motor: What's the Difference?

Watch this experiment on YouTube

• ▶ Watch full on YouTube