I Built My First Pancake Bifilar Coil for the Pulse Motor

Hook

I just finished my first pancake bifilar coil on the bench and it lit the light the moment I turned the pulse motor on—even though the switch started sticking right away.

Watch this experiment

The coil isn't pretty. It's not uniform, I don't have a proper winding spot, and everything is held together with plain electrical tape. Still, it's solid enough to test and that's what matters when you're figuring things out.

What you'll learn

You'll see exactly how I wired the 28 gauge and 26 gauge strands, what happened with the amps and heat, why the iron filing core caused drag, and why I decided to hook the hall effect again instead of fighting the mechanical switch.

From the bench

Right now I'm working on two things at the same time: generating electricity with this pulse motor and finishing the pancake bifilar coil. The first thing I noticed is that the spool I used had roughly 100 feet of wire. I don't know if I need a full 100 foot pancake coil though—I'm thinking 50 feet might be plenty and asked viewers to tell me in the comments what length actually works best.

How it works / what we changed

I wired it so one 28 gauge strand is by itself. Then the 26 gauge strands run one single file, two in series, then three in series so all six strands are used. The moment I turned it on the lights were already on. That felt pretty cool. But the switch started getting hot fast. You can tell because the amps climb when it sticks. Once it gets like that the switch is basically done and you have to throw it out.

100 foot pancake coil

The spool contained about 100 feet of wire. I debated whether the whole length was necessary or if cutting it shorter would still give good results on the pulse motor. I left it open for viewer input because this is my first pancake bifilar coil and I don't have hard data yet on ideal wire length.

foot pancake coil though

While building I kept wondering out loud if I really needed the entire 100 foot pancake coil though. My gut says 50 feet is probably good enough for this size rotor and core, but I wanted real-world feedback before committing to a second build.

hall effect again

The mechanical switch is the weak point—it gets hot, sticks, and the motor poops out right when it should speed up. So I think I'm going to hook up the hall effect again and see if we can't get smoother triggering and stop burning through switches.

filer coil

People sometimes call it a filer coil when they mean bifilar. That's basically what I built here—just a pancake style with the strands laid together and taped. My version isn't perfect but it still produced visible light on the first try.

pancake coil

This pancake coil is my first attempt. I used electrical tape instead of resin or proper insulation. Even with the messy build and the iron filing core causing extra drag, we still got the LEDs blinking right away. The coil has a lot of core in it which slows the rotor but also seems to help with the induction side.

coil though

The switch is the biggest problem with this coil though. It heats up, the amps rise, and the whole thing bogs down. That's why I'm switching back to a hall effect sensor—so the timing stays clean and we don't cook the switch every run.

Builder checklist

• Start with a spool containing roughly 100 feet of mixed gauge wire
• Decide target length (50 ft suggested for first pancake bifilar coil)
• Lay one 28 gauge strand alone
• Configure 26 gauge strands: single, two-series, three-series
• Secure everything with electrical tape if you're experimenting
• Add iron filing core and test for drag
• Prepare 22 ohm 0.5 W resistors for current limiting
• Have a hall effect sensor ready as backup trigger

Troubleshooting

If your switch gets hot and amps climb, it's probably sticking—time to replace it. Iron filing core adds a lot of drag and raises current draw; you may need to reduce core volume or adjust rotor gap. When the motor poops out right before it accelerates, mechanical contact bounce is usually the culprit.

Safety

These switches can get hot enough to burn you or fail suddenly. The 0.5 watt resistors are undersized for sustained runs—watch for smoke. Keep fingers clear of the spinning rotor with neodymium magnets. Always use current limiting and don't leave the bench unattended while testing.

FAQ

How much wire did the spool have? About 100 feet. I wasn't sure if I needed the whole 100 foot pancake coil though.

Why did the switch fail? It gets hot, sticks, and amps rise until the motor bogs down.

What core are you using? Iron filings packed inside the pancake bifilar coil—creates noticeable drag.

Are you sticking with the mechanical switch? No, I'm going to hook the hall effect again for cleaner timing.

Related on this site

• How to Wind Coils for a Pulse Motor (Step by Step)
• Using a Hall Effect Sensor in Your Pulse Motor Build
• Best Wire Gauge for Pulse Motor Coils (AWG Guide)
• Understanding Back EMF in Pulse Motors

Watch this experiment on YouTube

• ▶ Watch full on YouTube